Cold weather starting using headers?????
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500, 472, 425, 368 Discussion, Cold weather starting using headers????? in Cadillac Engine Technical Discussion; I have a 1975 500 that I want to put in a Jaguar and run headers. With the current set ...
  1. #1
    lead sled is offline Cadillac Owners Member
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    Cold weather starting using headers?????

    I have a 1975 500 that I want to put in a Jaguar and run headers. With the current set up there is a some hardware coming off the back of the passanger side exhaust manifold with a tube going to the front of the intake manifod and branching off to the the carb and distrubrator. My understanding is that this setup is used to run hot exhaust gas to the intake to aid in cold wearther start up.

    How can I help cold weather start up if I elimanate this exhaust gas feedback?

    Also what should I do about the EGR valve, I assume thats what this thing is in the back of the manifold behind the carb? I really don't think that it is working at peak performance since it is covered in rust. I live in MO as of yet I don't have to worry about meeting any kind of emission standards but at the same time I don't want to eat away the ozone either. Any suggestions????

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  3. #2
    BluEyes's Avatar
    BluEyes is offline Cadillac Owners Enthusiast
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    Re: Cold weather starting using headers?????

    That is the EFE valve, or early fuel evaporation.

    It has nothing to do with initial startup because the valve is open at that time (no vacuum)
    It does recirculate exhaust gasses, but not really to warm the carb. There are other systems that help warm the carb. What this does is force the engine to reburn some of the exhaust on a cold start. Since the choke is on during a cold start and the engine has a rich mixture, there is still unburnt fuel in the exhaust, and this is working to burn that fuel to lower emissions. The vacuum hose for this should be connected to a TVS (thermal vacuum switch) that will shut off vacuum to the valve once the engine has warmed up enough for the choke to be off, and allow the valve to open.
    As for doing this with headers, I dunno. If your headers will bolt in place of the stock manifolds then there is a chance you might get it to work, but otherwise no. The valve will probably also limit what size exhaust pipes you can run.

    The carb is warmed by the exhaust crossover in the intake and the heat riser valve. The exhaust crossover heats the intake below the carb to reduce fuel puddling. The heat riser is the tube from the air cleaner snorkel to the exhaust manifold. It pulls hot air in when the engine is cold to reduce freeway icing, and improve throttle response in cold weather (really cold air does not atomize fuel very well). Both of these help you when you are driving on a cold engine, but still do nothing for the initial start. Only the choke helps on initial cold start.

    As for the EGR, that's a touchy issue with many. I know most people will just yank it, but GM has found that EGR can actually give you more part-throttle power by cooling combustion, and allowing more spark advance to be used. At WOT the EGR closes anyways, so it has no effect on WOT performance.
    The EGR also should have a TVS on the vac line to it, only this one is just the opposite as for the EFE. It is closes (no vac passes) when the engine is cld, and opens when the engine warms. I think some cars had a three port TVS that switched the vacuum from the EFE to the EGR when the engine warmed, but I am in no way sure about this, it just makes sense because that would prevent two exhaust recirculation devices from working at the same time.

    Will making sure all these systems work take more time? Yes. Will your car run better and pollute less? Probably, but it will take more time to get it right than a simple system that you tossed everything on.
    I would try and do it. Really, these emissions systems don't affect performance much if at all. It was those crappy pellet style cats, small camshafts, single exhaust, and low compression that made the '70's cars such dogs compared to their '60's counterparts.

  4. #3
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Cold weather starting using headers?????


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