do automatics need to run a bov?

[Duk]

http://autospeed.com.au/cms/A_2188/article.html has a nice little screen grab of a high speed data log of pre-throttle body turbo boost pressure in an engine without a BOV.

Without going into Justin's comments (which I'm not doubting) and the high speed data log picture, I will say that, if a pressure spike did occur, you would be hard pressed to overcome the physical strength of the compressor wheel before it came in contact with the compressor cover.

There are a lot of rumors getting about. Stories like the Group A Cosworth Seira's using opposite threads on their compressor wheels to prevent them from being undone/loosened after a high boost, throttle off period. But they are rare (stories) and without back up evidence.

Similar for stories of running stupid high boost pressures straightening compressor wheel blades. Maybe a back fire that wasn't notice/acknowledged/mentioned, but (relatively) progressive increase in boost pressure............?

[river]

Hi,

Yea who normally has such little faith and much cynacism...you must be getting old and soft to be so compliant River Where's your evidence based decision??

I know fuck all about turbos and such shit, so I depend upon someone, who I regard as more knowledgable as I, to enlighten me.

So, here I am with Dave, who has a lot of experience in such things, saying the BOV will lengthen the lifespan. I think even Jason (YellaRolla) said the same - another person who has more experience with turbos than I.

Then there is you - also someone who has more experience than I, saying the BOV is not going to lengthen the lifespan of the turbo.

So, see my dilema......

seeyuzz
river

[JustenGT8]

http://autospeed.com.au/cms/A_2188/article.html has a nice little screen grab of a high speed data log of pre-throttle body turbo boost pressure in an engine without a BOV.

That's a neat little bit of testing...my haltech log showed similar. Part of the reason boost response was better was boost pressure didn't drop away ie the turbo had less work to do upon reopening the throttle. I don't think the Haltech had the resolution to show that pulsing as i didn't really see that, but you'd expect that pressure effect as the reflected pulse bounces back and forth in the intake tract between turbo and throttle plate....might even be from the compressor blades but if it's spinning at 50,000+rpm unlikely?

As i said i have seen one turbo failure from a high boost setup that basically snapped the shaft. It was a big turbo running big boost and quite likely already outside it's design parameters. I too have heard stories of compressor wheels spinning off etc.

I suspect by far the majority of failures are from over speeding. The forces increase exponentially with rpm, so that last 5psi you want to try might well double the stress the turbo is experiencing

Anyways, until someone does multiple side by side testing in controlled conditions over many 10,000kms we can't say what the difference in life is....i'm happy that it's not significant enough to worry about. The slight increase in boost response and less complexity in plumbing with no BOV is worth any tradeoff in turbo longevity. LOL, how many of us have seen 100,000km from their setup without changing something anyways?

[BlackSupra]

did the old turbo f1 cars rn them?

what about older group B rally cars?

Pretty sure the old F1's ran a similar setup directly off the plenum.

[JZA20]

thanks for the replies guys, i didnt think it would start such a heated debate! i have a new blitz bov from an old project but i might see how it goes without it. if its ok i might just sell it

cheers,
josh

[Duk]

Pretty sure the old F1's ran a similar setup directly off the plenum.

Later F1 cars had an over pressure relief valve on there plenums to directly limit maximum allowable boost pressure (multiple throttle engines). And so acted as true blow off valves.

[Gavatron]

AFAIK the main damage from not running a BOV is only on bush bearing turbos. The flutters flog the thrust washers out with the back and forth motion. No such problems on a modern BB turbo.

[JustenGT8]

Pretty sure the old F1's ran a similar setup directly off the plenum.

No BOVs, pressure relief valves totally different thing and purpose.

[Z2TT]

I've seen a few vids of people showing off their dose/flutter where the whole turbo and intake pipe shake during the flutter, surely that must be a bit damaging to the internals if the force is great enough to shake the whole turbo and intake pipe??

