964 intake flapper - method of operation
 

What determines when the 964 dual resonance intake flap changes position?
Is it just based on RPM?
thanks,
Chris

load and RPM. (vacuum and RPM)
Mk

Pin23 on the DME plug
http://forums.pelicanparts.com/uploa...1068756533.jpg
http://forums.pelicanparts.com/uploa...1068756609.jpg

Thanks guys. In the absense of a MAP sensor I assume "load" is derived from RPM and air flow?
-Chris

Load is determined by a vacuum line of the throttle body. high vacuum, the flap is engaged. simular to the dual resonance system of teh 928S4.

mk

Thanks Mark. So the DME just enables/disables the load/vacuum's effect on the flap at certain RPM's?
-Chris

I hope you'll forgive me for asking a super-duper ignorant question. What does this dual resonance chamber thingy do? I have a 964 and I read Bruce Anderson and Original Porsche 911 etc and, at first, I thought I understood it. But now I'm not so sure. So is this thing intended to improve throttle response, HP, fuel efficiency, engine life, torque, or just cost more money?

Cylinder charging (getting air into the cylinders) is enhanced at a certain rpm corresponding to the resonant frequency for that intake. If you can change the size of the intake; and thus its resonant frequency, you can have more than a single "sweet spot". The flapper allows the intake to have two sizes.
-Chris

So that makes it...faster? More responsive? Is this like being "on cam" (whatever *that* means) through more of the rpm range...

NOTE: Driver carries less automotive knowledge than he appears...

faster, yes, as it improves the shape of the hp curve, by boosting lower end torque with the resonance chamber/different runner length effect, and giving the hp gains of shorter , larger diameter, and less restrictive runner system.

the effects are close to cam effects, as after all, its all about increasing mass flow into the cylinder chambers.

MK

The flap is indirectly controlled by a solenoid which is controlled by the DME, the solenoid allows the vacuum can on the flapper to see vacuum when it is engergized by the DME. I assume the solenoid is triggered by the DME based upon throttle position (ie full throttle) and engine speed based upon the predetermined maps in the DME.

Controll of the flap is not done by any sort of load measured directly from intake vacuum since there is no map sensor as already mentioned so the DME has know idea of load based upon vacuum.


Todd

I believe that the signal is only rpm dependant, custom chips often alter the operating rpm point stock is(from memory, ~5500rpm). If there is no stored vacuum it, of course, can't work.

The whole point is to increase the area ubnedr the hp curve. That is where useable acceleration comes from.

I hope it is just RPM dependant. If so "I have a clever plan."*
-Chris
* Baldrick of Black Adder

Yes, speed (RPM) dependant, but if there is no load, there is no vacuum. interesting thought, if you are on a high RPM decel, will the flap open on the way down????

Must have a throttle position sensor input too. when the throttle is more than 75% or something may be that is part of the solonoid signal.
Mk

QUOTE]Originally posted by tholyoak
The flap is indirectly controlled by a solenoid which is controlled by the DME, the solenoid allows the vacuum can on the flapper to see vacuum when it is engergized by the DME. I assume the solenoid is triggered by the DME based upon throttle position (ie full throttle) and engine speed based upon the predetermined maps in the DME.

Controll of the flap is not done by any sort of load measured directly from intake vacuum since there is no map sensor as already mentioned so the DME has know idea of load based upon vacuum.


Todd [/QUOTE]

Chris,

Thanks for asking this question. I have often wondered whether mine is operating correctly. My car's (72 w/92 3.6) acceleration has always seemed less than spectacular at higher gears at over 4500 rpm. In fact I drag raced Dave Buhain (sp?) three times at Willow a year ago. Our cars are almost identical. I could get a jump on him each start, rolling or stopped, half a car length. Once in third from 80 mph+ his car would smoke mine. A full car length in third alone! Fourth was an embarrassment. I know its not very scientific, but my motor can not be that down on power????

Bill, Todd and Mark,

Great info and insight. So how to trouble shoot? Checking the electronics is easy. But checking operation while on the run is a bit different. I guess I would need to put it on the dyno.

Thanks again.

Tinker
Tinker

When you turn the key at startup, you can hear the plenum getting tested, I'm pretty sure.

Dave's car is scary-light, though, and might be more modified than he's letting on. He's a parts guy, after all. ;)

Hey Jack,

I am concerned that even though I can hear it cycle at rest, is it working at speed? When I get my car out of mothballs, I am going to:
1. Test the signal to the solenoid at speed.
2. Try to get to a dyno.

Dave's car probably has a few more tricks than mine, but Jack during third gear it was like I was tied to a post. I can't believe the weight or a chip could make THAT much of a difference!!!!!

Tinker

Mark

If you re-read Bill's reply you will see there is a vacuum storage canister to allow for opperation of the vacuum can for the flapper in the presence of no or low engine vacuum. Again the actuating canister for the flap does not directly 'see' engine vacuum, the solenoid is inline such that if it is closed regardless of the engine vacuum level the actuating canister doesn't see it and thus the flap stays closed.

Todd

Tinker, when you're ready to Dyno, let me know. We can both go to the one in Reseda on the same day, and you can see more of an apples-to-apples comparison.

true, it doesnt matter how much vacuum the engine is developing, the canister provides the force, even at WOT, when there is minimal vacuum. I guess the solinoid signal is rpm, but also load, as it would be opening under decel as the vaccum is great. however, if Its taking a signal on top of the Throttle plate, it will be ambient, so there will be no vaccum .
Hmm. all I know is mine is working and it is easy to test on the dyno, and harder to test in idle. plan on reving the engine hard to 5000rpm really quick and marking the shaft output if you can see it on the manifold. the S4 can be seen and marked easily. the 993, may be too hidden.

MK