exhaust manifold - Pontiac GTO Forum
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post #1 of 5 (permalink) Old 01-14-2011, 01:53 PM Thread Starter
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exhaust manifold

One of my Ex manifolds has a flapper inside of it and what I'm guessing is a heat sensitive coil on the outside.
What the heck is this for?
Can I get rid of the flapper?
thanks as always
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post #2 of 5 (permalink) Old 01-14-2011, 04:55 PM
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One of my Ex manifolds has a flapper inside of it and what I'm guessing is a heat sensitive coil on the outside.
What the heck is this for?
Can I get rid of the flapper?
thanks as always
Its purpose is to restrict exhaust flow/heat on that bank, forcing more of it to instead flow through the heat riser passages in that cylinder head, through the intake manifold passges under the carb, and into the other head and out the exhaust on that side. It's supposed to help the carb work "better" in cold temps by warming it up and also to warm the intake manifold to help prevent fuel from dropping out of suspension from the air flow. If you're plugging/blocking the head heat passages, then you'll want to also disable/remove this flapper. Otherwise the exhaust flow on that side will be significantly restricted.

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post #3 of 5 (permalink) Old 01-14-2011, 07:32 PM Thread Starter
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so I need to block some passage(s) on the head(s) ?
where are they?
what do they look like?
are they on both heads?
thanks

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post #4 of 5 (permalink) Old 01-14-2011, 08:29 PM
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Topkat, my suggestion is to leave the heat passages alone on the heads and intake, and to make sure the flapper moves freely. You're not building a race car, and the GM engineers knew what they were doing. Blocked exhaust pre-heat passages help keep the incoming air fuel mixture cooler, offering more power potential. They also make for a poor running engine on the street when cold, and cause a street engine to take a long time to warm up and run properly. This lack of heat when cold causes raw fuel to contaminate the engine oil, wash the cylinders of oil, and can shorten engine life on a street driven engine. If you're building a car for the track, no pre heat is fine.
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post #5 of 5 (permalink) Old 01-14-2011, 10:30 PM
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Topkat, my suggestion is to leave the heat passages alone on the heads and intake, and to make sure the flapper moves freely. You're not building a race car, and the GM engineers knew what they were doing. Blocked exhaust pre-heat passages help keep the incoming air fuel mixture cooler, offering more power potential. They also make for a poor running engine on the street when cold, and cause a street engine to take a long time to warm up and run properly. This lack of heat when cold causes raw fuel to contaminate the engine oil, wash the cylinders of oil, and can shorten engine life on a street driven engine. If you're building a car for the track, no pre heat is fine.
. Topkat, plugging those passages and the like are mods that are done in the interest of getting all the performance you can. As was pointed out, there is a cost in terms of cold operation and also in not being "original". Unless you're really trying to chase max power, you're probably better off making sure all those systems are functioning as designed.

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