Contour Enthusiasts Group Archives Forums Modifications Forced Induction Let's talk about Blow off valves

I know what they are and what they do...but what makes one "good".
We know about turbos and balancing and construction, and wastegates and the seals etc, but Blow valves? What's the deal...why do some handle more boost than others?

It's mostly due to design... the good ones that can handle lots of boost have properly designed valving inside so that the boost pressure is acting on a much bigger area then the manifold pressure. That way the BOV can never blow open. You'll notice that lots of the common cheap ones that people complain about do not do this.

And then there are material differences.

Look at the price of a good Tial BOV compared to some of the junk people run...

how about diverter valves and blowoffs?

what are the pros/cons of both?

What is considered "junk", though? I have had a very good experience with the TurboXS RFL. It took a few tries to get the washers set up right for the correct spring pressure, but it's a "set it and forget it" kind of thing. The only thing I don't really like is that it's a blow-off to atmosphere type. I don't like the thought of all that metered air blown off into space, but it's for such a short time... :shrug:

What do most contour people use? Ive heard nothing but rave reviews about the HKS SSQV

Im not familiar with the exact turbo setup so i dont know if the BOV is before or after the MAF, so what do people run VTA or Recirc?

For the amount of boost any Contour would run.....just about any BOV would work within its effieciency range. A lot fo BOVs start to fail once you run more boost.

I have past experience with HKS and Greddy, both seem to be really good VTA and are adjustable. Both handle up to 22-25 psi.

Some of the better BOV's are the ones that come from the factory.. the subaru one is actually pretty good but the flange on it is retarded.

I've read good things about the HKS SSQV in that it meets the design standards i said above.

Many people here have had good experiences with the TurboXS's but most people who are running lots of boost have lots of problems with them because from what I recall.. and don't quote me on this... but they don't meet the design I noted above.

BOV vs. BPV (or diverter valve I guess)

BOV = dump to atmosphere
BPV = dump to post-MAF/pre-Turbo

For a MAF system you "should" have a BPV. The whole metered air thing and all that jazz. Now technically the BOV would only be open when you're under vacuum such as when you let off the throttle and there's a big pressure differential so you only really get rich conditions between shifts and dropping out of WOT (some people like it for the flame shooting effect). Lots of people get away with BOV but it's technically not the correct way to do it.

This is all with a draw-through system... if you're go blow through i think most of them put the BOV before the MAF and they can use a BOV just fine. Seems like that would cause some reversion through the MAF but what do I know.