Mazda Rotary Club

Ok, so I\'ve just spent quite a while reading all about BOV\'s on the aussie rotary forum and the general consensus, from what I could see, is that you don\'t need one?

The Pink Panther is in at WGT at the moment for a few jobs, one of which was to fit a BOV as recommended by Pip as there isn\'t one on it at the moment.

What should I do? Apparently I\'ll lose the wastegate flutter if I get  BOV, but some say that a BOV will protect the turbo.

It might be irrelevant, because if Pip has finally received the part tomorrow, then it will get fitted, but at the moment I\'m toying with the idea of phoning Pip in the morning and telling him not to bother with the BOV if it hasn\'t arrived yet (been on backorder for over a week).

I\'m highly confused.:confused:

a stock car has both but because of the design set up you cant here them, on my other 2 rx\'s both non standard, they both have wastegate and bov and you do get that chatter. No fear of damage or stalling the turbo\'s if you have both, if your turbo is weak it blow it. IMHO just my 2p worth.

I don\'t run a BOV and love the chatter !!!

However it depends what Turbo you run, mine is a Garrett GT ball bearing with a strong shaft [spindle],
 
If running an older style Turbo with plain bearings and small shaft without a BOV, you risk twisting the shaft as it can\'t cope with the changes in pressure on either side of the Turbo upon lifting off the throttle.

l will however be useing a BOV from now on for Drag strip only use to try and speed up my gear changes.

l am sure people with much more knowledge than me will further this debate .

Taking a worst case scenario, if the turbo goes is it usually just the turbo that needs replacing, or will bits make their way through the IC and wreck the engine?

forget the ic, more likely to get parts into the engine and goodbye.

If the shaft fails I\'m not sure how yer motor is going to digest bits of your turbo...?

I just wasn\'t sure if the IC would just block up with most of the bits - after all, the passages aren\'t too big through the IC.

obviously safety first, if it was recomended to get one then go for it.

out of the 2 choices then wastegate EVERY time:D

Ok, no BOV shortens the life of the turbo.  In high boost applications no BOV can cause immediate damage by twisting the turbine shaft.  Every cool little chatter is a violent stoping and restarting of the turbo and a load and unload of the thrust bearing.  I have seen plain bearing turbos go bad in a month of highboost with no BOV and ballbearing turbos go bad in 6 months.  The bad thing about blowing a turbo this way is that they usually don\'t smoke until after the compressor wheel is machined 2mm smaller from contacting the compressor housing.

To quote a few bits off the Aussie forum that got me thinking...

Rice Racing -

QuoteTo put some numbers to it, even if you were making 1000bhp worth of air flow this would result in a massive amount of 3kg or there abouts of air weight acting against the impellor trying to escape out back past the compressor wheel in one second (if it could maintain turbine speed, which it does not!) so this peak load of 3kg is far less after 1 second in a 1000bhp application! Aluminium is pretty strong last time I looked, you could apply over 50kg or more to the tips before you would bend them and this would have to be a very very big load or force, such as waht is generated via a backfire to casue such damage.

QuoteYou would never generate enough force to casue damage in a closed throttle situation. And you could not overspeed either as the throttle is shut too, some clowns go on about the "stress" on the shaft again BS, the turbine does not speed up in stages, it is slowing down in stages as soon as the throttle is shut, untill it reaches a speed that the compressor will not open the WG on a trailing throttle, it is very very simple stuff and it is easy to see that you have been sold a lie by people who realy have no idea what they are talking about in regards to what merits their "performance products" I would go as far as saying the potential failure of a BOV will at least casue you a performance loss and at worst cost you a turbo failure due to overspeeding

Examples of cars not running BOVs (all from the aussie forums again)...

One example of F1 cars from 1986 running at Monza G.Berger was pulling 4.5bar gauge pressure that is 65+psi again no BOV. No special compressor wheel materials either mind you or turbo design !

Tractor pulling machines running three staged turbos in a row pull up to 250psi boost pressure in some examples, guess what they don\'t use BOV\'s either and all on old tech turbo\'s.

