So what you're saying is that if I put a 5 inch exhaust on my 160hp Explorer it will make more power than if I put a 2.5 inch one on? Does that also mean that I will make more power if I go to a bigger exhaust than the 2.5 that I have on my 500hp Cobra?

Well, anything is possible. I'm saying that from what all I have learned over the years is; back pressure kills horse power. Now if someone wants to show me that this is wrong I'm all ears.:D

I'll see if I can look it up from someone who actually knows. The way it was explained to me, it had to do with cylinder pressure affected by the back pressure in the exhaust line. Cylinder pressure relates to torque. Certainly it's not a matter of maximizing back pressure either, its just that reducing it as much as possible (like taking your manifolds off) isn't the right thing to do either. There's a balance point depending on the rest of your motor setup. Spooling up a turbo adds another complex parameter.

I think Top Fuel Dragsters and funny cars run stepped headers. That is smaller diameter off the block going to larger diameter down line, specifically for maximizing this effect. Or at least that's what I thought. They have the room to run larger straight pipes right off the block. So why don't they? :huh:

I'm looking for headers and they typically come in 1 3/4 vs. 1 7/8. They explicitly say don't go to the larger size, until you're making very considerable horsepower, like beyond 500whp to the wheels in a SBC/V8 like setup. The costs are the same. Why would manufacturers make and distributors stock different size headers for the exact same car. Is it just marketing BS?

There's got to be some good docs, maybe with dyno comparisons according different exhaust setups on the same basic setup.

If that were the case then everyone would be running the largest header they could fit on their car. Back when I had the 396 in the Chevelle and it was making about 350hp I switched from 1 3/4 primary tube Hedman headers with 2.5 inch exhaust to 2 1/8 primary tube Hooker headers and 3 inch and I lost power. I went from turning 104mph to 102mph. Back then the car was very consistant. It's my opinion (not a fact just an opinion) that because of the larger size I lost some of the scavenging effect and thus power.

Similarly I've seen guys at the track who say they consistently ran slower after using cutouts, or my personal favorite, the Hondas that actually hack their exhaust off right by the manifold. This is anecdotal, but tends to support the same hypothesis.

I've made a new thread for this subject.

http://www.motorgen.com/forum/showthread.php?t=1008

Good plan good sir... I was beginning to feel hijacked... LOL

Sorry about that. Did you get it installed today?

Haha no worries my fellow enthusiast! I enjoy learning additional information! I'm glad there is a second thread about exhaust theory...

Not yet, I'm waiting to receive some exhaust clamps the seller forgot to bring... should have them on friday or saturday. will be going on sunday hopefully

You should take some video of the sound of the stock exhaust and then the new exhaust as well as pictures to post up on here when your done.