Afr's And Bov's.

[Daboss]

Hey forum was doing a little experimenting on my vehicle, my mods are in my sig, most recent is a pull type bov tht I have venting to atmo. I kno that this will cause the car to run rich and I need to get a proper ecu to tune it properly but, that's not wht I am asking I just want an explantion as to why the spring rate of the bov affects the afrs so drastically. I noticed when I have the bov spring adjusted hard the car afr's on light load reads in the 12, 13's but when I adjust it soft the afr's read 9-10. What causes this to happen? It goes rich at 2500 rpm after 2500 rpm it goes back to 14-16 afr at cruise/light load with hard spring rate. Now with the bov adjusted at a soft spring rate at light load at 2500 rpm the afr drop to below 9 and stay there till about 3000 rpm and if I keep throttle at same position the afr goes to 14 but, the minute I give partial throttle without building boost the afr's go rich. I was wondering if anyone could explain this to me as it relates to the bov spring rate, not the ecu as i know the ecu is just adding fuel for the recirculated air its expecting that isn't there.

[bubba]

Softer spring rate would be letting more air out..

Are you measuring afr's with a proper wideband? if not, I wouldn't bother paying much attention if it concerns you, get it on a dyno and use a wideband.

[Daboss]

Yea I have a proper wideband. So adjusting the spring harder on the bov would that affect my boost response? Would a harder spring rate make boost come on slower and a softer spring rate make it come on quicker?

[bubba]

No, it's all about how much air is vented and how quickly. The harder the spring rate, the more pressure it will take to open fully so likely less air is escaping. Making it softer means it opens easier and more air is vented thus resulting in being richer than when it was hard. Too soft and it might be opening when you don't want it to..

[Cubes]

From your post it sounds like when you back off the bov it leaks on when making a little boost/cruise.

Best off to wind it right up so it doesn't let go until it see's around 15psi.

It will choof choof etc at part throttle and around 15psi but response will be noticeably up. OR.. just block it off and run no bov with improved response.

Aftermarket bov's are a pain in the arse; std gtr bovs ftw if your going to use them. I personally don't bother using a bov.