As you have probably gathered, I am making my exhaust!

The standard Sierra down pipe is 500mm from the manifold flange to the point where the 2 pipes join - I am probably going to have to have mine more like 600mm at the joint. Will greatly affect power or anything else I haven't thought of? My new pipes are 45mm ID and the Sierra ones are 37mm ID.
Rescued attachment ExhaustLength.jpg

Exhaust downpipe length, if tuned to the engine, can have an effect on power. Supposedly, each 'pulse' from an exhaust cycle can be used to provide a 'pull' to the next, increasing exhaust flow.

Thats why you see such massive convoluted exhausts on F1 cars - they must all be the same ideal length.

I seriously doubt that road cars follow these rules! My V6 outlets (3 each side) join together almost as they exit the head!

I was once advised by someone that had knowledge of my engine to make the downpipes 'as long as possible' before they converge. Im not into that level of hassle - I have suffcient already!

There will be more precise methods!

Jaspers car, in his avatar, show a long path to the converged section.

atb

steve

calcs for exhuast lenghts

required data

deg btdc exhuast (cam data sheet should have this)
rpm for optimum power
cc of cylinder

pl = ((850 * (180 + deg)) / rpm ) - 3

pid = square root ((cc / ((pl + 3) * 25))) * 2.1


if you have the pid
then the length can be calculated by

((4.41 * cc) / (25 * (pid * pid))) - 3


[Edited on 1/9/03 by timf]

What is "deg btdc exhuast "?

degrees before top dead centre for exhaust valve at full lift

I think the pipes are going to have to be as long as the need to be to reach the silencer. If I loose a little power - tough!

Is this theory only suitable for 4 into1 type calculations , and how do the characteristics of 4 into 1 exhausts differ from 4 into 2 into 1 exhausts.

Can you do a demo calculation for my 1800cvh.

Peak Power Revs 5500
Cyl Capacity 442.25
Exhaust Full Lift @ 116 BTDC

Thankyou

Dave

for a 4-1
for the figures given the primary lenghts work out at 42.75" with an internal bore of 1.3" if you want the calcs done for a 4-2-1 let me know and i'll do it tonight

Tim

Yes please 4-2-1 calcs.

Is there any software on the net you can get for these calculations?

Am I right in thinking that the higher up the rev range the power is the shorter these pipes would be?

So if it was calculated for 3000 rpm it would be right round the car!!

i have an excel spreadsheet with macros on it that allow you to enter the data and calc if you want a copy letme know