What's the truth about headers & free flow exhaust ?

Some people claim more HP & Torque and Faster 0-60 , and some claim you loose low end power but gain top end power . ... I don't wanna loose any low end power .

The truth is they will help you. Stock exhaust sucks, especially the manifolds.

Martin

here's what happened when i switched from the stock manifolds, no cat, 2 1/4" stock intermediate pipe to stock muffler to edelbrock 6872 headers, catco 6007 3" converter, and flowmaster 17151 3" catback. does that answer your question?

http://www.fl-thirdgen.org/mrr23/images/dynosheet/dyno108-1.jpg

there you go.Good answer. I say you need a tad of back pressure. Thats why I run a cat now instead of a of road pipe. The cat gives me that extra bit of pressure so my bottom end is good.

Stock manifolds stink. The stock y-pipe (or should I call it a "T" pipe?) really stinks. Stock cat isn't too bad assuming it's in good shape. The stock muffler is a bit of a restriction but it also doesn't have much growl to it, either, which is reason enough to replace it.

You'll pick up power EVERYWHERE in the RPM range with a good exhaust from headers back. Expect no miracles, but it'll be a noticable seat-of-the-pants improvement even on a stock engine, and greater gains are possible on more heavily modified engines.

Originally posted by Geezer powered
there you go.Good answer. I say you need a tad of back pressure. Thats why I run a cat now instead of a of road pipe. The cat gives me that extra bit of pressure so my bottom end is good. Backpressure is always bad, regardless of RPM. It has to do with velocity...

Yep....you wanna slow down the exhaust flow....reduce backpressure....

Is it necessary to get an aftermarket chip after installing headers? Or is it just when you mod engine internals?

Just wondering cuz I have a 3" pipe from the cat-back into a flowmaster 2 chamber 80 series (I think its an 80 series) muffler with dual 2-1/4" outlets and its pretty damn loud. However, I still have the stock exhaust manifolds and was considering installing headers.

I'd do headers before catback exhaust...no matter how well your exhaust flows...if the headers in front of them dont' flow...it's pointless...the majority of people get exahust for sound tho not performance...so they do catback before headers...even tho the headers are probably worth more HP since the stock manifolds suck.

Originally posted by StealthElephant
Yep....you wanna slow down the exhaust flow....reduce backpressure.... Ummmm, no. You don't want to slow down the exhaust. You want it to be able to exit the system as quickly as possible. That is velocity. Now depending on your engine setup and what you want out of it will determine the exhaust tubing size. Larger sizes have a greater velocity at higher RPMs, smaller sizes have greater velocity at lower RPMs but lose it up top. If you want to slow down your exhaust I will tell you how to lose a bunch of velocity. Put on stock manifolds, design a ypipe like the stock one and use single 1.5" pipe and three mufflers. There ya have it, you slowed down your exhaust. On the other hand 1 7/8" headers and dual 5" exhaust wouldn't be good for your application because it too would kill velocity. Get it?

Larger diameter flows slower, by doing so it reduces static pressure. Your confusing volume with velocity. You want to move the same volume of exhaust out, at a lower velocity. How can you maintain a lower velocity but still move the same volume of exhuast? You increase the diamater of the exhaust pipe, thus slowing down the velocity, but maintaining the volume. This reduces backpressure...all your trying to do is reduce backpressure...your always going to move the EXACT same volume out, you want it to come out slower, so you have less static pressure.

So you want to exhaust to move in the pipe slower?

Just remove the exhaust from the rear back and test it. See if it helps at all.

Also, I had LPE redo the EPROM after the intakes and headers. With each set of mods you could feel a difference. However, I felt it did not run up to the full potential so I had the EPROM reburnt and that fixed it right up. BBTW, I use my wife as a test. If she can feel the difference, there is a difference. She has no clue of what does what around the car.

Well I'm not sure how it works in exhaust...but when I do duct design for HVAC we use static pressure in water column....basically, when the velocity goes over 1000-1500 FPM two things happen, it gets noisy, and the static pressure goes up alot. Think of it this way....you have a hose, you let water come out.....now imagine you use your thumb to block off part of the outlet...the water comes out with more velocity...the same amount of water is coming out pretty much...but you've increased the velocity....imagine blowing air through a straw...then someone pinches the end of the straw somewhat, you have to blow harder to get the air out....

You can flow the same amount of exhaust out of any diameter pipe within reason....however the smaller the pipe...the higher velocity it must come out...the higher the velocity...the harder it is for the air to move, it will still move, but it makes it harder, that's backpressure. The volume of air needs to move out...however in order to come out it must maintain a certain velocity...if the pressure to get out is more then the pressure to stay in....it doesn't want to go out....something like that....I dunno exactly how it works....

Here, just check this out. (http://www.thirdgen.org/techbb2/showthread.php?s=&threadid=33246&highlight=backpressure)

Yea I've read that before....larger exhaust does slow down exhaust (as noted in that post, also noted, you dont' want to slow it down too much) but I was speaking about an engine that has stock manifolds "choking" power away....you can go too big yes....but I was talking more about when your being choked....that larger exhaust piping slows down the exhaust velocity.....again...you dont' want it to slow down to much....but in general...a larger exhaust is more "free flowing", doesn't necessarily flow faster....but more freely....