I am currently running a nizpro manifold on my N/A vehicle (BA)with the butterflies sill in place inside of the lower half of the manifold. In the near future I am looking at installing more aggressive cams , 4.1 diff gears and a stall converter. I am also thinking of opening the lower half of the manifold up removing the butterflies somewhat similar to what has been done in the picture below a RPD ported manifold.

Before doing this I am just after some advise. Do you think that the runner openings are too large if I was to do this, how would it effect performance? Do you think it would benefit a vehicle that only revs to 6500rpm. Would the intake velocity decrease considerably and effect the performance? Would it be better to simply remove the butterflies and port match the intake with out cutting out the material between the butterflies and other openings?

As I say I will be doing the diff ratio and stall converter so a loss in low down power and torque is not a big concern.

i could be very wrong, but removing the butterflies will reduce low down torque considerably wont it?

Depends on cam choice and compression??
If you have a cam that won't have torque under 2000 rpm ?? The bbm may not make much difference ? Also restrict power when cam etc starts to work...
There are 1000's of these manifolds around !! Soif you want to go back its not an issue...Around 10 to 1 compression with good cam ? But some timing may need to be re calibrated?? In peak torque range...
I'd say give it a go...

Last edited by EBXR8380 on Fri May 30, 2008 12:37 pm, edited 1 time in total.

in an NA application...yes... pm "Fast xr" (vince) to hear all about that.....

I have basically lost all low down torque already due to fitting the nizpro manifold. It does not have dual runners. I only have the butterflies fitted at the moment to restrict air volume and the runners are always short. I don known how much more lowdown torque I would really lose by removing the butterflies completely?