Changing Bovs

[Waxhead]

Probably a stupid question but here goes anyway.

I currently have aftermarker BOVs fitted to my GTR and they currently vent to atmosphere. I want to install the standard recirculating BOVs and was wondering if it will cause any dramas with my tune when I take my foot of the accelerator given that they will vent back into the system instead of externally.

Can I safely return to the standard BOVs or will my tune need adjusting slightly.

Thanks in advance

[lilcrash]

What ecu?

[Waxhead]

Nistune

[R31Nismoid]

It's hard to say if it will/won't.

Only way is to see.

[lilcrash]

Personally i would retune. Once your bovs open you will create a lean spot. But I'm not a professional so my opinion is probably invalid.

[bubba]

I also reckon it will create a lean spot as the tune will not be expecting that vented air to return (i.e. it would have been tuned so as not to create a rich condition on throttle lift off when the atmo bov dumps the charge air)

[Waxhead]

Thanks guys, thought it might have an effect. I will get them installed and tuned at the same time I get my new exhaust installed.

[Hanaldo]

I'd actually quite like a tuners input on this. How much messing around is done to the AFR's when tuning for an atmo bov? Is it just a little bit of fuel removed to prevent stalling/backfiring at low rpm, or is it enough to cause an issue if it was changed to recirculation? If the adjustments are made for low load cells, ie. ~2000rpm and below then I don't see how a slight lean spot would be an issue. Unless you really have to take out a lot of fuel, or it causes an issue on decel at high rpm, I wouldn't think a retune would be necessary?

Experienced opinion?

[Piggaz]

^

When I had my twin entry ARC cooler on my GTR I had to remove the BOV return piping to make it all fit. My car had AFM's at the time and it played havoc with the tune. The tracer while tuning would float around. On the road it was horrible!

[Hanaldo]

^

When I had my twin entry ARC cooler on my GTR I had to remove the BOV return piping to make it all fit. My car had AFM's at the time and it played havoc with the tune. The tracer while tuning would float around. On the road it was horrible!

I've blocked off my bov before, didn't seem to make any difference at all. Didn't backfire, never dropped revs on decel let alone stall. Only noticeable difference was the sound.

However I never got it tuned like that, so I don't know how much of a difference it was really making. Makes me a bit nervous because I'm not going to have a chance to weld on my bov before I get the car tuned after the Plazmaman install, my fabricator has just had a baby so he is a bit busy. I'd quite like to know if not having a bov on for the tune is going to cause problems...

[Piggaz]

It idled fine, started fine but it sent the AFM's into spaz mode. Fuel economy was horrible as it would just 'shuffle' under light load.

I know some guys have no issues and maybe it was just my setup (Choof Choof twin GTRS's).

[GTSBoy]

I've blocked off my bov before, didn't seem to make any difference at all. Didn't backfire, never dropped revs on decel let alone stall. Only noticeable difference was the sound.

The difference between a blocked BOV and a venting BOV is nearly infinite with regard to the effect on where the air goes after it has been through the AFM though.......

Not the same question at all.

[Hanaldo]

The difference between a blocked BOV and a venting BOV is nearly infinite with regard to the effect on where the air goes after it has been through the AFM though.......

Not the same question at all.

Yes I know, I wasn't implying they were the same, I just thought perhaps the methods of tuning around it were similar given the only real way to do it is to 'trick' the AFM into thinking it's seeing less air. Which means it will have a similar effect when returning it to a plumb back setup, no?

[GH05T]

The difference is the air dosnt escape with a blocked bov it simple goes through the turbo then down the pipes not bypassing the turbo, as I understand it. According the the sensors the air is not "missing"

[Hanaldo]

The difference is the air dosnt escape with a blocked bov it simple goes through the turbo then down the pipes not bypassing the turbo, as I understand it. According the the sensors the air is not "missing"

It's not missing, but it passes through the AFM again so it gets measured twice. So the effect of the AFM 'thinking' there is more air in the system then there really is is the same, so more fuel is dumped. I imagine the only way to tune around that is to find which cells are becoming too rich, and then leaning those cells out. Now these cells are most likely to be at very low rpm, correct? You're not going to have issues with stalling because you're running a bit rich at 5000rpm, the issue comes around when you clutch in from higher RPM and return to idle. So the cells adjusted should be at a very low load point, meaning whatever lean spot is created by actually having that air in the system shouldn't cause any issues?

Or am I missing something?