I have a question for you BSP/SM guys. Do any of you have any partial throttle surging or BOV "stuttering"??? Or do all of your cars have as smooth of boost response as a stock EVO?? The problem I am running into is that in my quest for more power and torque, partial throttle surging keeps getting worse. The faster I get the turbo to spool, the worse the surge gets. I'm to the point where I need make a decision whether an added 50whp and 50tq is worth never being able to use part throttle (that is, always full accelleration or decelleration).

I just had my car retuned and gained 40 ft# of torque at 3000 rpms, but I don't know if the tradeoffs will be worth it. . .

 

Yeah, certainly. Any part throttle acceleration causes this. I get it a lot more on the road course, but it is expected. I just drive through it. I can minimize it by setting my Forge RS to minimum spring pressure, but I prefer to have the boost holding, so I keep it stiff.

 

I'm glad I'm not the only one.

I've struggled with this issue forever with no real "solution", only partial imrovements here and there doing leak down tests and tinkering with the adjustments of the APS BOV.

I've been trying left foot braking more and more to simulate partial throttle while maintaining full boost with marginal success-- I am by no means an expert. However, corner exits are much "sloppier" than the partial throttle strategy (which can upset the load of the car mid corner if it's "bucking" or fluttering badly).

 

im not sure if i have the same issue. does it sound like if the car is trying harder to accelerate?

heres a vid of my car. at the 7 second mark u can here my exhaust "stuttering" a bit.

is that what you're talking about?

http://www.youtube.com/watch?v=LjuZU07xhtQ

 

No. we're talking about BOV flutter caused when you're part throttle boosting with a lot of boost on a strong BOV.

What you experienced in that vid was what happens when accelerating hard out of a turn usually while the car is trying to get traction on all 4

 

Yes! My Forge RS dv flutter drives me NUTS! At the road course and autox it is a major pita. When I've had riders with me they think something is wrong with my car. It definitely hurts me not being able to be modulate at part throttle. I can't believe there isn't a solution to it.

 

ok i have the same bov. but i havent experienced it autoxing yet.

i get it all the time during daily driving. its ok sometimes but there are times where flutters a little too long and its annoying.

 

You can use a weak BOV or not run so much boost. It's just a give-and-take.

 

Last season I played with about 22psi and a lot of timing to combat this and it worked pretty good...sacrificed some power but drivability was much better...

 

Mine does it on low boost also. I guess I just need to turn loosen up the dv a little more or throw on the stocker. I might as well be running the stocker at that point. Hopefully I'll find the perfect balance of holding good boost and just slight flutter when I tinker with it a little more

 

It doesn't bother me. I just drive through it.

 

i'm surprised nobody mentioned seats... i recently obtained a bride zeta iii seat with their fg rails set on the lowest setting... what a difference it makes! i'm 155ish 5'7'' and the stock recaros would fling me around... but now with the brides i'm glued to the seat and i noticed i can corner without bracing myself and feel in full control, my level of control has greatly increased; feels like i'm one with the car...can't wait to autox in them, those seats/rail combo are also lighter than the stock combo so you save a few lbs near the front axles...

 

Evolutionary and other aero hungry people,
If you haven't seen it the latest issue (Feb 07) of Racecar Engineering has some good articles on testing Aero w/out a wind tunnel. They also have another article regarding rear diffuser's and angle of attack effects on downforce. Looks like an interesting issue to say the least.

As for partial throttle BOV flutter, I get it w/my 2003 9.8 turbo and the E9 BOV. I haven't noticed any driveability issues though.

 

I'll get a nice fixed-back seat when the car goes full race with a cage and harness, but for now, it's just the stock seats, stock belts, and a CG LOCK. I'm 6'2" 225lbs, so I fit snugly into the seat. The CG lock helps me from having to use my elbow on the door.

 

Good info... I've gotta check that out.

Corey #89 STU