Hello All, Im currently having some issues with my 04 evo 8 where im getting flutter/surging at partial throttle/WOT in 5th gear and was wondering if I have the wrong spring in my BOV.
My Turbo is the MHI 18k evo 8/9 w/18or19psi wg and BOV is the Tial Q BOV with the 10psi spring, when I got the BOV i believe it had the 8psi spring in it but when the car fluttered/surged the car would buck hard so my tuner swapped to the 10psi spring and the bucking went away. Stock 2.0 motor with S2 Cams. I have a video of the car warmed up at idle. Also If i can repost it the car on the dyno where you can hear it surging.
Idle:

Dyno: (7-8specs in you hear the surge for a few seconds)
https://fb.watch/aFzMbswdQJ/

Im looking for answers as to how I can resolve this. I have spoken to Robert at FP about it being the turbo issue he thinks its BOV related and I have spoken to David at Buschur about it he thinks its turbo related.
PS I have done my research on here and cant seem to figure it out there was a post with a video on here but i cant find it that shows the boost gauge bouncing at WOT just like mine does but im having trouble finding it again. here is one of the sound it makes in 5th gear(Not my car just for reference)

 

Well first off you need to know what your vac is at warm idle. Once you know that you would go to Tials website and look at the bov spring chart. Guessing on what spring because it flutters isnt the way to go.

 

I made the video of my vacuum at warm idle and it was between 12-15 inHG and thier chart calls for the -8psi spring. when that one was in according to my tuner who installed the BOV the car would buck/jerk when the flutter happened so the tuner swapped the spring with the -10psi spring the bucking/jerking stopped but is the BOV suppose to leak that much air or move that much like in the video at idle

 

ok I didn't watch the videos but the 8 lb spring is correct. Who is tuning your car? With the 10 lb spring you will get compressor surge. I had this same problem way back in the day when I had s2 cams. I solved it by using the white spring. I would swap the spring back to where it should be at. The bucking and jerking is all tune related.

 

Okay I will order the 8 spring put it in and report back I might even order the 6 as well just incase. My boost gauge sits at -2inHG when off and when car is on it coes to about -12inHG so...going by thier chart if my boost gauge is an actually reading at idle its -12ish which would be the 8 and if its -10ish then it would be the 6? my other question was is the BOV suppose to be hissing/leaking out that much air and fluttering like that at idle.

 

The 6 will be way to light. I get what your saying about the inhg stuff. The bov should stay open a little bit at idle. I know mine does when it idles but I think I have way to little spring in mine. Back to the video that seems normal to me. Its been a while (2 years) since I have actually saw my car idle so its hard to remember. I think your ok with the 8 lb spring. The fluttering in 6th gear is part throttle flutter. That seems normal being your in a high gear and there is alot of air being moved with the long gear and being part throttle there isn't enough to keep it open or shut so it flutters.

 

The 10psi spring is in it right now so you mean thats its okay right now or should i swap springs still and try that?

 

I tested the QR with a few different springs and a slightly crushed 9 BOV.
The 9 BOV works MUCH better part throttle and at any throttle angle. I found that it started to leak air on my fp red around 28-32psi or 530whp IIRC.
Since you are making less then that I would recommend the stock Bov if possible. I had my fab guy make an adapter to make it work.

 

put the 8psi spring back in it and leave it. If your tuner can't figure out why the car bucks get a new tuner. I have never had this problem since i swapped back out to the correct spring even with my setup and switching cams. I know I have to change springs but even a light spring is better then a compressor surging turbo

 

Why over complicate **** when all he needs to do is put the correct spring back in his bov? That is a lot of unnecessary work to do and a **** ton more money to pay for a simple spring change.

 

Easy . Is that normally how you speak to people where you live? lol

Its less then 100 bucks in materials and a welder to adapt it to the flange. I've had a small turbo, mivec and a 2.2 for many years and the stock valve just drives better at moderate power levels.

Have you had a small turbo that rides the compressor surge line often?

Just my .02.

 

My point is ur 100 dollars and a welder vs a 20 dollar spring.