Kinda sounds like an SR-4 compound air brake valve. It has 2 sides to it, one air activates the emergency brake line, and the other controls the service brake line http://www.bendixvrc.com/itemDisplay...ocumentID=4818 or here is a single pilot valve http://www.anythingtruck.com/Merchan...de=061-109264X

 

Nick, that looks a bit overly large and complex, and I'm betting slow reacting. https://www.surpluscenter.com/item.a...-A&catname=air
That is basically what I am after, just needs an adjustable spring return on the spool, so I can set a pressure differential between boost and drive pressures.

Remove all the drive pressure, and the RA will slow/stall because of the pressurized air back flowing on the intake side. Give it a vent upstream so the air continues in the same direction and doesn't slow/stall the RA. Should prevent shaft breakage and help keep boost up, and guys like Jason would appreciate that. If its an electronic control on a throttle micro switch, when an auto goes from 3rd to 4th locked and rpm drops to the point of not enough drive pres. to keep the turbo from barking, the BOV will vent off the pressure to prevent said barking.

 

Maybe I am confused on what the valve actually has to do, but would this work?

https://www.surpluscenter.com/item.a...55&catname=air
or
https://www.surpluscenter.com/item.a...43&catname=air

 

I say for 6 buck, buy that surplus one and figure out how to modify it.

 

IMO, I think that the blow-off valve would work better on the turbocharger side of the intercooler.

 

Brett, in the normal position, (as in the pic), the manifold pressure is fed to the top of the BOV to keep it closed. Boost is also acting on the spool to push it to the left, with drive pressure and an adjustable spring forcing to the right. When you let off the throttle, drive pressure disappears, the boost pressure pushes the spool to the left. When the other envelope is engaged, vacuum (supplied by the vacuum pump) will act on the top of the BOV to blow off the pressure in the intake tract. Once the pressure is dissipated, the spring will return the spool to the normal position with manifold pressure acting to close the BOV. It would just be so much easier if they made a BOV with ports on top and below the diaphragm like on an external gate.

I might just try that $6 valve and see if I can add a spring on top of the spool.

 

Tate, I suggest you should do some pressure measuring, I bet that your drive pressure isn't dropping as fast as your boost is. That helps to explain the compressor stall/surging. Your right if the drive pressure is drops off, you should be ok. Surge would occur if you still have energy to increase discharge pressure. If there is no energy to increase pressure you'll be ok. The trick is to dispate the discharge pressure at the impeller, not the entire air tubing under the truck.

 

How can you dissipate the pressure at the compressor, but not in the tubing? Need a check valve in the piping. A check valve in the air tube would prevent the back flow, but the compressor wheel will still slow down. Release the pressure in the pipe, keep the wheel speed up and once drive pressure is restored, the wheel will be past the boost threshold faster than if it came to a stall.

 

We can try some expermenting, I have a few ideas for surge and stall.

 

Tubing bending under the hood eh? So you are trying to balance TIP to Boost for surge control or stall? I was thinking of delta P switch with boost and exman pressure inputs. When the diff gets outside of a comfortable setpoint you could trip BOV in either the exhaust or intake.

I think I get what you are doing and if you do dump all exhaust pressure at once you would get stall, but if it bleeds slowly as you approach setpoint probably not. Like a regulator for differential instead of an absolute trip point.

 

Might be easiest just to drill and tap a port on the bottom side just like a wastegate...

 

Sounds like you get the idea. Usually, boost:drive is around a 1:1 ratio, sometimes a little larger at low boost, and much lower at high boost. The plan is to have the valve so it will take around 10psi more pressure on the boost side to open the valve than exhaust pressure, for those situations where drive ratios are fairly good. If it goes over the 10psi differential, it will vent the cold side to atmosphere.

I also had another thought last night, in one of my late night engineering moods, and figured I might be over complicating this. I think the reason gassers need the vacuum signal is, typically, there boost pressures are too low to blow open the BOV by themselves and need the help. It also creates a convenient signal. If I plumb drive pressure directly to the top of the BOV with drive pressure, I should get the same effect. Generally the barking of a turbo comes at over 20 psi, which should be enough to pop it open. I might have to buy one of these to experiment. I have a spare intake tube laying around, so if it doesn't work, I can just swap the old one back in.

 

Vacuum opens a normal bov. I suppose with a light enough spring boost would too (as in the gasser world that is why they offer different springs for BOV to keep them shut if you are running high boost, I have had a few leak and need to be shimmed or crushed in order to hold the boost I was after). Hmm, now that has me thinking, with like a 3psi spring, and drive pressure to the top, you might be onto something there.

The only problem of course is that if some how you end up with a really efficient turbo setup, you may see a point were you would get better then 1:1 boost to drive.

Definitely would need to run a filter between the bov and the drive source.

 

In a gasser, the same pressure trying to open the BOV is the same pressure trying to close it from the top. The vacuum isn't so much what opens it, as the pressure differential. With the drive closing it, we have our pressure differential that we need. The spring that needs to be run would be whatever max pressure diff. would be when at running conditions, such as a good running setup that has better than a 1:1 boost/drive ratio. I think I'm gonna go buy one and we can maybe try it out next week before I go to work.

 

With that system you would be setting the spring tension for your differential. I seem to think an adjustable regulator might help to make the ratio adjustments something you could do on the fly. I was gonna ask Shane if maybe the guts from a level controller might do the same thing only use the input as the deltaP across the two manifolds.. ??????