Flapper or no flapper??
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From: Aurora, Ontario, Canada
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From: Philly PA
if you dont go over 3500 RPM then yes you can leave it disconnected.
Otherwise it is very hard for the flappy to come unhooked unless someone was pulling hard on the line or the connector hose got oil or some other chemical on it.
The only way to fix it is to remove the intake,
use compressed air to blow out all of the sand and other crud from the intake base,
and the injectors where they fit to the intake so nothing falls down into the cylinders
Otherwise it is very hard for the flappy to come unhooked unless someone was pulling hard on the line or the connector hose got oil or some other chemical on it.
The only way to fix it is to remove the intake,
use compressed air to blow out all of the sand and other crud from the intake base,
and the injectors where they fit to the intake so nothing falls down into the cylinders
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From: ɹəpun uʍop 'ʎəupʎs
A non-working flappy valve in the intake doesn't affect max power (it opens above around 4500rpm from memory).
However, it will detrimentally affect torque lower down the rev range. Fix it
However, it will detrimentally affect torque lower down the rev range. Fix it
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From: Stockton, CA
it does make a difference..... 928's with broken flappys tend to feel flat through midrange & working ones have much better midrange....here is a before-after dyno run that shows the difference
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From: Philly PA
Hilton i think you have it backwards, the flappy doesnt open till about 3500 RPM to change resonance flow through the manifold, so it affects midrange RPM power
Notice the dyno charts they all have power increasing from about 3500RPM.
You can check flappy operation ,
remove the rubber cover on the top of the manifold,
put a small piece of blue tape on the center shaft with a piece of it sticking up so you can detect movement.
Go start the car and while its starting watch the tape move, if it doesnt move then ,
either the vacuum line is not connected
or the flappy valve is connected backwards or the valve harness isnt connected.
Note to verify flappy valve connections,
the line with engine vacuum should not be connected to the outside air when pulling a vacuum on the respective port,
the line that goes to the flappy is open to outside air
Notice the dyno charts they all have power increasing from about 3500RPM.
You can check flappy operation ,
remove the rubber cover on the top of the manifold,
put a small piece of blue tape on the center shaft with a piece of it sticking up so you can detect movement.
Go start the car and while its starting watch the tape move, if it doesnt move then ,
either the vacuum line is not connected
or the flappy valve is connected backwards or the valve harness isnt connected.
Note to verify flappy valve connections,
the line with engine vacuum should not be connected to the outside air when pulling a vacuum on the respective port,
the line that goes to the flappy is open to outside air
Last edited by Mrmerlin; Nov 8, 2010 at 12:03 AM.
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Team Owner
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From: Philly PA
reference this post Louie Ott has a detailed explanation and a few posts later Erkka has a diagram of the opening RPM its at 3500
https://rennlist.com/forums/928-foru...appy+operation
https://rennlist.com/forums/928-foru...appy+operation
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From: ɹəpun uʍop 'ʎəupʎs
Stan - look at the graphs posted above.
There's no change in horsepower (or torque) at higher rpms with the flappy working or not - it doesn't affect high rpm power (looking at Jorge's graph, above around 5020 rpm there's no difference).
The flappy changes the intake resonance at lower rpm's to produce mid-range torque, giving the characteristic double-hump torque curve of an S4.
I predict we're going to get Kiborted this evening.. when Mark chimes in to explain that he's been racing for a billion seasons with his flappy disconnected
There's no change in horsepower (or torque) at higher rpms with the flappy working or not - it doesn't affect high rpm power (looking at Jorge's graph, above around 5020 rpm there's no difference).
The flappy changes the intake resonance at lower rpm's to produce mid-range torque, giving the characteristic double-hump torque curve of an S4.
I predict we're going to get Kiborted this evening.. when Mark chimes in to explain that he's been racing for a billion seasons with his flappy disconnected
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From: Boulder Creek, CA
Just wondering for now really..and very curious what the difference in curves is like.
..and I now see it. The link to that other thread listed, was invaluable.
Sure would like to see how to keep it open all the time, just to see.
Intake refresh is on the way soon tho.
Might just do the flappy fix as a quickie..when I do the thermostat and injectors here soon. Bout to do some vac leak testing here in the next week or two (waiting on parts from Rog)...and see how far in I need to go now..while saving up spare parts (spare intake and cam covers, water bridge) to do it all fully later with everything all pretty to keep downtime low.
Last edited by Speedtoys; Nov 7, 2010 at 11:52 PM.
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From: Philly PA
Hilton please follow the link i posted it has a factory diagram of the flappy operation it opens at about 3500 and closes at 5250 RPM
see page 2
I think i used the wrong words to describe the operation its not the Hi RPM but midrange , thanks
see page 2
I think i used the wrong words to describe the operation its not the Hi RPM but midrange , thanks
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From: ɹəpun uʍop 'ʎəupʎs
Gotcha, I had the open/close events round the wrong way - its closed at high rpm's.
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From: San Francisco Bay Area, Santa Clara
My issue with vacuum was a leak under the fender. There was hardly any vacuum at the 4 way fitting by the brake reservoir. I plugged the line to the fender (contains the vacuum reservoir) and now everything works - heater, flappy valve etc.
Obviously now I need to go inside the fender and figure out whats leaking.
Obviously now I need to go inside the fender and figure out whats leaking.
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From: Germany
An easy check is to disconnect the vacuum line to the flappy at the solenoid and put a vacuum pump on it to see if the flappy works. The solenoid sits in easy access on the right timing belt cover.
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From: ɹəpun uʍop 'ʎəupʎs
The flappy solenoid gets its vacuum from the manifold up by the booster, which is also connected to the HVAC system and vacuum reservoir. Its possible a large vacuum leak elsewhere in the system is causing the flappy to not get any vacuum (although it'd have to be a large leak - the flappy doesn't take much to open it).
Doing this test will tell you whether the flappy is actually broken, or just being hampered by other systems