Not running a BOV
 

I've got a new Apexi rx6D/P27 turbo. What's the opinion on running it without a BOV? Research suggests is safe and the full kit doesn't include one. I'm looking for educated input. Thanks!

Recirc valves are to prevent noise. Blowoff valves are to make a lot of ricer noise. Neither are required, on any turbo.

BOV are not just for Ricers to make whoooshing sounds. But like peejay said are also not needed . However your turbo will thank you for having one. The blow off valve prevents the turbo compressor housing from surging when you let off the throttle suddenly. There a lot of information on the web about this .

Right, but I've always been lead to understand that compressor surge will break a weaker turbo. Which is why I was asking. And it seems most run a blow off valve. Do you guys run a BOV? What turbo are you running?

I planning on running dual BOV for this coming year on a BW S480. But it's strictly a track car . Every car I've worked on has had BOV's . I've actually seen it more common not to run a wastegate . But with no wastegate to much boost on the wrong sized turbo equals engine failure.

This may or may not be anecdotal but I have been running no BOV on the stock turbo and intercooler for the last 4 yrs. I have not seen any degradation in turbo performance or accelerated wear. I have no idea the exact mileage on the turbo but I know for sure its had a hard life before me.

I dont feel like the car would drive differently with on. Ive been daily-ing this car as well ~15,000 miles a year.

i've got a stock turbo car with no BOV, and it is LOUD. even 1-2 psi it makes neat race car noises at full volume.

i don't have many miles on mine at all, but i also tossed together a turbo from random parts just to get it running, and its been like 3 years and its still hanging in there, with no BOV the whole time. so i wouldn't worry too much about having one, unless you need a quiet car

Ok, I think that's all good information. Has anyone had any experience, or witnessed any incident, of a turbo catastrophically failing that was linked to compressor surge caused by the absence of a BOV? And this is assuming that the turbo was properly sized for the engine and was not operating outside of the surge limit of its compressor map.

The bov also has the benefit of allowing the turbo to freewheel in between shifts and should allow for quicker transient response. I may only be very slight. But a slight benefit combined with the benefit of not forcing the turbo to surge is good enough for me.

That, and if they were not a benefit of some sort, I doubt BW would have gone through the effort of designing a recirc valve into their EFR line.

Compressor surge UNDER LOAD will kill turbos, if you don't first blow piping apart or crack your exhaust manifold apart from the shaking. You have to work hard to get the turbo combination screwed up enough that you're spooling that far too early.

A little giggle off throttle, which by definition means there's no exhaust flow to drive the turbine end, isn't going to do any harm.

If you're concerned about turbo life, run a turbo with a water jacket... water cooling is the real reason why modern turbos last basically forever compared to the 80s.

Thank you for making that clear.

If the turbo isn't surging under load, then the "surge" from closing the throttle plate is negligible to the compressor

In effect, it would seem that the actual real function of a BOV would be preserve some amount of boost responsiveness and perhaps protect a turbo that operates close to, or slightly beyond, it's surge limit?

I started this thread with the preconceived notion that the above was true. But everywhere I turned online it seemed "you need a BOV" was the gospel.

it also reduces noise, and THAT matters to the OEM's. i think there is probably also a benefit between shifts. those two things are why every OEM car has one.

From Borg Warner press release-

EFR turbo compressor housings incorporate an integrated BOV. Yes, you read that right - the BOV is a recirculating style *built-in* to the Compressor Housing. The major performance advantage in this design is that it redirects the high-pressure compressed air from the outlet of the compressor wheel -> right at the low-pressure inlet of the turbo. This helps to keep the turbo spooled between shifts and offers cost savings/convenience while keeping MAF-based engine mgt happy. With this in place, there is no need for a BOV or flange on the charge piping. The only downside of this feature is the fact that it makes the compressor housing about 1" (~25mm) longer in axial length. For the hardcore racers who want to use an external traditional BOV, and for applications that can not fit or do not want to use the internal valve, we offer a disabling cover plate. This cover plate installs in place of the plastic cover and uses the original diaphragm to seal the port.

From Borg Warner EFR training manual-

61
Chapter 9: EFR Installation Features
CRV
We have had great success with integrating the comp
ressor recirculation valve (CRV) into the compressor cover for quite a few
years on OE gasoline engine applications. The major benefits are of course the underhood packaging space that is freed up by not having an external device and the cost savings from integrating it into the turbo assembly.
Recirculating the flow back into the compressor inlet helps keep MAF
engine management systems “happy” and also helps keep turbo speeds
high during the shift. The only downside of this feature is the fact that
it makes the compressor housing about 1” longer in axial length. For
the users that opt not to use the internal valve, we offer a disabling
cover plate. This cover plate installs in place of the plastic cover and
uses the original diaphragm to seal the port. As a service replacement
item, spare plastic cover plates (with hose nipple) are sold as part of a
CRV service kit. An external valve (BOV) can be used in place of, or in
addition to, the BorgWarner CRV if desired.

