mods and MPG

[coil222]

Hi, no CRZ here but thinking about switching out my 07 impreza for one. Assuming you're not driving aggressively (as mods can make you have a tendancy to do) would simple mods like I/H/E make your gas mileage worse on these cars?

[northbridge]

no.

bolt on mods dont make the engine more powerful per se. What they do is make the engine more efficient and in that case your MPG should always stay the same at worst or improve.

Intake: either provides cooler air for more efficient combustion and denser air or a less restrictive intake path. If you drive equally, no loss in MPG - should see gains

Header: NA on this car because the Mani is integrated. You will end up with something like a downpipe.

Cat delete: instead of exhaust gas flowing through the cat core you have a pipe with no restrictions. No decrease in exhaust gas velocity, no restrictions which leads to further efficiency.

Exhaust: more efficient, less bends - reduces back pressure.

All of these things should make your car more powerful AND efficient.

[drkato]

[QUOTE=northbridge;60572.

Cat delete: instead of exhaust gas flowing through the cat core you have a pipe with no restrictions. No decrease in exhaust gas velocity, no restrictions which leads to further efficiency..[/QUOTE]

doing anything to the catalytic converter will cause the check engine light to come on. PCM monitors output to make shure it is functioning propperly.

[northbridge]

The O2 sensor is before the second cat on this car so a cat delete does not throw a code.