Audi Motorsport did a world record 24hr speed trial in Italy in 1988 in a road car equiped with a S1 Quattro motor (fitted with a KKK27 turbo no BOV running 2.5bar boost) it averaged well over 320kph for the 24hrs and covered over 7000km. ( It was lifting off a few times during the lap for corners on the speed bowl slowing from almost 400kph!)

many Many 24 Le Mans races have be won dating back from Renault in 1978 (first turbo car to win it) running 28psi all day and night! to Porsche 962 and almost every car in between...... all of which ran NO BOV, so I would say reliabilty is not a problem  

Remember these guys are on full boost for 24hrs! or over 5500km of racing ! that is more than ANY drag or road car would do in 20 life times  @ that load level, to say that the turbos are un reliable is complete BS  We are not talking high tech either a majority in the early days up to 1987 ot there abouts are all plain bearing truck derived units, same as what a majority of us run today  

Every International Group C sports car to 1991 NO BOV
Every F1 car from 1979 to 1988 NO BOV
Every Indy car from 1970 to NOW NO BOV
DJR Group A Sierra till its last races NO BOV

You want a current example from Japan (the home of the BOV), find a down load of Rod Millens Toyota Tacoma truck (runs 1000bhp 4 cyl single turbo) and it runs NO BOV, turbo flutter in all its glory  



These are all quotes from other people, but it makes you think, doesn\'t it.

That\'s right its not needed :flamed

I wonder about the wisdom of comparing race engines which are probably well built and maintained with road going cars...
 
I would also say that a 24 hour race - yes there will be lift of events, isn\'t the same as daily driving - where the stop start nature of the driving puts more frequent although lesser loads on the whole car.  The average driver is not going to be gear changing as fluidly as a race driver, so the dump events will be more prolonged and more frequent.
 
It may be that the bov/recirc (car manufacturers go for recirc more often than not) has more to do with emissions / noises / fuel economy rather than mechanical reliability.
 
Just some thoughts...

wow Rice talk about bringing a thread back from the dead LOL :rollin

6 years old was the last post before yours hahaha

PS I dont run a BOV for the last 3 years

I didnt run a bov on the stock twins for nearly 2 years at 0.9bar and still on the same set boosting fine over 3 years on.
 
Thought i had seen this thread before lol

If people are worried about using or not using a bov the easiest solution would to be to use a manly sized turbo that has a ported shroud?? By manly I mean a gt40 upwards sized turbo.

Or, man up and run it aspirated :Giggle

Quote from: Brett;721171Or, man up and run it aspirated :Giggle

That\'s why I\'m going na 13b pp in my rx4! Maybe embarras a few turbo boys up the drag strip when it\'s done!

That\'s more like it :D

3 years on my 200sx at 1 bar and then the last year at 1.2. As soon as i get my fd3s im ditching the ssqv and releasing the pigeons!
 
Oh and its not wastegate chatter, its called compressor surge.

Quote from: STU13 B;7302613 years on my 200sx at 1 bar and then the last year at 1.2. As soon as i get my fd3s im ditching the ssqv and releasing the pigeons!
 
Oh and its not wastegate chatter, its called compressor surge.

(http://files.sharenator.com/Thread_Crap_Wont_Die_RE_mega_zombie_forum-s300x371-97014.jpg)

you mean compressor stall, surge sounds like this and is very very bad (it\'s when gas flows backwards through the compressor whilst it\'s operating, i.e. on full boost):

True Compressor Surge (http://www.youtube.com/watch?v=nCj6Spwl1CU)

