Technical aspects of automobiles

revving an engine to "warm it up"

I recently had a discussion on this topic. I have heard that revving
the engine may do harm and does little to "warm" the car up. This is an
older car with an engine that has been modified. This guy revvs the
engine at the house and still seems to have trouble making it down his
driveway (about 1/4 mile steep downhill) without stopping and revving
his engine halfway down and then again at the bottom. Is this type of
"warm up" accomplishing anything or is he just destroying his car?

.
posted by admin in Без рубрики and have Comments (24)

24 Responses to “revving an engine to "warm it up"”

  1. admin says:

    huts wrote:
    > I recently had a discussion on this topic. I have heard that revving
    > the engine may do harm and does little to "warm" the car up. This is an
    > older car with an engine that has been modified. This guy revvs the
    > engine at the house and still seems to have trouble making it down his
    > driveway (about 1/4 mile steep downhill) without stopping and revving
    > his engine halfway down and then again at the bottom. Is this type of
    > "warm up" accomplishing anything or is he just destroying his car?

    It’s probably not good for the car; however, if the engine is "modified"
    it may have issues with a cold start, esp. if he has a chokeless
    carburetor (sometimes people who don’t live in particularly cold
    climates will mill the choke housing off the carb for better airflow)
    therefore he may have to play with it a little to keep it from stalling.

    I know a friend of mine has an old Studebaker with a 383 Chev "crate
    motor" in it; he doesn’t have the specs on the motor (bought the car
    pretty much as it is) but it is pretty hairy (and fun to drive) even
    after both of us threw all our tricks at it to get it to start and run
    without a long period of sitting still and revving the engine, the "fast
    idle" had to be set at about 2000 RPM and it still doesn’t always start
    on the first crank.  (of course, it also has dual AFBs on a low rise
    Offy intake, probably not the hot setup for anything but WOT but it
    looks cool)

    I am guessing the PO didn’t ever plan on driving the car in cold
    weather; neither carb had a choke on it when he got it.  We did install
    an electric choke on the rear carb and that did make a lot of
    difference, although it’s still not the kind of car you’d want to hop in
    and drive to work (well, I might, but I’d still probably have to leave
    it sit and "idle" – using the term loosely – for a minute or two in the
    AM before driving off.)

    But yes, your basic premise is correct – the best way to handle a normal
    cold start, unless it’s bitterly cold, is to simply start the car and
    drive off, but drive "easy" until the engine is fully up to operating
    temperature.

    nate


    replace "fly" with "com" to reply.
    http://home.comcast.net/~njnagel

  2. admin says:

    huts wrote:
    > I recently had a discussion on this topic. I have heard that revving
    > the engine may do harm and does little to "warm" the car up. This is an
    > older car with an engine that has been modified. This guy revvs the
    > engine at the house and still seems to have trouble making it down his
    > driveway (about 1/4 mile steep downhill) without stopping and revving
    > his engine halfway down and then again at the bottom. Is this type of
    > "warm up" accomplishing anything or is he just destroying his car?

    Both!  Yes, that can reduce the time to warm the engine.  But, WHY are
    we warming the engine?  Primarily to ensure proper lubrication from the
    oil. If we rev it up before that, we are not getting proper lubrication,
    so why do it?  This is kind of self defeating.

    We ordinarily think of warming the engine before stressing it as
    contributing to reduced wear.  But if we wear it excessively WHILE
    warming, we gain nothing.

    Admittedly, if this is an older car with a carburetor, drivability
    improves when the car is warmed up.  But again, drivability is bad when
    he is revving it anyway.  Better to ease it along and warm it that way.
      If it tends to stall, he should play with fast idle rpm setting.

  3. admin says:

    Not the best for it, but likely it is stalling out so needed.

    I have a carb engine that came stock with a ‘timer’ choke.  The sucker
    goes open according to how long the engine has been running with no
    reference to how ‘hot’ the engine actually is.  These types of chokes
    are a pain in the ass up here in Canada.  I would stall every time I let
    off the gas pedal in the first 1/4- 1/2 mile unless I revved it until
    the engine had really warmed up.  3 foot driving style or heel toe on
    the gas brake for a while.

    I fixed it’s case by putting a manual choke in.  I now can keep the fast
    idle at 1200 until it is actually warmed up and drive away in any
    temperature.

    Mike
    86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    88 Cherokee 235 BFG AT’s
    Canadian Off Road Trips Photos:  Non members can still view!
    Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    (More Off Road album links at bottom of the view page)

    - Hide quoted text — Show quoted text -

    huts wrote:

    > I recently had a discussion on this topic. I have heard that revving
    > the engine may do harm and does little to "warm" the car up. This is an
    > older car with an engine that has been modified. This guy revvs the
    > engine at the house and still seems to have trouble making it down his
    > driveway (about 1/4 mile steep downhill) without stopping and revving
    > his engine halfway down and then again at the bottom. Is this type of
    > "warm up" accomplishing anything or is he just destroying his car?

  4. admin says:

    huts wrote:
    > I recently had a discussion on this topic. I have heard that revving
    > the engine may do harm and does little to "warm" the car up. This is an
    > older car with an engine that has been modified. This guy revvs the
    > engine at the house and still seems to have trouble making it down his
    > driveway (about 1/4 mile steep downhill) without stopping and revving
    > his engine halfway down and then again at the bottom. Is this type of
    > "warm up" accomplishing anything or is he just destroying his car?

    Exhaust is often shut off, and other things are closed for quick warmup.
      shouldn’t push the engine under these conditions as you can cause
    stuff to wear out more quickly.  Probably not as hard on newer cars, but
    also even less beneficial.


    Thank you,

    "Then said I, Wisdom [is] better than strength: nevertheless the poor
    man’s wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

  5. admin says:

    huts wrote:
    > I recently had a discussion on this topic. I have heard that revving
    > the engine may do harm and does little to "warm" the car up. This is an
    > older car with an engine that has been modified. This guy revvs the
    > engine at the house and still seems to have trouble making it down his
    > driveway (about 1/4 mile steep downhill) without stopping and revving
    > his engine halfway down and then again at the bottom. Is this type of
    > "warm up" accomplishing anything or is he just destroying his car?

    He will minimize the wear on the engine during warmup by just getting
    in the car and driving it, keeping the engine at a steady and low rpm.
    If the engine doesn’t idle well when cold it is probably in need of
    repair.  Much less likely in my experience is that the car is a highly
    tuned street racer.  The many cars I’ve driven over the past 15 years
    all use an engine computer to make warmup and overall running very
    smooth.  If taken care of there should be no problem with a modern
    engine holding an idle when cold.

