aggravation

I'm about to put the flappy back in the intake and if I set the flappy shaft in the closed position the first chance you get to have the spring tensioned is maybe a half of a revolution of the springs hook relative to it's 'hooking' point.

Should I add another full revolution to that or would that be too much spring load for the vacuum actuator to overcome?

KLVA

I just did mine and you just hook it up to the peg with no extra tension.. In Dwayne's fantastic writeup he said to wrap it around a couple of times but that will not work because only vacuum pressure is used to open the diaphragm valve on the flappy, so only enough tension so it will return to closed is needed. I basically just sucked on the vacuum line to watch it draw open and then watch it retract....it is not like the throttle spring that is pulled by the throttle cable. I hope you were able to replace the flappy bearings when you had the intake off because they can leak all sorts of vacuum and that can really be why the flappy won't open ....that was my experience last month and I got my bearing s from Roger in Texas ....sent them very quick too. Thanks Roger !! After that I did a test on the whole intake w/ the pressure test setup and it held perfect and the flappy works great...also did the 2 knock sensors plus all the gaskets for the intake ..Good Luck Kevin

928autobahndreamer

I followed dwaynes writeup and intitially thought that two times around felt like too much tension. However, on testing with my mitivac it starts to open at 6-7 in Hg and is fully open at around 12 in Hg.

I have not installed my intake yet so I will be watching closely for a concensus on amount of spring tension.

aggravation

I wonder if the forces at work inside the intake could overcome the spring tension if it isn't wound up at least one+ times? I know the pressure, in theory, is equal on both sides but there must be some turbulance or pulsation to the way the air moves in there, if the flap gets pushed open a bit due to a lightly wound spring will air push by opening it more and then keep it open when it shouldn't be? How about on a supercharged car like mine?

Vacuum actuators in this car seem to be stronger than I would have guessed just by looking at them. If you manually push or pull some of the things they move you'll see what I mean...pretty strong resistance they overcome.

KLVA

NOW you got me wondering again.....I think we need to ask DR about this..both my 88 stock setup and your SC. I cannot believe that a central intake would not cause completely equal pressure on both sides w/ little or no tubulence....maybe different in the super charger intake....justs seems to me the spring only needs to have enough tension to get the plate back to closed and I have even read on rennlist about just leaving it open all the time ..still chewing on that thread...hmmmm HEY DR, you there ???

blown 87

How much vacuum is there available at WOT?
Unless it is getting the vacuum source from someplace other than manifold vacuum you are not going to get much.

I have no idea where it come from, just a thought, but I am going to find out.

DR

zzzzZZZ.....zzzzzzZZZZz ...huh what, OK Mom I'll get ready for school...zzzzZZZZ zzzzZZZ....... WAKE UPPPP!!!

Oh OK, what was the question??

Oh yeah, flappy spring pressure.... 1/2 wrap ain't gonna cut it, little too much turbulance around that round thing inside there.

zzzzZZZZZZZ zzzzzZZZZZ

OH... one more thing, vacuum for flappy is supplied from the Venturi Vacuum, is "protected" by a check valve and has access to the vaccum storage tank so WOT vacuum is irrelevant. HVAC and/or cruise actuator (78-87) vacuum leaks ARE an issue!

zzzzzzzzzzzZZZZZZZZZZZZZZZZZ

blown 87

Now I don't have to look.
I plan on stripping my intake this weekend, how many turns should it have?

DR

IIRC at least a full turn. maybe a little more. If I get a chance tomorrow I will count on a couple different intakes to be sure.

EDIT: checked a couple and all are definitely at least one full turn. This is a little subjective depending on your idea of when you think the tension starts. Basic rule of thumb is at least 1 full turn of tension. This could be 1.25, 1.5" etc depending on your accessment. It doesn't need to be as tight as you would initially think it should be.
.

Mrmerlin

dont forget to SET the hex stop for the flappy it must be set to prevent the flappy from jamming closed .
The stop is tapped onto the roll pin that sits adjacent to the flappy pivot shaft.
If your stop is missing simply cut the head of a bolts off IIRC a 17mm head will do then drill a hole into one side off center of the bolt shank, then add a drop of loctite and tap it onto the pin so it holds the flappy stop open a hair.
Also as a note Dwaynes intake RnR job was missing this piece when he pictured the install, the roll pin is clearly visible. I am not sure if I mentioned this to him

928autobahndreamer

Whoa, Whoa, Huh, What?
Didn't realize there was a "hex stop" any photos of what you are describing. I think I get it but want to make sure.

blown 87

What I realized from his post was that there are so many ways to build a 928 engine as screw it up.

Guess I need to lay off the glue and beer for a while, at least until I get my motor built.

Mrmerlin

I dont have any pictures but you should take a picture of the flappy B4 you remove it.
If you go to Dwaynes pictures on the intake you will see the picture he took that shows the roll pin in question and his stop isnt on the pin
The picture is near the bottom of page 2, the roll pin is also used for the flappy spring hook

928autobahndreamer

OK. Is there another piece that is supposed to attach to the pin to act as a stop for the flappy spring?

I took some pictures just now of my flappy in its current state.

blown 87

I have gigs of pictures of the teardown of my engine, most shop mechanics never do engine rebuilds any more, cheaper and less risk to buy one.

I take tons of pics of cars we take apart, customers like to see not only the parts that got replaced, but why a 300 dollar part cost thousands of dollars to install sometimes.

So many that keeping track and especially finding the one picture is a problem.

I have a 500 gig drive that has just pictures on it, ok some of it may not be repair stuff, but it is not **** related.
Got a different drive for that.