Axi-symmetric stall or compressor surge
Axi-symmetric stall, more commonly known as compressor surge; or pressure surge, is a complete breakdown in compression resulting in a reversal of flow and the violent expulsion of previously compressed air out through the engine intake, due to the compressor\'s inability to continue working against the already-compressed air behind it. The compressor either experiences conditions which exceed the limit of its pressure rise capabilities or is highly loaded such that it does not have the capacity to absorb a momentary disturbance, creating a rotational stall which can propagate in less than a second to include the entire compressor.
The compressor will recover to normal flow once the engine pressure ratio (http://www.mazdarotaryclub.com/wiki/Integrated_Engine_Pressure_Ratio) reduces to a level at which the compressor is capable of sustaining stable airflow. If, however, the conditions that induced the stall remain, the return of stable airflow will reproduce the conditions at the time of surge and the process will repeat.^{[1] (http://www.mazdarotaryclub.com/forums/#cite_note-Kerre261-0)} Such a "locked-in" or self-reproducing stall is particularly dangerous, with very high levels of vibration causing accelerated engine wear and possible damage, even the total destruction of the engine.
 
http://www.youtube.com/watch?v=LZUbo_mNDZM
 
Thats compressor surge.

interesting chat / debate occurring.. the latter vid shows a decent amount of engine movement too.... am thinking it might need some new mounts! :eek: :chat

Quote from: STU13 B;731152http://www.youtube.com/watch?v=LZUbo_mNDZM
 
Thats compressor surge.

Thats compressor stall, the throttle plate is being "shut" during lift off of the throttle causing the compressed air going through the compressor wheel causing the noise

Quote from: jackaleks;730739True Compressor Surge (http://www.youtube.com/watch?v=nCj6Spwl1CU)

Correct this is true compressor surge, in this instance the throttle plate is "open" but the amount of compressed pressurised air is not being fully ingested by the engine normally caused by a restrictive intake manifold or incorrect sizing of the compressor housing on the turbo

Haha, your not wrong, but its a retro fit. The 200sx s13 never came with an SR20DET, it had the CA18DET. The 180sx silvia had the red top SR20 fitted as standard. Useless info on a rotory forum but you might be intrested lol
 
The later in the paragraph is what Jack is on about, if you get that.... bang as his vid shows. Ideally if your going to do this you should have a ball bearing turbo so it dosnt put to much strain on the shaft when it stalls. There are lots of myths and old wife tails that compressor surge will route your turbo blah blah blah .... but as said mind has never missed a beat the whole time ive run no bov.

Quote from: BlitzBoy;731154Thats compressor stall, the throttle plate is being "shut" during lift off of the throttle causing the compressed air going through the compressor wheel causing the noise



Correct this is true compressor surge, in this instance the throttle plate is "open" but the amount of compressed pressurised air is not being fully ingested by the engine normally caused by a restrictive intake manifold or incorrect sizing of the compressor housing on the turbo

excuse my ignorance here, but my understanding of it was that compressor stall was when the pressurised charge downstream of the turbo had the effect of \'slowing\' or stalling the turbine off-throttle, thus making it harder to spool again as it\'s working against backpressure rather then a vacuum??

The thermodynamic definition of compressor surge is where (for whatever reason) the compressor can no longer push enough mass flow through to sustain the discharge pressure. This results in the flow reversing direction and forcing its way back through the turbine. What happens next is that the reverse flow then re-pressurises the intake side and normal flow direction is recovered. If the original cause is not corrected, this pattern continues many times per second and puts massive stress on the turbine blades as the flow goes back and forward.

I\'m agreed that compressor surge is indeed worse, i\'m a process engineer and i\'ve been standing next to north sea gas compressors (variants of the RB-211s which used to power commercial jet planes) when they\'ve gone into recycle mode (essentially a recirculating BOV) to protect against surge and it sounds like the end of the world!! I\'ve seen a video of a $6mn compressor actually hitting surge when the recycle valve failed and vibrating itself clean off it\'s mountings!!

The anti-surge (or recycle) control systems that these babies have are usually worth in excess of £1mn, which goes to show that its a problem that\'s taken seriously in industry. For that reason alone I will always go for a BOV.

graeme

Quote from: trotter;731218excuse my ignorance here, but my understanding of it was that compressor stall was when the pressurised charge downstream of the turbo had the effect of \'slowing\' or stalling the turbine off-throttle, thus making it harder to spool again as it\'s working against backpressure rather then a vacuum??
 
