Quote:
Originally Posted by BRUTAL64
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.  |
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?
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.