964 dual resonant intake

Is there any way to check that the dual resonsnt intake system on a 964 is working correctly? I understand that it is supposed to move a flap or something at a certain engine speed to change the intake plenum crosspipe volume. Does anyone know how I can check this, cheers.

It sounds like you are referring to the varioram of the 993. I wasn't aware of such a setup in the 964 series.

There definately is some kind of active dual resonant system on a 964. The owners maintenence manuals calls for checks of the 'dual resonance flap operation' at 15,000 mile intervals. Bruce Anderson also describes the 964 system as two different sized cross tubes connecting the plenums on top of each runner stack. The inlet air is routed to the big cross pipe, with a mechanical system triggered by engine speed opening the small cross pipe at certain RPMs. If you look at a 964 intake system you can see the different sized cross pipes, but I can not find the resonance flap.

The 3.2's used a single resonance system with the intake 'tuned' to a rpm band.

I understand that the 964 series uses the same principal, but applies it to a wider rpm range by the use of the 'dual' resonance system.

The varioram on the 993 is a more elaborate 3 stage system. The 993's use a more complex system that has sliding sleeves inside the intake, as well as a resonance flap connecting 2 intake plenum volumes. This system is very good at 'tuning' the intake over a very wide rpm range, giving the 993 a wider torqure band. I think this was applied to 96 993 and explains the power difference between the 95 and 96 models.

Question: Does anyone know how to check the operation of the 964 resonance flap, and at what rpm it operates at?
Cheers.

beetos:

If still interested. Their is a little butterfly underneath in the middle towards the right of the plenum and it has a little rod that goes to the other side.(other valve) You should be able to move it to the left and it will spring back to the right(which opens and closes the valves)The valves open by a vacume hose which you should see right in front of you. I beleive at close to 6000 rpm the vacume will suck and the vacume mechanisium will open the valves instantly. I simply tested it by touching the butterfly and rod and then raised the engine to 6000 rpm and then felt the the butterfly open instantly.

Hope this helps!

Thanks JH, I figured this out also. I saw the the flap opened up at 5800rpm

It's great to see more 964 owners on the board! Didn't know my car one these dual plenum thingers, I'm going to check it out just for fun.