The thermodynamic definition of compressor surge is where (for whatever reason) the compressor can no longer push enough mass flow through to sustain the discharge pressure. This results in the flow reversing direction and forcing its way back through the turbine. What happens next is that the reverse flow then re-pressurises the intake side and normal flow direction is recovered. If the original cause is not corrected, this pattern continues many times per second and puts massive stress on the turbine blades as the flow goes back and forward.
 
I\'m agreed that compressor surge is indeed worse, i\'m a process engineer and i\'ve been standing next to north sea gas compressors (variants of the RB-211s which used to power commercial jet planes) when they\'ve gone into recycle mode (essentially a recirculating BOV) to protect against surge and it sounds like the end of the world!! I\'ve seen a video of a $6mn compressor actually hitting surge when the recycle valve failed and vibrating itself clean off it\'s mountings!!
 
The anti-surge (or recycle) control systems that these babies have are usually worth in excess of £1mn, which goes to show that its a problem that\'s taken seriously in industry. For that reason alone I will always go for a BOV.
 
graeme

Agree on that. My lecturer (auto eng, lufbra uni) explained to me why the BOV is needed from his past rally car experience. to put it simple it is there for perfomance, to keep the turbo spinning,and the sound:D
 
ofc theres a lot of theories behind that. there\'s always a reason why the stock FC\'s or 200SX have the recircu valve as stock.
 
Louis

Quote from: yiug412;735215Agree on that. My lecturer (auto eng, lufbra uni)

Just out of interest, don\'t know a guy called Alan Baker do you? :)

Quote from: yiug412;735215Agree on that. My lecturer (auto eng, lufbra uni) explained to me why the BOV is needed from his past rally car experience. to put it simple it is there for perfomance, to keep the turbo spinning,and the sound:D
 
Louis

Ask you lecturer why most turbo rally cars dont run a BOV then?

Also F1 turbo cars in the 80s did not run BOVs, two reason, one a BOV would have a hard time not leaking under 3-4 BAR of boost, second the time lost in recompressing the air in the intake system which be lost when vented by a BOV versus the time gained in keeping the turbo spinning , they found it was better to have the performance advantage of not venting the already compressed air.

Quote from: yiug412;735215there\'s always a reason why the stock FC\'s or 200SX have the recircu valve as stock.
 
Louis

Yes noise surpression in the case of recirc valves

Here we are BMW F1 turbo engine, not a BOV insight.
So sorry I dont buy the performance claim of BOVs, I can see why recirc valves would be used on small shaft tiny turbos in terms of noise surpression and maybe the relabilty of protecting the small shaft of a small turbo.

But a BOV giving a performance gain I disagree. Otherwise you would have seen them on the F1 cars and the group B rally turbo cars

Wow... you really have a grudge against BOV\'s :eek:

Quote from: BlitzBoy;735606Ask you lecturer why most turbo rally cars dont run a BOV then?

Like most lecturers they don\'t know sh7t from clay! cause they have never done anything real in their life :eek Most academics are the same!

I had one Thermodynamics lecturer tell me in the early 90\'s that no cars can exceed 100% volumetric efficiency! I told him rotary engines can and have done easily from NSU to Mercedes tests, he did not believe me so I brought in the tests to show him! he changed his mind quick!

If the "lecturer" who has an "opinion" about BOV\'s got off his ass like I do for example and invested say $50,000 in instruments and his time to measure a real car (like I do) he would see that a BOV is pointless and is actually a negative step in regards to pressure and turbine speed on gear changes! ...... but this is why he is in a class room and not making fast turbo cars! :Talking1 rather he is doign this to students :Talking1

:Giggle BOV\'s are rubbish :spank

I wont be running a bov either :Nono! lol.

No BOV on mine, apexi rx6 turbo, greddy gt spec front mount, apexi wastegate, stock injectors, sounds amazing:burnout

So, i\'ve read the ultimate thread spanning over 6 years! I\'m trying to digest the information, but understandably my small mind is finding a bit of a task. Basically BOV\'s are pointless except for the sound they make? They are more or less for people in their subaru\'s to try and look good? Or are there some uses for them in road use? It seems that when talking about BOV\'s in this thread everyone is talking track use, how does this relate on the roads? As i\'m sure i speak for a few people on this forum and its safe to say my FC TII will spend more time on the road than on the track.

