Blowoff valve question.

[John Hartman]

Ok, so I know its fine for my blowoff valve to leak at idle because I am running speed density.

I also know you are supposed to adjust your valve just as tight as is needed to keep it closed at idle.  Any tighter and you run into surging/trailer hitching.

Now, with my Forge, it leaks(more like hair dryer on cold) at idle.

So I toss in the yellow(second strongest) spring in there.  Less air but it still leaks.  As soon as you snap the throttle it closes, no problem, but it leaks at idle.  Maybe not a hair dryer now, but still quite a volume of air.

So I put in a couple of shims.  Same thing.

Then I put in the red spring.  Its pretty stiff, almost up to a crappy valve spring.  Strong.  STILL getting air at idle.  Less, its harder to detect, but its definately still there.

So I take it apart while its running.  I see that the engine vacuum is sucking the piston upwards into the "hat" part of the valve, as its supposed to, even with the red spring in there(wow, actually).  And when its sucked fully up to the top, it can't block off the port into the intercooler pipe, so of course it leaks.

Anyone come across this before and/or know what to do?

[Jordan Kruger]

What model of forge bov do you have?
That might be a stupid quesiton, but I dont know anything about the forge bov and its construction. But it may act as a pitot tube does on a regulator. the "leak" may be intentional by design to allow the valve to make quick adjustment when on and off throttle.
My Greddy Type R stays closed until boost has to be vented. You're forge Bov may in essence allow the valve to float closer to its open and closed postition for quick response. Early type S bov's had an additional nipple on the bottom side of the diaphragm which allowed some pressure to go in and assist in the valves response.

[John Hartman]

its a piston design.  Piston moves up and down by spring, vacuum and boost.  When down, the bottom of the piston closes the port.

[Jordan Kruger]

http://www.evoxforums.com/forums/showthread.php?t=17255

[Jordan Kruger]

My old type RS would float open at idle.  That write up has a person from Forge responding to a customers questions about the Forge bov. Sounds like open at idle is normal with almost every valve.

[KevinBuckham]

Assuming you are recirculating why not let it leak at idle?  Even with a MAF the factory valves leak a bit at idle (both my 2G valve did and one of my 1G valves did).  It should only help by slightly increasing VE (decrease pumping losses) as it gives a small but straight shot from air filter pre turbo to the upper intercooler pipe.  My Greddy Type S leaks at idle and if adjusted any tighter really causes issues with part throttle lifts on track.

If you aren't recirculating then it's a great source of dirty air.   I run speed density and keep it recirculated as I can't adjust my valve to not leak at idle without other problems.

[John Hartman]

no, its not recirculated.  I do plan on doing it once I can get down to RG.  I am of the school that says all that air under pressure can keep the turbo at least a bit spooled between shifts.

I did suspect that maybe it has to be leaking at idle.  I had read that you are supposed to adjust your valve until it just barely doesn't leak at idle, but mine won't.  I wonder if a small solenoid in the vacuum line, hehe.  Just over complicated I would guess, for no real benefit.

[Jason Harwood]

no, its not recirculated.  I do plan on doing it once I can get down to RG.  I am of the school that says all that air under pressure can keep the turbo at least a bit spooled between shifts.

I did suspect that maybe it has to be leaking at idle.  I had read that you are supposed to adjust your valve until it just barely doesn't leak at idle, but mine won't.  I wonder if a small solenoid in the vacuum line, hehe.  Just over complicated I would guess, for no real benefit.

My OEM 2G OEM 1G and Greddy BOV all leaked a bit. I thought this was just normal on DSM's.

[KevinBuckham]

I am of the school that says all that air under pressure can keep the turbo at least a bit spooled between shifts.

Me too.  Not sure if really does help, but why waste the air and potential energy?

[Robert Vorley]

I read a test in redline magazine where they compared venting to no venting and no bov, as I recall the best time occurred without one at all.

I believe the wrc cars run without. Of course they normally run anti-lag which gives instant response.

[John Hartman]

yea short route piping helps, and having a budget that can replace turbos after every race is different.

Compressor stall is bad for the turbo 

[Robert Vorley]

I knew someone would say that, john.  

Stall, anti-lag and surge, three more reasons to get a bb turbo, hey a sponsor wouldn't hurt either, or with the money you save not buying a bov you can pay for a rebuild on your old thrust bearing turbo.  

........

So I dug up that Redline issue (#141) and the diff was 7/10ths of a sec from 20-80mph (1st-4th gears or 3 shifts) between the fastest (basically tied between none and recirc) and the slowest, dump to atmosphere.   They were using a Sunny GTI-R for the tests but noted a larger difference on other motors.  With their Audi S3  recirc was the slowest.....

[John Hartman]

I have a ball bearing turbo.  And I plan on either selling it as a good condition one, or keeping it for a long time. 

[Robert Vorley]

I  thought you might be about to trade in your 3076 for a 68 after that sales pitch to Kevin?    jk

[John Hartman]

thought about it to be honest.