Quote:
Originally Posted by Daox
Modifying the exhaust will alter your powerband. However, this is much more drastic on a turbocharged engine. On a naturally aspirated engine the effect is much less and the ECU should be able to compensate for it.
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With a 4 cyl. powerplant, exhaust modification is much more noticeable in the lower range of the power band than with a v8. However, it also depends on how many liters you're packing, especially on a naturally aspirated motor.
My 2.4L 4 cyl 240sx responded quite nicely to 3" exhaust, netting me a nice MPG gain along with my free flowing air intake system. However, my built 1988 CRX HF with a "mini-me" 1.5L (with a 16v head) lost power, torque and mileage after even a 2.5" exhaust upgrade (115 FWHP before to 101 FWHP after).
If one truly treats an engine like it is an air pump and balances the volume of air in to the volume of air out with proper tuning, I see no reason why one cannot have both performance and economy here. Personally, I've had a 272 rwhp/278 rwtq 2.0L turbocharged motor in a 2700lb car pull down over 35 mpg due to the fact that it it was tuned correctly. The air to fuel on any car is key, not just putting a washer in the 1" tailpipe to fool the computer into thinking that it's running rich/lean. Attack the programming, optimize it, help the engine out by making it operate as the air pump it was really meant to be.
God knows, you can actually go fast while being thrifty...at least one could start out with something aerodynamic.