I had some issues crop up on a Evo I was tuning today and I'm racking my brain trying to figure out what is going on with it.

So I figured I would tap into this great collective we have here.

First off, the vitals:

2005 Evo GSR

Buschur Racing GT35R turbo kit with cast exhaust manifold
Cosworth head and valvetrain
2.3L stroker shortblock
HKS 272/272 cams
HKS cam gears at -4/-1
Nisei FMIC and piping
Open air filter
PTE 880cc injectors
Perrin Fuel Rail
Walbro 255lph fuel pump
TBE no cat
Blitz SBC-iD electronic boost controller
HKS ignition amplifer
APS bov
OEM MAF
OEM ECU
SMC meth kit 50/50

I had this car in a couple weeks ago but a leaky bov cut the tune short. It came back in today with a different BOV and instantly gained 40whp.

Started tuning it for the different bov since it held boost better but about 3 pulls in, as soon as the turbo would spool the car would buck like it hit fuel cut. 1 pull it did a little small buck then pulled clean, the next bucks until I let off.

Here is a log of a clean pull, however looking back now over it, there is a slight dip right after spool at 4300 or so. At first I thought it was just the normal 2byte drop-out but now I remember feeling a little twitch at that point. However, the wideband AFR and powerbands did not show this blip.



Then the next pull:



Bucked like crazy until I let out.

These are the things I checked:

MAF - thought it might have sucked the honeycomb in, honeycomb still intact
Plugs - look fine, gapped low at .022
HKS ignition amp - disconnected and did a pull, same problem
EBC - turned off its warning feature which pulls boost over a certain psi, still same problem

I know I am getting close to maxing out the 2byte load on this car, but over 360 load doesn't happen until further into the powerband. This car hits this bucking problem right after full spool, around 4250 rpm.

peak numbers:

365 peak 2byte load
2860 peak 2byte airflow
57 peak lbs/min
28psi peak, 27 psi @ 7600
11.5 AFR straight across

Anyone have any suggestions?

 

What backside is on that turbo? And is the compressor cover anti-surge?

I would guess that this is compressor surge.


Eric

 

Compressor surge can buck like fuel cut? It's a pretty violent buck.

 

Depends on how bad of a surge is happening. When it's true compressor surge, the airflow is completely stalling or reversing, so it can act just like fuel cut.

Usually, signs are a rapidly bouncing boost until you are out of the surge area. Since his car is spooling that 35r so fast, I would put my money on that.

Plotting points on the compressor map calculator spreadsheet that I have, it definitely shows him being in the surge area until about 5000 RPM or so.

Eric

 

Interesting. I wonder why it's happening all of a sudden, although the new BOV did help spool by about 300 rpm.

Maybe its time for a anti-surge compressor housing?

That 2.3L is indeed spooling that GT35R fast as hell. 27psi at 4100 rpm or so.

 

Well, that's just my guess at this time. I don't know if it's right or not, but it seems like a strong possibility.

One other thing that it can be also is misfire. Did you log the wideband at all? Usually misfire will show very big spikes in the wideband reading.


Eric

 

Yes I did log wideband on the dyno. On the pulls that it would do a little buck the AFR seemed to be stable. On the pulls that it would buck like crazy, of course everything would be all over the place.

I thought it could be misfire at first too but I've never had a misfire feel like this. We are going to check the coils and such anyway.

So if it is surge, we should be able to start a pull at 5k or so and it shouldn't be there right?

Thanks for you input as always Eric.

 

unlikely...did the rom get upgraded and the boost cut timer (I know that can't be the right verbage) not get reset?

 

boost limit is at 319 and timer is at 20000.

Same place we had it last tuning session. No issues then.

 

That's how I would go about testing to see if it is surge or not.


Eric

 

I ended up having surge on the stock turbo until i found out my AFR was too lean during spool up dropped it 1 point and its been fine. I wonder if what happened in my situation would apply here?

 

Thanks for posting up a thread about the issue Bryan... and thanks for your help today.


I have the BR 35R kit and the hotside has a FP stamped on it so I'm not quite sure what the size is. I assume it's 0.63, but I could be wrong.

The compressor cover looks like this:

 

Here are some pictures of the hotside

 

That looks like an anti surge cover to me.

Since your monitoring AFR what is your AFR during spool up?

 

Hmmmm.... the bucking looks similar to the video in this thread. Go to where there's about 23 seconds left in the video where it zooms in on the speedo and tach:
https://www.evolutionm.net/forums/sh...84#post3438484


TedB says something interesting in post #21, third paragraph, of the same thread:
https://www.evolutionm.net/forums/sh...02#post3602402