So I decided on this current build to run no BOV just to see what would happen. I know this ruffles a lot feathers on internet car forums. I did some very extensive searching through every service manual and technical document I had from multiple manufacturers: domestic, German, Japanese. Some of you may have seen all the random excerpts from manuals I post--I have a large library of stuff. And for the life of me I couldn't find anything that described a blowoff as anything other than a noise reduction or overboost protection device on stock cars. I didn't see one mention of a blowoff valve extending the life of the turbo from any car manufacturer's internal documents. So I said what the hell, I'll gives this a shot.

The turbo is a Garrett T04R/T67 that I bought used with maybe 2000 miles on it. It is journal bearing presumably with the 360 thrust. I guess I haven't put a ton of miles on it (only about 1500) but I've been running over 16psi for a while now and I haven't noticed any axial shaft play. There was a tiny bit of radial shaft play on the turbo when I bought it (and that hasn't changed), but that's not uncommon on larger turbos it seems.

Figure I've experienced compressor stall thousands of times by now because I drive it pretty hard when I do take it out. Here's something interesting: the sound of the compressor stalling changed significantly when I switched from a shorty K&N filter (about 3.5" long, whatever one was posted in that thread a while back) to a 7" filter. The shorter filter seemed to have more a flutter to it. The longer filter has more of a whoosh and doesn't sound much different from your normal BOV sound. Nobody seems to be able to tell that I don't have one. I've gotten "so what blowoff valve is that?" several times, and when I tell them "none" I usually get a confused or mortified expression on that person's face.

But if I do break something I'll try to post up about it, and you can all say "I told you so."

 

Interesting.....Keep us posted, thanks.

 

Any moment now.....

 

You'll put your eye out!

 

1500 miles in 8 months. Post results in another 3500 miles, and again 5000 miles after that.
Do you know the suggested lifespan of the turbo in normal operation with a BOV?

Have you noticed any benefits to running w/o one?

It ruffles my feathers when people suggest to others not to run a BOV, because I can find multiple sources that clearly detail why you should run one.

From Garrett Website,
"Blow-Off (Bypass) Valves
The Blow-Off valve (BOV) is a pressure relief device on the intake tract to prevent the turbo’s compressor from going into surge. The BOV should be installed between the compressor discharge and the throttle body, preferably downstream of the charge air cooler (if equipped). When the throttle is closed rapidly, the airflow is quickly reduced, causing flow instability and pressure fluctuations. These rapidly cycling pressure fluctuations are the audible evidence of surge. Surge can eventually lead to thrust bearing failure due to the high loads associated with it.
Blow-Off valves use a combination of manifold pressure signal and spring force to detect when the throttle is closed. When the throttle is closed rapidly, the BOV vents boost in the intake tract to atmosphere to relieve the pressure; helping to eliminate the phenomenon of surge."

From Turbonetics Website,
"Q: Should I run a Blow-Off/By-Pass Valve (BOV) on my turbocharged car? What does it do?
A: Yes, all turbo cars can benefit by running a BOV on their vehicle. A BOV works by relieving the compressed air pressure trapped in the piping when the throttle body closes. The turbocharger continues to spin from the exhaust gasses exiting the engine and the compressed air has nowhere to go. The BOV opens and prevents the compressed air from "backing up" onto the compressor wheel causing surge. By venting or re-routing the trapped air, the BOV allows the turbocharger to spool up quicker between shifts and prevents long term damage from continual surging of the compressor wheel.
NOTE: If your vehicle has a Mass Air-Flow Sensor, it is important to re-route or By-Pass the air back into the inlet of the turbocharger (behind the MAS) so that the vehicles computer does not raise/alter the air-fuel mixture, causing the car to potentially run rich between shifts."

 

I love that you are doing this. Knowledge at someone elses expense. For that, i encourage you to keep going. It sounds painful and i love it.

Please keep it scientific, i want to know the results. :-D

Rob

 

Although i am against running without a BOV, it has been done since the early days of turbo. And con be perfectly safe when done right.

Almost every turbo diesel truck runs without a BOV, and thats for one main reason. and that is most of them come with an anti-surge compressor housing. Letting the reversed air bypass the turbine blades and come out the intake of the turbo. Is yours an anti-surge compressor?

But with all the money spent of safety when building a motor, ie. stronger seals, pinning, tuning, AI injection, ect. ect. Why skip out on the BOV?




off topic/side note: Turbos can also be ran without a wastegate and get the desired boost. But this is VERY hard to get right. The turbo has to basically be designed to run exactly for your motor or it can continue boosting until it either breaks your motor, or breaks itself...