  6. admin says:

    dnoyeB wrote:
    > huts wrote:

    >> I recently had a discussion on this topic. I have heard that revving
    >> the engine may do harm and does little to "warm" the car up. This is an
    >> older car with an engine that has been modified. This guy revvs the
    >> engine at the house and still seems to have trouble making it down his
    >> driveway (about 1/4 mile steep downhill) without stopping and revving
    >> his engine halfway down and then again at the bottom. Is this type of
    >> "warm up" accomplishing anything or is he just destroying his car?

    It depends on the car. If its an older car that is unmodified or lightly
    modified, he’s got a PROBLEM that needs fixing (choke flooding the
    engine or not applying sufficiently, etc.)  Even fairly heavily modified
    engines can be made to behave ‘tolerably well’ when cold if all the
    systems are working right.

    If its an extremely highly modified car, being horribly cold-natured is
    just part and parcel of living with a high-strung engine. Its hard on
    it, but its probably not designed with longevity  anyway. If its a
    question of stopping to rev up and blow the unburned fuel out, versus
    stalling and restarting over and over- then revving it a bit is the only
    choice.

    > Exhaust is often shut off,

    That is without a doubt one of the sillier things I’ve ever read on an
    automotive tech newsgroup.

    The BIGGEST risks for a cold engine are:

    1) fuel dilution in the engine oil and "washing" down the cylinder walls
    with raw fuel. Mostly a problem with carb’d cars, though EFI does this
    to s limited degree as well. Prolonged idling to warm the car makes this
    much worse than just driving gently.

    2) Excessive wear because clearances are larger when cold. This isn’t
    normally a big deal as long as you give it time to get the oil
    circulating before putting a full load on it. Even audible piston slap
    doesn’t really cause excessive wear most of the time. BUT, the car is
    more sensitive to how HARD its driven when cold. Romping on a stone-cold
    engine will wear it more than driving it gently for a few minutes until
    things come up closer to operating temperature.

  7. admin says:

    dnoyeB wrote:
    > huts wrote:
    > > I recently had a discussion on this topic. I have heard that revving
    > > the engine may do harm and does little to "warm" the car up. This is an
    > > older car with an engine that has been modified. This guy revvs the
    > > engine at the house and still seems to have trouble making it down his
    > > driveway (about 1/4 mile steep downhill) without stopping and revving
    > > his engine halfway down and then again at the bottom. Is this type of
    > > "warm up" accomplishing anything or is he just destroying his car?

    > Exhaust is often shut off, and other things are closed for quick warmup.

    Do you mean that incoming air is first routed over the exhaust manfold
    to warm it and thereby speed engine warmup?

    - Hide quoted text — Show quoted text -

    >   shouldn’t push the engine under these conditions as you can cause
    > stuff to wear out more quickly.  Probably not as hard on newer cars, but
    > also even less beneficial.

    > —
    > Thank you,

    > "Then said I, Wisdom [is] better than strength: nevertheless the poor
    > man’s wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

  8. admin says:

    On 3 Mar 2006 19:13:31 -0800, "John S." <hjs…@cs.com> wrote:

    >dnoyeB wrote:
    >> huts wrote:
    >> > I recently had a discussion on this topic. I have heard that revving
    >> > the engine may do harm and does little to "warm" the car up. This is an
    >> > older car with an engine that has been modified. This guy revvs the
    >> > engine at the house and still seems to have trouble making it down his
    >> > driveway (about 1/4 mile steep downhill) without stopping and revving
    >> > his engine halfway down and then again at the bottom. Is this type of
    >> > "warm up" accomplishing anything or is he just destroying his car?

    ============================================================

    >> Exhaust is often shut off, and other things are closed for quick warmup.

    What really happens in a *modern car* is the thermostat opens
    gradually, and in cold weather might take 20 minutes to open fully.
    It doesn’t *snap open* like a switch.  It starts out fully closed, but
    as soon as the engine gets to about 170 degrees F, it opens a little,
    and as the coolant becomes hotter, it opens more, until at around 200F
    it is fully open and oscillates back and forth allowing the water to
    become a little warmer, and than a little cooler, producing something
    like a sine wave with respect to the temperature signal coming from
    the engine heat sensor.

    >Do you mean that incoming air is first routed over the exhaust manfold
    >to warm it and thereby speed engine warmup?

    I don’t see how that would make any sense.  True that the coolant is
    circulated through the heater core according to dashboard settings,
    rather than the thermostat.

    Lg

    - Hide quoted text — Show quoted text -

    >>   shouldn’t push the engine under these conditions as you can cause
    >> stuff to wear out more quickly.  Probably not as hard on newer cars, but
    >> also even less beneficial.

    >> —
    >> Thank you,

    >> "Then said I, Wisdom [is] better than strength: nevertheless the poor
    >> man’s wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

  9. admin says:

    - Hide quoted text — Show quoted text -

    Lawrence Glickman wrote:

    > On 3 Mar 2006 19:13:31 -0800, "John S." <hjs…@cs.com> wrote:

    > >dnoyeB wrote:
    > >> huts wrote:
    > >> > I recently had a discussion on this topic. I have heard that revving
    > >> > the engine may do harm and does little to "warm" the car up. This is an
    > >> > older car with an engine that has been modified. This guy revvs the
    > >> > engine at the house and still seems to have trouble making it down his
    > >> > driveway (about 1/4 mile steep downhill) without stopping and revving
    > >> > his engine halfway down and then again at the bottom. Is this type of
    > >> > "warm up" accomplishing anything or is he just destroying his car?

    > ============================================================
    > >> Exhaust is often shut off, and other things are closed for quick warmup.

    > What really happens in a *modern car* is the thermostat opens
    > gradually, and in cold weather might take 20 minutes to open fully.
    > It doesn’t *snap open* like a switch.  It starts out fully closed, but
    > as soon as the engine gets to about 170 degrees F, it opens a little,
    > and as the coolant becomes hotter, it opens more, until at around 200F
    > it is fully open and oscillates back and forth allowing the water to
    > become a little warmer, and than a little cooler, producing something
    > like a sine wave with respect to the temperature signal coming from
    > the engine heat sensor.

    > >Do you mean that incoming air is first routed over the exhaust manfold
    > >to warm it and thereby speed engine warmup?

    > I don’t see how that would make any sense.  True that the coolant is
    > circulated through the heater core according to dashboard settings,
    > rather than the thermostat.

