[Cool53]

Another long winded story from me. And forgive me for delaying Moose's response, but I was on my way to Florida to work on the house and just got time to sit down.
I took a class on headers at PRI several years ago, and it was put on by one of the leading header manufacturers. Leading meaning expensive.
He spent over an hour explaining all the math that his company uses to make sure the correct size tube, the correct length of the primary pipes, the right flange, the right length and diameter collectors are use, yadda, yadda. He was very informative. I was just about ready to order a set for my next customer when he put down his chalk, walked away from the board, and sat on the table in front. Now, he says, real life takes over. We do all this figuring and find out that on a certain body style with a certain engine needs 2" primary tubes that need to be 38" long. and that the collector diameter needs to be 4" in diameter and 12.5" long. But when we get to the car we find that the 2" tubes can't possibly be used, because there is insufficient room to use them and get by the steering box and shaft. And we find that we can't stuff 38" long tubes in the chassis, there just isn't enough rom. So we switch to 1 7/8" tubes at 35". and we can only get a 3.5" collector that is 8" long under the car and around the transmission and crossmember. so that's what we go with.
At the end of his presentation I went over and thanked him for making a decision not to waste my money on his more expensive headers. I think he then realized how he had shot himself in the foot.
So headers are a bitch. If you are going racing and need to get everything you can out of your engine you are going to spend a lot of time or a lot of money getting things where they need to be to eek out that last half a horsepower. If you are going to go to the track and have some fun, run closed exhaust like I do, and have some fun, then use what fits the chassis, make all your bends and connections as smooth as you can. Use high flow mufflers and make sure the exhaust ports match on both sides and you should be fine. If you have a dyno hat will work with you and you want to make sure you aren't going in the wrong direction then that's fine, but it is tie consuming.
Pro Stock cars spend as much time on the headers as they do on the rest of the engine, sometimes.
Sorry I don't have better news. We are using a dynamic fluid program to make the tubes for the 292 straight six I am helping Leigh Walker with on his '46 pickup. Should be fun.

[themoose]

Jef

That's good information to know. I'm sure we've all been influenced at one time or another by the hype that the header manufactures use to convince the buyer that they can expect huge gains in HP by just bolting on a set of their headers. It looks like if you install a reasonably efficient system on your car you should be good to go in most real world cases. Thanks for your response.

Moose
 

[ghost28]

i do like a good set of headers, but for the most part the old corvette ram horns work the best in my late 20s to early 30s  cars. I guess the main reason is that they fit under the hood with out touching the hood sides and burning off my paint, and the other reason is with a cross steer applicatiion instead of the traditional steering, the steering box and components get in the way constantly. I might try to put a more traditional steer in my buick and use these down through the frame since I won't be running hood sides.

[Cool53]

Even guys that make custom headers that look great and fit well can't guarantee hp gains.  Moose and Ghost28 stated real life perfectly. And good manifolds don't loosen up all the time.  Some of the aftermarket manifolds look great and work well, like Sanderson, but stock manifolds used on GM, Ford, and Mopar high performance products worked reasonably well. And cast iron manifolds have lots of meat if you want to match ports.
Something I forgot to mention in more detail is transition plates. We usually make these out of aluminum or hot rolled, making it easier to work with. These are a match for your header flanges and bolt in between the headers and the head. With these you can blend the ports on either side of the plate. Saves scrapping a decent set of headers, makes better flow, and gives better spark plug clearance.car show and fly in at the Palatka, Florida Airport this Saturday. Draws a fairly big crowd. See you there!