Compressor Surge with S2's?
 

Anyone else have this issue with S2's on an evo ix with a maf? FYI Im using a stock BPV with a ETS intake. I will be switching to Speed density as soon as my Tial gets in, but Im just curious. This usually happens right at 0 vacum or maybe at 1-2 psi partial throttle. I had a slight issue with thi sfactory however every evo Ive owned with factory turbo did this. ANyone else experience this?

It's the stock turbo, not the cams. It spools faster than the engine needs it to, so it surges. Delay the boost threshold to the 3600-3800rpm range and it won't be as noticeable..

yes, had it happen with HKS 7460 KAI on a E9 with S2 cams. We also had the ETS intake on that car and it would not idle properly due to some weird resonance in the metal intake pipe...
Now the car is on SD and everything is perfect apart from slight surge, again on cruise, light throttle, but it doesnt affect the fueling anymore.
I think the main culprit is low vacuum for the stock blow off...

awesome thanks guys!, and to letsgetthisdone, I've been lazy as hell and have a hallman MBC on the car right now, have a 3 port chilling in a baggy in the kitchen lol. and Kikiturbo I think your right as well about the intake my 3 previous evo's had slight issues with the HKS intake and AEM but nothing compared to this.

we switched to stock intake and that cured most of the idle problems.. but only after we went to SD did it cure it completely... the car idles at 950 rpm or less with 14.7 AFR.. rock stable. ETS intake back on, of course..

S2's will build boost earlier than stock cams on an Evo 9. I saw it on my own Evo with a BBK Full. It does add some surge-like behavior at the vacuum-to-boost transition on quick spooling turbos. I don't think its actually surge though, at least based on conventional definition of surge. I think its more that the DV isn't able to smoothly release excess pressure in the charge piping under gradually changing load/boost.

yeah, I always felt that the DV doesnt open soon enough with the S2 cams on the car..

Wish I could "like" Your response Mrfred you explained the EXACT issue Im running into lol. Still waiting on my damn tial bov so I can switch to speed density. But "Bucking" or "surging" is VERY annoying.

why do you have to wait for tial bov? SD will work fine with stock BOV..

The intercooler piping I have is flanged for it that has the IAT bung welded in. Didnt care for doing speed density off of fuel temp, and I dont want to drill and tap my Stock route ETS piping due to resell value.

I mean technically I could just do it now off the fuel temp and switch it later... to be honest ive just been lazy, and yesterday my AEM took a ****, So I gotta dig up my old Innovate LM 2 and jack the car up to install and etc, and ide rather just have the front bumper off and do the short route install etc, all at the same time.