    > Lg

    Go back and look at cars with carbs in the ’70s and you will see this
    air ducking from the exhaust manifold to the air cleaner. You talk about
    "What really happens in a *modern car*" well computers and EFI are a
    different world from a modified engine with not exhaust heat to the
    intake manifold, no choke on the 2 4 bbl carbs and that has a cam that
    when the engine is warmed and running normal will not idle at less than
    1200 rpm and best of all was high test leaded gas for 36 cents a gallon.
    Stan

    - Hide quoted text — Show quoted text -

    > >>   shouldn’t push the engine under these conditions as you can cause
    > >> stuff to wear out more quickly.  Probably not as hard on newer cars, but
    > >> also even less beneficial.

    > >> —
    > >> Thank you,

    > >> "Then said I, Wisdom [is] better than strength: nevertheless the poor
    > >> man’s wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

  10. admin says:

    - Hide quoted text — Show quoted text -

    "John S." wrote:

    > dnoyeB wrote:
    > > huts wrote:
    > > > I recently had a discussion on this topic. I have heard that revving
    > > > the engine may do harm and does little to "warm" the car up. This is an
    > > > older car with an engine that has been modified. This guy revvs the
    > > > engine at the house and still seems to have trouble making it down his
    > > > driveway (about 1/4 mile steep downhill) without stopping and revving
    > > > his engine halfway down and then again at the bottom. Is this type of
    > > > "warm up" accomplishing anything or is he just destroying his car?

    > > Exhaust is often shut off, and other things are closed for quick warmup.

    > Do you mean that incoming air is first routed over the exhaust manfold
    > to warm it and thereby speed engine warmup?

    He is talking about a heat riser valve that shuts off one bank of a V
    engine’s exhaust and routes it across the intake for warming the
    fuel/air mix.

    Mike
    86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    88 Cherokee 235 BFG AT’s
    Canadian Off Road Trips Photos:  Non members can still view!
    Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    (More Off Road album links at bottom of the view page)

  11. admin says:

    - Hide quoted text — Show quoted text -

    Mike Romain wrote:

    > "John S." wrote:

    > > dnoyeB wrote:
    > > > huts wrote:
    > > > > I recently had a discussion on this topic. I have heard that revving
    > > > > the engine may do harm and does little to "warm" the car up. This is an
    > > > > older car with an engine that has been modified. This guy revvs the
    > > > > engine at the house and still seems to have trouble making it down his
    > > > > driveway (about 1/4 mile steep downhill) without stopping and revving
    > > > > his engine halfway down and then again at the bottom. Is this type of
    > > > > "warm up" accomplishing anything or is he just destroying his car?

    > > > Exhaust is often shut off, and other things are closed for quick warmup.

    > > Do you mean that incoming air is first routed over the exhaust manfold
    > > to warm it and thereby speed engine warmup?

    > He is talking about a heat riser valve that shuts off one bank of a V
    > engine’s exhaust and routes it across the intake for warming the
    > fuel/air mix.

    > Mike
    > 86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    > 88 Cherokee 235 BFG AT’s
    > Canadian Off Road Trips Photos:  Non members can still view!
    > Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    > (More Off Road album links at bottom of the view page)

    I believe this is what he is talking about. Scan from an old Chilton’s.
    http://users.erols.com/srweiss/expipe.gif
    Stan

  12. admin says:

    - Hide quoted text — Show quoted text -

    Stan Weiss wrote:

    > Mike Romain wrote:

    > > "John S." wrote:

    > > > dnoyeB wrote:
    > > > > huts wrote:
    > > > > > I recently had a discussion on this topic. I have heard that revving
    > > > > > the engine may do harm and does little to "warm" the car up. This is an
    > > > > > older car with an engine that has been modified. This guy revvs the
    > > > > > engine at the house and still seems to have trouble making it down his
    > > > > > driveway (about 1/4 mile steep downhill) without stopping and revving
    > > > > > his engine halfway down and then again at the bottom. Is this type of
    > > > > > "warm up" accomplishing anything or is he just destroying his car?

    > > > > Exhaust is often shut off, and other things are closed for quick warmup.

    > > > Do you mean that incoming air is first routed over the exhaust manfold
    > > > to warm it and thereby speed engine warmup?

    > > He is talking about a heat riser valve that shuts off one bank of a V
    > > engine’s exhaust and routes it across the intake for warming the
    > > fuel/air mix.

    > > Mike
    > > 86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    > > 88 Cherokee 235 BFG AT’s
    > > Canadian Off Road Trips Photos:  Non members can still view!
    > > Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    > > (More Off Road album links at bottom of the view page)

    > I believe this is what he is talking about. Scan from an old Chilton’s.
    > http://users.erols.com/srweiss/expipe.gif
    > Stan

    No, all carb engines have heated air cleaners, that has zip to do with
    the exhaust except to suck warm air from a box over it.  Modified
    engines tend to have aftermarket air cleaners missing this so can ice up
    easy.  That heat pipe opens and closes as the temp of the air filter
    changes so you can drive without the carb turning into a block of ice.

    They also need to heat the air in the manifold for a more efficient warm
    up.  This is done various ways.  Some older Jeeps for instance used a
    heat riser like the V8′s but the newer carb’ed Jeeps used a heater
    element at the carb base with engine coolant flowing through the
    manifold.

    The older V6′s and V8 used a manifold cross over and shut off one bank
    of the exhaust with a weighted flap on a bi-metal spring.

    I must be showing my age here…..

    Mike
    86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    88 Cherokee 235 BFG AT’s
    Canadian Off Road Trips Photos:  Non members can still view!
    Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    (More Off Road album links at bottom of the view page)

  13. admin says:

    its not good to "rev" a cold engine.

    the heat "riser" routes exhaust heat….off the manifolds up to the
    air filter housing. Its not exhaust…its heat. There is a valve in
    the air filter housing that controls the heat (it often wears out over
    time.  THe valve regulates the amount of cold air through the regular
    air pathway, and the amount of hot air coming off the exhaust.  Thats
    the way it works on the older GM vehicles.  I don’t imagine that any
    car re-routes exhaust….its just the heat coming off the manifolds.
    No connection to turb equipped cars and trucks.

    On Sat, 04 Mar 2006 10:17:04 -0500, Mike Romain <roma…@sympatico.ca>
    wrote:

    - Hide quoted text — Show quoted text -

    >"John S." wrote:

    >> dnoyeB wrote:
    >> > huts wrote:
    >> > > I recently had a discussion on this topic. I have heard that revving
    >> > > the engine may do harm and does little to "warm" the car up. This is an
    >> > > older car with an engine that has been modified. This guy revvs the
    >> > > engine at the house and still seems to have trouble making it down his
    >> > > driveway (about 1/4 mile steep downhill) without stopping and revving
    >> > > his engine halfway down and then again at the bottom. Is this type of
    >> > > "warm up" accomplishing anything or is he just destroying his car?

