Rb25Det - Hks Gt2835 Kai Compressor Surge?

[89CAL]

Hi all

Just finished getting my car tuned with the new turbo (HKS GT2835 KAI) and we are having a bit of issue when the boost gets around 16psi in 5th gear. The problem only seems to occur in 5th so thats why we stopped chasing the issue after about an hour today, as I can live without hitting that mark for now till I work it out

Anyway, the problem. It sounds like its starting to compressor surge a little bit, as it makes a very light fluttering noise in this 16psi area, now I was running the PFC boost control kit and we played around with it and we couldnt really fix it, so we scrapped that and just ran straight to the actuator and adjusted it to about 18psi. Still having the issues however, so not quite sure what it is

It had proper compressor surged when it spiked once or twice and went to about 20 psi (The turbo makes a very loud, almost dose-ing noise) but the surge at 16psi is sorta sounds like the wastegate flap opening and closing really quickly and the gasses flowing out then stopping etc, not the compresor wheel itself making the noise. Running just the actuator has improved it a little but still not sure what this issue is.

Other mods:

Power FC

Z32 AFM

Tomei Fuel Pump

Nismo 555cc injectors

3" Intercooler piping and GKTech 76mm thick FMIC

Front facing Plenum (Greddy rip off)

HKS GT2835 KAI

3" X-force turbo back exhaust

One thing I havent thought about is the exhaust but I wouldnt have thought it would be an issue at the power it should be running (wouldnt be seeing more then 280rwkw atm I dont imagine, Road tuned so far)

The turbo itself has the anti surge slots, similar to the T04Z's as well...... Just after some peoples thoughts on this. My tuner tried playing with the map a bit but couldnt seem to fix the problem with the tune. So hopefully someone else has had these issues and can help me out

Let me know if you need any more information

Thanks

Callan

[wolverine]

I assume there is an aftermarket BOV on there. You can try softening off the tension on the spring until the light load surge ceases.

[89CAL]

Yeah I have a rip off greddy bov. It works fine but yeah I've backed It off now. Had it really tight to make sure it wasn't leaking

Surge is foot to the floor 5th gear. About 3200rpm

[DVS JEZ]

there might be too much air trying to push its way into the motor at 3200RPM and 16psi, try making the turbo a little laggier by loosening the tension on the gate or by setting the gain on the boost controller lower, i know this is a step backwards for power but it should fix the issue.

do you have adj. cam gears? could try setting these differently to move the power up a little higher in the rpm range.

[R31Nismoid]

Yep given it is repeatable it sounds like it's simply flowing too much air @ that point and hitting the "left" side of a comp map which is the surge area.

No real instant way around such a problem unless as stated, you back it off a bit which is not really adventageous to the situation and might just move the surge point up 200-400rpm anyway.

Is it build to the 18psi @ 3200rpm in 5th? I'd say it probably would be given it's full load, but gotta ask

Overall though this is quite odd for that turbo size to do such a thing, never heard of a 3071/76 doing that.

GT3040s (600hp) did/mine as an example, but that was around 200-2400 rpm just as boost started to build under full load and only very very slight and didnt have a major effect to the overall result so i was lucky in that respect.

But then i had an exhaust manifold and factory intake, so slight differences there.

[joeyjoejoejuniorshabadoo]

so what happens in 4th?

[89CAL]

4th gear is fine (double checking afr's tomorrow morning before my tuner goes home)

But we only seemed to encounter the problem in 5th. It's not a big issue seen as it only appears to happen in 5th but would be good if we could solve it anyway.

Tune seems perfect apart from this one issue.

We have tried bringing the boost on slowly with the boost controller and quickly as well. Probably played with the target boost and duty for a solid half hour or so.

With the actuator not controlling the boost it comes on alot harder but still encounters this problem in 5th.

I'm confused as to why it does it at 16psi but when it pushes past this it's fine at 18psi (or seemed to be anyway :S)

[wolverine]

Can you post up the AFR's and IGN timing at the point of surge when you check it out tomorrow.

[discopotato03]

I gather thats your turbo in your sig ?

Its compressor housing appears to have the drilled recirc holes rather than the longer jellybean shaped ones most OE port shrouded compressor housings have . Mr Wollaf should be able to tell you what the 2835 Pro S comp housings snout looks like .

My best guess is that like Nismoid said its trying to pump more air than the engine wants to accept at 3200 revs and the engine loading in 5th at those revs would be considerable . Off the top of my head R33s have a 0.759 5th overdrive ratio so its demanding a lot of torque in that gear at those revs .

Tell me , what sort of revs are you changing into 5th at to load up at 3200 - or are you mainly just opening up in that gear at those revs and getting the subtle woofing sound ?

Maybe HKS needs to make a 0.86 A/R version of their T3 flanged GT28 turbine housing . Really should have done that a long time ago but it is a costly exercise .

The only other thing I can think of is to get a boost controller thats capable of having a lower boost setting just in that rev band in 5th only .

A .

