John H

Anyone out there dynoed their car with a cat only and then run it with cat bypasses? I have a dyno sheet from my car with cats and "supercups" i.e. no baffles. Just wondering whether I will help or hurt myself running cat bypasses and baffle-less exhaust pipes. It sounds faster

Do straight exhausts cause a gain or loss of HP and/or torque?

And yes I did a search but I am not sure I constructed the search terms appropriately bcause I am sure this has been discussed here.

Mark in Baltimore

John,

I thought I had read here that bypasses, while sounding great, take away from hp and/or torque.

pcar964

John, can't help you with your question - but you have the best avatar on Rennlist! haha "shall I turn it up?"

TroyN

If you decrease exhaust backpressure you should get an increase in top end HP, but a decrease in low-end torque. Generally. No dyno numbers for my recent bypass install, but the butt-dyno seems to agree.

993inNC

Only if you couple that with a strait through exhaust, and even then as has been represented here, the top end benefits but the down low punch goes away. I run by passes with motorsound muffs (for street) and it rockets of the line. Top end differences are marginal at best (couple hundred rpm)

John H

I am doing it as hard as I can.


Mark/Chris

That's what I thought I remembered. I am going to a NASA event next weekend. I may put it on the dyno just to see. I have a baseline with just cats and the rest straight thru. Right now, as the car sits, it is straight thru all the way. It would be interesting to finally know for sure. God knows I can't afford to lose any torque as slow as I am thru the corners.

TroyN

The January 2006 "911 and Porsche World" magazine had an article on a 964 where the owner removed the cat and the shop that did it dyno'd a 15 horsepower increase. Would likely be similar with the 993.

poorb0yw

I lost power on mine with straight pipes. Less power on the dyno and slower times on the drag strip.

Sound on decel is badass tho.

993inNC

964's are so restricted its not funny. I think its something like 20 hp gain by replacing the heat exchangers with 993 exchangers. The problem is that the heat'g system is different, but if you don't live in a cold climate........

pcar964