    >> > Exhaust is often shut off, and other things are closed for quick warmup.

    >> Do you mean that incoming air is first routed over the exhaust manfold
    >> to warm it and thereby speed engine warmup?

    >He is talking about a heat riser valve that shuts off one bank of a V
    >engine’s exhaust and routes it across the intake for warming the
    >fuel/air mix.

    >Mike
    >86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    >88 Cherokee 235 BFG AT’s
    >Canadian Off Road Trips Photos:  Non members can still view!
    >Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    >(More Off Road album links at bottom of the view page)

    ———–
    Elbert
    a…@me.com

  14. admin says:

    On Sat, 04 Mar 2006 10:09:33 -0500, Stan Weiss <srwe…@erols.com>
    wrote:

    - Hide quoted text — Show quoted text -

    >Lawrence Glickman wrote:

    >> On 3 Mar 2006 19:13:31 -0800, "John S." <hjs…@cs.com> wrote:

    >> >dnoyeB wrote:
    >> >> huts wrote:
    >> >> > I recently had a discussion on this topic. I have heard that revving
    >> >> > the engine may do harm and does little to "warm" the car up. This is an
    >> >> > older car with an engine that has been modified. This guy revvs the
    >> >> > engine at the house and still seems to have trouble making it down his
    >> >> > driveway (about 1/4 mile steep downhill) without stopping and revving
    >> >> > his engine halfway down and then again at the bottom. Is this type of
    >> >> > "warm up" accomplishing anything or is he just destroying his car?

    >> ============================================================
    >> >> Exhaust is often shut off, and other things are closed for quick warmup.

    >> What really happens in a *modern car* is the thermostat opens
    >> gradually, and in cold weather might take 20 minutes to open fully.
    >> It doesn’t *snap open* like a switch.  It starts out fully closed, but
    >> as soon as the engine gets to about 170 degrees F, it opens a little,
    >> and as the coolant becomes hotter, it opens more, until at around 200F
    >> it is fully open and oscillates back and forth allowing the water to
    >> become a little warmer, and than a little cooler, producing something
    >> like a sine wave with respect to the temperature signal coming from
    >> the engine heat sensor.

    >> >Do you mean that incoming air is first routed over the exhaust manfold
    >> >to warm it and thereby speed engine warmup?

    >> I don’t see how that would make any sense.  True that the coolant is
    >> circulated through the heater core according to dashboard settings,
    >> rather than the thermostat.

    >> Lg

    ==============================================================

    >Go back and look at cars with carbs in the ’70s and you will see this
    >air ducking from the exhaust manifold to the air cleaner.

    I believe it.  If you’re into antique automobile, there are better
    n/g’s than this one.

    > You talk about
    >"What really happens in a *modern car*"

    Yes, that’s my point.  Modern car.

    > well computers and EFI are a
    >different world from a modified engine with not exhaust heat to the
    >intake manifold, no choke on the 2 4 bbl carbs and that has a cam that
    >when the engine is warmed and running normal will not idle at less than
    >1200 rpm

    What a waste of fuel.  My engine idles at 700 rpm.

    > and best of all was high test leaded gas for 36 cents a gallon.
    >Stan

    There was nothing *best* about those old tanks.  

    Lg

  15. admin says:

    In article <ccmj0257klii8q7e3ba00cip3a9bdfe…@4ax.com>,

     Elbert <a…@me.com> wrote:
    > its not good to "rev" a cold engine.

    > the heat "riser" routes exhaust heat….off the manifolds up to the
    > air filter housing.

    Heat riser or more correctly, EFE (early fuel evaporation) is
    often a vacuum or bi-metal controlled flap in one of the exhaust
    manifolds that re-directs hot exhaust gas to a  chamber on the
    bottom side of the intake manifold underneath the carburetor.  
    This passage often serves as the feed to the EGR valve also.
    Another method is to use an electrically heated grid that mounts
    under the carburetor, i.e., early 80s GM "X" and  FWD "A" bodies.

    > Its not exhaust…its heat.

    It’s both.

    > There is a valve in
    > the air filter housing that controls the heat (it often wears out over
    > time.  THe valve regulates the amount of cold air through the regular
    > air pathway, and the amount of hot air coming off the exhaust.  Thats
    > the way it works on the older GM vehicles.  

    You’re thinking of the Thermostatic Air Cleaner (Thermac).
    Entirely possible to have both a heat riser -and- a Thermac.

    > I don’t imagine that any
    > car re-routes exhaust….

    Here’s an example of  bi-metal spring operated one:
    http://cgi.ebay.com/ebaymotors/Scout-800B-304-V-8-Heat-riser-valve
    _W0QQitemZ8042253230QQcategoryZ33635QQrdZ1QQcmdZViewItem

    Here’s an example of a vacuum operated one:
    http://cgi.ebay.com/ebaymotors/83-88-Monte-Carlo-SS-Heat-Riser-Exh
    aust-Spacer-PERFECT_W0QQitemZ8043114547QQcategoryZ33635QQrdZ1QQcmd
    ZViewItem

    > its just the heat coming off the manifolds.

    That would be the thermostatic air cleaner.

  16. admin says:

    - Hide quoted text — Show quoted text -

    Mike Romain wrote:

    > Stan Weiss wrote:

    > > Mike Romain wrote:

    > > > "John S." wrote:

    > > > > dnoyeB wrote:
    > > > > > huts wrote:
    > > > > > > I recently had a discussion on this topic. I have heard that revving
    > > > > > > the engine may do harm and does little to "warm" the car up. This is an
    > > > > > > older car with an engine that has been modified. This guy revvs the
    > > > > > > engine at the house and still seems to have trouble making it down his
    > > > > > > driveway (about 1/4 mile steep downhill) without stopping and revving
    > > > > > > his engine halfway down and then again at the bottom. Is this type of
    > > > > > > "warm up" accomplishing anything or is he just destroying his car?

    > > > > > Exhaust is often shut off, and other things are closed for quick warmup.

    > > > > Do you mean that incoming air is first routed over the exhaust manfold
    > > > > to warm it and thereby speed engine warmup?

    > > > He is talking about a heat riser valve that shuts off one bank of a V
    > > > engine’s exhaust and routes it across the intake for warming the
    > > > fuel/air mix.

    > > > Mike
    > > > 86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    > > > 88 Cherokee 235 BFG AT’s
    > > > Canadian Off Road Trips Photos:  Non members can still view!
    > > > Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    > > > (More Off Road album links at bottom of the view page)

    > > I believe this is what he is talking about. Scan from an old Chilton’s.
    > > http://users.erols.com/srweiss/expipe.gif
    > > Stan

    > No, all carb engines have heated air cleaners, that has zip to do with
    > the exhaust except to suck warm air from a box over it.  Modified
    > engines tend to have aftermarket air cleaners missing this so can ice up
    > easy.  That heat pipe opens and closes as the temp of the air filter
    > changes so you can drive without the carb turning into a block of ice.