Ben

been running my stock FD twins without a BOV for a bit now. i\'ve yet to see a compressor wheel come flailing through my bonnet in a firey mess :Hammer

seems to pick up a little bit quicker after a gear change, this is probably all in my head though!

I don\'t have any real expertise on this but from reading it all I don\'t think referencing rally cars/F1 cars is really relevant the tolerances in their engines and turbo is far tighter than a production car and are likely to be rebuilt on a very regular basis.

Mazda and every production car manufacturer on the planet as far as I am aware have always but recirc/bov valves on turbo charged vehicles - this is an extra part that costs money to fit and offers no improvement in emissions or economy - why would they do this if it\'s unnecessary?  

No doubt they do the math 1 in x chance turbo will go pop, warranty fix costs for the cars that do VS cost of adding BOV

Might be a different story for aftermarket where production \'may\' be better

Just my 2 pence worth

Chris

Quote from: ChrisDubbya;762323No doubt they do the math 1 in x chance turbo will go pop, warranty fix costs for the cars that do VS cost of adding BOV

That\'s how companies are making money :King

Another point to add to this, 80\'s F1, Rally and high budget race cars in those situations aren\'t looking to make a turbo last at least 60,000 miles and if they we\'re they\'d be loosing performance and potential reliablity anyway.
 
It might be advantageous performance wise and in 90% of race applications be completely unnecessary but road cars are there to be used as a relaible mode of transport on the road. And as Chris says if a car comapny can save itself £30 a car and turn that into pure profit, you know they\'ll go for it...

With the F1 car example I doubt the engine or ancillaries need to last very long lol I think with smaller shaft turbos it would make sense, on larger shaft turbos it isn\'t as much of an issue.

Quote from: ChrisDubbya;762323Mazda and every production car manufacturer on the planet as far as I am aware have always but recirc/bov valves on turbo charged vehicles - this is an extra part that costs money to fit and offers no improvement in emissions or economy - why would they do this if it\'s unnecessary?  

The reason why the FDs run recirc valves is noise reduction effort by Mazda

So do I purchase one for my TII or do I not? I\'m a total n00b I\'m afraid :(

When my BOV goes off the fueling can\'t keep up meaning it suddenly goes rich...causing some nice backfires and flames :D

Mazda has fitted a BOV as OEM, I have kept it as Mazda designed it and have a BOV fitted.

Quote from: m1tch;762385D

Mazda has fitted a BOV as OEM, I have kept it as Mazda designed it and have a BOV fitted.

Its not a BOV its a Recirc valve as stock

Quote from: BlitzBoy;762390Its not a BOV its a Recirc valve as stock

Which recircs to atmosphere inside the airbox

For the sake of being pedantic, it recircs back in after the AFM.... :p

Quote from: Brett;762400For the sake of being pedantic, it recircs back in after the AFM.... :p

Mine recircs back into the airbox onto the unfiltered air side, anyhow I don\'t really want hot compressed air being sucked back into the engine lol

it gets recirc back into the system as FCs have an AFM too keep the fuelling correct, if you vent externally hence why u pop and bang as the expected air has been dumped hence rich spots.

Its gets also gets recirc back into the system to suppress the noise, if you had no recirc valve then noises are heard every time you change gear (air passing through the turbo front housing) Mazda determined this noise as not desirable on a street car hence the fitting of a recirc valve

Okay, so I\'m definitely not confused. Honest. Reading this has been great information but I\'m totally not taking it all in.

1. Is a blow off valve worth having on a stock(for now) TII
2. Does this do a similar job to a wastegate?
3. What are the main differences?
4. If starting fresh with a pretty stock TII what would be recommended?

Sorry for being a simpleton, I\'ll admit this is actually my first turbo charged car so I\'m just trying to learn what everything does and what the best route to take web modifying my rotary.

