No Bov, And Turbo Life-span

[Kaido_RR]

Hi,

I've started this topic, as after alot of searching i have yet to come up to a real answer to my question. but before i get onto that i would just like to state this has NOTHING TO DO WITH FLUTTER SOUND OR BOV SOUND, i dont care about any of these, im only interested in affects it will course good or bad.

Ok

Im currently running an rb25det with aftermarket turbo (hks gt2835 pros internal gate), it is running 11psi with all supporting mods. now due to kit having its own intake, i was force to run an atmosphere venting bov as it didnt have the opening for the return of the stock bov...

Now i had my car tune and it was running fine no problems with the BLITZ bov. Now after speaking to a few people and reading up on it, i through i would give no the bov idea a try. so i block up the vac line connected to the bov and gave the car a quick run. i found there to be a redue in gear change lag but not a huge change..

now

This is taken from an article by Autospeed:

Quote:

in Part 2 of our interview, we speak to a leading industry expert Simon Gishus about Nissan engines, Holden Gen 3 V8s, and directions for modifications...

What are some areas where people often make errors modifying their turbo car?

"The classic blow-off valve.

"The blow-off valve is designed as an emissions control device for OE manufacturers. It came about when smaller engines made more and more power using larger turbochargers and bigger intercoolers. As you close the throttle, the build up of pressure and the larger volume inside the intake has to go somewhere; it can't go into the engine because the throttle is shut. Instead, it has to do a U-turn and it comes screaming out the airflow meter. That creates the 'gobble-goggle' sound.

"The gobble-gobble sound is something the public has grown to love.

"The airflow meter is not all that smart and does not realise the air is going in the wrong direction; it therefore measures the air twice (once going into the engine and again going out in the wrong direction). The computer now tips in twice as much fuel as what's required, making it run rich - making it not pass emissions.

"Therefore, manufacturers fit a blow-off valve - or a recirculation valve as they are actually called. A recirculation valve opens when it senses manifold vacuum, returning the air trapped at the throttle body to between the airflow meter and the turbocharger. As such, the airflow meter does not take a double reading - the car now passes emissions.

"Unfortunately, we've had people ringing up and wanting the "audible gear change alarm".

""What audible gear change alarm?" we ask. "You know, when the Sierras were running around and just when they went to change gear it used to go whoda-whoda-whoda" they tell us.

""No pal, that is the dump valve..."

"Some people do think that at the absolute upper extremes of boost levels - about 30-plus pounds - the blow-off valve does, somewhat, save the compressor wheel and shaft from trying to rotate backwards. It doesn't actually rotate backwards at all - all you're hearing is cavitation. What happens is, you've shut the throttle, the turbocharger is doing 100,000 rpm and now has a boost spike of 50 psi. Because it's working in a higher region than what it's designed for, it slips; it basically does a skid like a car tyre does when you dump the clutch. That's the noise you hear - the whoof-whoof-whoof is the air doing a skid."

Is there any performance gain to a blow-off valve?

"We've tested one on a manual gearbox performance car run at Winton Raceway. I think it was running 1 minute 40s back then, but it would lose 2 seconds a lap putting the gobble-gobble valve on. When you look at data acquisition, what you find is - as you change gear - the blow-off valve dumps all the pressure built up through the intercooler and pipes. It then goes back to zero manifold vacuum when you get back on the throttle, you have to build all that boost back up.

"The fact that people think that they keep the turbo spinning is a problem. The people that suggest this have never had an engine on the dyno and never had a turbo tacho in their hands. What people don't realise is, when you shut off the throttle, you shut off the air supply to the engine - this shuts off the exhaust gasses coming out of the engine. When there is no exhaust flow, there is no energy to keep the turbine spinning - the turbo slows down at an alarming rate.

"If you change gears at quite a good speed, you can actually get a boost spike on changes; if you're trying to hold a constant 30 pounds, when you do a racing change you'll get 32-33 pounds when you crack the throttle open again. If everything's working well, you've got a full head of stream waiting to go into the throttle as soon as it's opened.

"I've done this on a rally car and it was quicker through every timed section without a dump valve. You'll never hear a World Rally Car going pssshhht because they don't use a dump valve - you get the woof-woof-woof noise instead."

now that is the reason why i gave the no bov a try. Also i know that some* d1 drifter requirment that you do not run a bov, as it helps to redue lag by a given amount.... Also i know personal of one drifter in perth which run over 300rwhp on an rb25 without a bov and has yet to see a problem (running now for 1year+)

BUT after doing some Searching on sau, its seem that alot of people belived that without a bov it causes damage to your turbo....

now who is right or is there an inbetween?

thankyou michael

p.s please keep this on topic as it has NOTHING TO DO WITH FLUTTER SOUND OR anything like that so please lets not turn this topic into that thankyou

