header design question

[techno550]

when calculating the optimal primary and secondary lengths for an exhaust system, what options are there in terms of altering the lengths. i.e. is half length ok? quarter length? what are the options/effects?

what other things can be changed?

I used a tool to calculate the target primary length for an I6 engine, and the recommended length before the 3-1 collectors is 36 inches, which space wise would be very difficult. what would be the effects of using 18 inches instead?

If using half length on the primaries, should anything be changed on the length of the secondaries?

 

[lambolex]

Hi, Maybe this site will help i found it quite useful, you need to register to log in, to get to the calculator program, it seems quite accurate hope it helps.

http://www.headerdesign.com

Regards
Graeme

 

[Fabrico]

The more you look into this science(?) the more questions you will have. There is still disagreement as to whether stepped headers actually do much good. And if they do, when and at what RPM range. Then there are different groupings like pairs, threes, Tri-Y's, 180 degree, and all-in-to-one's.

There have probably been over a million headers built. You're not going to re-invent the wheel. You need to start with your engine/vehicle requirements and go toward information in that type of use. See what sucessful others have done.

Unless someone has the exact same engine, setup the same way, used for the same purpose, and driven the same way, they cannot tell you what is best. It's fun to play with but too easy to over-engineer things and end up wasting time and money.

 

[techno550]

Thanks for the replies. I've used the headerdesign.com website for calculating/verifying the calculations on the target lengths.

My main question was, if space/packing does not permit the full length that is desired, is there a "compromise" length that is suggested. Instead of just doing "all the same length, but shorter", is there a next target length. As in, if you cannot make something fit that is L, is L/2 acceptable/desirable? Or is it a case of, if its not exactly the calculated length, and must be shorter, any length will be equally bad.

 

[Fabrico]

Automotive headers with 18" tube length can breath well but are too short to provide tuned scavenging. Making them equal length won't do much either. Since the header is not doing anything special the secondaries just need to flow well. What you will have is a nice tubular manifold. You might as well go for the fit and cool looks.

You might look into buying a "block hugger" or "shorty" type manufactured headers.