 

I can go look at 2 diesels right now that do not have an anti surge housing a 97 dodge and a 07 ford... the reason diesels dont need a BOV is there is no throttle to shut, therefore no chance of stalling the compressor.

I personally cant think of a factory installed (gas) turbo that doesnt run a bypass or blowoff valve. Way I look at it car companies wouldnt put them in if they werent needed to avoid warranty claims. Im not saying your going to grenade your turbo but what benifit are you hoping to see?

 

I have been going with out one for 3 years and covered over 40 000 miles in that time. No problems.

BOV is a waste of money and time.

 

To be honest, I can't tell a difference. Seriously. It drives the same--it's not any more or less laggy. It's completely unnoticeable, at least on this car (on a car with a MAF it may cause problems). As far as the Garrett and turbonetics quotes, well I've been trying to steer away from any sources that are designed for marketing or public consumption. I'm only looking at internal technical documents (mostly manual and technical guides).

Yes there is no throttle plate. On another note you have to keep in mind the difference between what I consider "real" compressor surge--running the turbo under load in a range it wasn't designed for--and just letting the turbo vent charge air out the inlet. In the latter case, there's hardly any exhaust driving the wheel anymore because the throttle has been shut.

I mean maybe I'm wrong on this point, and if I'm wrong I'll have a blown used turbo. Big deal.

Z31 300zx turbo. It has an overboost relief valve in the event of wastegate malfunction, but no regular old blowoff valve. Note that this service manual uses the term "bypass valve" but they are really referring to an internal wastegate valve and internal wastegate actuator.



All the documentation I have collected just talks about eliminating noise. What benefit do I hope to see from this project? Well, nothing material. I'm just doing it cause I can. Lately I've been going out of my way to test long held beliefs, such as "the Power FC can't control boost effectively" believed by Rx-7 owners, "the factory wideband is useless" believed by STi owners, etc. If I blow a turbo, I blow a turbo. This kind of stuff keeps me from getting bored with the car honestly.

 

^^ and there it is

~S~

 

Quoting from website of company which have only one goal in mind-money is IMO meaningless...

When you shut throttle, exhaust stream is also immediately shut so turbo is not "surging", it just slows down a bit. As I understand, surging - really bad surging - caused by mismatched turbo/engine can stall compressor-not mass of air in charge pipes between compressor discharge and throttle body escaping through compressor...
WRC cars doesn´t run BOVs, turbo cars from good old Group C didn´t either-arguments that these are race cars are not valid as they performed all day long in 24 hour races at much higher pressure ratios and mass airflows without failing. Question should be why they didn´t run BOVs?? Probably answer is that they haven´t any important reason to fit such ballast which can fail and in such situation(like not sealing right) can cause overspeeding and real damage of turbo...

 

I have run without a BOV at 30psi held boost for maybe 20k without the turbo failing on a VERY hard driven road car.
Did the same on other cars, just not as much boost, and all been fine.

Doing the same on the RX now, so far only 500 hard miles or so, but its a far from new turbo and done thousands of miles without an air filter fitted, so how worn it already is is unknown.

But then again ive run very aggressive ALS for about 13k with no damage, and if you listen to most people (who have never tried) they reckon a turbo shouldnt last more than about 100 miles like that...

 

crazy Aussies, of course you have a 700hp on pump gas and water injection so all I can do is listen and learn.

 

eh whats the point? there are no negatives to running a bov, other than the possibility of the bov leaking. faster spool time between shifts, easier on turbine wheel and bearings, i dont see why not. if you dont want the noise, just route it back into the TID

 

I have faster spool time between shifts WITH NO BOV. Anyone who thinks you get faster shift times with a BOV IS FUCKEN RETARD. I have done back to back to testing and you have better response between gears with NO BOV. The bov drops all pressure in your system hence turbo having to respool every gear change.

Of course what would i know. Ive only tried it.

Like i said.

My car on its current 700rwhp 35psi setting has No BOV AND ABSOULTELY RIPS AND has been doing so for a fair while no and turbo is mint condition. Ill take another pic tomorrow of comp wheel and show no oil etc.

Factory turbo cars have bov purely FOR NOISE and EMISSIONS. IT IS THAT SIMPLE.

 

I love you guys.