[paulr33]

that is all complete frogshit, i dont care what magazine or what he does

the facts;

blow off valves were designed to prevent excess turbocharger failure. without a recirculating blow off valve the compressor wheel experiences violent surges and also it hampers turbocharger response. a side affect of this is you get the VL turbo chop or "flutter" sound. this can be replicated by talking into the back of a desktop pedestal fan. it will chop your voice as you talk.

when the introduction of blow off valves was done on the nissan range, nissan altered their turbocharger servicing internals on the turbocharger from 50,000k's to 100,000k's

turbocharger reliability is of very high importance to a car manfacturer so there would be no risks taken at any cost. hence why the r32 gtst and nissan oem's have a bov.

so in summary;

a bov provides the following features;

1) protection against compressor wheel surge or chop on throttle body closure (usually associated with gearchange)

2) helps increase turbocharger spool up, as the already processed air is reused

without a bov you will experience the following

1) compressor surge / chop / flutter when the throttle body closes

2) reduced turbocharger compressor lifespan

if you have an atmo bov

1) it will stall as the AFM has measured the air and tells the ECU 100 units of air is present. as soon as the ATMO bov dumps this air there is only say 10 units of air in the manifold but the ECU is still told there is 100 units present so it adds the corresponding amount of fuel to suit 100 units and because there is only 10, the mixture is way off, overrichens and stalls instantly

the bov ore recirculation valve has NOTHING to do with emissions

[Kaido_RR]

hmmm ok

1-A) When running my HKS bov on my stockish car it did not stall once.... due to bov

1-B) When running my blitz bov on my new setup 300rwhp+ it did not stall once

now in relation to your 1 and 2, do you have fact to back up what you are saying?

at the moment i find there is alot of hear say about the damage running no bov will cause... and without hard fact, its hard to make an inform choice...

i am going to research this more.....

[paulr33]

i could tear all those comments to shreads, each of them is full of flawed of comments (the ones from the so called expert)

[Kaido_RR]

hmmm...

again im suck in the middle.. its quite possable that what you are saying is correct but then i take alook at chases in which people do not run bov and do not have turbo failure...

[paulr33]

' date='9 Jun 2006, 11:03 PM' post='2244045']

hmmm ok

1-A) When running my HKS bov on my stockish car it did not stall once.... due to bov

1-B) When running my blitz bov on my new setup 300rwhp+ it did not stall once

now in relation to your 1 and 2, do you have fact to back up what you are saying?

at the moment i find there is alot of hear say about the damage running no bov will cause... and without hard fact, its hard to make an inform choice...

i am going to research this more.....

1a) depends on how the bov was setup and if it was in recirc or atmo mode or half half

1b) depends on how the bov was setup and if it was in recirc or atmo mode or half half

it has NOTHING to do with how much power you make or how much boost.

if its on full AMTO and you haven't tuned around the brain-dead stalling then it will stall.

think about it. pressure is building up, the throttle body closes, instantly you chear a chop chop chop flutter sound, just like if you talk into the back of a pedestal fan. whats the likely conclusion? the pressure has bounced off the throttle plate, collided with the compressor wheel and basically done a sonic boom on itself.

people when they insist on modding the stock bov or fitting an aftermarket bov that runs in ATMO that doesnt stall, they all report much more lag or turbo lag response, as it has to wind up from scratch again instaed of re-using the built up air velocity (reused in recirc mode)

[paulr33]

ok now lets forget everything we know about turbocharges and various components.

what advtanges do you have by not using a BOV?

what do you hope to gain by not using one?

[Kaido_RR]

1a) depends on how the bov was setup and if it was in recirc or atmo mode or half half

1b) depends on how the bov was setup and if it was in recirc or atmo mode or half half

it has NOTHING to do with how much power you make or how much boost.

if its on full AMTO and you have tuned around the brainded stalling then it will stall.

think about it. pressure is building up, the throttle body closes, instantly you chear a chop chop chop flutter sound, just like if you talk into the back of a pedestal fan. whats the likely conclusion? the pressure has bounced off the throttle plate, collided with the compressor wheel and basically done a sonic boom on itself.

people when they insist on modding the stock bov or fitting an aftermarket bov that runs in ATMO that doesnt stall, they all report much more lag or turbo lag response, as it has to wind up from scratch again instaed of re-using the built up air velocity (reused in recirc mode)

ok

they were both FULL atmo mode...

on the stock setup, i was not running any sort of aftermarket ecu, piggyback or full... the car was just a stocker with a HKS bov and had no problem, it never stalled, it did run richer but that wasnt a big deal as any aftermarket mods on a stock ecu make the car run rich...

on my current setup.. i was running stock PFC BASE TUNE with all my mods on (inc the blitz bov on full atmo mode) and i drove it around for about 1-2weeks before getting a tune and had no problems with stall...