    > They also need to heat the air in the manifold for a more efficient warm
    > up.  This is done various ways.  Some older Jeeps for instance used a
    > heat riser like the V8′s but the newer carb’ed Jeeps used a heater
    > element at the carb base with engine coolant flowing through the
    > manifold.

    > The older V6′s and V8 used a manifold cross over and shut off one bank
    > of the exhaust with a weighted flap on a bi-metal spring.

    > I must be showing my age here…..

    I don’t think so, if you say all all carb engines have heated air
    cleaners. In the ’60s check out the muscle cars and show me a heated air
    cleaner.
    Stan

    - Hide quoted text — Show quoted text -

    > Mike
    > 86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    > 88 Cherokee 235 BFG AT’s
    > Canadian Off Road Trips Photos:  Non members can still view!
    > Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    > (More Off Road album links at bottom of the view page)

  17. admin says:

    - Hide quoted text — Show quoted text -

    Lawrence Glickman wrote:

    > On Sat, 04 Mar 2006 10:09:33 -0500, Stan Weiss <srwe…@erols.com>
    > wrote:

    > >Lawrence Glickman wrote:

    > >> On 3 Mar 2006 19:13:31 -0800, "John S." <hjs…@cs.com> wrote:

    > >> >dnoyeB wrote:
    > >> >> huts wrote:
    > >> >> > I recently had a discussion on this topic. I have heard that revving
    > >> >> > the engine may do harm and does little to "warm" the car up. This is an
    > >> >> > older car with an engine that has been modified. This guy revvs the
    > >> >> > engine at the house and still seems to have trouble making it down his
    > >> >> > driveway (about 1/4 mile steep downhill) without stopping and revving
    > >> >> > his engine halfway down and then again at the bottom. Is this type of
    > >> >> > "warm up" accomplishing anything or is he just destroying his car?

    > >> ============================================================
    > >> >> Exhaust is often shut off, and other things are closed for quick warmup.

    > >> What really happens in a *modern car* is the thermostat opens
    > >> gradually, and in cold weather might take 20 minutes to open fully.
    > >> It doesn’t *snap open* like a switch.  It starts out fully closed, but
    > >> as soon as the engine gets to about 170 degrees F, it opens a little,
    > >> and as the coolant becomes hotter, it opens more, until at around 200F
    > >> it is fully open and oscillates back and forth allowing the water to
    > >> become a little warmer, and than a little cooler, producing something
    > >> like a sine wave with respect to the temperature signal coming from
    > >> the engine heat sensor.

    > >> >Do you mean that incoming air is first routed over the exhaust manfold
    > >> >to warm it and thereby speed engine warmup?

    > >> I don’t see how that would make any sense.  True that the coolant is
    > >> circulated through the heater core according to dashboard settings,
    > >> rather than the thermostat.

    > >> Lg
    > ==============================================================
    > >Go back and look at cars with carbs in the ’70s and you will see this
    > >air ducking from the exhaust manifold to the air cleaner.

    > I believe it.  If you’re into antique automobile, there are better
    > n/g’s than this one.

    > > You talk about
    > >"What really happens in a *modern car*"

    > Yes, that’s my point.  Modern car.

    > > well computers and EFI are a
    > >different world from a modified engine with not exhaust heat to the
    > >intake manifold, no choke on the 2 4 bbl carbs and that has a cam that
    > >when the engine is warmed and running normal will not idle at less than
    > >1200 rpm

    > What a waste of fuel.  My engine idles at 700 rpm.

    > > and best of all was high test leaded gas for 36 cents a gallon.
    > >Stan

    > There was nothing *best* about those old tanks.

    > Lg
    > >> >> > This is an older car with an engine that has been modified.

    When someone asks about a modified engine telling them about your
    factory stock / modern car does them little good. The point is to answer
    the question that was ask.
    Stan

  18. admin says:

    On Sat, 04 Mar 2006 14:17:13 -0500, Stan Weiss <srwe…@erols.com>
    wrote:

    - Hide quoted text — Show quoted text -

    >Lawrence Glickman wrote:

    >> On Sat, 04 Mar 2006 10:09:33 -0500, Stan Weiss <srwe…@erols.com>
    >> wrote:

    >> >Lawrence Glickman wrote:

    >> >> On 3 Mar 2006 19:13:31 -0800, "John S." <hjs…@cs.com> wrote:

    >> >> >dnoyeB wrote:
    >> >> >> huts wrote:
    >> >> >> > I recently had a discussion on this topic. I have heard that revving
    >> >> >> > the engine may do harm and does little to "warm" the car up. This is an
    >> >> >> > older car with an engine that has been modified. This guy revvs the
    >> >> >> > engine at the house and still seems to have trouble making it down his
    >> >> >> > driveway (about 1/4 mile steep downhill) without stopping and revving
    >> >> >> > his engine halfway down and then again at the bottom. Is this type of
    >> >> >> > "warm up" accomplishing anything or is he just destroying his car?

    >> >> ============================================================
    >> >> >> Exhaust is often shut off, and other things are closed for quick warmup.

    >> >> What really happens in a *modern car* is the thermostat opens
    >> >> gradually, and in cold weather might take 20 minutes to open fully.
    >> >> It doesn’t *snap open* like a switch.  It starts out fully closed, but
    >> >> as soon as the engine gets to about 170 degrees F, it opens a little,
    >> >> and as the coolant becomes hotter, it opens more, until at around 200F
    >> >> it is fully open and oscillates back and forth allowing the water to
    >> >> become a little warmer, and than a little cooler, producing something
    >> >> like a sine wave with respect to the temperature signal coming from
    >> >> the engine heat sensor.

    >> >> >Do you mean that incoming air is first routed over the exhaust manfold
    >> >> >to warm it and thereby speed engine warmup?

    >> >> I don’t see how that would make any sense.  True that the coolant is
    >> >> circulated through the heater core according to dashboard settings,
    >> >> rather than the thermostat.

    >> >> Lg
    >> ==============================================================
    >> >Go back and look at cars with carbs in the ’70s and you will see this
    >> >air ducking from the exhaust manifold to the air cleaner.

    >> I believe it.  If you’re into antique automobile, there are better
    >> n/g’s than this one.

    >> > You talk about
    >> >"What really happens in a *modern car*"

    >> Yes, that’s my point.  Modern car.

