Im considering installing them just to kill the awful smell pump gas makes these days. I even get around my car after its been run and i can smell the fumes on me. And no its not an overly rich condition. Anyone run the 3" cats and did they kill a lot of power?

If it is not running that rich, it shouldn't smell that bad? Cats aren't going to 'fix' the issues it sounds like really. Sounds like the car has other issues perhaps... (I have a friend with a couple of carb'd cars still both with larger cams, aftermarket most things, stroker engines, etc and no smells out of them really.


And I have a modern engine swap in my car and don't run cats (I have the rear O2 sensors tuned out)...can't see a reason to run an exhaust restriction if not needed..

If you can smell it then it's running rich. The new gas doesn't smell any more than the old stuff if the car is tuned right.

If its running rich... or slightly different situation you have some air fuel charge running through the engine at low RPM due to a high overlap cam, the cats won't like it. They will try to "burn" it, then overheat, then plug up and fail. Hopefully not cause a fire in the process.

With a high overlap cam, ignition timing helps clean up the idle. 20 degrees as a ballpark. With timing set, carb tuning helps. Still, there may be some smell. I have it with a 243 degree @.050 cam. Nature of the beast. Probably not an issue with intake duration of ~220 degrees or less.

what's the combination, and how do you know it's not a rich condition? have you check using a gas analyzer?

I hear ya. Mine is a custom Bullet cam with 255@ .050. I have a custom carb that will do anything i want it to as far a getting rid of a rich condition. It reeks ( more or less)no matter where i put it. My last car was a 5.0 mustang with fuel injection. With the cats you could stand behind the car all day. With the cats off via off road h pipe it would still gag ya, and it was clean burning.

That is a pretty different animal. You are comparing a mild cammed, fuel injected, computer controlled catalyst setup to a big cam carbureted car.

For sure. My stock 360 Magnum EFI without a cat and it stinks too. Everything from my 1 bbl to 6 bbl make your eyes water.

But, (quote from an online SRT Engineer session) converters cost 25 hp.

I've also noticed that alot of the older engines left in production with converters (like the Magnums) crack heads. I've even run into a fellow that had it happen on a 5.7 hemi.

Your best option is to run leaded fuel, that's what I do.

If you can smell fumes on you, you've got tune issues. Its not the gas.