Developing branch manifolds in general and motorcycle header pipes in particular, requires endless hours on the dyno making comparitive tests.
We tested four into one headers with conventional four into one configuration collector, (i.e. not with a rotational 1-3-4-2 firing order collector), using various header diameters and lengths.
Once we were happy with primary lengths and diameters, as well as link pipe and silencer canister spec for maximum power, we tested the same header lengths and diameters converging into a rotational firing order collector. Each and every one of these dyno tests was done on the same bike using the same intermediate pipe and silencer which we had already developed previously. Continue reading HOT AIR; About Branch Manifolds (Headers)
Let us take a look at 5 cylinder and 6 cylinder branch manifolds:
The only 5 cylinder branch in S.A that I know about, was developed specifically for the 2.5 VW Microbus, and later the 2.3 and 2.6. The motor was borrowed from the Audi 500 in those days for the development of the VW Caravelle Microbus. A turbo’ed double overhead cam derivative of that motor is still employed in the Audi RS3. Initially a five into one was developed which worked reasonably well. We achieved approxamily 10% more horsepower on the dyno, where the five into one suited this set up. Although VW dealers denied this, newer batches of the 2.5 Microbus had a less powerful motor and the 5 – 1 did not work too well on these newer batches of 2.5 Microbuses.
We decided to re-develop this branch and opted on a 5-2-1 format with the idea of improving mid-range power specifically and to try and widen the power band as much as possible. Continue reading HOT AIR: More About Branch Manifolds
I would like to dwell for a bit on another 6 cylinder animal, the VW VR6
When these cars were first introduced into the S.A. market everyone was clambering for a set of branches to enhance power. The power delivery in stock form was smooth and torquey, but a little disappointing. An imported branch was available (at considerable cost) but power gains were negligible. My good buddy Joos Claasens had a VR6 Golf ‘lying around’ in his garage covered in white sheets waiting for the next Concours d’elegance competition…. He was assured his baby would be needed for not longer than two weeks to design a proper performance exhaust system…
Little did he know… Continue reading HOT AIR: More About Six Cylinder Branch Manifolds
Generally speaking, the bigger the exhaust pipe diameter, the more effective the power gains will be at higher r.p.m. and conversely, the narrower the diameter the more effective the power gains will be at lower r.p.m.
This, however is a general rule and there are many exceptions to this rule appearing almost daily.
The previously mentioned VR6 for example:
When the exhaust pipe diameter was reduced from 63,5mm to 57,15mm, the general expectation was that there would be an increase in bottom-end and mid-range power with a resulting power drop on top end.
The results were almost the opposite: There were major gains in top-end power and mid-range power! Continue reading HOT AIR: What is the Best Exhaust Diameter?
One day a customer, whose car was in for muffler replacement, looked through some photo’s of performance exhaust mods on my counter and commented after a while:
“These are photo’s of brand new cars!” pointing to pics of an Audi TT and a Mini Cooper S, “How come they need exhaust replacement already; anyway, aren’t the latest stock exhausts of stainless construction?”
He had always been under the impression that exhaust replacement was just a necessary evil, a grudge-buy! So he was amazed at my answer to his question, which was that a lot of new vehicles are brought in for performance enhancement through the use of custom-fabricated performance exhausts. He had no idea that a car’s performance can be greatly enhanced by means of a properly tuned exhaust! Continue reading HOT AIR: V8 Headers