How do I test '95 Flapper Valve
 

It was brought to my attention that this dyno curve (RWHP / RWTQ below) may reflect an improperly working or broken flapper valve. Notice how quickly the torque curves falls.

Engine has '95 intake and engine management. Cams are bigger than stock: 993 Super Sport w/ solid lifters. Engine peters out at 6200 rpm, which seems a bit low.

Any thoughts on how to test the flapper? It is vacuum actuated. I've thought about using a vacuum tester at idle and look for some fluctuation. Is that sensible?

Thank you,

Doug

Graph File
:2VKY842.025
Description: 71 911 3.6
03/08/2006 A:0.996 X:1.100
Speed Ign. RPM Power Torque Temp Air/Fuel VacBoost
MPH RPM HP FtLb OF Gasoline (Atmos)
50 2629 108.2 216 72.5 13.1 -0.1 inHg
52 2731 115.8 223 72.5 13.1 -0.1 inHg
54 2843 120.9 223 72.5 13.1 -0.1 inHg
56 2952 125.4 223 72.5 13.1 -0.1 inHg
58 3061 133.8 230 72.5 13.1 -0.1 inHg
60 3173 137.5 228 72.5 13.1 -0.1 inHg
62 3281 142.1 227 72.5 13.1 -0.1 inHg
64 3389 145.6 226 72.5 13.1 -0.1 inHg
66 3499 149.0 224 72.5 13.0 -0.1 inHg
68 3603 156.8 229 72.5 13.1 -0.1 inHg
70 3718 167.8 237 72.5 13.0 -0.1 inHg
72 3832 175.0 240 72.5 13.0 -0.1 inHg
74 3944 184.9 246 72.5 13.1 -0.1 inHg
76 4059 189.9 246 72.6 13.0 -0.1 inHg
78 4161 201.2 254 72.5 13.0 -0.1 inHg
80 4275 209.6 258 72.5 13.0 -0.1 inHg
82 4391 221.5 265 72.5 13.0 -0.1 inHg
84 4501 232.6 271 72.5 13.0 -0.1 inHg
86 4609 240.7 274 72.5 12.9 -0.1 inHg
88 4720 243.4 271 72.5 12.9 -0.1 inHg
90 4830 249.3 271 72.5 12.8 -0.1 inHg
92 4935 254.0 270 72.5 12.8 -0.1 inHg
94 5052 257.0 267 72.5 12.9 -0.1 inHg
96 5159 263.1 268 72.5 12.9 -0.1 inHg
98 5261 267.4 267 72.5 12.9 -0.1 inHg
100 5367 267.7 262 72.5 12.9 -0.1 inHg
102 5475 267.6 257 72.6 12.8 -0.1 inHg
104 5568 260.6 246 72.6 12.8 -0.1 inHg
106 5672 266.8 247 72.6 12.8 -0.1 inHg
108 5776 266.0 242 72.6 12.8 -0.1 inHg
110 5879 272.8 244 72.5 12.8 -0.1 inHg
112 5981 271.6 239 72.6 12.8 -0.1 inHg
114 6094 270.4 233 72.5 12.7 -0.1 inHg
116 6189 266.9 227 72.5 12.6 -0.1 inHg

Here is a jpeg of that dyno (red), along with a similar spec motor that has more high end power:
http://forums.pelicanparts.com/uploa...1179454594.jpg

Motor specs:
http://forums.pelicanparts.com/uploa...1179454646.jpg

Pete,
Nice compilation of the data - thanks!
Ted's engine was run on the same dyno, though different day.
Mine was on pump gas. We monitored the advance curve, which did not retard under load. We concluded that the knock sensors were not sensing detonation and retarding the ignition.

Ted's cam profiles are definitely bigger than mine.

Interesting how the curves look quite similar, but just "phase shifted" relative to RPM.

Can anyone think of a good way to ensure my flapper is working?

