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Old 06-03-2008, 02:10 PM   #1
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Warm Air or Fresh Air?

My 1988 Escort 1.9L TBI has the old heat riser system that runs off of vaccumn. My question is if I blocked the door to get warm air from the exhaust manifold all of the time would that help my gas mileage or would it make it act more like a choke since it would not be getting any fresh cool air from road draft.

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Old 06-03-2008, 02:19 PM   #2
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The passage through the heat riser will be free flowing enough so that the engine isn't "choked" (unless there is a mouse/mud dauber nest in the heat riser).

Your current system was designed so that the engine is always drawing air of a certain temp by mixing hot and fresh air. You could play around with it and do experiments to see if the factory setup is optimal or if you could do better with a max hot setting.

IMHO, I think that drawing only hot air on a hot day might be a little too hot.

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Old 06-04-2008, 08:26 AM   #3
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my truck does the same thing, called a pre-heater hose. it's meant to maintain a certain intake air temperature because the ECU doesn't calculate air density from temperature to get mixture. in other words, CAI/WAI doesn't really do much to affect fuel usage, just mixture.

your ECU may or may not be set up that way so the effects may or may not be the same. it shouldn't be choked but you'll have to experiment to find what's best.
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Old 06-04-2008, 08:42 AM   #4
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there have been mixed opinions on this as far as warm air vs cool air (normal intake)

my car had good results and others have had no positive results. someone also mentioned some other sensor that could potentially be damaged by too high a temperature intake air (can't remember what it was called).

mine typically runs in the neighborhood of 135-150 deg. I did hit 160 once and I haven't had any issues with overheating (yet).

personally, I think it is worth a try just don't expect huge gains from it and do more research because of that one sensor I mentioned. I don't know if that is true or not, just what I heard.
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