964 Resonant Intake
 

Has anyone (and I'm sure someone has) experimented with the resonant intake manifold on the 964 engine. I have searched for this information on the web and found nothing much about it except that the flapper valve in the connecting tube opens at 5500 rpm. If one of you can elaborate on this, or point me to an explanatory web site I would appreciate it. My main questions are:

What happens, seat-of-pants-wise, when it opens. Can you feel it?

Was this done as a performance enhancement or for emissions? Or for both since they're somewhat intertwined.

What are the detrimental effects of not having it.

The reason for all of these questions is that because of it's airflow characteristics I am thinking of using this intake on another project that may not have the capability of actuation the valve. In that case should it be blocked open or blocked closed?

The resonance flap changes the cross sectional area of the intake manifold. If it isn't functioning there will be a noticeable decrease in torque/hp above 5k.

Would this hold true for any engine it was mounted on, or just the particular combination of thing in the 964 engine?

Where this is all headed is that I'm thinking of using the 964 manifold for an EFI SC engine I'm contemplating. It appears to me the 964 intake has a much better flow path than the CIS intake.

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Paul,

The Rothsport intake system works VERY well on a large-port SC motor yielding performance thats far beyond the OEM systems. Naturally, this requires Engine Management to operate and someone who knows how to tune it.

Our spec-911 engines typically see 255-260 BHP with far quicker throttle response at all RPM's. These are bone-stock SC engines with 1.5" headers and a good race muffler.

Thanks Steve (and everyone else). Hadn't heard of that one, I will look into it.

on the rothsport itb set up, is the resonance flap rpm operational? is it rpm triggered or load triggered?

I did my final year Mech. Eng thesis on this topic :)

My literature study included the following reference:

E.Rutschmann, L.Theilemann,“Energy From Pulses, Beter Cylinder Filing via Decisive Pressure Pulses in the Intake System,” Christophorus; The Porsche Magazine, No. 223 April 1990.


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The article from Christophorus provides excellent info on the workings of the 964 manifold.

I also came across some other relevant info on the workings of resonance type manifolds (non Porsche):

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YES.....resonance charging manifolds can provide significant gains:

(Apologies for the non Porsche test mule....student budget didn't allow for a 3.6 Carrera :). The 2.5 Alfa engine was generously loaned to me for the purposes of this Thesis)

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All flat 6 engines for street use from Porsche from 964 up use resonance tuning

I don't know what JG(Rothsport)uses to control his but on 993 they have 2 inputs, throttle greater than 50% and 5920 rpm, I'd need to look up the specs for the others from Porsche but suspect it's similar.

Note that there are 2 throttle valves, 1 resonance flap and 6 variable length intake tubes on a 993 vram
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This is all great info.....and does anyone know the apron increase over a standard intake setup these give for the 3.6's ? :)

Bill, how does that twin throttle body arrangement on the 993 work?

I can see (from the schematic you posted) that when the vram is in "long pipe" mode, the engine breathes through the one throttle body only.

But as soon as the vram switches over to "short pipe" mode, then both throttle bodies can feed air to the engine.

Are the throttle bodies mechanically linked whereby the secondary butterfly starts opening only once the primary throttle is 50% open....and then they both open up to 100% simultaneously?

great stuff costa and bill, thank you guys for posting.

the alfa v-6 is another wonderful motor btw..

Bill i think u meant "All flat 6 engines for street use from Porsche from 964 up use (variable) resonance resonance tuning "?

most motors in the modern era all have resonance tuning. the intake track lengths/diameter along with the plenum, airbox, valve timing all have at least a minimal effect... even the venturi size of the carb do. its just that they are fixed and set up by the factory. some not very well at all due to the compromises made for production applications.

the most elaborate ones i know of is the wonderful infinitely variable " trombone " ones on the 4 rotor kadzu LM motors. like a F1 airbox and horns, you can see them moving to the engine loads. the sound and theatrics are wonderful!

back to the plastic 964 intake...so are the resonance valve are vacuum or electrically (probably not hydraulically) actuated ? im curious since im doing some motor work and im trying to figure out how to incorporated on a 3.2 twin plug .

interestingly enough both alfa and 964 graphs shows valves opens around peak torque 4500 to 5000rpm. they come in effect for the last few ponies at the last 1500-2000 rpms.

cheers pf

Electronically actuated but the flapper is opened or closed (depending on year) by vacuum.

thats great.... seem like it can be easily adapted if thats the case

you can trigger by something simple like a shift light...

Yes. My Haltech EFI system has a general purpose output just for such an application and I use it to control the flapper. You could also use an RPM activated window switch discreet from an ECU.

pf, there have been various ingenious designs with infinitely variable length inlets from Audi, Ford (Tickford), BMW, etc

AutoZine Technical School

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It seems though that their complexity & cost ultimately brought about their demise.

Yes it is and RPM triggered by the ECU.

To be correct, electronically triggered, but vacuum actuated. :)