Just yesterday after a short drive from work i experienced a pretty sudden drop in power in the upper rpm of the engine and i picked up a high pitch sound from the exhaust. The local rotory shop says that the one of the cats has probably plugged up and the sound i am hearing is the exhaust trying to escape through a small hole. my car is a completely stock n/a 88 vert. my question is am i risking damage to the engine driving with the added back pressure. i don't plan on driving on it for longer than a month and i don't put that many miles on it weekly. i figure it would be a good time to pick up a complete after market exhaust system since the stock cats are a couple hundred a piece anyways.

 

its fine as long as you don't try to drive it in the range where its really bad for long periods.

but yeah if its suddenly slow, and makes whistling noises something collapsed, lol. it might just be a muffler though.

 

Pull the precats and inspect. Look through the cats and see if you can see any light coming through. If not just hollow them out. You only need the main cat for smog.

My mufflers were plugged on my TII when I first got it. So it does happen.

 

I think a whole new exhaust system will be the best remedy i'm set on a superflo mid section and racing beat cat back but can't decide if the racing beat headers at worthy for a car that won't get many if any other engine work. My only other plans were for Atkins 5th 6th Ports.

 

Those Atkins port sleeves supposedly produce a noticeable power gain. I never got around to installing my Pineapple Racing sleeves so I can't give first hand testimony though.

I really felt my Corksport header produced power gains, and I already had the precat deleted. My only other power mods were twin high flow cats and a catback. But the real substantial gain from the headers was the sound

 

How much louder was your car with headers

 

s4's need some backpressure in the exhaust.

 

My headers didn't make my car too much louder since I didn't have a precat even before the headers, but they were noticeable.

 

Only 2psi right. Decided not to do the headers

 

Not sure about the PSI. I would just hollow out the precats and leave the main cat alone. Doesn't cost anything and is worth a try.

 

What shop did you go to?

On one of my NAs, I had RB header, pre-silencer, to dual oldschool RB RSR exhaust. Worked and sounded fantastic!

 

Hollowed out cats sound like cack.

I had headers, a 3 inch catback, and twin high flow cats and it was enough to open the 5/6th port actuators, so don't worry about that.

 

That's good to know. You guys make it hard to decide

 

Yes, I agree. But if you hollow out just the "PRE-CATS" and leave the main cat alone you really can't tell a diffrence at all.

It cost no $ to do this and may eliminate the clogged cat problem. I've done this on 2 prev 7's and they passed smog no problem while also running better!

 

^ I agree with you too. That precat is supposedly on there just for start-up emissions purposes.

 

why s4's and not s5's

 

s5 NA's 5th/6th ports are actuated by the air pump, not backpressure from the exhaust. Its a much less crude way to go about it since backpressure can change depending on so many different parameters.

 

any issues passing smog with that setup? Im out in California.

 

shouldn't be. in fact there is a 99% chance that the precats already are hollow, its pretty rare to find one with something in it.

if want numbers though, i just smogged an S4 na with no precats, and it was really clean. you should see the main cat too, it looks BAD. it did like 36ppm HC, 0.06co and 200ish NOX.

 

thats good to know. so i'm set on the headers after all, rb headers, bonez superflo, rb cat back

 

i did a 1st gen with headers and a cat, i think HC's went down. i don't recall the other two though, CA has changed the limits, and it used to be we didn't care about the other two

 

This setup isn't legal. To pass the visual portion of the smog check, you need to have all 3 cats.. 2 precats and 1main cat.

 

My 88 s4 passed smog with flyinig colors a year later after the precat hollowing. I'm in Cali also!

 

I agree.. just hallowing out your pre-cats will not cause an issue with smog in CA. As long as they are on there you will pass the visual, and the main cat should be enough to pass the emissions portion.

 

if anyone is considering removing your cats, don't hollow them out, sell them to me! i pay $130 for the main 2nd gen cat and $25 for each pre-cat