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Running no BOV or recirculating valve

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Dstarperformance01

Proven Member
880
172
Mar 5, 2016
Mustang, Oklahoma
So, I’ve been reading and hearing that a bov or recirculating valve isn’t necessary to have on a throttle blade set up and doesn’t have any ill effects. This goes against what I know but want to know what’s the deal? Is it a size of turbo being ran or in general?
 
I saw the video you are talking about and does pose a good question about compressor surge vs bov activity.
 
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.

Source:
"Turbo Tech 101 - Basic"
Published by Garrett.
https://www.garrettmotion.com/turbo...orks/basic/?utm_campaign=redirect_Day1Garrett


I know many people have run turbos without bovs in the past with no/minimal issues. My father ran a turbo on his Z28 for many years of autocrossing and drag racing in the mid 80s without the use of a bov. But for the minimal cost of installing a bov of some variety I'm not sure why you wouldn't want to. Especially if turbo manufacturers are recommending them.
 
I would think for protection and such a reasonable cost most would want to run a BOV. I have heard my compressor surge after a 2 step so I think I will keep mine installed to ward off the thrust bearing wear. Interesting topic and video though.
 
*On throttle* compressor surge is bad compressor surge. Off throttle has virtually no load since the amount of exhaust backpressure when the throttle is shut goes to nothing nearly instantly. Lots of cars/trucks come without BOV's. MR2's, every diesel out there (and we all know how long holsets run on a cummins without issues). The only surge that will cause damage is when you're on the throttle. I have very small cams in my evo for the FP black/stroker setup I run, the car makes full boost ~3000 RPM's and it flows enough air to create very bad ON throttle surge at low RPM.

For the cost of a BOV I don't see why anyone wouldn't just run one, but you're not going to hurt anything running without so long as it's not generating on throttle surge.
 
Or a log from someone not running one would be interesting also! Maybe I should go cap mine off and do a pull........:shhh:
 
Also note that diesels don't use throttle bodies so the air is never hitting a "wall" when coming off the throttle.

Interesting topic none the less. I would be curious to see data for boost recovery after a shift.

Technically we aren't "hitting" a wall either since the IAC opens and the throttle plate is never fully shut. I'll go digging through my old logs, we capped the BOV on my evo while diagnosing the on throttle surge. I have some logs from ~6 years ago somewhere.

Try running no bov in a car running real boost, you’ll blow the throttle plate into the manifold.

I'd say 26lbs of boost through an FP black and stroker is reasonable amounts of boost. I'd be certainly impressed to see the two small springs that hold tension on the throttle plate having enough pressure to prevent intake pressure from just opening the throttle plate. No plates in my intake manifold.
 
I’ve got engines out there pushing 60 and I run 40-45 in my personal car all the time. No bov would spell disaster in those setups.

Even at 26 you’ll kill that black with no bov. The only cars that get away with no bov typically run under 10 psi.
 
Technically the air charge going back into the turbo inlet reduces the lag. Compressor surging back through the intake would result in some interesting issues depending on your fuel delivery method, and cause the turbo to stop mid spin.

If youre going to argue against a bov i would argue that you could move the throttle body to the turbo air inlet and just eliminate comrpressor surge immediately by restricting air thats already been calibrated for by the ecu, instead of just discharging it.
 
Even at 26 you’ll kill that black with no bov. The only cars that get away with no bov typically run under 10 psi.[/QUOTE].

Lol, Under 10! The reason I posted this is because on my dd fb pages guys are running them and pushing way more than 10lbs of boost w/ no issues.
 
Maybe we need to define "kill". If running no bov causes extra stress on the center section/bearings then maybe the turbo will last 50k miles instead of 75k. I have no idea what level the increased wear might be but it is possible their lack of bov hasn't affected them when their turbo has minimal miles. Just a thought.
 
I’ve got engines out there pushing 60 and I run 40-45 in my personal car all the time. No bov would spell disaster in those setups.

Even at 26 you’ll kill that black with no bov. The only cars that get away with no bov typically run under 10 psi.

Once again, exhaust back pressure drops to virtually nothing once the throttle plate closes, OFF THROTTLE surge isn't going to hurt anything. I get off throttle surge at every shift if it isn't WOT, going on 50k+ at well over 6 years on this black and it's just as tight as when it was new. Factory gas engine cars come without BOV's. ON THROTTLE is bad, off throttle isn't hurting anything.
 
The "possible" benefits of running a bov/bpv far out weigh the defecits when not running one. It's a safety device, they can be cost effrctive, and there's really no reason not to run one.

I remember reading about all the mr2 guys swearing bov's were snake oil and unnecessary or "ricer" pieces because mr2's didn't have them factory. 90% of the other factory turbo cars out there run some form of pressure relief, seems like a good reason to run some cheap insurance vs maybe some kind if gains without one?
 
Once again, exhaust back pressure drops to virtually nothing once the throttle plate closes, OFF THROTTLE surge isn't going to hurt anything. I get off throttle surge at every shift if it isn't WOT, going on 50k+ at well over 6 years on this black and it's just as tight as when it was new. Factory gas engine cars come without BOV's. ON THROTTLE is bad, off throttle isn't hurting anything.
Again, run some real boost and see how it works out. I see zero single digit cars at the track with no bov. They must just like wasting money.
 
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I have a hard time believing that was caused by compressor surge. The throttle springs are not strong to hold a steel plate shut enough for it to bend on itself.

Once again I'm by no means condoning running without one. The $200 you spend on a good tial is plenty cheap insurance to not have any issues. I'm just saying I think you guys are overreacting to the possible effects of OFF THROTTLE compressor surge considering the amount of manufacturers that felt they weren't needed on daily drivers.
 
I feel this thread will just become an age old argument. Even a knock off is 30$ and works why wouldn't you run it? In my opinion do what you want it's your car I just want to know is there any evidence that the car holds boost more without one or is that air all going to escape to atmospheric pressure as if a bov let it out?
 
That’s my point. What works in a daily driver doesn’t always work in extreme environments. Manufacturers send millions of turbo cars out the door with cast pistons too.
 
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