DeWolf

Hi All,

How much difference does a working flappy make to the performance? I've got the manifold off the S4 and if I suck on the hose to the flappy actuator it just pulls air and the rod does not move. If it doesn't make a diffrence i'm not going to pull the manifold apart to replace it.

Cheers
Scott

ammonman

The resonance flap extends the peak torque range from 2800-3600 rpm to 2800-4800 rpm and steepens the horsepower curve in the 3600-4800 rpm range. It doesn't open until about 3600 rpm as the torque is starting to drop off and closes again at around 5400 rpm when there isn't any more gain to be had. When it works properly you will notice that as the motor starts to flatten out around 3500 rpm it suddenly starts pulling hard again. It is well worth installing a new actuator while you have the manifold off.

Mike

WallyP

Before you replace it, make sure that you were sucking on the right hole...

One hose fitting is the vent, and won't hold vacuum. The other is the actuation, and will hold vacuum.

hacker-pschorr

Timely thread, I was just in the garage playing with the flappy on the 87, using the Mighty-Vac on the two lines going to the flappy solenoid.

Neither holds vacuum so I've got that going for me....... I was bored so having to pull the intake is a pleasant addition to my to-do list.


On a side note, these plastic vacuum lines are horrible.

UpFixenDerPorsche

Makes about 30hp difference at the top end, but the performance is sharper from 4k up.

I too had this problem and I liken removing the manifold to poking hot needles under my fingernails (not that I've actually done that but I did get a little splinter once).

Decided to do something about it as I wanted the lost horses back: (Apologies to Dwayne )

WARNING: THIS CANNOT BE UNSEEN :WARNING

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Manifold is now off as I had to fix an oil leak er flood from a tired gasket at the base of the filler neck.



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J1720

Very creative!!

Hilton

I used to think that - however I'm putting the plastic lines back onto my 89 after 6 years of silicone vacuum lines, as the prospect of fuel in silicone lines worries me. The factory system of plastic and rubber elbows is at least more fuel proof and gives a longer opportunity to notice/diagnose a running problem before the car goes "woof".

John - thats an impressively engineered solution!

The flappy makes no difference to peak horsepower. It closes again at around 4500rpm so when its not working its the same at low rpms and high rpms a it it were working.

What it does do is change the intake performance to add a second torque peak in the mid-range, filling in a large hole in the torque curve - it makes a very noticeable difference in pulling power. There's a factory chart of the difference between op/inop which gets posted from time to time.

mark kibort

I did the dyno test with no flappy vs flappy.
yes, as we all know, low end torque is happy with flappy, but past 4000rpm there is no difference

so, when racing , I never drop below 4000, so there is no difference with or without flappy.

It doest hurt top end HP BUT, if it doesn't open up, it will kill HP in the 5k range, so better to wire it open or remove it as I did, then to worry about it not opening up.

Hilton

Here's the factory chart:

J1720

Great chart!

UpFixenDerPorsche

My mistake Hilton. You're dead right.

I was thinking of the power difference at the rpm of the second torque peak (or not).

Have marked it on same chart below. It's about 20kW (25hp).

Cheers.

mark kibort

so, again, if you lock it open, if you never go below 3600rpm in anger, it's not a factor, and you don't need flappy. But, if it isn't working.... its costly!

SMTCapeCod

So is the main issue with a retrofit onto S3 the linkages?

The fitment is same at the head, right? Or are the fuel rails also a problem. Guess that's rhetorical, typing fingers let my brain actually work...

Too bad, the intakes would be cheap, the flappy functionality would probably be a hoot with the S3 cams, and the increased space could afford more creative approaches to broken intake bits and victor-type forced induction.


Edit, as is often the case- sketchy idea already/previously asked and well-answered.
https://rennlist.com/forums/928-foru...-s3-block.html

hacker-pschorr

The cloth covered flexible hose I use is rated for fuel.

It looks great, lasts a very long time and holds better than the plastic lines & elbows.

I have 3 different sizes on hand.

https://vwparts.aircooled.net/3-5mm-...-p/n203531.htm

Roger can get it by the foot.

PcarMiami