Bypass valve

XxSlowpokexX

Registered User
Is there any reason I cant use a recurculating bypass valve such as those used with turbos and centrifigal blowers on an eaton or twin screw setup? There are lots pf high quality options. Seems you may get less leakage then you would with the typical setup that comes from eaton or lets say kenne bell.

So is cost the only reason for going the way Eaton or Kenne Bell did or is there another reason?

Thanks all
 
My theory is that they don't make a big enough size recirculating blow-off valve for a reasonable cost, the SC bypass is about 45mm and most turbo valve's are 25mm, it might cause idle issues and from tinkering around with them, they seem to open slower which could cause a lean condition in between shifts.

Your also constantly trying to figure out how much spring tension is required since a 15lb spring may not equate to holding 15lbs of boost, there also seems to be a reliability issue resulting in a weak seal but on the flip they do seal better when adjusted correctly but noting that some valves create the seal on inside (the opposite of an engine valve seal) this makes it that much harder to hold a lot of boost, however some valve have an inverted style diaphragm which would make the seal look like an engine valve, a better seal, they may have that information posed on a Greddy website.

The SC valve, from what i've seen, creates the seal on the wall it is enclosed within, from experience I took the valve out and poured some water on them, to check for leaks, a few drops did seep through, however, if you apply a small finger pressure to the pressure side of the plate, there is no seepage as that would be a realistic condition if 10-15 lbs air pressure were acting on the inside and vacuum on the outside.

If you can fork out an extra $150 on a high quality turbo style valve then I don't see any reason why it can't be used. I opted for the remote Eaton bypass for my next setup.

My 02
 
I thought about the leakage thing for the stock SC bypass valve. You can get some around the sides of the plate. However, I decided it wasn't a big deal for me because there is already some leakage through the "crosstalk" hose between the inlet and return plenums. So unless you are blocking off the crosstalk hose, don't worry about it. It just makes your plenums a little "chattier". :p

On the other hand, if you have a vacuum / boost leak around the bypass valve shaft, that could be a problem. The shaft rides on needle bearings with integral seals. It is a bit of a pain, but you can change them. It is actually hard to find the correct bearings with seals, but there is a workaround. I chased down the parts last year sometime and posted the info in another thread.

http://www.sccoa.com/forums/showpost.php?p=688146&postcount=13
 
Dont flame me for this................

My bypass valve leaks a little around the edges. Cant you just put JB weld around it to seal it or is it suppose to leak a little.
 
Dont flame me for this................

My bypass valve leaks a little around the edges. Cant you just put JB weld around it to seal it or is it suppose to leak a little.


They tend to leak around the shaft where it goes into the bearing. The bearing has a seal that wears out over time and can let a lot of air go past it. Enough to cause an idle problem in some cases. The other bearing supporting the shaft is capped on one side and doesnt leak as it is a pressed fit. I dont know where you would put JB weld at:confused:

Ken
 
On the firewall side of my MP inlet by-pass valve the shaft had a bad leak around it, enough that it would suck your finger to it while the motor was running. I took a good ol' Lincoln penny and copper RTV'd it on the opening, now no more leak and it runs great, been about 2 years like that..............:D
 
Dont flame me for this................

My bypass valve leaks a little around the edges. Cant you just put JB weld around it to seal it or is it suppose to leak a little.

I can't tell where you mean. As Ken is saying, you can't really JB-Weld anything where the shaft is rotating. If it leaks past the butterfly valve inside the plenum, then you might be able to tighten the gap with some JB-Weld. But you can't mess with the shaft.

The stock seals are soft rubber so they don't abrade the shaft too much. But they do wear out. The bearings are totally replaceable, and separate seals are available too. It's just a little hard to replace the bearings because they have to come out to the outside. You can't press them through the housing because there is a step in the metal that hugs the shaft closely.

Okay, I have to stop typing shaft now.
 
I have a lot more to learn...........

I thought this was the bypass valve. Mine is leaking around the edge with the arrow. I have three of them and they all have a little leak around that edge.
 

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Oh, thaaaaaaat edge. I thought you meant the edge of the butterfly valve inside the plenum. You might be able to seal that up with some JB. The way it works is the vacuum pulls on the diaphragm, which moves the arm, which pulls the lever, which turns the shaft and opens the bypass valve in the plenum. When vacuum is released, the diaphragm springs back and closes the bypass valve.

To check if the diaphragm is actually sealing correctly, try moving the lever to open the valve. Then cap off the vacuum nipple on the can. (Your thumb will work in a pinch, but a vacuum cap will do best.) See if it holds its position. If it can hold for any length of time, I wouldn't worry about it. If it can't, try again after you seal the edge. If it can't hold after you re-seal it, then you have a tear or crack in the diaphragm and you need a new can.
 
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