    >> > well computers and EFI are a
    >> >different world from a modified engine with not exhaust heat to the
    >> >intake manifold, no choke on the 2 4 bbl carbs and that has a cam that
    >> >when the engine is warmed and running normal will not idle at less than
    >> >1200 rpm

    >> What a waste of fuel.  My engine idles at 700 rpm.

    >> > and best of all was high test leaded gas for 36 cents a gallon.
    >> >Stan

    >> There was nothing *best* about those old tanks.

    >> Lg

    >> >> >> > This is an older car with an engine that has been modified.

    >When someone asks about a modified engine telling them about your
    >factory stock / modern car does them little good. The point is to answer
    >the question that was ask.
    >Stan

    Hair dryer.  Is what I use on my landscaping equipment in wintertime
    to get engines/carburetors warm enough to start.  It is the only thing
    that works for me 100 times out of 100.

    No iced carbs, no frozen fuel lines, just vrooom putt putt putt

    Hair dryer.  For my landscaping equipment.  A car?  Lift the hood, use
    remote switch, blast hairdryer on carb.  vrooom putt putt putt

    I still say, 1.8 liter is little more than a lawnmower engine where I
    live.  Not to sound like a snob, I owned a Renault R8, and a Fiat
    Sardine Can for many years.  I know the problems that go along with
    these *more economical* vehicles.  That’s why I will never own one
    again.

    Lg

  19. admin says:

    Nope, you are talking about the thermostatically controlled air filter
    and it’s heat pipe.

    The GM V8′s and V6′s of the 70′s and 80′s with carbs and TBI’s used a
    heat riser valve to shut off the driver’s side exhaust manifold forcing
    all the exhaust to cross over under the intake manifold and exit out the
    passenger side pipe until it warmed up.  I haven’t checked the newer
    ones specifically for that.

    Here is a link that shows both:

    http://www.hedman.com/pages/emissions-access.html

    The first photo shows the air filter heat pipe setup and the last photo
    shows the heat riser valve to shut off the exhaust on that pipe.

    Mike

    - Hide quoted text — Show quoted text -

    Elbert wrote:

    > its not good to "rev" a cold engine.

    > the heat "riser" routes exhaust heat….off the manifolds up to the
    > air filter housing. Its not exhaust…its heat. There is a valve in
    > the air filter housing that controls the heat (it often wears out over
    > time.  THe valve regulates the amount of cold air through the regular
    > air pathway, and the amount of hot air coming off the exhaust.  Thats
    > the way it works on the older GM vehicles.  I don’t imagine that any
    > car re-routes exhaust….its just the heat coming off the manifolds.
    > No connection to turb equipped cars and trucks.

    > On Sat, 04 Mar 2006 10:17:04 -0500, Mike Romain <roma…@sympatico.ca>
    > wrote:

    > >"John S." wrote:

    > >> dnoyeB wrote:
    > >> > huts wrote:
    > >> > > I recently had a discussion on this topic. I have heard that revving
    > >> > > the engine may do harm and does little to "warm" the car up. This is an
    > >> > > older car with an engine that has been modified. This guy revvs the
    > >> > > engine at the house and still seems to have trouble making it down his
    > >> > > driveway (about 1/4 mile steep downhill) without stopping and revving
    > >> > > his engine halfway down and then again at the bottom. Is this type of
    > >> > > "warm up" accomplishing anything or is he just destroying his car?

    > >> > Exhaust is often shut off, and other things are closed for quick warmup.

    > >> Do you mean that incoming air is first routed over the exhaust manfold
    > >> to warm it and thereby speed engine warmup?

    > >He is talking about a heat riser valve that shuts off one bank of a V
    > >engine’s exhaust and routes it across the intake for warming the
    > >fuel/air mix.

    > >Mike
    > >86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    > >88 Cherokee 235 BFG AT’s
    > >Canadian Off Road Trips Photos:  Non members can still view!
    > >Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    > >(More Off Road album links at bottom of the view page)
    > ———–
    > Elbert
    > a…@me.com

  20. admin says:

    - Hide quoted text — Show quoted text -

    Stan Weiss wrote:

    > Mike Romain wrote:

    > > Stan Weiss wrote:

    > > > Mike Romain wrote:

    > > > > "John S." wrote:

    > > > > > dnoyeB wrote:
    > > > > > > huts wrote:
    > > > > > > > I recently had a discussion on this topic. I have heard that revving
    > > > > > > > the engine may do harm and does little to "warm" the car up. This is an
    > > > > > > > older car with an engine that has been modified. This guy revvs the
    > > > > > > > engine at the house and still seems to have trouble making it down his
    > > > > > > > driveway (about 1/4 mile steep downhill) without stopping and revving
    > > > > > > > his engine halfway down and then again at the bottom. Is this type of
    > > > > > > > "warm up" accomplishing anything or is he just destroying his car?

    > > > > > > Exhaust is often shut off, and other things are closed for quick warmup.

    > > > > > Do you mean that incoming air is first routed over the exhaust manfold
    > > > > > to warm it and thereby speed engine warmup?

    > > > > He is talking about a heat riser valve that shuts off one bank of a V
    > > > > engine’s exhaust and routes it across the intake for warming the
    > > > > fuel/air mix.

    > > > > Mike
    > > > > 86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    > > > > 88 Cherokee 235 BFG AT’s
    > > > > Canadian Off Road Trips Photos:  Non members can still view!
    > > > > Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    > > > > (More Off Road album links at bottom of the view page)

    > > > I believe this is what he is talking about. Scan from an old Chilton’s.
    > > > http://users.erols.com/srweiss/expipe.gif
    > > > Stan

    > > No, all carb engines have heated air cleaners, that has zip to do with
    > > the exhaust except to suck warm air from a box over it.  Modified
    > > engines tend to have aftermarket air cleaners missing this so can ice up
    > > easy.  That heat pipe opens and closes as the temp of the air filter
    > > changes so you can drive without the carb turning into a block of ice.

    > > They also need to heat the air in the manifold for a more efficient warm
    > > up.  This is done various ways.  Some older Jeeps for instance used a
    > > heat riser like the V8′s but the newer carb’ed Jeeps used a heater
    > > element at the carb base with engine coolant flowing through the
    > > manifold.

    > > The older V6′s and V8 used a manifold cross over and shut off one bank
    > > of the exhaust with a weighted flap on a bi-metal spring.

    > > I must be showing my age here…..

    > I don’t think so, if you say all all carb engines have heated air
    > cleaners. In the ’60s check out the muscle cars and show me a heated air
    > cleaner.
    > Stan

    Ya ya, they fall into the modified class in my book and I have helped a
    pile of those owners retrofit the heat pipes once they realized their
    carbs were turning into ice blocks come winter so they could use them
    year round.  Along with a second set of rims and snow tires….  Most
    just parked them come cold weather.

