[QUOTE=Miggidy]

There is no need to release to atmosphere, none at all[/QUOTE]

While most of us know the whole atmo thing is more for the BLING factor, some may argue that recirculating the pressurised air can often raise inlet temps. Eg- the charged hot air fed back into turbine compressor again is going to be warmer than uninterupted cooler air coming straight from air filter etc. Of course, this may not be that significant and so in either case the intercooler may take care of the added temperature... but it is a 'worthy' argument to investigate.

As I mentioned before, having an audible reference point (vented to atmosphere) can often reveal a few things I find useful out on the track. ;)

As far as the negative effects... AGAIN I'll just re-iterate, this has nothing to do with whether a BOV is plumbed back or vented to atmosphere! It is related to your ECU and it's tune. So yes, fitting an atmo to your existing factory ECU setup will increase fueling... but if you had an aftermarket ECU, you can tune to suit open or closed... no need to blame it on the BOV!!!

[QUOTE=subarooboy]While most of us know the whole atmo thing is more for the BLING factor, some may argue that recirculating the pressurised air can often raise inlet temps. Eg- the charged hot air fed back into turbine compressor again is going to be warmer than uninterupted cooler air coming straight from air filter etc. Of course, this may not be that significant and so in either case the intercooler may take care of the added temperature... but it is a 'worthy' argument to investigate.

As I mentioned before, having an audible reference point (vented to atmosphere) can often reveal a few things I find useful out on the track. ;)

As far as the negative effects... AGAIN I'll just re-iterate, this has nothing to do with whether a BOV is plumbed back or vented to atmosphere! It is related to your ECU and it's tune. So yes, fitting an atmo to your existing factory ECU setup will increase fueling... but if you had an aftermarket ECU, you can tune to suit open or closed... no need to blame it on the BOV!!![/QUOTE]


I wasn't aware it was possible to tune the BOV issues out. How can the ECU accommodate for the missing air? Was pretty sure that was impossible, but happy to be proven wrong.

I would certainly say that a FULL Atmo vent will cause issues - This is why the 50/50 Hybrids were developed. I run one on 50/50 .. Purely for wank factor (I'm not going to deny it) ..

I like it so it's not massively audible though (I'm not paying 500+ for a Deceptor Pro) .. So i have a GFB WRX Hyrbid in 50/50 with the trumpet removed. No idling/backfiring issues at all, and can only hear it when i'm on full boost.

Best of both worlds :) Anyone who thinks an aftermarket BOV on a stock car is kidding themeselves but, makes no difference at all.

IF you have the need to run an aftermarket BOV, make sure you get a Jap one...they are the best quality and the least likely to leak!!! i.e. HKS Super Sequential, Greddy Type S or Type R, etc.

[QUOTE=Miggidy]I wasn't aware it was possible to tune the BOV issues out. How can the ECU accommodate for the missing air? Was pretty sure that was impossible, but happy to be proven wrong.[/QUOTE]

Are you referring to Subaru ECU or aftermarket?

Aftermarket you can make alterations to lean out the richness during loading on A/F Meter (Subaru ECU gets extremely rich to overcompensate changes- this is where the excessive roughness/ backfiring comes from etc), and as with many aftermarket ECU's, you can also ditch the A/F and run MAP which makes life easier.

These types of changes can often iron out the usual 'bugs' found when running an atmo with a standard ECU. While it won't eliminate the physical loading effect that an atmo BOV has on the A/F meter, it can certainly tone things down to a point where you won't notice the difference.

OK, so there's a bit more to it than I first thought.

After reading this thread through thoroughly, I'ce decieded not to fit an atmospheric valve, just leave it as it is. I'll be fitting TBE, doing the Air Intake and then installing and tuning a Power FC. That'll be it till the suspension/brakes/driver training ect is done.

When I fit a bigger turbo/IC ect however, I think I'll be leaning towards a 50/50 BOV mentioned by RichX and retuned without A/F as mentioned by subarooboy.

