View Full Version : 97 STS eliminate the converter?

01-15-04, 01:08 PM
I have a '97 STS, the exhaust is in need of replacement and I thought I would look for some performance out of the replacement. I would like to eliminate the converter and the resonator, then run straight 2.5 inch pipe into some dynomax super turbo mufflers and exit the stock tips.

Does anyone know if the computer will have problems with the O2 sensors located infront and behind the converter, I planned on putting them back in, in their original locations in the new straight pipe? I don't have emissions inspection here, so I am not worried about that aspect. Has anyone done anything similar with their cars exhaust?

Also, maybe someone has had a similar noise out of their car. I have what sounds like an intermittent growl on medium to hard acceleration, I kind of sounds like and induction noise, but I have checked out the induction system and everything is in tact. If I powerbrake the car to midrange RPM, it will make the growl constantly. Any help would be greatly appreciated.

01-15-04, 01:43 PM
you may not have emissions, but if you get pulled over, and they look down there its a HUUUUUGE fine. i think i heard like $20,000 for not having a cat. and your exhaust will smell really bad, so the cop would have a reason to look. Id go with a highflow cat (i did actually!).

without a cat, your car will throw codes, a cheap 02 simulator will get rid of this. even if you get a highflow cat, it may still throw codes (turn on the SES light) so id still put a 02 simulator on. ive got a 95, obdI, so i don't have a second 02 sensor

as far as ditching the resonator, you will get a drone on the highway. makes it a tad bit louder, but the drone is annoying.

97 concours
01-15-04, 02:27 PM
It's not going to be a bit loud, it's going to be real loud.

01-15-04, 05:50 PM
I hollowed out the cat on my 97 after having problems and prevented any codes from appearing by cutting the rear 02 sensor wires and wiring in 2 cheap radio shack resistors. 10,000 miles and no problem. I cannot remember the values I used, I measured the 02 sensor output with a multimeter when the engine was hot. Then using the heater wires, I built a divider to get that voltage and fed it into the sense wire.

I replaced the mufflers with Thrush Boss Turbos (please no cheapass remarks). The exhaust is real throaty, but not loud cruising on the highway, it is noticeable on acceleration and sweet at wot. I did have to insert a 2.5" (i think) pipe through the hollowed out cat to eliminate some very loud resonances.

You proposed setup will be very loud I think. I have heard negative reports about removing the resonator. Also some have said that the larger piping increases the noise level. I know that gutting the cat will make the exhaust louder.

Whatever you do, good luck.

01-15-04, 06:09 PM
I want to thank everyone for their imput. I got a hold of a local Cadillac tech who does a lot of conversion install with the Northstar, from sandrails to street rods. He also has his own STS worked over. Here is what he told me to do. Go to a hi-flow magnaflow converter, eliminate the resonator. We will run 2.5 inch pipes through the Y into 2.5 inch IMP turbo mufflers. If it is too loud then go to Magnaflow turbo mufflers. If still too loud then replace the resonator only if it is a straight through style (evidently there are two styles a stepped and a straight through)., if a stepped resonator replace it with a straight throught glass pack.

Anyway, I will post the final install and the results on Monday.

01-15-04, 06:17 PM
i would atleast use a glasspack for a resonator

i dont have a resonator, and there is a slight drone.