weber manifolds: Steel or Alloy - Medium or Long ??

[nky_84]

Hi guys, i currently have an shortish alloy manifold with a step up (not quite a swan neck) an am looking to buy a longer straighter one. The steel ones seem much more expensive, anyone know the reasons why and are they worth it? Engine is a 1293,mild to medium race spec circa 90bhp, is 6 inch over kill and i should be goig for a 5", or is it the longer the better if the weber box allows?

cheers

Nick

[Cooperman]

The longer the better as it increases the inertial ramming effect.

[DanGT]

The straighter the better the length gives more power at high rpm. Shorter more torque at lower rpm, there are limits to how far you can go.(I think thats the right way round). Steel ones flow better but some of the better ally ones can be nearly as good, some even clame better. The ram pipe lenghth also has an effect in the same way.

[FWDRacer]

Try and find a 5" Bob Waterfield Alloy manifold. Won't have to go crazy on bulkhead mods, and they flow nearly as well as the 6-7" maniflow steel items.

[haynes]

Sorry to contradict you Dan, but shorter gives more power, longer gives more torque - ive seen that demonstrated on the dyno at swiftune. Circuit racers like miglias use short 3.5" manifolds, 5" is better bet for hillclimber and road use. The maniflow ones flow better, ive not seen a back to back test with a webber, but on my twin SUs, comparing a decent cast manifold and the maniflow steel one the power shot up, i have a rolling road print out showing something like an extra 10%, so my vote goes with the maniflow steel manifolds. For best results you need to sort out an airbox in the bulkhead.

[DanGT]

haynes said:

Sorry to contradict you Dan, but shorter gives more power, longer gives more torque - ive seen that demonstrated on the dyno at swiftune. Circuit racers like miglias use short 3.5" manifolds, 5" is better bet for hillclimber and road use. The maniflow ones flow better, ive not seen a back to back test with a webber, but on my twin SUs, comparing a decent cast manifold and the maniflow steel one the power shot up, i have a rolling road print out showing something like an extra 10%, so my vote goes with the maniflow steel manifolds. For best results you need to sort out an airbox in the bulkhead.

Its been some time it was one way round or other, thanks for correcting me.