[QUOTE=subarooboy]Are you referring to Subaru ECU or aftermarket?

Aftermarket you can make alterations to lean out the richness during loading on A/F Meter (Subaru ECU gets extremely rich to overcompensate changes- this is where the excessive roughness/ backfiring comes from etc), and as with many aftermarket ECU's, you can also ditch the A/F and run MAP which makes life easier.

These types of changes can often iron out the usual 'bugs' found when running an atmo with a standard ECU. While it won't eliminate the physical loading effect that an atmo BOV has on the A/F meter, it can certainly tone things down to a point where you won't notice the difference.[/QUOTE]

Ok I'm not quite sure you got what I meant. You obviously know as bit about the workings of a BOV BVP etc. But basically when you vent ir into the atmosphere instead of back into the intake the engine has already matched the right amount of fuel for that air. When there isn't as much air going into the engine as the ECU thinks the car will run rich for a short eriod of time. Now AFAIK this is impossible to tune out stock or aftermarket ECU. THis is what I am getting at, I run a BOV I'm sick of it and I know its Bling factor, all I'm saying is that the air shoul not be vented to atmosphere 50/50 or not.

most good aftermarket ECUs will have a MAP sensor miggidy, not rely on the AFM

Miggidy- I hear what you're saying mate, and this is why I run the valve shut on most occasions.. well, that and I can do without the unwanted police attraction! (I currently have standard ECU).

To explain what the MAF is doing a little better.. it's actually not the extra bit of air recirculating back through that is being detected and causing the dramas, but more the MAF registering the extra 'drawing' effect through the system as the BOV vents to air. This 'surge' is created by air being lost out of the system via atmo BOV and resulting in a pressure drop past the turbo, in turn causing extra air to be drawn through the air-filter and MAF (INSTEAD of being balanced by the closed system of recirculated air from a plumb back BOV). This extra surge registered at the MAF is interpreted by the ECU as the car being placed under more 'load', and thus the ECU being the good little machine it is, dumps a little more fuel in for good measure- (for all you know, it thinks you're pulling a trailer up a hill on full boost during a 40deg day?!). :D

The question between standard and aftermarket ECU is HOW MUCH extra fuel the ECU is tuned to add in when this type of scenario occurs.
Subaru ECU tunes are notorious for over-compensating and adding shall we say 'generous' amounts of fuel at these points.. as well as other odd occasions when you fit a larger exhaust, raise the boost or drive up the top end of the rpm regularly. To them, richer mixtures= less warrantee issues associated with detonation etc. So if you have an aftermarket ECU, the extent of these 'generous' fuel increases can often be a lot less- in some cases barely noticeable. And if you can fuck off the MAF altogether and just rely on MAP... well!! ;)

As for never running atmo BOV's.. you'll often find on many of the big time racecars, BOV's are vented to air due to the recirculating pressures causing weird tuning problems... as a Malaysian friend of mine once found out!! Vebting or not venting really depends on your system, ECU and how much boost you choose to run. Like I said before, it's not the mechanical BOV's fault!!!

guys i know the difference between an afm an a MAF... it has already been metered by the mass air sensor, and when it blows off, the ECU will be injecting the wrong amount of fuel into the cylinders etc etc. Either way the ECU thinks there is more air then there is. The question is, is it possible to tune this out, obviosly the same amount of air is not always released.

Seems like a lot of work for Bling factor, I see your heat argument but though. But you can't say its totally safe to run a BOV, I know of people who have had problems with newer model wrxs If the condition is really bad, it can eventually foul spark plugs and even clog the catalytic converter as unburned fuel on the catalytic converter burns very hot, and too much of it can melt the cat etc etc. I just think these reasons are to make you feel better, a BOV/BVP is used to stop compressor surge, the bling factor is a bonus for some.

So would still like to know how you think its possible to tune out this rich period.