Is there such a thing as...

[TheKurgan]

Umm, the engine doesnt spin down immediately neither does the s/c. Additionally, theres boost already in "the pipeline". The TB blade snaps shut, WHAM all that boost that was made just a moment ago slams against the blade forcing the tube off.

However, as I mentioned, the tube coming off happens even ABSENT of a full boost pull and off throttle snap close. The D1 is building SOO much boost in the pipe that it cant exit out of the BOV fast enough and it cant rush past the partially open TB blade fast enough either.

Ill post video of this soon once I isolate it.

I think we are saying the same thing. It's the act of the TB slamming shut and not being able to bleed off the compressed air that causes them to pop off. Call it vac or boost. Mine did it on the dyno, but it wasn't tightened down. At least for Tial, they determine what spring size to be using depending on what kind of vacuum you are pulling, not how much boost you are running.

 

[19COBRA93]

I think we are saying the same thing. It's the act of the TB slamming shut and not being able to bleed off the compressed air that causes them to pop off. Call it vac or boost. Mine did it on the dyno, but it wasn't tightened down. At least for Tial, they determine what spring size to be using depending on what kind of vacuum you are pulling, not how much boost you are running.

We are talking about the same thing, but the pipes popping off as you slam the throttle shut has nothing to do with vacuum. It's simply the BOV not acting fast enough to dump that pressure. At high RPM that blower is still moving the same amount of air regardless of whether the throttle is open or closed (unlike a roots/ts). Once the throttle is closed, that pressure will build fast in the IC piping if it has nowhere to go. If a BOV doesn't act fast enough you'll get a pressure spike and any weak clamp will give out. You won't see this on a boost gauge because you're reading manifold pressure/vacuum which is behind the throttle body, not in front of.

And the Tial spring recommendations are for a turbo setup. You'll get part throttle surge on a centri SC if you follow their recommendations. On a turbo car the valve is closed at part throttle/cruise. On a centri SC you want the valve to be open at part throttle/cruise. The smaller the pulley, the softer the spring so it'll move more air at part throttle, simply because the blower is spinning faster. So not exactly boost related, but kind of.

 

[TheKurgan]

And the Tial spring recommendations are for a turbo setup.

Ahh, I did not know that. Makes sense the centri is spinning faster than the turbo at part throttle. Mine is actually spinning pretty fast even though I'm only at 12psi. I think I lose about 4psi between the intercooler and cams, but I can only go down 1 more pulley size. You certainly know more than I, but I'd say huge BOV and softest spring.

 

[19COBRA93]

Ahh, I did not know that. Makes sense the centri is spinning faster than the turbo at part throttle. Mine is actually spinning pretty fast even though I'm only at 12psi. I think I lose about 4psi between the intercooler and cams, but I can only go down 1 more pulley size. You certainly know more than I, but I'd say huge BOV and softest spring.

I'm spinning mine pretty hard too because of my high altitude. It's not making anywhere near the boost it would at sea level. And yes, I agree, big valve, soft spring.

 

[FalconGTHO]

So Tre is picking a 60mm size. Is that good enough?

 

[Twinscrewgt]

That should be plenty once you get the spring dialed in

 

[Tre06GTP1SC]

So Tre is picking a 60mm size. Is that good enough?

Talking to Pat yesterday evening that was the size recommended by those Boost Dudes (can't remember the name of their shop)

They are suppposed to get it fab'd up and on the car today. Just going to run one 60mm bypass

 

[Twinscrewgt]

It'll be loud but that should work nicely

 

[tjm73]

Not sure if it's been mentioned, but why not vent it into the exhaust system back behind the cats?

 

[Sky Render]

The TiAL "Q" BOV flows more than most others on the market. It also doesn't need to be adjusted for different boost levels. You simply change the spring in the diaphragm according to what your idle vacuum is. There is also an "Alpha Q" that is made to be recirculating. These BOVs are much quieter than most of the "ricer" ones out there, too.

