Need some advice on the lengths of both the primary and secondary. Header size is 1.5" for a 1916.
Let's start the bidding at 26" primary.......why...because it was on the net!

[Edited on 4-4-2003 by speedster356]

R we talking about Jets in a set of Webbers ???

Nope, exhaust.
primary = single pipe from head to the merg point.
secondary = merged length.
I think.......
Correct me if I'm wrong.

[Edited on 4-4-2003 by speedster356]

My feeling is that 26 " is the mid point, now I think that longer is more suited for low and mid power and shorter is for top end power.
The secondary I thought was the lenght of pipe after the merge to the outlet.
My oppinion - the shorter the better.
Or at least the least Back pressure the better.

You are looking for a simple answer to a very complex question. Tuned extractors are well nigh impossible to design on the drawing board - you are talking about finding a tuned length of a varying velocity of a gas of varying density at varying temperatures. You'd actually be best finding someone who has developed a tuned set of fully merged extractors for your engine combination (capacity, cam, heads, intake,) and buying it.

On a header, of course, the length of the secondary should be as short as possible - with the legth of the primary being as long as possible for street applications, short for strip... Equal length is important in any NA setup, not so important for turbo.

Yeah I understand that header/exhaust design is a very complex thing, what I'm looking for is a starting point.
An off the shelf system won't fit the bill due to my specific requirements. I'm aiming for a replica system as below.
Thanks for the input:thumb

now thats an exhaust system.
Love the look of that ceramic coating

Yep, that's a header!

You'd have a bugger of a time trying to get away with it on the street, however. The exhaust is not supposed to protude past the body of the vehicle...

of course a mid engined 356 would be different story.

Looks like I'll have an overhang out the back but what the hell........

I was originally keeping quiet on this subject, in a hope someone smarter would enlighten us all. Since this post has hit the 2nd page I guess that ain't going to happen. I am also interested in info since I will be building extractors soon.

in a 4-1 system, the 4 is the primary's, and there are no secondary's.

in a 4-2-1 system, the 4 is the primary, and the 2 is the secondary.

The only equation that I could find (so far) gives you the length to the final merge (the start of the 1).

L = (850 x ED)/RPM - 3

Where L is the pipe length is inches
ED is 180 plus the number of degrees the exhaust valve opens before TDC
RPM is, well rpm.

That formula is a rough guide given in Graham Bell's book, "performance tuning in theory and practice".

They is apparently a computer program called "engine analyser" that is good for designing headers, and requires heaps of info like exhaust port size and length...

You might also wanna check this out

http://www.bgsoflex.com/auto.html

go to "best header" in the menu on the left. Seems very simplied but might be another check on the length your after.

oh, and here's some useful conversions
1inch = 25.4mm
1mm = 0.03936996 inch
1 cc = 0.06102374 cu.in
1 cu.in = 16.38706 cc

I reckon it's out of what though. The lengths it estimates are out of whack. They seem too short.

[Edited on 11-4-2003 by Baja Wes]

[Edited on 11-4-2003 by Baja Wes]

ur right wes, they do seem a bit short on it......14"? hmmmm:o

you can download a demo version of the "engine analyser V3.0" here
http://www.performancetrends.com/download.htm