Recap-
1) Better response on throttle transition ( I really noticed your foot can "dial-in" any boost you want going on or off of the throttle- not the case with traditional turbo BOV coming off throttle).
2) Better engine management on MAF ECU
3) Borg Warner makes the block off plate and endorses its use.
4) The EFR IRL/CART turbo compressor covers do not have any BOV (can you imagine a more strenuous environment?)

At least with conventional turbos/BOV combinations the people who have actually data logged fast up changes on the track have had higher boost on re-applied throttle in the next gear without rather than with running a BOV, there was an autospeed article about it floating around. It also makes sense for anyone who has used centrifugal pumps in an industrial application as if you throttle a pump off it absorbs less energy as it is moving less mass and doing less work, wheas if you bleed back like a BOV the pump is still doing work and absorbing more energy. In our case, looking at a gear change with a coupled pump/turbine and no real turbine input energy with the throttle shut we rely on inertia of the shaft and wheels to keep it spinning, drawing down energy by pumping mass across the compressor and out the BOV means less shaft speed when you come back on throttle.

It may be different if BW have spent a lot of time on aero in the compressor cover of the EFRs but unless I see data logs of both states I wouldn't be confident of them maintaining higher shaft speeds with the bleed back. The fact that their assembly inertia is so much less however means that once turbine input energy is restored it speeds up to start pumping again much faster anyway so picking the difference in transient response on an EFR really would require decent logging.

On a conventional turbo setup I would only run a BOV/recirc if noise was an issue and in that case I would probably run it with a 3 port solenoid in line with the normally open port post throttle for normal BOV operation and the normally closed port plumbed pre-throttle so I could do track work with the valve disabled with solenoid active.

This is my understanding as well... cars where turbo response with throttle jockeying is important don't use any kind of dump valve, unless that valve dumps to a reservoir for storage/reuse, or even the exhaust manifold...

My argument is, you worked so hard to build that boost, why are you now throwing it away?

Do you guys remember the BOV before vs after the intercooler controversy/conversation?
Talk about throwing away boosted and cooled charge....

On turbine engines the BOV is called a wastegate. It is only in use as the engine accelerates from idle to 100%. If it malfunctions there is an terrible series of what sounds like explosions (at about the same frequency as our little flutter noises).
They definitely need to relieve the pressure.... but we don't need to.

I tried ARGH?'s (Raymond Herchenroder) idea of running without one. It worked well and was relatively quiet between shifts (....but I am relatively deaf).

By having BW's EFR drop the pressure with their internal BOV the blades no longer stall and by reintroducing the relieved pressure back at the leading edge the wasted boost then reenergizes the compressor rotation and becomes a win/win for us. (an attempt at this was made by afgmoto1978 (Adam Griffith) on his early V-mount mod.

Just some thoughts,
Barry

Integrating a recirc valve into the compressor cover is nothing new. My 14 year old Volvo's TD04-12T has one. Goes pshooo all the time.

There doesn't appear to be much, if any, attempt to direct the airflow in any given direction.

Another possible benefit to the recirc valves in an OEM application besides noise (mine didn't pshoo until after I lost the intake snorkus that went between the airbox and the inner fender) is MAF reading. When in surge, the airflow is starting and stopping, and depending on when the PCM reads the MAF, it may get a false reading, thanks to the staccato airflow. A recirc valve eliminates the staccato, makes the MAF happy. We never install BOVs or anything on turbo Buicks, and they surge for what seems like minutes after brake torquing to 15-20psi and those old computers don't seem to care, but then a pocket calculator is probably more sophisticated than that old hardware.

While I'm on the subject ;) I spent some time driving a turbo Miata this summer. The owner installed the big mongo HKS blowoff valve. It was very.... apparent. I found that it was possible, under certain conditions, to get enough throttle to get the turbo spooling up, while still being under enough vacuum to open the blowoff valve. Result was the turbo spinning VERY VERY FAST and no boost, if you stayed into it. Going by the pitch and assuming that turbo speed = boost pressure, the turbo would spin fast enough for about 5-6psi boost. So not enough to cause an overspeed condition, in this instance.

i'm putting a really old school FC together, and its not mounted yet, but we have a really old HKS blowoff valve for the car, its plastic! as soon as i mention it, i got a bunch of stories where people had those, had a backfire, and the valve was gone.

it looks cool though, and for this car, thats the important thing, its just a dumb street car. the valve looks like R2D2's wife