BOV or no BOV?

[m1tch]

Its not a BOV its a Recirc valve as stock

Which recircs to atmosphere inside the airbox

[Brett]

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

[m1tch]

For 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

[BlitzBoy]

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

[B.Martin]

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

[Vell]

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.

[billybobbooth]

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.

[BlitzBoy]

, 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.

[Miki]

most 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.

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.

+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

[BlitzBoy]

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

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

[B.Martin]

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.

[billybobbooth]

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

[B.Martin]

Good write up Billy

[BlitzBoy]

A 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

[billybobbooth]

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

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.