Getting Reversion With Stock Bov On Rb25

[Rolls]

I'm getting reversion with my stock bov as I am running a highflowed rb20 turbo on an rb25 and it makes a lot of boost quite early, eg 6psi by 1900rpm in 4th.

If I boost with minimal throttle and back off I get a odd fluttering noise from the intercooler piping, but not the same as flutter from running no bov, it actually comes from the pipes/intake on the right hand side instead of the pod.

Anyway this means if I get on boost with the throttle just cracked open and then throttle off to change gear it fuels up and means the throttle doesn't work for about half a second, this makes for clunky gear changes which is quite frustrating.

I'm getting the tune touched up on thursday and Im hoping we can tune a lot of this out but is there anyway to make the stock bov work better? It doesn't flutter when I back off but I'm getting all the side effects of reversion, eg the maf signal flaps around, fuels up and pops on gear changes now and then.

[scotty nm35]

The way Nissan get around it is to drill a small (4mm) bypass hole in the bov. Does yours have one?

Are you running the stock intake? The angle of the bov return can have a lot to do with it.

[Rolls]

It is the stock BOV, is it there from factory?

I am running a metal intake but the angle looks identical to stock, plus I had a very similar issue with the rubber intake.

[scotty nm35]

It is the stock BOV, is it there from factory?

I am running a metal intake but the angle looks identical to stock, plus I had a very similar issue with the rubber intake.

I don't know, I have the hole on mine and when I block the hole it can act like you mentioned.

The intake is the key, the stock bov return is on a crappy angle, it needs to point toward the compressor. If any air goes back up the intake the afm voltage will drop causing what you described.

[Rolls]

Will check both, might see about rewelding the return so it is on a better angle.

[Rolls]

Added another 15cm of silicon hose to the pod, completely removed the issue.

[DVS JEZ]

Added another 15cm of silicon hose to the pod, completely removed the issue.

So im guessing ur intake was very short before? As 15cm is a fair bit

[Rolls]

Yep, would have been maybe 10-15cm shorter than the stock rubber hose.

Edited May 19, 2012 by Rolls

[scotty nm35]

So the AFM was simply too close to the bov outlet? Do you have any pics of before and after by any chance?

[Rolls]

Yep pretty much that was the problem.

The metal intake pipe I have with the old silicon joiner looks identical to the stock bendy hose, it was just about ~10cm shorter, so the AFM was mounted a lot closer to the bov outlet than it should have been.

Will grab a picture of afterwards tomorrow if I have time.

edit: Oh the new hose has a ~90 degree bend in it as well, probably makes more difference than just having it longer as well.

Edited May 20, 2012 by Rolls

[scotty nm35]

That would definitely help with the reversion but I hope you aren't chasing big power. The silicone 3 inch bends can suck closed at less power than the stock rubber ones, mainly due to the intake being so close to the exhaust manifold.

[Autumn33]

sorry for hijacking but just wondering if it matters how short the intake pipe is if you don't run a blow off valve / have an aftermaket one?

I'm getting a metal intake pipe made up just wanted to know if i can get it made shorter then the stock ruber one.

Thanks

[scotty nm35]

Personally I would run the stock airbox and get a 3 inch alloy copy of the stock rubber pipe, its the best option for so many reasons. Why no BOV though?

[Autumn33]

I do have a bov (aftermarket), I was just saying in general aftermarket/no bov as theres no need for the return

I was thinking of just getting a copy of the stock rubber one but wanted to know if i could go shorter.

Thanks

Edited May 20, 2012 by Autumn33

[scotty nm35]

Not really as you need to run a plumb back BOV, you can only run an atmo bov if you go map sensored, and ditch the afm altogether.

[Autumn33]

I have read all the threads on atmo bov's but i have none of the problems stated in the theads, only trouble i had was my aac valve just had a breather on it for some reason, now all sorted & is running perfect.

I'll just get a direct copy of the rubber one.

Thanks

[scotty nm35]

I have read all the threads on atmo bov's but i have none of the problems stated in the theads, only trouble i had was my aac valve just had a breather on it for some reason, now all sorted & is running perfect.

I'll just get a direct copy of the rubber one.

Thanks

Perhaps you need a wideband to know how rich the engine is running at light loads and decel. All the cars with atmo's I see, the rear bar is covered in soot, the cats have collapsed and fuel economy is woeful. You can tune around it to some extent I guess, perhaps your tuner is a gun...

I make a direct copy if you have trouble finding someone local to make one.

[Rolls]

That would definitely help with the reversion but I hope you aren't chasing big power. The silicone 3 inch bends can suck closed at less power than the stock rubber ones, mainly due to the intake being so close to the exhaust manifold.

I am running a metal intake, it is just the bit that joins on the pod that is silicon, seems fine with 260kw where as the stock pipe used to suck closed on less than 200kw

Thanks though, will keep an eye out

If you are running no BOV at all the longer the intake the less bad the reversion will be as it will be buffered over a long time, you will still get it, it just might not be bad enough to stall the motor.