Blow off valves

[bduffman]

hey guys have just been reading ( reserching ) for a future turbo project and saw this page saying that for a maf sensor set up you should use a Re-circulating rather then vented bov
Recirculating Blow Off Valve

A re-circulated BOV is one where the boost pressure is re-circulated back into the intake just before the turbo. This type of set-up is a must for those that are running a Mass Air Fuel ( MAF) sensor. The reason for this is that the MAF has already accounted for the air that is in the intake manifold, and if it was allowed to escape to the atmosphere, the car would run overly rich due to the fact that the ECU still believes that the air is in the intake tract. A bonus to running a re-circulated BOV is that the air being re-circulated can be brought back into the turbochargers intake pipe at a location and angle so that the air pressure is forced directly onto the compressor wheel. This will aid even more in helping to keep the turbo spooled up and running in-between shifts, or times when you are quickly on and off the gas pedal.

[spency]

The later EVO's (correct me if I'm wrong) run an internal BOV system like this.

[Bennoz]

If you're gonna go to the trouble of turboing your car, go to the trouble of using an ECU that doesn't require a MAF. I don't even run a BOV either.

[bduffman]

how can you not run a bov ?
i thought you needed one so you dont create presure when the turbo is still spinning but the throttle is closed

well i was looking at I8A4RE turbo set up that he plans on making copys of as a quick less fuss way and hes using a GFB Deceptor bov but still running a maf sensor

[I8A4RE]

You can run recirculating or atmospheric with a maf, it does not matter.

The reason for this is that the MAF has already accounted for the air that is in the intake manifold, and if it was allowed to escape to the atmosphere, the car would run overly rich due to the fact that the ECU still believes that the air is in the intake tract.

Yeah it might run overly rich for about .3 of a second. The BOV is only working when you release the accelerator pedal. So unless you intend to drive by constantly putting your foot on and off the pedal, then you wont have a problem. However in saying that if you want it legal and to be engineered you will need to have recirculating anyway. Atmospheric BOV are illegal.

If you're gonna go to the trouble of turboing your car, go to the trouble of using an ECU that doesn't require a MAF. I don't even run a BOV either.

This is quite true and my ECU can run a MAP, so when I have cash ($180) I can easily remove the MAF.

[bduffman]

ok kool but will the recirculating one give more power ? im sure it wouldnt be much air but every little bit counts or would the engine just not suck in as much due to air already being in there

while on topic how hot dose the maf sensor wire get would it heat the air up at all or not

[spency]

Bens set up means when he changes gears, he keeps most of his boost as it's going back into circulation, instead of having to spool all the way back to full boost, it only has to spool the little bit it lost.

[I8A4RE]

Bens set up means when he changes gears, he keeps most of his boost as it's going back into circulation, instead of having to spool all the way back to full boost, it only has to spool the little bit it lost.

Mine does that 2

[Bennoz]

Plus my tubs are only little baby things. Not a huge amount of reticulating mass means they spool up super fast.

[phunkydude]

and Ben'z got those loud kappishhh..kapishhh sounds, even without a BOV.
Is that back pressure?

[Bennoz]

That's the sound of compressed air forced into the spinning compressor blades and stalling them dead, due to it having nowhere to go after I've shut the throttle

[bduffman]

isnt that really bad for your turbos though wont it blow the seals in the turbo

[gotboost?]

Yes, it's not the best thing for your turbo. However, if it's only a low amount of boost that's hitting against the blades at the time, then there shouldn't be too much of an issue.

Worst case scenario is that the constant bashing of air back against the compressor fins could possibly flatten them out or put the shaft out of alignment.

With regards to the recirculating systems, it's previously been mentioned that the benefit of these is that they provide better throttle response due to the compressed air being 'recycled'.

Now, depending on the way in which the recirculation is set up, one possible little downside is that the recirculated air might not be as cold and therefore, less dense. This can result in a slight loss in performance.

It's really all about the way in which it's all plumbed in, but I'd say that I'd be leaning more towards the recirculated system due to the fact that it provides better throttle response and keeps the boys in blue relatively happy.

[Delvance]

Everyone says that and sure makes sense in theory but i don't think anyone really has come up with conclusive proof/evidence for it. It's one of those subjects where some agree and some don't. I've a mate running a large turbo without a bov/recirv valve for a fair while on a street turned track pig and the turbo shows no signs of damage.

Personally i prefer running a recirc valve. You can also get 50/50 valves if you want some kinda bov - i believe turbosmart or gfb makes 'em.

[gotboost?]

Yeah, you won't see any signs of damage... You'll just see the little chunks of compressor wheel inside the engine when the shaft finally gives up the ghost...

[Delvance]

Well actually, it was running like so for years on the street then got turned into a drift pig at a semi pro level and all is still in good health.

Like i said, in theory it should damage but no one has shown any conclusive evidence. There are others on S.AU running no bov/recirc on their track pigs either and they have not had any turbo issues. I for one would like to see some conclusive evidence one way or another instead of internetz warring on the topic.

And don't link me to some performance manufacturer's website stating it's bad...of course they say that seeing as they're trying to sell their bovs etc.

[gotboost?]

Meh, not my car.

[bduffman]

That's cause your fto isn't turbo dispite your name being gotboost

[gotboost?]

Meh, not my car.

That's cause your fto isn't turbo dispite your name being gotboost

How does your sentence even bear any relevance to what I said?

I've got the username 'gotboost?' due to the fact that I've had several turbo'd cars in the past and performed several turbo engine conversions and sell parts for turbo'd cars. I decided the username best summed up what I'm into, so I've carried it across some of the forums I've been a member of.

I suppose the username bduffman must be a pleasant change from rogercordia...

[Shane001]

^^ someone get these 2 a room