MichelleJD

Betcha can't gut this cat!

86 951 Driver

Put a glasspack where the cat goes. It will help take away any of the rasp that you get with gutting the cat. Also gutting the cat causes a disturbance in flow for the exhaust. Just put a non louvered(s/p) glasspack in there and it will great.

Team SSR

Most of our cars are 15 years old or older. I would bet many of the higher mileage ones are running "gutted" cats wether they know it or not. That honeycomb stuff doesn't stay in there forever...

Campeck

and that exactly why it sounds good.
on an NA its another story. it can be any metal. i just said SS cause you did

you know what mustangs sound like with straightpipes? take that, make it ten times worse....and then stick it right between 3k-4.5k rpm.

on the turbo the turbo itself muffles the exhaust pulses so it doesnt sound like a bunch of big empty cans jingling around in your exhaust like with the NA.

Mike1982

Where is a sound clip when you need one... I know there are plenty of turbo cars (including myself) that could get a clip of a cat-less 951 but not a 944 NA. Someone out there has to have it plus a way to record it for this man!

Campeck

ive heard turbos are the shiznit with it. do it!!!

nas are the.....****...with it. dont. lol

mavfan

i did the bypass as well... DONT EVER DO IT! it SUCKS SO MUCH, and it rattles like hell ALL the time, and whether its closed or not its loud as...well you know!

Don 944 LA

I gutted my cat with a golf shaft from an old club and a big piece of rebar ..

I did not do it for performance.
The catalyst material had worn down and there was a big chunk that would turn sideways restricting ALL flow through, due to the honeycomb material.

I haven't noticed any performance change other than sound and the fact that it doesn't drive like there is a potato stuffed in the exhaust..

I plan on reinstalling a cat when I get the $$.

Don

chrly924s

My 924S came with a test pipe in place of a cat. Doesn't sound too bad, but I may try the glass pack in its place.

KuHL 951

If that is the case I would like to see how your NA car performs with zero backpressure. Go ahead, install a full 3"-4" pipe from your headers back and you be will wanting to ride a bus...you have to have some backpressure in an NA; reducing backpressure is much more critical on a turbo.

Campeck

BLAAAAAH!!!

its not backpressure its resonance!!!!!!
you need resonance not backpressure! gutting cat = messed up resonance. but not so bad. = everyone assumes its a "loss of backpressure" when its really a loss of resonance!

going to 4" exhaust will obvioulsy have no backpressure. but geuss what?! it will have no resonance either. ( you could tune for resonance. but the gas velocities will be uber-slo cause of the HUGE pipe. and will not be very good at getting the high/low waves up and down the exhaust)

let me go more technical. if an exhaust always had backpressure in it..instead of resonance. then what would happen is that every time the exhaust valve opened. the exhaust would resist coming out.
this would cause
1.) parasitic loses.
2.) contamination of the intake charge with exhaust gases. (which also slows combustion by blocking the flame from getting to the fresh AR mixture)
3.) hotter intake charge resulting in less density.

and if the valves overlap. like they do in an NA. then not only will the exhaust back up inot the cylinder. it will go right up the intake tract.

what you want is high/low pressure waves going back and forth up the exhaust at sonic speeds. you time the low pressure wave to get to the exhaust valve as it opens. not only does this help scavenge the exhaust gases out of the cylinder, but it helps pull the frsh AR charge into it as well.

now for all you who dont believe me. go put freekin restricters in your exhaust if you love backpressure so much and dyno your car.

944kid

did you learn this from the intake you were making(I believe it was you... ) I know all that talk went in my one ear, and then right out the other. Oh well.

chitown928s4

I dont know about a gutted cat but Speedy944 gutted his muffler and modified it so its basically a cat with a straight muffler and it sounds sick, as in really cool. I like the way it sounds. That sound is definately better than running it with a straight pipe which is what I did very briefly but went back to the cat cuz it sounded horrible.

tomrc

Like I said i have a straight pipe welded in the place of the cat and it's just crap pipe from Pep boys also. It doesn't sound loud or even bad at any RPM. Everything else on the exhaust is stock. So I'm not sure what all the fuss is about. I don't really even hear the exhaust much until I'm over 4k. No rattles either.

Odd.

xsboost90

backpressure isnt high enough to overcome 90-120lbs compression, it is simply enough to keep the flow out of the engine constant instead of choppy, which disturbs "resonance". In a turbo, the turbo hot side itself causes enough backpressure for the motor so beyond that no exhaust backpressure is required, but a nice exhaust w/ some resonance helps enhance flo. W/ an n/a motor, you need some sort of backpressure to keep the gases from excaping too quickly, for the engine to recover and helps return the exhaust valve w/o floating it. Tuning your exhaust simply combines both aspects. Run your motor w/ no backpressure and see if you burn a valve up!