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Old 04-27-2006, 10:55 PM   #7
wolfman
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Join Date: Jun 2002
Location: Texas
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Default Re: NA SOHC w/SAFC-II for increased mpg?

The heated air intake system discussed/used in another thread works to increase MPG in TWO ways. It makes the PCM "see" the hotter "thinner" air which causes the PCM to LEAN out the fuel mixture, AND (more importantly) it actually SUPPLIES that heated air. It works WITH the existing system instead of fighting with it, or trying to "fool" it.

(Gasoline also vaporizes more readily in HOT air than in COLD)

LEANER mixtures = HIGHER MPG
RICHER mixtures = LOWER MPG

The only real problem with running consistantly too lean is you risk burning valves due to increased combustion temperatures. The PCM should compensate for this well within reason, provided you are working WITH the OEM system instead of against it. In short, if you can provide the PCM with operating conditions like those seen in the desert (HOT thin air) the car will generally get better MPG numbers than if you provide the PCM with operating conditions like those seen in the arctic.

This is why turbo charged engines require higher octane fuel and most use intercoolers as well (to COOL the very HOT (but also dense) turbo compressed air, AND provide a fuel that RESISTS detonation at high temperatures.) In a HOT air NA (normally aspirated) system, the air is HOT but NOT dense. So a lower octane fuel can be used. (Its about the oxygen content in relation to the temperature of the incoming air charge)

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