[pandaah]

i think most people are missing one critical point, STANDARD blow off valves are of a plumb back nature and take the air out of the turbo to throttle side of the intake and put it before the charger... BOV's are needed in some cars so the turbo doesnt throw "regurgitated" air back thru the air flow meter making it run rich or shit during gearshifts or coming off the throttle...

ive NEVER seen a turbo fuk up due to running no blow off valve on stock boost, high boost applications yes it does work back against the turbo and could possibly premmaturely wear a turbo, yet i havent never seen it happen.....

point is... if your running standard boost, just ignore it cos your probly running standard turbochargers which wont suffer, theyll probly shit out the ceramic rear turbine wheel before the "flutter" wears them out

[peanutsfmx]

i run just over 1 bar on my 35r at the moment with no blow off valve.
justen is 100% right ive never had a problem with turbine faliure, i know of plenty of cars that run higher boost pressure than me with no poofter valve and still are in excellent condition (shaft play etc...)
for instance tristans v6 mr2 gt42 and a gt30 running in a compound setup. That has massive flutter/dose whatever you want to call it, bigger than any other setup i've heard and he doesn't run a blow off.

however i can see that in a manual car the chance of one failing because of "flutter" would be ever so marginally increased because your off & on boost more through gear shifts than what you would be with an auto.

I've driven both so i can make that comment

talk to adsport about flutter ... his corolla has vl hektik dose bro! acctually more dose than a lebs vl.
His turbo is in perfect condition absolutely zero shaft play!

[Z2TT]

Putting a BOV is not a good idea on a car that runs a MAF/AFM that is located before the BOV, as your venting metered air to the atmosphere, causing the car to run rich on gearshifts.

Also maybe the reason why people have never heard of a turbo fail from not having a BOV/BPV on the car is because it happens ever so slowly, as in it will last years with or without, so the extended life (if any) offered by having a BOV/BPV might be ever so marginal to notice.

[pandaah]

that would already have one standard in most cases and it would usually be a plumb back avoiding the rich running thru the gear shifts.. putting a bov for noises surves no purpose but for noise

problem solvered lol

[trdee]

i run just over 1 bar on my 35r at the moment with no blow off valve.
justen is 100% right ive never had a problem with turbine faliure, i know of plenty of cars that run higher boost pressure than me with no poofter valve and still are in excellent condition (shaft play etc...)
for instance tristans v6 mr2 gt42 and a gt30 running in a compound setup. That has massive flutter/dose whatever you want to call it, bigger than any other setup i've heard and he doesn't run a blow off.

however i can see that in a manual car the chance of one failing because of "flutter" would be ever so marginally increased because your off & on boost more through gear shifts than what you would be with an auto.

I've driven both so i can make that comment

talk to adsport about flutter ... his corolla has vl hektik dose bro! acctually more dose than a lebs vl.
His turbo is in perfect condition absolutely zero shaft play!

none of these cars have done 100,000kms on the turbo though

actually i doubt any of these cars have even done 20,000kms

[grue0038]

Show me a turbo, any turbo that has failed from absence of BOV????

for all the warnings i've read about needing a BOV, this statement has held true throughout- i've seen no evidence of any turbo that has failed from a lack of BOV.

BOV appeared regularly when NVH requirements and emissions basically forced them to appear. End of story.

this is the truth as far as i'm concerned as well. they first came primarily as emissions devices. on cars with hotwire MAF sensors, the compressor backwash would hit the sensor from behind and since the sensor doesn't know which way air is moving across it, it would tell the ECU to add fuel even though the air was already measured, causing overfueling.

i do believe that the ceramic turbos on the 3SGTE are more sensitive to any sort of weird forces on the impeller shaft, which is why the MR2 came with a factory BOV. an inconel turbine wheel turbo will have no issues running without one.

What would be good would be to measure wheel speed with/without and see what difference, if any, there is and which way it goes. That's obviously the most accurate way but a fairly difficult exercise.

an optical tachometer used to measure prop speed on R/C airplanes might do the trick if pointed at the compressor blades.

did the old turbo f1 cars rn them?

no. neither did group C, IMSA GTP, CART/champcar, etc.

Pretty sure the old F1's ran a similar setup directly off the plenum.

those were pop off valves. they only opened when boost pressure exceeded the limits set by the rules. same with champcar.

honda used intercooler bypass valves to raise the inlet temps for better BSFC, but no blow off valves.

BMW, renault and zakspeed used throttle butterflies on the turbocharger inlet that cut off airflow to the compressor when the main throttles closed. this allowed the compressor to spin in a relative vacuum, maintaining shaft speed when the exhaust energy was cut off.