Blow Off Valve
 

Is anyone using a blow off valve. They sound sick on a Subaru STI but I havnt heard one on a diesel. BD makes them and im sure they have to sound pretty **** nice just because of the amount of pressure were pushing. Is anyone running one??

I'd actually like to know a little about this also! Sorry to jack the thread.

Search for it on TDR. I (JCleary) posted about it a bit as I recall. Maybe on here, too.

Bottom line is-

If you have a manual tranny and are doing anything other than sled-pulling with it, then don't waste your money. You lose boost on every shift adding 1-2 seconds to your 1/4 mile time. Then, you'll have multiple issues with the valve sticking open at the most inopportune (is that a word?) times. In fact, I was on the way to Redding to the drags when the valve blew a seal out and created a boost leak-no racing for me that weekend as I had no tools in the truck.

With an auto they're ok. Probably a good idea with a big single. Since you're only backing out of it at the end of the 1/4, or after a run on the street you're not losing boost on shifts. This is also why I think they are good for sled-pulling. Since you're only backing out once at the end, it will bleed boost and protect your turbo from barking.

I actually ran two seconds faster in the 1/4 by unplugging the valve. Boost would go from 60-ish to around 40 on a shift, while the BOV would drop me to 10-15. I guess I could have speed-shifted to avoid actuating the valve, but I didn't want to trash my synchros like that.

A more elegant solution is to wire a switch to shut the controller off when you're racing. But then, what's the point of having the valve in the first place?

I probably spent 40-60 hours tuning and tweaking that valve with springs, shims, and settings until I gave up on it. If you set it up stiff enough to not bleed off all your boost on a shift, your turbo will bark. If you set it up to not bark your turbo, you loose all boost and get high EGT's.

I haven't heard anyone brag to much about it. In fact, my mechanic wasn't too excited about installing it in the first place.


It was funny to mess with turbo'd ricers and let off a 60psi PSSSSSHHHHHT! Got more than a few looks with that for sure. Sounds like a big rig setting their parking brake, but louder!

The main problem is that a diesel does not produce enough vacuum to operate it. Waste of money like said above.

I would have to say it wouldnt really help on a auto either because if your going down the track either pulling or racing you have it floored the whole way so the blow off wouldnt do anything, The way I see it diesels dont really need them like any gasoline engine because they dont have butter flys in the throttle body that closes creating back presure to the turbo, It might help it from jumping forward after you floor it and let off right away when your trucks turned up, Just a waste of money on a diesel, I dont know maybe I'm wrong?

Diesels produce zero vacuum...

The valve is actuated by a controller that senses throttle position. The controller controls a solenoid that works an air valve to release boost pressure from the manifold to the back side of the Tial BOV. This boost pressure, plus the spring pressure is what keeps the valve closed.

When you release the throttle, the solenoid opens the air valve and releases the boost. The BOV opens until manifold pressure drops to a pressure lower than what it takes for the piston to stay open against the spring.

Softer spring = less barking
Harder spring = more barking

Since the valve depends on boost pressure to keep the valve closed, it's a flawed design to begin with. If the valve is stuck open, how do you create boost to push the valve closed?

I tried everything. Including working with BD to iron out the issues. I even tapped the turbo housing for boost pressure (instead of at the intake manifold as per their instructions) to attempt to get boost on the spring side of the valve sooner to help close the valve more quickly.

Sheesh. The more I remember about it, the more frustrating I remember it to be!!!

It controls the bark when you let off.

Have you ever heard the bark you get at the end of a pull or even letting off the throttle at 60 lbs of boost? I've had multiple barks when I back of once WOOOF Wooof wooof wooof woof.

It can completely eliminate that in the right situation.

The idea is good, it just needs a more advanced controller. Not simply a box with 4 pots to adjust. It needs a controller I could adjust to my driving style with a laptop.

well I guess for that it would be nice if it worked, just seemed really high priced for so little

It is expensive.

But it did take a lot to come up with the package they have. I'm sure they're not selling too many of them. Probably the reason they have not created a better controller. If I was only an electrical engineer. I know what I wanted it to do and when to do it. I just don't know how to transform my thoughts into zeroes and ones, so to speak.

Personally I think it needs a separate compressor/tank to actuate the valve, pressure sensors on the manifold, and an electonic control module to make it happen at the right time and pressure. Obviously I'm oversimplifying, but I know how to get it to work. Just didn't have the patience or time to pursue it.

I bet Quad could figure it out using a Pac Brake compressor setup and one of his existing products... :D

This responce is so honest and detailed it should be in an FAQ section.

Great job John

I was just curious. I havnt known anyone with one on a diesel. I know they sound pretty good on a STI when your shifting hard and that you need one on a gasser but i didnt know how they were with a diesel. Thanks guys

SSS- Thanks!

jtrimmell- I thought it would sound good, too. It does, but in a different way. You don't hear the cool chirp you hear on gasser BOV's. Like I said, if I had the time and desire I'd get it to work right and sound right. It's all about valve placement and a better controller.

In BD's defense- With diesel boost being so high, they were limited to the choices of valves available. Apparently the Tial 55mm was the only one they found that could work at high boost levels. My installation proved that the Tial valve was less than perfect at anything over than about 40-ish psi.

http://i208.photobucket.com/albums/b...9_78688603.jpg

The seal on the piston in the 55mm Tial valve is a silicon (or maybe Viton) 0-ring about 1/8" thickness. It's held in place by the groove machined into the piston. I guess you could call it a "friction fit."

When you blow off at 60psi, the air rushes by the o-ring so fast that it pulls it right out if it's little groove. When the piston closes, the o-ring bulges out into one of the openings you see (at the bottom of the red part of the valve there are six rectangular openings-you can see the aluminum piston inside and in this pic just barely see the brown colored o-ring) and leaves the valve open about 1/8".

This creates a nice boost leak, and will ruin your 1/4 mile run. The first time it happened to me it ruined my day. I wanted to race, but had to watch. I had never had it happen before, so I had no way to know what it was.

Once I discovered the problem, I always kept the wrenches necessary to fix it in my truck. It took less than 5 minutes from then on.

It really benefits the gas engine better since when they are under high boost conditions and they let off the throttle the charged air dead-heads at the closed throttle plate which is a very violent condition for the compressor wheel of the turbo. The boost would build up so high then blow back through the turbo which basically takes that turbo that would be spinning at 60k to 150k RPM (depending on the turbo size) and try to stop it and spin it backwards. It puts so much strain on the aluminum fins of the compressor wheel that over time can cause it to fail. Since diesels are open ported with no throttle plate, there is always somewhere for the boost to go, but there will still be a much smaller pressure build up. But under very high boosting we see on some of the high horse power diesels, I could see it as an added piece of mind for turbo protection.

I got rid of my SRT-4 to buy my truck and really do miss that phissssst sound and thought of putting a BOV on my truck just for that sound, maybe after I step up to a bigger turbo.

pretty much the same thing I said[laugh]

Alright well thanks guys. I didnt really know to much about them. I knew that the pressure builds up against the valve in the throttle body then makes the wheel spin backwards but that was about it. Im starting to like the sound of my turbo more and more. If you shift just right it sounds pretty **** good. I cant believe how much of a difference the intake made.