I have installed an 18k that I've had for a while and am starting to dial in the boost curve. I am getting a nasty fluttering sound at spoolup when going WOT, hopefully evident in the airflow/load curves shown.





This clears up above 5k rpm and pulls smoothly. Stock block and head with HKS 272 cams. Was running a crushed 9 DV but have switched to a Synapse and am unable to dial it out.

Am I over-driving the turbo and getting real surge? Softening and delaying the spool helps but does not eliminate the noise. I would appreciate any advice.

 

Evo 8 or 9?

 

Good point. It's an 8.

 

With MIVEC you can decrease intake cam timing to promote flow, but obviously an 8 doesn't have that capability. With a single port actuated BOV you're pretty much screwed although you can play around with a softer spring. Your best bet would be to swap back to an OEM dual port BOV so it opens under part throttle conditions.

 

Is the MAP value an absolute reading (what MAP implies) or is that gauge pressure?

 

Also a good point. "MAP" is showing gauge pressure and just a label.

 

The posted logs are with the crushed 9 DV when I first experienced the issue. I have found the synapse to be more response at part throttle so far.

 

Hmm, odd you're getting surge at only 22-23psi of boost. Does it stop doing it if you lower boost?

 

It did seem weird. Thanks for putting some eyes on it. So do you think it is real surge?

It did not surge at lower boost, but the other runs were near wastegate and I have not found the "threshold."

Do we know any ballpark airflow/rpm #s for a stock motor? Do I just need to walk up the WGDC and find the curve?

 

The compressor can surge any time the turbo is discharging more air than the motor can ingest. It's hard to read your logs so perhaps post the actual log file, but is this happening when the throttle is 100% or is this happening during part throttle acceleration?

 

Understood. Yes, these are WOT logs. I am just surprised that it would be flowing so much (or head not flowing so much haha) and wanted to get some eyes on it.

Sorry, I thought the visual would be better to see the flutter/surge. True, everybody is used to their own software.

 

The 18K flows 54lbs/min without a ported shroud inlet so that is substantially more flow potential vs stock. I'm not surprised that is surges because it's making 23psi at 3500rpm and it doesn't have a surge cover. Instead of forcing 100% WGDC until full spool is reached, you're gonna likely need to dial down the WGDC during spool to cause it to delay.





If I look at the curve of the airflow I assume the area circled in red represents your surge issue, but please confirm.

 

Correct, that is the area. Thanks for taking a look.

Yes, I am coming from an older turbo with less flow so I wasn't expecting the response/airflow down there and I've never experienced a WOT surge issue before.

I will just work my way up with the WGDC and give the motor what it can take. Boost is just a number.

 

This is totally in another direction, but I once had this exact same issue when my turbo died. My surging at certain RPM/load was the wheel hitting the compressor housing. I assume there is no shaft play? Just tossing it out there because my luck is always such that I get the odd problems nobody else does

 

Haha yeah doubt it a bad turbo but I always worry too. It's new, I checked radial play before install, and I've got confirmed gauge pressure feeding off the oil filter housing straight to turbo. I'll give it a feel again next time I play with the DV.

I've had em die in other cars and I get that high pitched whining grinding on the housing but still constant flow. This was very much like that momentary part throttle lift-off flutter but was more violent and longer in duration, but then clears up in the higher RPMs once the motor catches up to the airflow. This also goes away when I dial down the WGDC too.

I guess just have to dial in the curve now with what the motor can take; no easy spool-up and go. Not a bad problem to have.

Are there any other cams that flow better in the 3500rpm area but still pull up top?