Here comes a book lol

As exhaust travels from the cylinder to the exhaust tip it is constantly cooling which causes the gasses to contract and slow which in turn reduces velocity and creates turbulence. High exhaust velocity helps pull the spent exhaust gasses from the cylinder as well as creates a small vacuum within the cylinder. These 2 things allow for more complete cylinder filling on the intake stroke since there's no "dirty air" in the cylinder getting in the way and at the same time the vacuum increases the intake charge velocity by "pulling in" the fresh air.

To increase exhaust velocity you want to step down your exhaust size the further you travel from the head. Since the gasses are contracting and spreading out the tube diameter needs to contract to keep the gasses from becoming turbulent. On a basic setup you'd want 2 step downs along the exhaust pipe for a full over the axle system. If you have 3" at the collector you'd then drop to 2.75" at the crossover (x or h pipe) and then 2.5" at the mufflers. Obviously if you start at a smaller diameter you're going to drop to a smaller diameter. Because of the work involved many people including oem's will run a single step or no step at all. On a car with the muffler before the axle the easy step down comes from a muffler with a smaller diameter exit. On a rear muffler car the step has to be done further upstream which makes things more complicated. A dual step is always more complicated so most don't bother.

For the headers themselves you're aiming for a primary size roughly equal to the size of the exhaust port plus a hair to make up for any port misalignment from the manufacturing process. You then go 1 step down about halfway down the primaries (full race headers can run multiple steps, but the cost is high). The merge collector also should have as smooth a transition as possible to prevent turbulence. For the full deal custom headers you can also use primary length to adjust where you want your powerband to fall. Equal length tends to put max power in a smaller rpm range while unequal length spreads the power over a greater range but with less peak. Because equal length is a nightmare to build and package very few people even think about it unless they're building a max effort car designed to run at a specific rpm range.

Header wrap and tape was developed before all of this science was understood. Now we have the science to better understand thermodynamics and metallurgy and can build the parts right to begin with instead of trying to make them work better after they're done.

 

Some great posts in this thread, this **** getting deeeep and I dig it.

 

I thought you might like it.

 

"Man I don't think I'd every spit out the coin for kooks, and if I did I'd have a hard time coating them, I love the look of raw stainless"

after the problems I had with TSPs and their Y pipe I gladly spent the money on a product that fits....my son was mad after he saw how well it fit......right after he had hell trying to make those TSPs i gave him work on his car

those TSPs were coated.....did not last to long

 

I hear ya, most exhaust systems are a massive paint to get all lined up and sorted. But I don't mind fighting something for a couple of hours to save a grand or so.

But I know how you do things, only the best of the best for your car and I don't hate that at all. I'd do the same if I had more free cash.

 

It's getting all sciency in here

 

I got Pacesetter's on my Truck, LT's that are coated. Had them on now for just a bit over 8 yrs with no issues or rust. Not as shiny as they once was but they ain't rusty. Having my new 2" Kooks coated to go on the Camaro when its finished.

I first bought 1 3/4 Kooks for the Camaro way back in '04 with just heads and cam. Bought some polishing strips and had the headers looking like chrome. Man they were pretty!!
I installed them and fired the car up and they turned blue, brown, yellow, green and within weeks looked like they had been on there for years! I removed them and had them sand blasted and coated and they lasted for 4 years until I pulled the motor with aspirations of a bigger motor. Sold them to a guy on here and he was elated about how they looked since they were used headers.

Coating works for me!

Chad

 

I like coating but I love the look of stainless headers! Especially when polished up

 

Jethot does a ceramic that looks like polished stainless. They call it classic polish (0100)

 

Brb gonna go look at header ****

 

 

Convincing video!