ChevyChad

iTrader: (50)

Should the bypass valve be open all the time when in vacuum? Just got done installing the procharger last night. I bought a polished plenum with a bigger procharger bypass valve, and upon initial startup noticed that the valve was open. So I pulled the throttle back manually and watched it as it closed with the throttle opening. But is it supposed to be open under idling conditions like that? That kind of worries me because I have a mecham hood, and there is a heat extractor right on top of the bypass valve and I can imagine rain possibly getting in there at idle…

White.Lightning

iTrader: (53)

EDIT....The valve should be closed unless under boost or WOT. I didnt finish reading your threrad. sorry

Yes, I was questioning this in a thread a little bit more down. The bypass is closed under boost and WOT. I personally think it sounds good. I'm jealous you're up and running. Makes me wanna buy my kit that much faster!

Andy

ChevyChad

iTrader: (50)

That doesn't make much sense ... So you're saying it should be open under boost or WOT

Ferocity02

iTrader: (60)

It should close when you give it some throttle. Since it works off vaccum, when you open the TB a little bit the valve will close because the vaccum goes away until the engine revs up and has vaccum again. What valve are you running? No matter what, rain can't get into the valve. The valve is always releasing air, so rain won't be able to get in. My bypass valve was adjustable, so I set it to where it just barely started closing at idle. That will make sure that it completely closes at WOT.

Azezial

when your at idle if your recirculating the air back through the maf then it wont matter, but if the bypass is open your engine is breathing unmetered air which can cause problems.

does your valve have any tightening adjustments?

White.Lightning

iTrader: (53)

Sorry, correction.....closed under boost or WOT. Right?!?

Andy

ChevyChad

iTrader: (50)

Don't have a picture right now. I'll get one tonight when I get home. I don't remember if it has an adjustment on it, I really haven't payed much attention to it... I know it says procharger on it and it is attached to the back of the plenum. Its probably 4" diameter.

ChevyChad

iTrader: (50)

Thanks for all the input guys

Ponyhntr

iTrader: (9)

So you have their red 'Race Valve'. All bypass valves used in supercharged applications should be normally closed with the engine NOT running. When at an idle (actually whenever the engine is in vacuum), the valve should be open. The valve will only close when the engine reaches 0 vacuum, and it will then go into boost.

Ferocity02

iTrader: (60)

Sounds like you bought my plenum, which Junior bought from me. If you have any questions let me know, since I built that plenum and went through adjusting that bypass valve.

ChevyChad

iTrader: (50)

Yes- I bought it from Junior. Cool- so at least I know where it came from now I don't like the location of the valve. I had to cut a little of the mecham hood underneath for clearance Probably works under a stock hood tho... It seems to already be adjusted like it should be from reading the above posts. I'll look at it closer tonight once I get the fuel pump relay in place and can give it some throttle.

Ferocity02

iTrader: (60)

I bought the plenum from another guy who did the welding on it, looks like **** huh? He never polished it back out. I never got around to it. Basically, the valve will close a little bit not matter where it is set when you rev the engine a little bit. Just loosen the silver nut, then screw the allen stud in and out. You will need to adjust it to your motor, since different motors have different amounts of vuccum. Like I said, I set it to where it barely strated closing at idle. I think this might be a little too much, because going up hills the valve would close because the motor is working harder. The valve should probably not close unless you are really romping on it.

DeltaT

iTrader: (5)

There are 3 forces that act on the piston of the bypass valve - the bypass valve preload spring, manifold vacuum/pressure, and boost pressure in the inlet piping. The first 2 are most important for this topic, if the bypass valve is sized properly for the system. If the bypass is too small for the system, the boost pressure could push in the piston just when you didn't want it to, wasting boost.

Here are the different states:

Engine Off: Spring holds piston shut
Engine Idle (High Vacuum or Low Proessure): Vacuum overcomes spring, piston opens
Engine low rpm, low load (Mid Vacuum): Vacuum overcomes spring, piston open
Engine mid rpm, approaches ambient pressure: Spring overcomes any remaining vacuum, piston starts closing
Engine higher rpm, or in boost (Ambient to Med Pressure): Pressure on back of piston complements spring pressure, piston closed
Engine at Hi Boost: Pressure on back of piston somplements spring pressure, piston closed
Engine at high rpm, throttle closed (High Vacuum): Vacuum overcomes spring, piston opens, pressurized air exits via bypass

The adjustment bolt allows you to change the preload on the spring, and change the vacuum/pressure point where the spring gets overridden. If you took it to an extreme, and cranked the bolt in all the way, the valve would never bypass. With somewhat less spring preload, you could have a bypass valve that only opened under the highest vacuum generated by the motor, so you could still get surge (and the chirping or gurgling sounds and possible damage to turbo/SC) if you almost took your foot off the gas, because the vacuum would not be high enough to overcome the spring preload.

Jim

Hershey Squirt

iTrader: (6)

Just for the record Ferocity bought the plenum, intercoolers, and piping from me. I never used any of it and did not do any work to it. I sold it the way I bought it and got a front mount. I bought the kit from nbm00ws6 on here. I think he was the original owner and the one who got the plenum welded. All I wanted was the head unit, bracket, and hardware everything else was sold.

Ferocity02

iTrader: (60)

Hmm... looks like ChevyChad is the 5th owner!!! It's cool the trace the history of parts.

Anyways, the position of the bypass valve, (open, closed, or in between), has little to do with engine RPM. It has MUCH more to do with throttle position. Even at 6000rpm the engine can still have vaccum in the intake, as long as the TB is closed all or most of the way. I still see what you are saying DeltaT, good post.

DeltaT

iTrader: (5)

The main point of the thread was lost after this...

Jim

ChevyChad

iTrader: (50)

Thanks for the write up DeltaT I think it is not closing all the way tho. Just got done taking my initial maiden drive with the newly installed system, and it didn't seem to want to go into boost. I wasn't giving it WOT, but I was giving it enough throttle to at least get into low boost #'s. But my gauge never went above 0. I think its the surge valve. I'll have to play with it tomorrow. Just glad its driveable again.

DeltaT

iTrader: (5)

When I was first trying to make boost I thought it was the bypass valve, but it was the belt tightness. I had no idea the belt had to be so tight that it was hard to twist it 90 degrees by hand. After I tightened mine, boost jumped up to 7.5 at 6000, at the motor.

I do have a dedicated 8-rib belt that only goes crank-blower-tensioner. Other accessories driven off factory 6-rib.

Do you see any rubber dust or fuzz anywhere?

Jim

ChevyChad

iTrader: (50)

Well I'll try tightening the belt. I haven't seen any dust anywhere, but I haven't really looked that close. I think if it was the belt tho, it should still at least see a little boost shouldn't it?? Is there a way I can manually keep the surge valve shut to test and see if that is the problem?

DeltaT

iTrader: (5)

I also had to take apart my Mondo and lube up the shaft. It was binding so it didn't open and shut smoothly.

For a short testing session, you can crank up the preload in the bypass, to manually keep it shut. When you drive, bring it up to a rpm where you should see boost, preferably with a datalog turned on to take a snapshot, then let off the gas slowly so you don't surge. Check to see what boost level you got to. Then put the bypass adjustment back to normal.

Jim