I highly recommend it for any boosted application.

 

[Tre06GTP1SC]

It'll be loud but that should work nicely

Yeah I youtube'd it, it makes a very load "whoosh" but the noise won't bother me.

Not sure if it's been mentioned, but why not vent it into the exhaust system back behind the cats?

The problem wasn't were it was venting, the problem was, it wasn't venting fast enough.

Hopefully this 60mm will take care of the problems

 

[tjm73]

The problem wasn't were it was venting, the problem was, it wasn't venting fast enough.

I understand. But if the bigger units make too much noise on venting, dump that into the exhaust and you probably won't hear it. You get fast enough venting and not the crazy ricey noise.

 

[TheKurgan]

I understand. But if the bigger units make too much noise on venting, dump that into the exhaust and you probably won't hear it. You get fast enough venting and not the crazy ricey noise.

I don't know how you would do that on a Tial. There is no hose fitting or anything on the BOV to route it anywhere. I'm talking about the main blow off, not the little hose that goes back up to the manifold vac line.

 

[19COBRA93]

I understand. But if the bigger units make too much noise on venting, dump that into the exhaust and you probably won't hear it. You get fast enough venting and not the crazy ricey noise.

You're confusing a wastegate (exhaust) on a turbo setup with a BOV (intake side) that we're using on our SC's. Different animal altogether. No exhaust involved here.

 

[Twinscrewgt]

Yeah I youtube'd it, it makes a very load "whoosh" but the noise won't bother me.



The problem wasn't were it was venting, the problem was, it wasn't venting fast enough.

Hopefully this 60mm will take care of the problems

Just remember on a sc car the BOV is always slightly open except under wot. It's not the whoosh sound that gets old. It's driving around town at 2500 rpm sounding like a street sweeper lol

 

[Tre06GTP1SC]

LOL Yeah I hear ya. That Mondo sounds like that already.

 

[tjm73]

I'm sayinmg custom fab an interface to dump the BOV pressure into the exhaust in the same way a wastegate does. They are very similar. There is no reason not too do this just because it's "different".

 

[Sky Render]

I understand. But if the bigger units make too much noise on venting, dump that into the exhaust and you probably won't hear it. You get fast enough venting and not the crazy ricey noise.

Um, yeah, this is just a bad idea all around.

You're confusing a wastegate (exhaust) on a turbo setup with a BOV (intake side) that we're using on our SC's. Different animal altogether. No exhaust involved here.

^^This.

A wastegate on a turbocharger opens whenever the desired boost level is reached. It routes exhaust gasses around the turbo, keeping it from spooling up more. A "dump tube" or "screamer pipe" is where you vent the wastegate's exhaust directly to ambient. It's stupid loud. The "correct" solution is to vent the wastegate's exhaust to the downpipe (pre-cat) so it goes through the entire catalyzed exhaust system. I believe that's what you're thinking of.

A blow-off or bypass valve has nothing to do with exhaust. It vents boost pressure to ambient (or pre-compressor, in the case of a bypass valve) to prevent "surge." Surge is where boost goes back through the compressor (in the wrong direction) because it cannot go into the engine due to a closed throttle.

 

[Twinscrewgt]

Um, yeah, this is just a bad idea all around.

Agreed lol

 

[19COBRA93]

I'm sayinmg custom fab an interface to dump the BOV pressure into the exhaust in the same way a wastegate does. They are very similar. There is no reason not too do this just because it's "different".

I'm running a wastegate on my SC setup already, so I'm definitely no stranger to "different". Plumbing a BOV discharge to an exhaust system would be a piping nightmare. It's not like a turbo system where a downpipe is right there handy. In addition to that, the BOV's we're talking about here have no provision at all to add a pipe/tube to. Even if you could, the best option would be to simply direct it back into the SC inlet pipe like a recirculating bypass valve. So yes, there are reasons nobody does it.