Forgive the noob thread, I have searched well first!

My IX FQ340 with 3" exhaust, AVC-R, modified airbox, Walbro, AVC-R runs nicely on full throttle. I can only induce compressor surge by boost braking at 2000 RPM in 6th gear where it will reach 14.5 PSI at 2000 RPM, usually it needs 2200 RPM for 14.5 PSI without boost braking, and follows with a surge free 24 PSI at 2500 RPM. No complaints there!

The IX FQ models have HKS intercooler and turbo inlet pipes as standard.

I run up to 26 PSI peak and 24 PSI held through the midrange, so I don't want a weaker BOV.

However, even with the AVC-R running zero duty cycle, at about 0 PSI on part throttle with partial lift off I do get a little bucking. It isn't major, more just an irritation. I am wondering whilst sticking with MAF based fuelling whether this can be improved? It happens regardless of whether I run a stock or modified fuel map, and the boost controller setting makes no difference because it is from very light throttle where the duty cycle is still zero.

I haven't tested for boost leaks, but all the clamps are tight and on the standard actuator I can run 22 PSI at 6000 RPM quite comfortably. I can run more but I have to retard the ignition too much on 99RON pump fuel so I don't.

Do I just live with it or is there a solution? It is mild compared to many modified cars, and I've had far worse before with Forge BOV on a Subaru with big turbo and FMIC etc. Speed density conversion sorted it, but I don't want to do that on the mildly modded Evo.

 

It will always buck if you do part-throttle, partial boost lifting unless you do a full lift. It's just standard for a boosted Evo with a strong BOV. That's why it works so well at WOT, because you build enough boost to make the BOV purge fully. A weaker BOV would not have this problem, but then it would also not be efficient when at full boost.

Go try it again by doing a quick, full lift of your foot off the gas pedal, and you'll see that the BOV will open fully instead of causing fluttering and bucking.

 

I had the same problem you are experiencing. I have just learned to taylor my driving style to it (lift off quick), and try not to let it bother me.

A Warrtalon said, it is because it is a strong DV. Sorry i couldnt be of more help, just thought you should know that you are not alone...

Heres my thread..

https://www.evolutionm.net/forums/sh...d.php?t=238885

 

To further clarify, I have a Forge RS, which has an adjustment knob for the spring stiffness, and I keep it clamped down pretty hard in order to ensure max efficiency for the 26.5psi I run daily. If I set it to minimum, the effect on drivability is severely reduced, but of course that also means the spring is not as stiff and not as efficient for high boost. The good thing is I can set it wherever I want whenever I want. My tolerance for the effects of the spring being stiff is high, so I keep it there.

 

Why not have the compressor housing surge ported by either Turbodynamics or Essex Turbo? This shouldn´t cost you that much since you´re local and you can provide the core.

 

That won't fix anything. Surge is a function of spoolup, not transition.

 

Thanks all. It is fine with a quick lift, and if it is normal for the stiff IX BOV then I'll just live with it.

 

I have got the APS bov, it can be tuned/adjusted to get rid of the buck that the standard IX DV does (especially in high gears). I have my APS adjusted pretty much on the maximum stiffness so minimum noise.

And no fluttering...

 

+1

I have the same problem... and D*MN is it ever annoying

 

noob? Yeah Right.

I would think OEM DV is the most unlikely DV to cause bucking, unless it is installed backwards of course.

Funny thing is backwards stock DV hold boost rather nicely

I wonder if your FQ IX DV is the same part number as the USDM IX. Don't have an image handy, do you?

 

I thought I had a big issue when I felt the bucking. I'm relieved.

 

I have found that any BOV that holds high boost bucks. Its almost a linear relationship from my experience, the higher max boost the BOV can hold the more bucking at part throttle lift off.

I know the TIAL is regarded as the best BOV out there, although its not recirculating, does it still induce bucking?

 

Yeah,
It is annoying some times, worst for me is high speed cruise, like 90mph or so on a slight incline, I'll start to boost 1 or 2 psi then the bucking starts as you try to lift ever so slightly or even maintain constant throttle. I actually found it was better to go stiffer on my forge rs, when I had it too loose it was way worse and would do it up to 9psi or so, now with the forge set stiffer it's only an issue at a couple psi.