Cat Delete
 

I've been surprised to find almost no information on the site regarding exhaust modification. I'm specifically curious about the effects of replacing a catalytic converter with a testpipe. I know the cat is typically the most restrictive portion in an exhaust and opening it up typically results in a few HP gained, just not sure how this correlates to efficiency. As a general rule (and assuming a properly functioning cat) would you expect to gain, or possibly lose, power from freeing up exhaust flow?

CAT deletes are discouraged on this site. The CAT might be a restriction at maximum engine output (max load & rpm), but if you're driving to get good fuel economy (where you're not pusing THAT much air through the engine), the CAT will never be a restriction. Add to the fact that it is illegal and it does keep the air we breathe clean and there really is no reason to remove it.

ditto what he said.
1. exhaust systems(from the mainifold to the tail pipe) are only 'restrictive' (if at all) at wide open throttle.
2. there have been several discussions on exhaust systems. I have posted a chart that shows pipe sizes vs max hp several times. bottom line.......you'll NEVER use the full potential of the stock system.
3. If you look at the dyno graphs that aftermarket companies (sometimes) use to advertize a product: cai, wai, test pipes, etc......the gains are almost always at the top of the range. 5k rpm & up. I drove a 02 Infiniti Q45 V8 w/ 340hp and saw 5k rpms for a total of maybe 15 minutes in 278,000 miles.

Thanks for the replies, that actually makes a lot of sense considering the light throttle/low rpm conditions we're going for.

there you have it! you go it! :thumbup:

look up some of the exhauts threads.....they've been very informative.

check under 'catback'

a more worthwhile venture would be to modify the exhaust to maximize torque, after all horsepower is simply a function of torque.

If its fully functional there is no reason to mess with it.

you imply that:
1. torgue needs to be 'maximized'
2. that somehow the current stock systems are terribly flawed.

please explain.

stock systems do a pretty good job, but long tube headers with a crossover pipe can help, depending on the engine in question

My 98 Tacoma 4x4 was cat less a egr less. Long tube headers no cat and a muffler off a silverdo. Custom intake and amsoil stage 2 filter.

I was netting 28 -29 mpg when trying. ( rated 20 highway) 24ish with out eoc or trying hard.
But that's from a torquey 2.7 4 cyc truck motor.
Also had 11lbs flywheel. I think 30lbs was stock.

Would I do it again. I dout it.