emwporsche

I am just curious:
when my car had an exhaust leak it was backfiring.
my dad (ex racer/mechanic) said it's really bad to do that,
because it's shooting flames back into the engine and out the exhaust.

Now I've noted that people on rennlist say when they take out their cat it backfires.
I am planing to take out my cat.

Is it really shooting falmes into my engine?
Will this reduce the longevity of anything?

rhesus

i was under the impression that it was just unburned fuel igniting as it hits the hot exhaust (instead of the cat)... i don't see how it could go back into the engine though

PorscheDoc

what is this about shooting cats? that sounds like fu......oh wait, shooting flames without a cat installed....ahhhhh i was getting excited there for a minute No offense to cat lovers.....just joking around

turbo944

I am under the same impression. Turbo cars if running right will usually be running a bit rich and when you come out of a hard acceleration you'll have extra fuel that doesn't get burned going through the exhaust, into a hot turbo and igniting. The cat would normally absorb most of that and control it, but without that restriction, it zips down the exhaust and out the tailpipe and can make that popping sound. If it happens too much (ie you are running too rich) you can clog up the cat.....kinda like a hairball I guess.....

emwporsche

when he stated this, my headers had a big hole in them.
so it didn't take anything but a quick throttle movement to make it pop.
(it had no exhaust pressure)

So you guys are saying that with no leak but without a cat, it will only pop when when coming off a lot of throttle quickly? only when you get into boost?

I imagine that yes if your giving it a lot of gas and in boost, the pressure would carry it out the tip, away from the engine.

thanks a lot,

Eric

roadrunner

A true backfire blows back into the intake - do our fuel injected engines do this? I've had carburetor fires because of backfires, but I've never seen a fuel injected engine shoot a pressure wave back into the intake...

W88951

emwporshce, your original problem was probably not related to an over rich condition. What was occuring when you car backfired was this. When under throttle your exhaust system becomes pressurized because of the exhaust flow. When you let off the throttle there is a point where a vacum will occur and fresh air from outside will enter the exahaust. Hot exhaust with unburned gas + fresh supply of cooler combustion enabling oxygen = Backfire.

emwporsche

so what your saying is that it doesnt hurt the engine or the exhaust pipe when it pops - because the cat is removed.

thanks a bunch,
Eric

86944turbo

Karl2bdc,

You 'otta be ashamed. CATS ARE PEOPLE, TOO. They're just smaller targets. I own 3 cats. Or, is it 3 cats own me. 4, if you include the one I've had in my shed for 10 yrs. that's watin' for the price of platinum to go up.