 

How does a BOV help with emissions o.O

thewird

 

I've never run a MAF based car without a blowoff valve, but I suspect that not having one at all would confuse the sensor just like when you vent a blowoff to atmosphere. the result would be a rich mixture, backfiring, high HC emissions, etc.

 

I don't mean to complicate the thread, and hope i don't sound stupid. But aside from compressor surge, i thought the BOV would also protect against detonation when one lets off the throttle.

Example:
I'm under hard boost, throttle to the floor. The second i let off the throttle, the injectors instantly let up on fuel (due to the TPS).

A ton of pressurized air is still sitting in the intercooler/intake piping and wanting to go into the engine.

Lots of air + less fuel = potential detonation.

Is this a possible outcome? Or does the valve in the throttle body shut enough when the throttle is moved to block out all of the pressurized air in the intake piping?

 

the air will not make it into the engine as the TB is shut.

 

I agree about the surging due to improper sizing of the Turbo Charger, but...

"To minimize lag on a turbocharged engine there is what is called a "dump valve". The dump valve also helps to save the turbocharger bearings. The dumpvalve is an airvalve positioned on the airhose after the turbocharger (on a RS Cosworth it is right after the turbo). When the turbo has spun up and creates some boost and one suddenly lets go of the throttle the throttle housing will cut off the airflow into the engine and the turbo will build up a huge pressure in the plumbing between itself and the throttle body. This pressure will try to burst the pipework, try to stall the turbo as fast as possible and push the compressor wheel against the bearings very hard compared to in normal boost situations. This is not good and because of that the dump valve will release this pressure. On an original RS Cosworth it will release the pressure back to the plumbing between the airbox and the turbo to lessen the noise. This will allow the turbo to keep spinning while the throttle is "off". So when the driver decides it is time to hit the throttle again the turbo will already be spinning at a good speed and it will take less time before the boost reaches the desired level compared to without the dumpvalve. The drawback of the original setup on the Escort RS Cosworth (from a performance standpoint) is that it vents the air form the dumpvalve back to the airbox and that the dumpvalve sits before the intercooler and not after. If one lets the air from the dumpvalve vent to the atmosphere instead it will not put even more unwanted hot air into the turbo and the pressure will vent away easier. The dumpvalve should also be positioned as close to the throttle housing as possible. This is to avoid the heat from the turbocharger and to still have some pressure in the system while saving the turbo bearings just as much as with the original placement of the dumpvalve."
http://www.wrc-cosworth.org/tech/tur...bocharged.html

"The blow-off valve is more commonly used to keep the turbocharger spinning
when the throttle plate is suddenly closed. When the turbocharger is
generating maximum boost pressure at full throttle and then the throttle
is suddenly closed, compressed air coming from the compressor slams
against the throttle, generating extremely high pressures that travel
backwards to the compressor stopping the compressor from spinning. When
the throttle plate is again opened, the engine must spool the turbocharger
shaft again. The effects of this high pressure can also be very damaging
to the turbocharger.

Brian Wright
Washington University in St. Louis Formula SAE Racing"
http://www.newton.dep.anl.gov/askasc...9/eng99202.htm

http://www.valveindustry.com/news-571/dump-valve.html

http://www.essortment.com/hobbies/tu...erkit_sdar.htm

http://www.rallycars.com/Cars/bangbang.html

http://partsofturbocharger.blogspot....ed-system.html

 

with no exhaust driving the turbo, it doesn't matter much either way. Like I said, I can't tell a difference. Of course the best way to settle that would be to somehow log the speed of the actual compressor wheel. But that's not going to be easy without lab-grade equipment.

exactly. whether you have a blowoff valve or not. How fast do you really think a turbo can spin with basically zero exhaust driving it? How fast can any pump spin if there is no energy driving it and you have various frictional forces slowing it down? Again, we don't have the equipment to answer that question.

So far none of the dire predictions have come true, but I guess I'll find out eventually and I'm still reserving judgment on this point. My hypothesis is that this matters mostly when the turbo is being run in the surge portion of the map (engine under load), rather than when the throttle is released. I had a previous setup where my blowoff valve wasn't working for about 2000 miles (because I didn't hook it up to a proper vacuum source, an oversight really). Most of that was running 18 or 21psi. I didn't have any problems with that turbo, but I suppose I didn't give it enough time.

 

arghx, do you track your car at all? Just wondering what type of use your putting on the no BOV setup. Thanks.

thewird

 

What souce did you hook the BOV up to that wasn't sufficient?