4-2-1 Extractors or 4-1? Pros and Cons?

[Rollux]

I got close to 25hp gain with a good set of headers on my 16v

how? and is it a 16v 4age or 16v 302 v8
was it stock?
what was the rest of the power curve like?
torque?

Pacemaker headers on a worked 308 16v in my VK

Sorry to disallusion all you 4AGE boys!!

[RedMist]

4 -1 is a dead technology. As VVega said its easy to tune so you might see some gains over a poorly specified 4-2-1
4-2-1 is traditionally used to gain mid end while supposedly loosing some top end. However with modern good split interferance collectors (toss Coby crap out the window) you get an all around performance increase over the 4-1 solution.
Tuning is very difficult however. Try and copy someone elses proven solution, for your specific cam timing and cylinder cc. I run a set of extractors with an unusually long primary, specified by Lynn Rodgers, however it works amazingly well.

The idea is to keep heat in the gasses in the exhaust system. Stainless is much better at doing this than mild steel. However is more brittle and does require some precise welding. I've seen some heat dissapation stats and mild steel with an exhaust wrap gets close to that of stainless.

[mister2]

If you were reasonably serious about it, theres a decent book called "Wave Action Manifold Design" in the engineering library at varsity which does a good job of explaining things. Also, you can't really go past "Tuning the A Series" by David Vizard... of course, as has been previously said, you'd be probably better off to just stick the 20v manifold on there because the gains you will possibly get by trying to improve on it wont be cost effective.

In fact, I have heard (internet knowledge though) that it is pretty hard to improve on the cast 16v design and that theres only a couple of hp from upgrading that to the TRD one.

Nick