Thanks

1 : Depending on what your using your car for. For a street use, get one you\'ll be fine.
2 : Similar, but not on the same air flow. The WG release the exhaust flow before the turbo to manage the boost. The BOV (or anything like a relief valve or so...) is here to keep the intake (post turbo) under a low pressure.
3 : WG = exhaust, dedicated to manage the boost pressure. BOV = intake, avoid pressure when the throttle plate is closed.
4 : If you want it full stock without any troubles like backfires, the stock design is recommended. If you don\'t care or you think it\'s cool, threw it away and run without it.

For every car with a MAF it\'s necessary to get the car driveable everyday.
For every car with a MAP it\'s unecessary unless it\'s a weak turbo.

just my 2p
you dont want turbo stool (the nice so called waistgate chatter) the noise is air being forced back against your turbo, bad stops the turbo spinning in the right direction properly as the boost that is in the pipe when you let off has nowhere to go except back out the air filter.
my 2p get your self a good ajustable bov like blitz witht e screw on the top and the right spring in it then you can ajust it to vent at the right level to stop this prob also put the bov as close to the tb as posable then all the air is flowing the same way as when the turbo is spooling. if the bov is near the turbo all te air still has to trave backwards.
also help to save the turbo a bit.
 
quick example if you have to escilaters next to eachother one going up (the way you want to go) and the other is coming down if you run up them you can do it but its alot harder trying to go up the wrong one.
now imagin the escilater is the boosted air and your the turbo trying to spin farward (the right way) you can still sping but its alot harder with the air trying to come back at you.
same with a bov air can easly get out but its alot harder with no bov as the air is always trying to come back on the turbo.
i would always fit on helps spool up times and saves life in the turbo and if the bov is near the tb as you can get it you get faster responce from the throttle too.

Quote from: billybobbooth;789859, bad stops the turbo spinning in the right direction .

most common misconception, do you actually think a turbo compressor wheel spinning at 150000rpm actually stops between gear changes!? the answer is no


As I said before in real world figures I went faster in the quarter when I disabled my BOV. Rally cars dont use a BOV as it hinders performance and spool up time.

Quote from: BlitzBoy;789860most common misconception, do you actually think a turbo compressor wheel spinning at 150000rpm actually stops between gear changes!? the answer is no

+1
Problem is that many people probably heard that "something" stalls and goes backward -actually little bit of air but internet wisdom of experts changed it to compressor physically spinning backwards:2Confused:2Rolleyes

For those who would rant about surge - yes, since airflow goes almost to zero and there is pressure in manifold due to throttle plate closed, compressor for fraction of second will operate in surge, but not under load, since turbine is not powered - no damage can occur.

Quote from: BlitzBoy;789860As I said before in real world figures I went faster in the quarter when I disabled my BOV. Rally cars dont use a BOV as it hinders performance and spool up time.

+1

Only thing which I dont uderstand is why some all out drag cars are using multiple BOVs?:confused:
Given that they are clutchless and they are under boost from startline to finish? It cant save them from intake backfire so why would add another point of possible failure?

Maybe just to keep sponsors happy about their "performance" product:Santa

Quote from: Miki;790059Only thing which I dont uderstand is why some all out drag cars are using multiple BOVs?:confused:
Given that they are clutchless and they are under boost from startline to finish? It cant save them from intake backfire so why would add another point of possible failure?

Maybe just to keep sponsors happy about their "performance" product:Santa

This is a mystery to me also , the throttle plate is open all the time in the run on those cars, so the said BOV never actually operates , I think there is a 50:50 split with drag cars that run them and those that do not

I think running them for road and occasional track use is fine, mine only seems to operate where there is a fair amount of air to blow off. I can see everyones argument though as far as drag cars are concerned.

A drag car uses normal 2 bovs  to get rid of all the air between the tb and intercooler.
As for the note about the turbo spinning backwards it doesnt get as far as spinning backwards but that is what the air is trying to make it do.

Note on rally cars no they don\'t use bov because they run anti lag when + they use a sequential dog box so there is no let off. And when you let off the throttle in a rally car there are devices to keep the revs up and turbo spinning. You can\'t compare a street race car to a full on rally track car. They are worlds apart and about 200000k apart to.

