The physics of your exhaust?
 

So I was having some trouble with emissions... Long story short -- I was driving my 91 NA around with a cat that was too short.

While I was driving the car like this, I noticed a few things;

1. It sounds like shit. I mean really REALLY bad. Not really a big surprise to me.

2. I had NO power what-so-ever. This surprised me. I do have an SAFCII set from -10 to -20. This might be why. Or the 190k mi w no rebuild.

I thought that you could just chop off your exhaust (like a cutout) + get more power? Or do you need a long exhaust to get the engines full potential?


Discuss.

lol....search, there are many exhaust threads.

Search under the user rotarygod. I think I may have created a couple of threads.

Ok instead of searching let me just say this.

The BEST possible exhaust set up is NO EXHAUST AT ALL. Plain and simple if you really want to set your engine bay on fire to get really good exhaust flow, go righth ahead and let us know how it turned out.

I am gonna have to disaggree 100% in a NA application

a good header system scavanges between rotors aswell as other things........

original poster, you confuse me with what you said..... so you are running a cat that is unhooked at the rear from the rest of the system? or what? If it isn't an original cat what is it?

Not to make a huge debate out of this thread that could have been searched for, but at least with my old blazer oepn headers killed that thing. Granted, it was a 350, but I think the same principles apply since it was N/A. In higher rpm's it was okay, but accel sucked. Did sound SICK though! :ylsuper:

Anyway, I believe a properly designed system is a must for anything not going straight for a 1/4 mile or full race prepped. Even then sometimes they benefit from an exhaust system depending on application.

^^^ I think you burn the valve seats or guides up on a SBC super rapid with no exhaust, dont remember which

doesnt sound fun

An exhaust system is not just a restriction, it's a power adder. You'll make more power with a properly designed exhaust than no exhaust.

I think that's wrong...the drag racers do it all the time, right? I only did it for a mile to the exhaust shop. Now, had I been running NO headers, the story would be a little different.

And yes, I agree with the exhaust being a power adder.

And na fc open header sounds like an angry weed eater on crack. No good.for driving around town.

I think for turbo though, anything after the exhaust manifold is a restriction since there's no scavenging done there.

Should of clarified i meant no headers or anything on the heads,......

Not to mention it is louder than most people can imagine. Think dragsters at full throttle.... With just the exhaust manifold, turning it on would set off car alarms from several blocks away.

^ I would do that just to be an ass :D

for a turbo, the less backpressure the better. for n/a a properly designed exhaust will add power

Yep, no exhaust equals shit for power, at least in the low end. My ears would not allow me to get into the higher RPM range to find out any difference.

just a funny thought but my dad has a 91 bronco with straight pipes after the cats and he started it up one day in the pep boys parking lot and both cars beside his alarms went off :rlaugh:

serious open header drag cars are designed for high rpm and the motors are rebuilt all the time. As for an na you want a properly designed exhaust. If you go to big you will lose scavaging and low end power. on a turbo car you want the least restriction....
But about passing emission what where you numbers what gas/s did you fail for. You will need to have cats to pass emission.

So I had some aftermarket cat (maremont or something like that) But it was too short, so I had it unhooked after the cat/before the Y pipe.

Yeah, It totally sounded like an angry ass weed whacker on crack.

I failed emissions because of HC while driving. Required is 150ppm, I got 162. Fresh plugs, even tried the denaturalized alcohol or whatever it's called.

I have the new cat w an extension pipe welded on it so it should fit now.