mrb455

There seems to be a lot of opinions as to what to do with the main cat on a stock system. I have a 88 n/a and was thinking of guting the main cat but some say it doesn't have that much restriction and some say it will help a lot and the 5th and 6th ports will still open.--- How much restriction is there and would I realy see that much difference ?

offthewagon

if you're driving an n/a, taking out the cat will result in a fairly large loss in backpreasure which will give you at the very least a few horses, maybe more. this also results in ALOT of noise...the bad noise. sounds like a 50cc if you have stock mufflers. you might also realize a small increase in your gas mileage as less resistance from the air on either end will mean a more efficiant engine. a loss in backpreasure also means that the auxilery ports won't open all the way, if at all. youll require some other means of opening, such as wiring them open, or a kind of air valve, using excess created by the air pump. if you do a search on this website, or on the web, i'm sure you'll find a website with the writeup on how to do it.

oh, and the smell coming out the back with will pretty bad as well. unburnt rotary burnoff smells a hell of alot worse then your average piston engine.

all in all, i've taken my race pipe out and left the cat in. it sounds better, it smells better, and the performance loss isnt enough to warrent the other two.

mrb455

I was wondering about that, I dont want the noise and if the gain isn't that great it doesn't sound like it is worth it. Thanks

JerryLH3

iTrader: (11)

I've heard (and driven) a friend's car with stock mufflers, stock manifold and an RB downpipe/presilencer combo. It's not loud at all, and sounds very good. The smell is not bad. I didn't motice it at all unless I was standing right behind it. In which case, it smelled like a rotary, not much more offensive than my car with a catalytic converter (which I'm positive has failed anyway).

So, there you go, you now have completely contradicting opinions. Smells and sounds are completely objective - you need first hand experience to tell what will work for you.

Going with a presilencer combo from RB would see significant gains, and my friend's S4 has no problem opening the auxiliary ports.

cds00bsmg

iTrader: (1)

I have a 87 SE auto. with 79k on it. I gutted the main cat. and the secondary cat. I replaced the primary cat. with the pipe from a s5 car, and am running a stock exhaust system into 2 new OEM mufflers. I also replacked all the exhaust gaskets and sealed them with high temp. copper sealer, and replaced all the exhaust bolts. The car has a good tone, and is not loud at all in the car, until its at about 6.5k or so, but even then its no louder than a my 00 z24 cranked to about the same RPM. Its not loud at all, and it doesn't really draw any attention unless I'm reving the crap out of it. Smell wise, I think the only odor is that coming from an exhaust leak I had between the primary pipe and secondary pipe which I have since fixed. As far as backpressure for my secondaries, they open fine, if not better than before, and I get about 21-22mpg city while still driving the car a lot more agressively than my wankalier (cavalier).

91_fc

well offthewagon is talking about just the gutted cat. JerryLH3 is taking about the RB header/prescilencer combo. The gutted cat sounds like ****. period. i'm not sure however how much hp you will gain from it. The RB header/prescilencer combo says that you will gain about 18 horses. (i called them) and gives your car a nice exhaust note without being ridiculously loud. in either case, you will lose low rpm power and gain top end. i'm personally planning to buy the RB system after getting smog checked.

ridesnowx4

Well, if you combine it with an aftermarket exhaust it is a pretty good increase. I noticed because I at first got just a catback exhaust and there wasnt any real gain, so I took off my cats and put a straight pipe and holy ****, there was power! Loud, definately, but it sounds good with an aftermarket exhaust, nice and deep.