lilblackZ28

Just as the title states. I have mac mids with 3 in straight pipe exhaust.No cat or muffler.

Puck

iTrader: (17)

Due to the widespread myths and misconceptions on the internet about backpressure, this may get some arguments going.

No 4-stroke engine "needs" backpressure, it needs scavanging...which is a product of header design(primary length, diameter, shape, etc), not any exhaust restriction from cats or mufflers. To be blunt, anything after the collector is a restriction and bad for power. What misleads a lot of people is that some find it hard to realize that air is both taken in and exhausted in pulses, not steady streams. You want the vaccum following behind one pulse to literally pull the next pulse of air out of the engine. That has nothing to do with backpressure, but some backpressure is introduced in a properly tuned header that increases scavenging.

That being said, of course you will need the proper tune to see a benefit. Without a tune you could very well hurt performance. That is also not counting problems which may arise from things like haveing the o2s catch outside air and give inaccurate readings from too short of an exhaust or open headers...

lilblackZ28

thanks

lt170chevelle

iTrader: (2)

car craft magazine actually did a test on a mustang with open exhaust versus 2 1/2" versus 3" and actually found the best combo was a stepped exhaust system consisting of 2 1/4" at collector to 2 1/2" at x pipe to 3" at muffler.it was like a 15ish ft lb and similar hp versus open headers. this basically created a very effecient scavenging system and can be done similar on an f-bod.

Formula350

iTrader: (3)

To me that makes sense