Doug

bump

Doug, from the factory manual:

Checking Resonance Flap for Operation:

When the ignition is switched on, the resonance flap is closed by vacuum action. When the ignition is switched off, the resonance flap is opened (rest position). The opening and closing noise is audible in the engine compartment.

4. Resonance Flap

The DME control unit activates a vacuum-controlled diaphram valve which either opens or closes the resonance flap.
The resonance flap is closed between 3,000 prm and 5,000 rpm and at throttle opening angle of > 60 degrees.
Due to the ignition sequence, the intake system is alternatively supplied by both tanks. Due to the firing order, air is drawn in an alternating manner from both intake system tanks. If resonances occur, the intake frequency of one row of cylinders matches the natural frequency of the pressure vibrations in the respective tank. The natural frequency is determined by the geometry of the intake pipes, the resonance pipe and the tanks. A crucial factor, however, is the total length of the pipe from the actual intake cylinder to the next cylinder being supplied, the distribution in intake and the resonance pipe lengths as well as the depth of the tank in the direction of flow. In the no-current state, the resonance flap is open. As soon as the ignition is switched on, however, it is triggered and closed. If the DME control unit detects that the engine is being started, the resonance flap is opened again.


Pin 1 from the DME unit is used to control the resonance valve.

Steve, thanks for that info, is that for a '95 or for a varioram car?

Steve,
Is it fair to assume that the resonance flap shouldn't effect top end?

The reason I was exploring is due to the way my engine peters out at 6100 rpm (on the last dyno run).

If you see the torque curve, it drops fast above 5300.

Doug

This info is for a 95 motor. Resonance flap operation should affect top end - you can also see in the dyno curves of 964s when their doesn't work because the hp starts rolling off after 5700 rpm.

So were you able to tell if your flapper is working with the above procedure? Curious...

No, my car is stored an hour away because we've been remodeling our home (including adding 400 sq ft to the garage). I need to pay a visit to it soon.

Doug

I just want to confirm Steve's information, as I'm using a 964 plastic intake on my 3.0 SC, controlled by Megasquirt II.

From idle to 3,000RPM, there is NO current: flap is open
From 3,000RPM to 5,000RPM, there IS current: flap is closed
From 5,000RPM to redline, there is NO current: flap is closed.

This is in conflict with some other posts on Pelican such as http://forums.pelicanparts.com/2016476-post8.html and Adrian Streather's info on pg. 141 of his book "The DME control unit opens the resonance flap when the engine speed exceeds 5500RPM ... The flap closes when the engine speed drops below 5400RPM."

I'm not fussed either way, since I just need to enter the points into the ECU, but perhaps we could come to a consensus.

You will need to optimize the resonance flap on a dyno

for a stock 964 pin 23 controls the flap, it opens at 5500rpm and closes at 5400

it audibly cycles every time the ignition is switched to on, a cycle is close to open to closed

the 993 non vram engine is different
pin 1 controls the flap, the flap is closed from 3000rpm to 5500rpm w/ throttle angle > 60*, as w/ 964 it audibly cycles, a cycle is open, close open

vram 993s use a more complicated scheme

Thanks Bill. I can get MSII to operate the flap without any problems. Just wanted to know what parameters to put in. Cheers.

Ben,
What noise does it make when it operates? Is the signal from the computer 12V or 5V to operate the vacuum switch?
I need (still) to check mine. Thanks for reviving! Was thinking I could use a 9V battery to operate the switch.

Thank you,

Doug

Doug, when it energizes, it makes a clack. When it turns off, it makes a light whoosh ... I guess it's just letting the vacuum escape. I tried energizing it with a 9v battery, but it doesn't work. I've got 12v going to it, operated by MSII. Hope that helps.

Thank you.

In parallel, I tried this test: turn on the ignition and remove the connector to the vacuum switch. When I touch the switch contacts I can hear the clack of the solenoid and if I look closely can see the center of the flapper rotate - this is the small shaft in the center of the intake manifold nearest the crankcase and retained with a small c-clip. Of course, the vacuum diaphragm moves, too.

I guess mine works.

Doug