velocity stack info

[lance1a]

Anyone know about the effects of size-length of stacks on a carb setup? I ran my Mikuni's with 170mm X 50mm stacks and the low end torque was good but it was breathless above 4000rpm. I removed the stacks and went for filters on the carb body and got loads of revs but little low end torque. I am trying to find a happy medium by using a 130mm x 35mm stack with a 45 degree bend but, the join between the stack and the inlet of the carb has an area of about 30mm where the diameter opens up again to 50mm. Will this cause any negative effects on the airspeed? The inlet manifold from the carb to the head is 150mm x 50mm.
Any help is appreciated!

Cheers

[lance1a]

Please would the mods mind moving this to the drivetrain section? Thanx.

[lance1a]

hilly said:

For a basic inlet length calculator look here ......

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

Cheers, but maybe it's me, I don't get that. Are they talking about the inlet runner as a whole (IE: including the filter-to-carb rams and the length of the carb venturi and inlet manifold together)?


What I would like to know is the diameter as well.
250mm (including bike carb venturi) gets me good torque between 2500/4500 rpm with a 35mm ram into a 36mm venturi and a 40mm inlet. But this loses guts over 4500rpm. When I remove the rams I get a significant reduction in torque but a wider rev range, with more power over 4500rpm.
Is there a calculation based on cubic displacement per cylinder that would give the info about what length and diameter of pipe? The site you linked shows that I would only get a 4th phase pulse at 5000/6000rpm at a very low percent increase. 10% at 10-11k is off the chart for my car.

[lance1a]

knighty said:

lance1a - have you ever thought about running half the trumpets at the longer lenghth, and the other half at the shorter length, so say for a 4cylinder engine, cyls 1 & 4 would be the short length, and cylinders 2 & 3 would be the long length, this is exactly how by black-bird bike engine was from the factory, only about a 10mm difference though, and I have seen many V8 can-am cars using this technique too.....it should be worth a try

I have noticed this on certain bike trumpets. Will it not affect the motor adversely in any way.....balance, fueling etc?