I am fabricating a new exhaust manifold for my blackbird powered car. It is going to be a 4 into 1 design for better top speed (worse in lower revs). Of course Iam trying to get all the 4 pipes exactly the same length. Question is what length from exhaust valves to 4-1 collector.
There should be a formula somewhere
in which this can be calculated so I can be very close to the best length for a certain rpm.


regards Cor

This was posted a while back by someone (sorry, can't recall):

I checked my copy of A. Graham Bell's Four Stroke Performance Tuning, and this excel file has the same formulae.

looks very much like Mr David Ashursts spreadsheet.

Sure he'll pop by soon and confirm if it is.

Ah, yes, that's him! Very useful stuff. Thanks, David!

ive got std Blackbird 4-1 manifold on mine, around 24/25" from head to collector, i assume Mr Honda got it pretty close.