Yes i did notice increase lag in gear changes when running my aftermarket atmo bov on my stock setup...

im not hoping to gain anything...the reason why i switch to running no BOV, as i was sick of the sound the atmo bov made and it is currently not possible for me to run a stock or full plump back bov without modding my intake pipe, which i currently dont have time to do..

when running stock bov, it was leaking and this cause problems which i was not happy with

also alot of drifters (australian and jap) have their thinking that it helps to reduce lag when runnning no bov (this may be myth)

[bogcock]

your both half right. the bad thing about an atmo bov it the fact that it does dump all pressure from ur manifold/cooler etc, so the turbo is having to repressurize the lines. The good thing is the turbo DOES keep its revs up sigificantly, and will boost up again fairly quick. But it does have a run rich situation.

Now as for a non bov system, the air inside the turbo does get chopped when it cavitates a closed throttle. BUT as it cavitates, it DOES NOT blow it back out the afm, it keeps trying to pressurize it, causing the ch ch ch (flutter) sound.

As for plub back bovs, they can be detimental to the system as they DO allow air to flow out of the afm. the air is pressurized when released, and the turbo is at lower revs than when the air is released and cant suck all of that air back through the system. So this leaves air not going anywhere but out through the afm, causing a rich scenario.

conclusion: The only afr friendly way to have a turbo d engine is WITHOUT any bov at all. BUT this WILL decrease the turbos life span and could in rare cases spin the shaft and cause serious damage.

at the end of the day, its your choice.

[paulr33]

right, and so what have you learnt after doing that (not stalling with an atmo bov). what have you achieved ?

[Kaido_RR]

right, and so what have you learnt after doing that (not stalling with an atmo bov). what have you achieved ?

ok im tring to achieved the best setup for my current use of my car (street daily driving and track time in the form of drifting)

now the old problem i had when running stock bov on my oldsetup, was that it would leak and would result in boost spiking.

with my current setup, i can only compare no bov and atmo bov and it seems that there is a maybe alittle less lag during gear change but i cant be 100% sure as i only took it for a 15mins drive.

ALSO if u read what i wrote in my 1st post the reason i was running an ATMO bov is that it was not possible to run a plumb back one due to the intake pipe not having that option and i didnt have the time to mod it so i could uses a plumb back bov

[paulr33]

so fix the stock bov so it doesnt leak

or change to twin gtr stock bovs

the purpose of the thread, as far as i can see if to find out if there is any myth to compressor wheel failure, why are bovs factor standard, what does flutter mean and so on

[Kaido_RR]

so fix the stock bov so it doesnt leak

or change to twin gtr stock bovs

the purpose of the thread, as far as i can see if to find out if there is any myth to compressor wheel failure, why are bovs factor standard, what does flutter mean and so on

yes you are correct - thats is the purpose of this thread..

Can i ask what would the speed, of the air be that is hitting the turbo and casuing compressen surge (sp)

[paulr33]

800km/h

[paulr33]

actually perhaps compressor surge is not the correct word for it, by definition compressor surge is;

when pressure past the compressor outlet is greater than what the compressor can physically supply. ie: seeing 23psi pressure in the manifold and having a turbocharger where its compressor map dictates that in the optimum flow it can achieve ~16psi compression.

so perhaps compressor chop or flutter is the right word

[Kaido_RR]

800km/h

is this an est or are you pulling the piss (sorry if you arnt i just have no idea of the average speed of the air)

so the base idea when running no bov is that the air does a u-turn and head back into the turbo, which is spinning at a very high rpm and the air therefore forces the turbo shaft to move in the opposite direction of travel?

is this correct?

if this is so, do you know the possible value for;

turbo shaft rpm speed (at say a constant boost level)

intake air speed

the returning air speed

[paulr33]

gary posted it up some time ago, the air travelling in the pipe work is around 800km/h. i could only imagine the reverberation from when the throttle plate closes to be very violent without a bov, hence the loud flutter.

yes the plate closes, the air has to go somewhere so it does a uturn and goes boom into the compressor wheel. this places excess stress on the wheel, the bearings and also likely the silicon joiners as they deal with a big mid air collision

[bogcock]

' date='9 Jun 2006, 11:40 PM' post='2244156']

is this an est or are you pulling the piss (sorry if you arnt i just have no idea of the average speed of the air)

so the base idea when running no bov is that the air does a u-turn and head back into the turbo, which is spinning at a very high rpm and the air therefore forces the turbo shaft to move in the opposite direction of travel?

is this correct?

the turbo NEVER spins backwards, it just loses velocity very fast, causing the flutter

[Kaido_RR]

ok...

so the turbo is moving in x direction and the air places a force in y direction...

and therefore the force in y direction add stress to the compounds in the turbo therefore reduing turbo life span?

ps im not tring to me smart im tring to get a basic idea and try and do some calucation

[paulr33]

yeah im not sure if it goes backwards, that sounds unlikely but it certainly does collide and really slow the compressor wheel down. this is evident by numerous people reporting more throttle / turbo lag present when not running a bov. most people report that its slower to come on boost when not runing a bov