Starfox07

I was browsing through various threads and PM'ing a few people about exhaust setups and I thought of something that I hadn't 'really' seen before. What if, instead of using a resonator or straight through muffler after he header as a silencer, I used a high-flow cat? Seems like cats would better withstand the temperature (my current dynatec lasted less than a year) and it might be nice to not have the unpleasant burning oil/gas smell (or at least less of it) while I'm sitting at a light or the drive through with my windows open.

Do high-flow cats require a source of air or are they sort of 'stand-alone?'

Will they take the abuse of being right after the header of a naturally aspirated 13b?

Will they do anything to quiet the exhaust? I figure they would because removing or gutting cats seem to make cars quite a bit louder.

I figure I would lose a few hp, but I don't think much.

Otherwise I'm just going to get a cheapy resonator from dynomax or something.

j9fd3s

iTrader: (3)

ive played with this on a couple of cars.

the first was a 20B FC, it had an RB turbo back exhaust, the older black 80mm one. and we subbed the center muffler for the biggest cat we could find (its for a 7.4L truck, the core is wait for it, just a little smaller than the stock FC but with 3" in/out). power and response were nearly unchanged. it actually got a little louder, and the exhaust note wasn't quite as good, but since the car was really quiet anyways, it wasn't a problem. i did melt the F%&k out of this one, but it was an ECU problem, and since it was like 1" past the heat shield it melted the carpet, it got hot enough (i kept driving, i was NOT walking to work), that one of the RB tips changed color, the other one was plugged, as the cat actually liquidized (spell check says thats a word?), and plugged the other one. this is why i no longer own a haltech

second. same car, but with a 13BT. subbed the same RB presilencer for the main cat that you're supposed to buy for the FC. peak power was the same, but response was so bad, i sold the car, it sucked, it took ALL of the fun out of it. noise was about the same? passed smog...

third! a GSL-SE. when i plopped the new engine in, it got a collected RB header, with an aftermarket cat and extended pipe to replace the RB presilencer, kind of like what mazdatrix sells now. http://www.mazdatrix.com/e-gray.htm power and noise VS the presilencer were about the same, however the presilencer is only like 1.75" ID, and the cat was 2" so it wasn't making big power with either one! it passed smog like this, actually it was very clean.

the air connection to the cat is not needed, but you should have the air pump and ACV so it can get PORT AIR.

also since there is room move the cat as far back as you can, but not so far back that there is no heat shield over it, otherwise it will melt things.

also i'd oversize the cat, the aftermarket cats are much smaller than the OEM, and um they don't flow as well, but you can get em with bigger pipe sizes. and it is a legal move to run like a 2 or 2 1/4" exhaust with a 2.5" cat...

Starfox07

I have no emissions needs as the car is older than 25 years (in texas that means no emissions test). Sounds like it's more of a headache than anything. I've already taken off the ACV and air pump, I would rather not add weight. That was a much more in-depth post than I was expecting, thanks for your response! I think I'm going to get a dynomax resonator.