    - Hide quoted text — Show quoted text -

    > > Mike
    > > 86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    > > 88 Cherokee 235 BFG AT’s
    > > Canadian Off Road Trips Photos:  Non members can still view!
    > > Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    > > (More Off Road album links at bottom of the view page)

  21. admin says:

    On Sat, 04 Mar 2006 18:55:08 GMT, Neil Nelson <nonel…@sbcglobal.net>
    wrote:

    - Hide quoted text — Show quoted text -

    >In article <ccmj0257klii8q7e3ba00cip3a9bdfe…@4ax.com>,
    > Elbert <a…@me.com> wrote:

    >> its not good to "rev" a cold engine.

    >> the heat "riser" routes exhaust heat….off the manifolds up to the
    >> air filter housing.

    >Heat riser or more correctly, EFE (early fuel evaporation) is
    >often a vacuum or bi-metal controlled flap in one of the exhaust
    >manifolds that re-directs hot exhaust gas to a  chamber on the
    >bottom side of the intake manifold underneath the carburetor.  
    >This passage often serves as the feed to the EGR valve also.
    >Another method is to use an electrically heated grid that mounts
    >under the carburetor, i.e., early 80s GM "X" and  FWD "A" bodies.

    >> Its not exhaust…its heat.

    >It’s both.

    >> There is a valve in
    >> the air filter housing that controls the heat (it often wears out over
    >> time.  THe valve regulates the amount of cold air through the regular
    >> air pathway, and the amount of hot air coming off the exhaust.  Thats
    >> the way it works on the older GM vehicles.  

    >You’re thinking of the Thermostatic Air Cleaner (Thermac).
    >Entirely possible to have both a heat riser -and- a Thermac.

    >> I don’t imagine that any
    >> car re-routes exhaust….

    >Here’s an example of  bi-metal spring operated one:
    >http://cgi.ebay.com/ebaymotors/Scout-800B-304-V-8-Heat-riser-valve
    >_W0QQitemZ8042253230QQcategoryZ33635QQrdZ1QQcmdZViewItem

    >Here’s an example of a vacuum operated one:
    >http://cgi.ebay.com/ebaymotors/83-88-Monte-Carlo-SS-Heat-Riser-Exh
    >aust-Spacer-PERFECT_W0QQitemZ8043114547QQcategoryZ33635QQrdZ1QQcmd
    >ZViewItem

    >> its just the heat coming off the manifolds.

    >That would be the thermostatic air cleaner.

    now that I think about it…I believe you are right.
    Many of the 70′s year model cars had all kind of crap in the emission
    controls, and other junk.  I think I do remember some type of valve
    in the exhaust manifold (one side) of my 78 z/28. Of course those went
    in the garbage (had to install headers).  I believe it was a
    "butterfly" value in the exhaust manifold and had  metal rod that
    operated it off a vaccum valve (is this right….anyone recall the GM
    Crap?)  

    I bought the car used and the first thing that went was that valve
    "thing" in the exhaust, and on went dual exhaust. Then the intake
    and the smog carb went away too. Dual plane and holley went on next.

    I was wrong in my statement above…  thats been a few years ago.

    I know that "valve thing" does not do much justice to the item but
    maybe you’ll understand :)   Thats been 20+ years ago now.

    Boy all that crap on those cars was about useless. I remember the smog
    pumps, and all the crazy vaccum lines.  I think the stock 78 z/28 had
    about 180 HP…boy what a machine :)

    The factory air clearner went out the door too.  I had a lot of fun
    with that car….especially after it ate a rod bearing….re-built the
    motor / trans and added a mild stall converter.  Pretty hot street
    machine then.

    Long story short….I was wrong.
    ———–
    Elbert
    a…@me.com

  22. admin says:

    - Hide quoted text — Show quoted text -

    Mike Romain wrote:

    > Nope, you are talking about the thermostatically controlled air filter
    > and it’s heat pipe.

    > The GM V8′s and V6′s of the 70′s and 80′s with carbs and TBI’s used a
    > heat riser valve to shut off the driver’s side exhaust manifold forcing
    > all the exhaust to cross over under the intake manifold and exit out the
    > passenger side pipe until it warmed up.  I haven’t checked the newer
    > ones specifically for that.

    > Here is a link that shows both:

    > http://www.hedman.com/pages/emissions-access.html

    > The first photo shows the air filter heat pipe setup and the last photo
    > shows the heat riser valve to shut off the exhaust on that pipe.

    > Mike

    Again here is the link which shows a GM engine from the ’70s with
    exactly what Neil is talking about.
    http://users.erols.com/srweiss/expipe.gif
    Stan

    - Hide quoted text — Show quoted text -

    > Elbert wrote:

    > > its not good to "rev" a cold engine.

    > > the heat "riser" routes exhaust heat….off the manifolds up to the
    > > air filter housing. Its not exhaust…its heat. There is a valve in
    > > the air filter housing that controls the heat (it often wears out over
    > > time.  THe valve regulates the amount of cold air through the regular
    > > air pathway, and the amount of hot air coming off the exhaust.  Thats
    > > the way it works on the older GM vehicles.  I don’t imagine that any
    > > car re-routes exhaust….its just the heat coming off the manifolds.
    > > No connection to turb equipped cars and trucks.

    > > On Sat, 04 Mar 2006 10:17:04 -0500, Mike Romain <roma…@sympatico.ca>
    > > wrote:

    > > >"John S." wrote:

    > > >> dnoyeB wrote:
    > > >> > huts wrote:
    > > >> > > I recently had a discussion on this topic. I have heard that revving
    > > >> > > the engine may do harm and does little to "warm" the car up. This is an
    > > >> > > older car with an engine that has been modified. This guy revvs the
    > > >> > > engine at the house and still seems to have trouble making it down his
    > > >> > > driveway (about 1/4 mile steep downhill) without stopping and revving
    > > >> > > his engine halfway down and then again at the bottom. Is this type of
    > > >> > > "warm up" accomplishing anything or is he just destroying his car?

    > > >> > Exhaust is often shut off, and other things are closed for quick warmup.

    > > >> Do you mean that incoming air is first routed over the exhaust manfold
    > > >> to warm it and thereby speed engine warmup?

    > > >He is talking about a heat riser valve that shuts off one bank of a V
    > > >engine’s exhaust and routes it across the intake for warming the
    > > >fuel/air mix.

