boost bypass valve

JD1964

there is enough sticking out to grab on to
15 Year Member
Jun 28, 2013
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I want to learn about boost bypass valves. Not blow off that dumps, but bypass that sends the discharge back to the blower inlet tube.

My V3 setup was the entry level kit when I first got it so it did not come with a boost bypass valve. I'm assuming that's because entry level boost is only 5-6psi. Well, I've changed pulleys a number of times and now I'm seeing a reliable 10psi and sometimes a little more. So, I think its appropriate to have a bypass valve on it now to prevent spikes against the turbine when I let off while shifting on hard acceleration.

I bought an adjustable bypass valve that comes with three different springs. I realize that the stronger springs will increase the piston pressure on the seat and delay the opening of the bypass valve. I also see there's a vacuum port that hooks to the opposite side of the valve piston. So, it looks like a combination of excessive boost pressure in the discharge pipe from the throttle blade closing and increased manifold vacuum, also from the closed throttle blade, will cause the bypass valve to open and bleed off any excessive pressure.

Now, while under full throttle, (calling for boost) the vacuum line will not actually be under vacuum, but instead it will also be under boost pressure and thus pushing the boost valve piston against it seat and allowing the boost to build and be delivered into the engine through the open throttle blade (WOT remember).

Am I basically correct in this description? If so, then......

What is the sweet spot adjustment? Obviously I can change the springs. But I'm always thriving to understand exactly what is the goal in the adjustment? What am I trying to make happen, and when do I want it to happen?
 
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I want to learn about boost bypass valves. Not blow off that dumps, but bypass that sends the discharge back to the blower inlet tube.

My V3 setup was the entry level kit when I first got it so it did not come with a boost bypass valve. I'm assuming that's because entry level boost is only 5-6psi. Well, I've changed pulleys a number of times and now I'm seeing a reliable 10psi and sometimes a little more. So, I think its appropriate to have a bypass valve on it now to prevent spikes against the turbine when I let off while shifting on hard acceleration.

I bought an adjustable bypass valve that comes with three different springs. I realize that the stronger springs will increase the piston pressure on the seat and delay the opening of the bypass valve. I also see there's a vacuum port that hooks to the opposite side of the valve piston. So, it looks like a combination of excessive boost pressure in the discharge pipe from the throttle blade closing and increased manifold vacuum, also from the closed throttle blade, will cause the bypass valve to open and bleed off any excessive pressure.

Now, while under full throttle, (calling for boost) the vacuum line will not actually be under vacuum, but instead it will also be under boost pressure and thus pushing the boost valve piston against it seat and allowing the boost to build and be delivered into the engine through the open throttle blade (WOT remember).

Am I basically correct in this description? If so, then......

What is the sweet spot adjustment? Obviously I can change the springs. But I'm always thriving to understand exactly what is the goal in the adjustment? What am I trying to make happen, and when do I want it to happen?

For 10 psi a bosch style valve wouldve been sufficient, I actually have a metal version of it that i used to 13.5 psi when i was mass air and never had an issue . If you are using some type of tial bov that you are recirculating you need like a 2lb spring for it. Any heavier of a spring you run into surge issues and you will break the valve and also risk the chance of leaking seals in the blower. What valve did you purchase?
 
What valve did you purchase?

This one > Powergo Motorsport Made in China :(, oh well. Bosch style metal.

It's an aluminum body with an aluminum internal piston. The top screws off to change springs or add / remove spacers for preload. There's an o-ring that seals the cap and two o-rings that seal the piston to the internal body wall. It appears fairly well made.

It came with the heaviest spring installed. I've tested using my Mightyvac tool. The lightest spring allows valve opening at 5Hg, medium 8Hg and heaviest 11Hg. I did not experiment with preload spacers. The valve opens smoothly.

So, should I just go with the lightest spring? Obviously that would protect the blower seals the best, but what might be a drawback of too light a spring?

One concern is how well this thing will hold up and perform after being subjected to the heat under the hood. It will be in proximity to the passenger side header when installed. There is a light coat of clear silicone lube on the oring seals out of the box. Does anyone have a recommendation for a good heat resistant lubricant for these o-rings?

You can see the pics and info in the ebay listing but here's my pics too.

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I ran the plastic version of that style Bosch bov with a couple of different supercharger set-ups I had over the years.
I never had any issue with it , did what it was supposed to do.
I don't remember being able to change the springs in the one I had and I ran it anywhere from
5-10 psi boost.
I would start with the lightest spring and see what boost levels you get.
 
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Lightest spring , I’d shim it some and call it a day . I ran mine in the same spot as yours for years it’s fine . You want it to hold shut in boost but open right up Off the pedal . 10 psi is nothing to worry about with swapping springs and stuff .

The Vortech one I have now is slightly undersized so I was having a problem at 19psi keeping it fully shut . By cranking my adjuster down ( pre loading the spring ) it kept it shut on the pulls but in reality I need the bigger bv57 they make.
 
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I want to learn about boost bypass valves. Not blow off that dumps, but bypass that sends the discharge back to the blower inlet tube.
Too much surging. Difficult to maintain stable idle.

My V3 setup was the entry level kit when I first got it so it did not come with a boost bypass valve. I'm assuming that's because entry level boost is only 5-6psi. Well, I've changed pulleys a number of times and now I'm seeing a reliable 10psi and sometimes a little more. So, I think its appropriate to have a bypass valve on it now to prevent spikes against the turbine when I let off while shifting on hard acceleration.
This is exactly why you want to configure it as a blow off valve (BOV).

I bought an adjustable bypass valve that comes with three different springs. I realize that the stronger springs will increase the piston pressure on the seat and delay the opening of the bypass valve. I also see there's a vacuum port that hooks to the opposite side of the valve piston. So, it looks like a combination of excessive boost pressure in the discharge pipe from the throttle blade closing and increased manifold vacuum, also from the closed throttle blade, will cause the bypass valve to open and bleed off any excessive pressure.
It only dumps (blows off at idle).

Now, while under full throttle, (calling for boost) the vacuum line will not actually be under vacuum, but instead it will also be under boost pressure and thus pushing the boost valve piston against it seat and allowing the boost to build and be delivered into the engine through the open throttle blade (WOT remember).

Am I basically correct in this description? If so, then......
Correct.

What is the sweet spot adjustment? Obviously I can change the springs. But I'm always thriving to understand exactly what is the goal in the adjustment? What am I trying to make happen, and when do I want it to happen?
Valve closed at 0inHG (i.e. 0 psi boost). Realistically, about 10 inHG. It's mechanical & not that precise because it doesn't need to be.

Valve needs to be located at outlet of blower, before intercooler, if you have one.
This is a Greddy type valve, about 1 in Dia. Doesn't need to be too big.
Mounted down low, almost out of the engine compartment.
IMG_0890.JPG
 
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I've read that BOV should only be used with blow through MAF. My MAF is on the inlet side of the blower and that's why I should be configuring as a bypass, rather than BOV. I'm just learning about these things but does this sound correct?