sans-audi

Okay let's review: How much sheer abuse did BOV folks endure here before this?

nyet

Not ONE of them offered any explanation as to why BOVs were superior to BPVs.

Not ONE of them offered any explanation as to how to avoid running rich.

Not ONE of them said anything about running rich during idle due to the BOV being open.

Not ONE of them said running BOVs wasn't necessary if running low boost.

They OBVIOUSLY all wanted it ONLY for the sound but would not admit it.

sans-audi

Well, yeah.

Singletrack

Some people admitted it, in their defense : )

donistook

The Audi doesn't really run any richer than other cars....look at a c/o reading and you will find the same specs are mandated. Under boost, the fuel pressure goes up "slightly" to richen the mixture. To be more specific, I would have to look into it a little further.

shortyq

Don:
A couple things to consider. First, the S1 Pikes Peak rally car I saw at Monterey '99 had a cheapo plastic bosch valve routing the dump to 4 smaller hoses aimed radially (quite deliberate in target) at the turbo intake blades. The car didn't have the injector in the EM (could have been removed), but audisport was at least "hoping" that the blow effect would do something (I doubt much either).

Secondly, a BPV (I use BOV to describe the absolute boost pressure device downstream of the t-body in the IM)vented to atmosphere must be shimmed/cranked closed at idle, or it is a leak by definition. The problem with using BPV open to atmosphere is it causes rich fuel spikes because just at liftoff, the "fart" creates a quick air flow thru the MAF. This is pretty well documented with the mitsus and Supras as WJM pointed out. This can cause some interesting bad side effects to O2's, cylinder walls and cool looking flames burning up cats (depends on size of turbo, FI etc. Most likely not a problem with your "application"

IME/O there really isn't any harm in putting the BPV blowoff back into the intake tract (anywhere between the MAF and the turbo inlet), keeping it as metered air really has no downside that I can think of. Put another way, if your argument for the shims is that it's a leak otherwise, at somepoint (vented to atmosphere) it becomes one. Logic would tell me that you'd want that "leak" at idle before you'd want it coming off WOT.

Regarding the BIG valve. My understanding is that air pressure and flow is strictly a cross-sectional area argument, you actually could get even more air out by using two smaller valves. My thinking is that you could find some benefit (especially in racing) by putting in two smaller valves, and staggering the spring preload. Specifically, have a light vacuum BPV and a full lift vacuum BPV. Have you tried this?

Thanks for taking the time out to share your practical secrets of speed. Most interested in your thoughts on the above.

Scott Justusson
'87 T44tqw
'84 RS2URQ project
'83 Urq

markbradford

Thanks for the instruction at BHawk.

Singletrack

Very interesting, as are your cars : )

WJM

If you could look into the engine wash effect a bit more, and if venting to atmosphere may induce this in Audis would be interesting to know.

Thanks for the feedback
regards
-Will

STKSKI

I just purchased the Turbo XS type H Blow off valve with the adapter for an a4 1.8t. After reading your writeup i am confident that this could possibly work. I will make sure i install it correctly and make sure it doesnt open on idle. I will then see if i loose any throttle response, gain any turbo lag, rough idle, lag between shifts and so on. Hope this works! Wish me luck!