ok, so let's say I end up pushing 8lbs of boost, and this thing says it's made for 10-25 psi...will it function properly for me?

If yes, I think i'll go ahead and go with the Turbo XS RFL

Thanks,
Dave

 

The job of the blow off valve is to vent pressure from the intake piping when the pressure in the intake piping is greater than the pressure in the intake manifold.

I think the problem is that your supercharger is always trying to work at pressurizing air, and therefore at partial throttle, when it's making more pressure then the throttle body is letting in, it will vent it.

This is just a theory, but I am guessing that this will happen with any blow off valve...

Chris

 

So Chris, shouldn't he pretty much set the BOV to release when intake piping pressure reaches, in his case, 8psi or more?

As far as it being rating at 10psi, and if in fact you cannot loosen it a bit more, then, what happens is you get air pressure forcing back onto your compressor wheel (or compressor side of the supercharger?). In a turbo setup, after the throttle body is closed, enough pressure eventually builds (to 10psi in this case) to release the extra air. Since I'm not all too familiar with superchargers, I couldn't comment on EXACTLY how that works, but I'd imagine it'd be pretty similar.

Hope this helps, and guys, if anything is wrong, feel free to correct me.

Johnny

 

I had a Turbo XS type RFL on my 3000gt vr4. That thing was 140 decibals at 10 psi according to Turbo XS. All I know is it would scare old ladies on the sidewalk when I shifted under full boost at 15 psi. It comes with washers so you can adjust the stiffness of the spring inside. The price is very reasonable. THE most excellent sounding blow off valve ever. (I think RFL stands for really f'n loud.)

 

ok, I ordered the RFL BOV...what exactly do I do with it? Put the spring on the lowest setting and run the car and see what boost I reach? Then keep trying until I reach my max boost? This sucks not knowing what my max boost will be since I've had this problem ever since I installed the front mount intercooler...and smaller pulley.

Also, CJB, I think I understand what you're saying about the BOV leaking boost with the SC setup...but just want to clerify. When I'm WOT, it shouldn't leak correct? You're saying that the SC builds boost and under normal driving conditions (speed up a little here, slow down there) it will leak the boost out because the throttle is decreasing...correct? But if I'm at the track or whatever...and I'm running the car as hard as I can, it shouldn't leak boost until I shift or let off the gas completely...correct? It won't release pressure while the RPM's are rising and i'm full throttle. Or am I misunderstanding you completely?

Thanks for the info guys!
Dave

 

The bov should only be venting (opening) when the throttle is closed. The washers with the RFL make the spring stiffer. Try starting with 2. Rev and make boost then let off the throttle. Have someone helping you listen and watching the bov with the hood open. It's pretty much trial and error. It shouldn't take too long to figure out how many washers you need. After you get a good idea from revving at a stop, take it on the road and watch your boost gauge. Hopefully you have a high quality boost gauge with peak hold features. The RFL should be loud enough to hear if it is opening under boost and not when the throttle closes. Iff it opens under boost or partial throttle, add another washer and so on and so on. I hope this helps. The RFL is good to 30 psi if I remember correctly. It should not affect the amount of boost your car makes, only how well it gets vented to the atmosphere when you shift or let off the throttle.

 

So what is my ideal setting, how do I know when I've got it? I can hit it...hear nothing...until I let off? How would I know if the spring is too tight? Maybe I'm over thinking things and just need to wait until I have this thing in front of me. It's probably a lot easier than I'm making it out to be.

Dave

 

You are correct, if your throttle body is open completely then you will have equal pressure before and after the throttle body, and therefore you should not have the BOV open. Turbos don't build much pressure unless they have load, but a supercharger is always working to pressurize, this gives you good throttle response and predicability.

Anyways, if your throttle body is partially closed then the motor is trying to eat the air behind it, and the supercharger is trying to push more in. If the throttle body is closed, then you will have less pressure behind the throttle body than you will have in front of it, thus the BOV will open to vent the pressure. The spring pressure is supposed to hold it closed unless there is a large pressure difference (shifting, or going from WOT to no throttle) Thr Tial is not adjustable so you'll have to deal with it, or swap to something that you can tinker with.

If the spring is too tight, then it won't open unless you have a large pressure variation, say you ahve 7 psi pressure in front of the throttle body, and -12 psi in the intake manifold, then it will vent, but if you have 2 psi in front of the TB, then perhaps it won't open....

My Tial opens sometimes with my turbo setup at idle. Especially when you rev the car and then let off the throttle. The turbo is trying to push air through the intake system and it jsut got a surge of load, but the air has no where to go.... It creates a whistling noise.

Chris

 

awesome, thanks cjb...that makes much more sense to me now.

I really appreciate the help!

Dave