[Jeff Higgins]

Originally Posted by ckelly78z

I have always heard on a header collector for a race car, they run the engine wide open on a dyno (or otherwise) until the header collecter (just downstream of the end of the header) starts turning red from the heat. They then cut off the pipe an inch or two beyond the red area.

In my drag racing days, our "poor man's" approach was to paint a stripe down the collector and cut it off a couple of inches past where it quit burning. Everyone knew this "top secret" tuning tip...

Originally Posted by ckelly78z

As far as determining the equal lengths of each header tube, it does depend on how many obsticles suchas motor mounts, starters, and steering controls come into play that need to be routed around. I'm sure there is a formula out there somewhere that outlines the most advantageous diameter with which head/valves size you are using, and what the best length of each diameter should be used.

Speaking in generalities, longer tubes are for low end power, shorter tubes for high end. There is a lot of leeway in each range and overlap between the two.

Unfortunately, V8's introduce a whole 'nother conundrum - they are not even fire on each individual side. That's why we see the "snake pit" on top of old Ford GT40's and many F1 cars of the day; they were trying to divide the motor into two even fire fours. Our flat sixes do this naturally, so there is no need to even try to make some elaborate cross over primary system like that.

Anyway, the fact that V8's are not even fire on either individual header plays hell with exhaust tuning. As such, each primary should theoretically be a different length, depending on how long it's been since another hole fired on that side and how long it will be before the next. It's kinda a no-win situation.

Then there is fitment on the car. That will dictate a range of primary lengths that can be made to work. Honestly, without a handle on the even fire problem, this is the thing that matters most - do they physically fit in the car, past all the other crap?

Originally Posted by ckelly78z

Sorry, i'm not an expert, but know just enough to keep the converstation going.

I think the manufacturers of headers are building a unit that will fit MOST applictaions. If you are truly building a deep breathing monster, then specially built hearrds are a must.

That kind of it in a nutshell. If you are in fact building something unusual, outside the range or normal bolt-on goodies, you likely have more physical room in which to play and then start working about primary lengths and such. In the end, for the vast majority of applications, it just has to fit the car.