My car is a 2006 evo 9. Some mods that recently went into the car were a GFP bov, 1000cc injectors/walbro, new sparkplugs (for the tune) upper and lower ic piping and a ported exhaust manifold. The car originally had a full tbe (no cat) and an intake, but I think ever since I have put on the bov the car holds boost better, but at high speed or when in boost if I slow release of the throttle the car will jerk whereas if i let off instantly in 1 motion it will not. Is there a reason for this or is this how aftermarket bovs are? Any way to improve driveability?

 

What you are feeling is likely compressor surge. I'm not sure if that DV is adjustable or not but too stiff of a setting can cause this.

Is it recirculated?

 

^ yes it can either be vented or recirculated. The setting I have the bov on right now is recirculated

 

im having the same issue, from what i understand it happens with the forge rs with EVERY person I talk to......I've adjusted it every which way, I just can't get used to it. It seems like I need to be either 100% ON or 100% OFF. backing off slow while in boost is just a miserable time. Is there ANY bov that you guys could recommend that DOESNT do this?

 

^ I feel your pain bro, it doesn't feel like a good thing. Just as a side note, when I full throttle the bov seems to flutter midway through the rpm range, is it maybe the bov that is damaged?

 

heres a pic that I took not too long ago, dunno if it will help...

 

If it doesnt do it at high rpm, i think thats surge. At least thats what i've been hearing from the guys i know. Mine does the same thing

 

Update: the car in 5th gear will not stop fluttering and jerking while in boost. All other gears are alot better but 5th gear pulls are nothing but a headache

 

yep thats compressor surge. i get that to sometimes. our small turbos dont have surge ports like the big ones so we get the worst of it when it happens

 

what's the AF on slow off throttle?

 

Your bov spring tension is too high...and at vacuum is not snapping open quick enough to vent the air, some of it is crashing back on to the compressor. You need to get a softer spring or loosen the adjustment knob if it has one.

I have a FORGE RS and Greddy type S....both hold boost nasty and in 5th gear i can feather the throttle and get no surge.

I'm on Speed density which actually helped on driveabilty in all areas. What is your vacuum/boost source for your bov?

 

I think its 10.8-11 but I'll double check

 

Yea that is what the tech at GFB told me. I am not speed density which could also be hurting me as well.