Removing BOV

fubar andy

fubar andy

Moderator & N/W Rep
Staff member
Let's get a few things out of the way first: :thumb:

  • Let's hear from people who ACTUALLY run a setup WITHOUT a blow-off-valve
  • Please share how long you've run this setup and what the pro's/con's are
  • Please share if you've suffered turbo failure while running this setup
  • Please, let's not hear from people making guesses or hearsay stories

And, just so we're clear, when I say "without a blow-off-valve" I mean.. without any type of release valve, VTA, recirc, or anything in between.

I've installed my new 2871R and at present I've removed my BOV while fitting the turbo, intercooler etc etc

I want to know how detrimental this might be to the turbo running at 1.6bar on track and the odd weekend drive, or would it be best to continue to run with my current BOV?

I'm looking reason and experience, not short basic answers or "its been fine on my car" or "I read on the internet somewhere"

Cheers
 
M

Makaveli_se7en

Member
I've written a few posts on this on here and the modifier site. In my opinion BOV are a waste of time. The purpose of a BOV is to release pressure in the intake system on closing the throttle. When the throttle is close the operating point on the compressor map suddenly moves to the left as the Pressure ratio upstream and down stream of the turbo is still high but the flow rate as dropped to near zero. Depending on where the turbo is operating at the time this can result in moving left of the surge line on the compressor map. This results in what is technically called "transient surge" and gives the rally car fluttering noise. This is very different to "hard surge" which is when the compressor is driven into surge through mis-matched engine/compressor/turbine. Transient surge at boost pressures up to around 2 bar is unlikely to lead to serious damage to the turbo, whereas hard surge will very quickly tear a turbo to bits.

Running off the left hand side of the compressor does marginally increase the thrust load, which can lead to increased bearing wear (particularly thrust bearings in a journal bearing turbo). However I do not believe this to be massively noticable. I have run the GT3071r on my car without a BOV for 12K at 1.6 to 1.8 Bar and there is no play in the shaft.

The advantage of not running a BOV in my view is that its one less thing to go wrong and one less place to leak boost. It should also give a slight improvement in transient response as there is no need to repressurise the intake system when coming back on throttle after a gear change.
 
PobodY

PobodY

Moderators
Staff member
Ed, is the BOV a legacy from when manufacturers weren't quite sure what they were doing with turbocharging? - An added safety measure (or over-engineering)?

I remember talking to someone about the early turbo rotarys; they had no idea what they'd do when they came on boost as they'd often be running it with no control. - In that situation I can see that maybe the BOV is a safety measure, but with modern wastegates and control you don't need to worry so much?

I'm keeping mine for now, but that's mainly because I've got nothing to put in the hole if I take it out. ;-)
 
gtirx2

gtirx2

Member
The only thing i would be concerned about is if the reversion or what ever its called lol would make its way back to the maf and interfear with it , possibly making it abit twitchy on part throttle lift offs.
 
keastygtir

keastygtir

Well-Known Member
I have run my R without BOV of any sort for the last 7 years without issue. It did have one on when I first got it but I thought it made it run like s***. I though it also built boost faster without one
 
fubar andy

fubar andy

Moderator & N/W Rep
Staff member
keastygtir said:
I have run my R without BOV of any sort for the last 7 years without issue. It did have one on when I first got it but I thought it made it run like s***. I though it also built boost faster without one
Click to expand...

What kind of turbo and boost levels was that?

Was that 7 years on the same turbo?
 
keastygtir

keastygtir

Well-Known Member
It has a standard turbo with 360 bearing, The original gave up after a year from oil starvation so the rest of time its been on that turbo at about 1.1 bar
 
jamesgtir

jamesgtir

Member
I've run without for 3 years. Cars mainly used on track. Spec is 2871r @ 355hp
touch wood no problems as of yet
 
T

the chief

Member
60000 miles on standard engine and turbo running 1.3 (and around 50000 on standard boost). Only changed turbo for more power but still fine when removed.
 
M

MarkTurbo

Well-Known Member
My Sunny hasn't had a dump valve fitted since about 2004 ;-)

In that time I've run my 3071 at 1.7 bar without one, it did fail but for other reasons. And I've been through 2 or 3 standard T28's but they were running a fair amount of boost so i doubt having a dumpvalve fitted would have extended their life by a great deal of time.

Makaveli_se7en said:
It should also give a slight improvement in transient response as there is no need to repressurise the intake system when coming back on throttle after a gear change.
Click to expand...
That was pretty much my reason for not having one fitted.
 
D

dencon

Member
I tried running my 512bhp LHD car on a couple of hills, mainly to try to reduce lag. To be honest I never felt much difference.
 
J

Jon Olds

Well-Known Member
It must reduce lag noticeably, mustn't it? The AFR must be better, as the Af meter is metering everything that goes into the engine, so those silly rich moments after the bov closes must be taken out. The only thing that worries me is does the compressor stall, or has it got enough enertia to make it through?
More tech boffin input needed
Jon
 
red reading

red reading

Active Member
Makaveli_se7en said:
I've written a few posts on this on here and the modifier site. In my opinion BOV are a waste of time. The purpose of a BOV is to release pressure in the intake system on closing the throttle. When the throttle is close the operating point on the compressor map suddenly moves to the left as the Pressure ratio upstream and down stream of the turbo is still high but the flow rate as dropped to near zero. Depending on where the turbo is operating at the time this can result in moving left of the surge line on the compressor map. This results in what is technically called "transient surge" and gives the rally car fluttering noise. This is very different to "hard surge" which is when the compressor is driven into surge through mis-matched engine/compressor/turbine. Transient surge at boost pressures up to around 2 bar is unlikely to lead to serious damage to the turbo, whereas hard surge will very quickly tear a turbo to bits.

Running off the left hand side of the compressor does marginally increase the thrust load, which can lead to increased bearing wear (particularly thrust bearings in a journal bearing turbo). However I do not believe this to be massively noticable. I have run the GT3071r on my car without a BOV for 12K at 1.6 to 1.8 Bar and there is no play in the shaft.

The advantage of not running a BOV in my view is that its one less thing to go wrong and one less place to leak boost. It should also give a slight improvement in transient response as there is no need to repressurise the intake system when coming back on throttle after a gear change.
Click to expand...
Ex turbo flow dynamisist wrote the above........
 
campbellju

campbellju

Moderators
Staff member
Jon Olds said:
It must reduce lag noticeably, mustn't it? The AFR must be better, as the Af meter is metering everything that goes into the engine, so those silly rich moments after the bov closes must be taken out. The only thing that worries me is does the compressor stall, or has it got enough enertia to make it through?
More tech boffin input needed
Jon
Click to expand...
Sorry Jon, I gave a jokey answer to Andy as I'm sure I've discussed this face to face with him the past.

When I've logged this in the past, not having a BOV improved transient boost response on my 3071 by a few mS. Not much but better than nothing. (I'm not as eloquent as Ed)

Doing this does help to get get rid of the rich moments when you come off the throttle. I did get some small lean spots in the instant you accelerate again as you still have some air surging out past the MAF whilst the engine is sucking it back in. This was small and easy to map around by increasing the equiavalant of an accelerator pump on my PowerFC
 
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