I\'ve worked for a tuning company we did quite a few tests on this. Bottom line is no you don\'t have to have one but it helps 2 is better than one but 1 is better than non unless your running things like methanol where you don\'t even need intercoolers

Good write up Billy :)

Quote from: billybobbooth;790189A drag car uses normal 2 bovs  to get rid of all the air between the tb and intercooler.

The BOVs dont operate on a clutchless drag car so why have them lol

I disagree on why rally cars don\'t have them on your explanation, there were no seq boxes in 80s

Quote from: BlitzBoy;790064This is a mystery to me also , the throttle plate is open all the time in the run on those cars, so the said BOV never actually operates , I think there is a 50:50 split with drag cars that run them and those that do not

again drag cars are diffrent to a street car and it comes down to what gearbox and ecu systems they are running

a full on drag car wont need one as again they use normaly a 3 speed auto or dog or sequentual gearbox or anti lag or a full throttle shift device (means you keep your foot planted revs stay at say for argument sake 6k meaning the tb never closes) makes a bov useless but due to the way it works it turns the tb and cylinders of the engine into a bov as the presured air just goes into the engine rather than the air. you can run lean on gear change but not anything to worry about.

all my 2p but it all comes down to what your running engine, fuel, gearbox and systems wise

easy way to know if you need one is if you hear the air flutter noise you should really have one on but its not a have to or it will all go bang and there will be a big fire ball. as said if it was me get a good quality ajustable one with a auto close spring in (like blitz) a vacume only activated one (baily) are rubbish as if you have things like afms as it makes a vent to air all the time your tb is shut you can get running probs a blitz spring vacume ajustasble bov activate when you let off but as soon as the air has gone it shuts alowing a afm to read the air flow properly.

Quote from: billybobbooth;790189A drag car uses normal 2 bovs  to get rid of all the air between the tb and intercooler.

Why the hell they would do that? Do you actually know what are you talking about?:Grrr

Quote from: billybobbooth;790189I\'ve worked for a tuning company we did quite a few tests on this. Bottom line is no you don\'t have to have one but it helps 2 is better than one but 1 is better than non unless your running things like methanol where you don\'t even need intercoolers

What?! How it helps? In what?:2Confused
Just face it, you don´t know anything about turbocharging as whole and just pushing your opinion:Talking1

If you would really do some tests you would see that there is zero impact on compressor deceleration and as some people already pointed out - they gained response without one:spank

Recirculating valves have only one reason - on older MAP based cars its purely NOISE suppression, on MAF cars its same reason + to keep MAF happy

Only reason I can see for running a BOV on, let\'s say a pro mod twin turbo drag car, if they get massive tyre shake and have built up 20psi on the start line from their 2step, and lag, whatever name you want to call it. Their run would be ruined any way so might as well release all that pressure built up and just cruise up the strip on tick over.

Also a BOV in this instance will be good for when the parachute is deployed over the finish line, release all the boost and shut down the engine. To save it for the next run and ready for a close inspection.

I ment to put turbo not intercooler on the bit where it says tb and intercooler.
I was using methanol as an example that running different fuels changes the things you need on a car.

Like i said its not the law that if you don\'t have one the world will end. I or you will never convince all the people if they should or shouldn\'t have one.

As for 80s rally cars they still run antilag and all the air going back in the world isn\'t going to slow a turbo spinning with anti lag force againt it. But on the other hand rally turbo only last high 100 low 1000 miles coz of it.

And yes not having a bov does slow the turbo spinning a little as the air only has 1 way out and it doesnt matter what anyone says that\'s what the air wants to do is get out. There are only 3 ways to stop it spinning slower 1 antilag 2 full throttle shift and 3 a bov. Only the last to help the air get out the first helps keep the boost in the piping.

Billy I think we agree to disagree, I have a bit more experience in the mapping and drag racing game then you, BOVs in the real world slow down spool up due to having to re pressurizing the pipes as you have dumped all the air out.