[s-cars] Bypass Valves and Pressure Losses - the basics first

[QSHIPQ at aol.com]

I don't understand this.  A "boost" surge as you describe it below means that 
you see boost when you lift the throttle.  That should show up on a manifold 
guage (I don't see how but...).  IF it does, then it's not a lift throttle 
situation it's a part throttle situation, in which case a BPV isn't the issue.  
Boost surge shouldn't show up on a manifold guage on lift, boost pressure is 
measured after the throttle body, hence it really isn't a bypass valve function. 
 It's a wastegate problem.  In the scenario below (assuming surge at full 
lift) an inadequate BPV shouldn't be the cause of a "surge" you should be 
stalling the compressor, or blowing the end tanks off your IC.

Surge at part throttle (which is what I assume you to mean, since I spoke to 
both Pederson and Davis at Steamboat last year) means that you don't have 
enough wastegate control for the turbo installed.  WGFV or WG. 

Now, IMO, what you did with this Mongo bypass valve is you actually are 
bleeding off part throttle boost with the valve.  That's a possible solution (as I 
posted before), but a frustrating one, since all "part throttle lift" is 
slightly different by definition.  So, you can partially solve the problem by 
'bleeding', but you won't ever completely solve the problem.  

When I read "the stock Mitsu EVO BPV couldn't hold my turbo's force" I think 
that's not a BPV problem, I think that's using the wrong device at the wrong 
side of the combustion chamber (but reading the below I could say that about 
the turbo as well).  I suggest that you try a simpler test to help Dave et.al. 
at ASW figure this out for you Hap.  Put a Pressure Guage pre throttle body 
(try one pre IC as well just for giggles).  I'm betting this will give a more 
convincing argument that *ANY* BPV; in any flavor, combination or count you 
choose won't solve the problem you are chasing.

Scott "hoping to get paid for this someday" Justusson


In a message dated 12/18/2003 3:23:45 PM Central Standard Time, 
CaptMagu at aol.com writes:
Gary

I have the H34 TurboXS right now. Do you have it plumbed from the side? In 
other words is the pressure feed from the turbo plumbed into the side of the 
piston. If not you'll want to reorient it this way and then you won't need 
any 
washers. In fact I went to a softer/shorter spring. I had shimmed my old H34 
like crazy, well beyond the provided washers and was still having a problem 
getting it to hold boost. I talked directly to the TurboXS folks a while back 
when 
there was a thread running on mounting BPVs backwards. They admitted that for 
high hp applications that this was the way to go and sent me a brand new H34 
configured for a hard mount at the side. Tha's what I have now but even with 
the softer/shorter spring I'm still getting that boost surge at throttle lift 
from boosted runs. It was Trevor Frank's idea to try a softer spring and it 
has 
greatly improved the problem but has not totally fixed it. My next try is a 
beefier diaphram unit. The stock Mitsu EVO BPV couldn't hold my turbo's force.