[scotty nm35]

I was thinking, you could control a bleed solenoid (with some ecu's) it wouldn't need to be very big, perhaps 5mm, and feed it back into the compressor at around that load/revs?

I get the feeling this kind of surge housing actually increases airflow as boost ramps as there is another path to the compressor blades...

[DVS JEZ]

what intake are you running?

[wolverine]

The factory BOV has the small hole in it which allows a small constant recirculating leak to the front of the compressor already. This seems to soften the opening of the BOV when there is light throttle comp surge.

Aftermarket BOV's seem prone to opening and shutting quickly when the pressure wave cracks them open. Lighter spring settings seem to reduce the alternating open shut cycle but there still might be something in the tune to help. Possibly by moving the peak cylinder pressures around ATDC might change the amount of still combusting exhaust gas making its way out of the exhaust valve.

With regards to fueling, if the tuner is sitting on the plateau of best leanest power (most economical edge of that plateau) or best richest (most responsive edge) perhaps moving it one way or the other might eliminate surge. I am guessing if you run a bit more advance in the cells around the 3200rpm on the current fueling levels (assuming it is not knock inducing) might get the job done but also going a whisker leaner but a little less advance might help.

Reducing later cycle combustion at that point might slightly reduce the energy acting on the turbine for a few 100rpm.

[89CAL]

Thanks for all the tips.

My tune is resonably rich. For the most part on boost it is around 11:1 slightly leaner at times. The bov we thought was the issue but not as sure ATM. Starting to think it is just a case of the turbo producing to much boost/airflow for the engine to handle

We experienced the problem between 3000 and 35000rpm so 3200 was just an average. But when we where trying this we were loading the car right up. Going from about 2000rpm or so up to the problem area.

Intake is the supplied 3" hard pipe that comes in the HKS kit. Because of that and the 3"cooler pipes I have, I dot think they are the issue. Bov could be the issue but because I have the greddy type flange on the pipes it's hard to return this to stock to try and see if the bov really is the problem. Is the genuine greddy bov worth trying or will it be basically the same as what I have now? The copy BOV is a good copy of the genuine item, it's an autobahn88 item if anyone has experience with them.

Tuner tried playing with mixtures/timing yesterday but had no luck. Will post up the maps if we get a chance to hit the cells where the problem is today. He has to fly out at 11 so we might not get that much done. Will let everyone know

Other then that. The turbo is amazingly responsive and gutsy, very nice improvement an we haven't even chased the full potential on a dyno yet!

[DVS JEZ]

^^^sounds like text book Yavuz talk Wolverine ^^^

[DaveO74]

I have the pro s sitting here in a box at the moment I will post up some pics late this arvo if it would help answer disco's question.

I am in no way a turbo expert but the Kai and pro s appear very different and the Kai has a rear in the standard bolt pattern just like the gtrs. Please correct me if I'm wrong but isn't the gtrs a little prone to surge as well and hence the reason for the port shrouding?

Seems as though hks is trying to save a few dollars here by having a kind of "generic" housing setup for a range of different turbos??

[wolverine]

^^^sounds like text book Yavuz talk Wolverine ^^^

I tried hard to edu-macate myself.

[tridentt150v]

One thing you could do is try taking off your aircleaner and seeing what effect that has on the surge. You don't say what aircleaner you setup you have, but could then use this an indicator to see if the problem can be solved on the intake side or not. You have to leave your AFM in place.

Dialling it higher or lower is not the ideal solution, you want to eliminate it altogether really don't you.

[89CAL]

Have a k&n pod. Pretty large one. Well large in terms of fatness not length. It's probably due for a new filter anyway

Not a bad suggestion at all

[GTScotT]

I have the pro s sitting here in a box at the moment I will post up some pics late this arvo if it would help answer disco's question.

I am in no way a turbo expert but the Kai and pro s appear very different and the Kai has a rear in the standard bolt pattern just like the gtrs. Please correct me if I'm wrong but isn't the gtrs a little prone to surge as well and hence the reason for the port shrouding?

Seems as though hks is trying to save a few dollars here by having a kind of "generic" housing setup for a range of different turbos??

You are correct, the new 2835s come in a skyline specific housing rather than the unique HKS item. It could essentially be a re profiled OP6 housing.

I can only imagine it to be detrimental to outright performance of the setup, yet that would of course depend on what setup it is run. At 1 bar of boost the KAI may yield more benefit to the original, for all we know HKS could be marketing these to a lighter market.. After all they are showcasing the item in reference to their GTRS.. It could be now marketed as the next level of beef on that plain rather than the next league itself (as we all usually know it).

Le sigh, I still wish I had an older model 2835

[89CAL]

figures against the Pro S are very similar. HKS graphs it on there website as the KAI having ever so slightly more peak power (only about 3ps) with a slight loss of peak torque. The torqutarts a little earlier with the KAI from what I can see,

But in saying that, its HKS saying there new turbo is better, they would never say its worse lol

But the performance does feel really good so far, I'm happy with it anyway, the response and power from just the road tune are very good.

Will troubleshoot a bit more when I get the time, have to get rid of an exhaust vibration so I can hear it a bit better.