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Old 11-05-2012, 02:23 AM   #15 (permalink)
RobertISaar
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Join Date: Jul 2012
Location: camden, MI
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MC SBX - '95 Chevrolet Monte Carlo LS
Last 3: 29.75 mpg (US)
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Quote:
Originally Posted by bestclimb View Post
The throttle plate restricts air at the TB. If you fit a smaller TB you will have more restriction there so you will open the throttle a little more for the same power. This will result in the same amount of air going in so the computer will send in the same amount of fuel.

The biggest change you may note is that it takes more "foot" so you will have to make your self push harder to go as fast as you did before. You may see an increase in mileage but it will be more of a driver behavior thing than from any magic happening at the throttle body.

A similar effect could be gotten by putting a heavier spring on the linkage.
this guy gets it. with a smaller opening, you'll just be opening the throttle more to let the exact same amount of air into the engine for the same situation as a larger throttle.

however, i think in the end you'll end up with worse fuel economy. reason being that a LOT of stuff in the PCM is dependant on TPS readings. larger TPS readings mean you are closer to kicking into power enrichment mode, so you'll run into richer AFRs a lot faster. larger amounts of TPS will also delay shift points for the transmission, meaning you'll stay in lower gears for longer amounts of time or even get forced out of higher gears entirely.

being a MAP or MAF system won't make much difference here unless your PCM goes into a failure mode, in which case a MAF car determines airflow almost entirely from RPM and throttle position and a MAP car is from RPM, throttle position and a few other load adjustment parameters. if that were to happen, since you are going to flow less than what the PCM is calibrated for, expect significantly richer AFRs until the O2 sensor catches up.
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