A while back I changed my old clogged up converter with a Rodney Dickman replacment and it made a noticable difference in the performance and gas mileage of the car. Now Im wondering if any performance or mileage increase is possible if I would straight pipe the converter. Im sure It wouldnt be a ton but just curious. + & - for doing it and not doing it?

Thanks,
Jason

No, not any increase in power by removing a modern monolithic converter.

JazzMan

Ok Jason, my before and after performance, mileage was negligible on my 87 automatic V-6. Performance actually increased just ever so slightly (low end) with the cat but the noise factor was so much improved in the automatic, the cat helps tremendously with the exhaust tone.
Now my 86 4-speed V-6 doesn't have a cat, mileage is just a touch less than the automatic, exhaust tone is acceptable to slightly bold without the cat.

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jetman
Silver 86 SE 2M6 4-speed, with "check wallet light"

The power increase from a straight pipe over a MODERN cat converter would be too small to register on anything but some sensative machinery.
Now over an old converter, there can be a small one (especially if the exhaust manifolds have been freed up) and anything will be better than a clogged one, but right now you would only be increasing emissions if you removed your cat.

Thanks guys for the posts! So how much louder is it without the cat??

Jason

I bought a 1988GT last Fall with the cat removed and replaced with a straight pipe to the muffler. I found it both raspy (not a nice sound) and noisy so that I ran with my stereo turned way up. I put a resonator in place of the straight pipe and it mellowed out nicely with a much quieter by deep sound. I plan on having both the engine and tranny rebuilt over this coming winter and expect to install a new cat and restore the car much to it's original config. I think the 2.8 with a few mods will serve me well.

Any power increase when removing the cat is really minor. Go port the exhaust manifolds and put in 1:6 rockers and you'll see and hear a difference. A very comprehensive tuneup will help, too.

As far as futzing with the emissions (removing the cat, disabling the EGR) I guess I'd politely ask you to leave those things in and make sure that they're working. Even if there isn't smog testing where you live, those smog components help to improve the local and global atmosphere. We've all heard (I'd hope) about greenhouse gases--but on a more local scale, the crap that's put in the air by smoggy vehicles (HC, NOx, and CO ) contributes to ground ozone and acid rain. In other words it makes haze and harmful particulants (Chicago gets hazy, doesn't it?,) polluted lakes (from nitric acid,) and dead or dying forests. If you have trouble believing in acid rain, take a trip to Gettysburg sometime and have a look at the statues and monuments. They're melting--and are visibly degraded from when I was a kid back in the 50's and 60's. As my H/S government teacher used to say frequently, "If you're not part of the solution, you're part of the problem." Back in the 60's that was a revolutionary statement.

I have to smog my cars every year here in Reno. Expensive and a pain in the butt. But kind of a badge of honor when they come in WAY below the standard. Funny you should mention cats, I have a new, less restrictive one coming from Fierostore--$150 and well worth it. On an 88 that doesn't drip or smoke.

quote Originally posted by BrewCheese: Thanks guys for the posts! So how much louder is it without the cat?? Jason

On a stock system with the exhaust manifolds ported the automatic is obnoxiously loud without cat.
The 4-speed is an acceptable stout with a bold tone, poignant but not overbearing as long as you don't get your foot into it, otherwise it's borderline obnoxious.
Amazing to me that there was such a difference in sound with the only difference being the transmission.

I agree with jetman, I took off the most of the exhaust system to put the strait pipe & some other things in and hated it, gave it a couple days, tore it back apart and installed a Catco . Still has the Fiero growl.