    > > >Mike
    > > >86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    > > >88 Cherokee 235 BFG AT’s
    > > >Canadian Off Road Trips Photos:  Non members can still view!
    > > >Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    > > >(More Off Road album links at bottom of the view page)
    > > ———–
    > > Elbert
    > > a…@me.com

  23. admin says:

    you are right….  I got caught up on the heat pipe to the carb and I
    clearly forgot about the other stuff.  I spent a lot of time removing
    all that junk. It did not stay on the car long (the one I had at the
    time) back in my HS days. (early 80′s)

    Thanks for correcting me….I should have thought through my answer
    and done a little research prior to my post.

    Elbert

    On Sat, 04 Mar 2006 14:42:10 -0500, Mike Romain <roma…@sympatico.ca>
    wrote:

    - Hide quoted text — Show quoted text -

    >Nope, you are talking about the thermostatically controlled air filter
    >and it’s heat pipe.

    >The GM V8′s and V6′s of the 70′s and 80′s with carbs and TBI’s used a
    >heat riser valve to shut off the driver’s side exhaust manifold forcing
    >all the exhaust to cross over under the intake manifold and exit out the
    >passenger side pipe until it warmed up.  I haven’t checked the newer
    >ones specifically for that.

    >Here is a link that shows both:

    >http://www.hedman.com/pages/emissions-access.html

    >The first photo shows the air filter heat pipe setup and the last photo
    >shows the heat riser valve to shut off the exhaust on that pipe.

    >Mike

    >Elbert wrote:

    >> its not good to "rev" a cold engine.

    >> the heat "riser" routes exhaust heat….off the manifolds up to the
    >> air filter housing. Its not exhaust…its heat. There is a valve in
    >> the air filter housing that controls the heat (it often wears out over
    >> time.  THe valve regulates the amount of cold air through the regular
    >> air pathway, and the amount of hot air coming off the exhaust.  Thats
    >> the way it works on the older GM vehicles.  I don’t imagine that any
    >> car re-routes exhaust….its just the heat coming off the manifolds.
    >> No connection to turb equipped cars and trucks.

    >> On Sat, 04 Mar 2006 10:17:04 -0500, Mike Romain <roma…@sympatico.ca>
    >> wrote:

    >> >"John S." wrote:

    >> >> dnoyeB wrote:
    >> >> > huts wrote:
    >> >> > > I recently had a discussion on this topic. I have heard that revving
    >> >> > > the engine may do harm and does little to "warm" the car up. This is an
    >> >> > > older car with an engine that has been modified. This guy revvs the
    >> >> > > engine at the house and still seems to have trouble making it down his
    >> >> > > driveway (about 1/4 mile steep downhill) without stopping and revving
    >> >> > > his engine halfway down and then again at the bottom. Is this type of
    >> >> > > "warm up" accomplishing anything or is he just destroying his car?

    >> >> > Exhaust is often shut off, and other things are closed for quick warmup.

    >> >> Do you mean that incoming air is first routed over the exhaust manfold
    >> >> to warm it and thereby speed engine warmup?

    >> >He is talking about a heat riser valve that shuts off one bank of a V
    >> >engine’s exhaust and routes it across the intake for warming the
    >> >fuel/air mix.

    >> >Mike
    >> >86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    >> >88 Cherokee 235 BFG AT’s
    >> >Canadian Off Road Trips Photos:  Non members can still view!
    >> >Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    >> >(More Off Road album links at bottom of the view page)
    >> ———–
    >> Elbert
    >> a…@me.com

    ———–
    Elbert
    a…@me.com

  24. admin says:

    thanks for the link….  yea I clearly forgot all about that…

    I remember telling the exhaust guy to through that crap away
    and put on some real dual exhaust.

    You guys were right on.

    On Sat, 04 Mar 2006 14:42:10 -0500, Mike Romain <roma…@sympatico.ca>
    wrote:

    - Hide quoted text — Show quoted text -

    >Nope, you are talking about the thermostatically controlled air filter
    >and it’s heat pipe.

    >The GM V8′s and V6′s of the 70′s and 80′s with carbs and TBI’s used a
    >heat riser valve to shut off the driver’s side exhaust manifold forcing
    >all the exhaust to cross over under the intake manifold and exit out the
    >passenger side pipe until it warmed up.  I haven’t checked the newer
    >ones specifically for that.

    >Here is a link that shows both:

    >http://www.hedman.com/pages/emissions-access.html

    >The first photo shows the air filter heat pipe setup and the last photo
    >shows the heat riser valve to shut off the exhaust on that pipe.

    >Mike

    >Elbert wrote:

    >> its not good to "rev" a cold engine.

    >> the heat "riser" routes exhaust heat….off the manifolds up to the
    >> air filter housing. Its not exhaust…its heat. There is a valve in
    >> the air filter housing that controls the heat (it often wears out over
    >> time.  THe valve regulates the amount of cold air through the regular
    >> air pathway, and the amount of hot air coming off the exhaust.  Thats
    >> the way it works on the older GM vehicles.  I don’t imagine that any
    >> car re-routes exhaust….its just the heat coming off the manifolds.
    >> No connection to turb equipped cars and trucks.

    >> On Sat, 04 Mar 2006 10:17:04 -0500, Mike Romain <roma…@sympatico.ca>
    >> wrote:

    >> >"John S." wrote:

    >> >> dnoyeB wrote:
    >> >> > huts wrote:
    >> >> > > I recently had a discussion on this topic. I have heard that revving
    >> >> > > the engine may do harm and does little to "warm" the car up. This is an
    >> >> > > older car with an engine that has been modified. This guy revvs the
    >> >> > > engine at the house and still seems to have trouble making it down his
    >> >> > > driveway (about 1/4 mile steep downhill) without stopping and revving
    >> >> > > his engine halfway down and then again at the bottom. Is this type of
    >> >> > > "warm up" accomplishing anything or is he just destroying his car?

    >> >> > Exhaust is often shut off, and other things are closed for quick warmup.

    >> >> Do you mean that incoming air is first routed over the exhaust manfold
    >> >> to warm it and thereby speed engine warmup?

    >> >He is talking about a heat riser valve that shuts off one bank of a V
    >> >engine’s exhaust and routes it across the intake for warming the
    >> >fuel/air mix.

    >> >Mike
    >> >86/00 CJ7 Laredo, 33×9.5 BFG Muds, ‘glass nose to tail in ’00
    >> >88 Cherokee 235 BFG AT’s
    >> >Canadian Off Road Trips Photos:  Non members can still view!
    >> >Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
    >> >(More Off Road album links at bottom of the view page)
    >> ———–
    >> Elbert
    >> a…@me.com

    ———–
    Elbert
    a…@me.com

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