Map Tracer Query

[benl1981]

Umm - I'd rather not have to be so careful with it if I can fix it. I was hoping to get as close to OEM driving behaviour with quite decent power.. I haven't heard of many others with this problem so Im thinking it may be in the turbo.

I just put on an Rb20 10 psi wastegate actuator, once I get the new injectors in and fix up whatever im going to do with the intake I will take it to the tuner and see what they can do..If still an issue will take the turbo off and get a different wheel put on it to reduce this effect.

Mine is an earlier GCG so I dont know if they have fixed them afterwards.

[Cubes]

I remeber the really early 500hp rated GCG's had issues with surge but that was when your getting stuck in to it. I don't remember any issues related to when u jump off the throttle.

So your bov hasn't been modded so to speak? that little bleed hole in it blocked off?

Any chance of a vid of you driving it and it doing the jerk when you get off the throttle so we can see just how bad it is?

[MANWHORE]

Instead of getting a different wheel, would putting on a larger exhaust housing, to shift the power band up later into the rpm help?

[benl1981]

Could do I guess..good idea..but the size of the exhaust wheel will still be the same..

Would have to get the R34 exhaust housing bored out to same size as my one though..

Might be able to get a little video cubes. No mods to BOV, stock one etc..

Thanks guys

Edited June 27, 2007 by benl1981

[BHDave]

Off topic>

I never had an issue with my old gcg high flow surging, and i had the stage 2 one which was supposed to be bad. Admittedly it was only on the rb25 for 6 months or so before it cracked the exhaust manifold (modified trust high mount) and the HKS kit went on.

Back when the high flow was on the rb20 and i had to flog it to keep it on boost, i found that by blocking the hole on the stock bov it caused the car to surge on partial lift off, which is basically mimicing the behavior of a tight aftermarket bov or no bov. It was still fine on acceleration

On topic>

I know my current surge issue is almost entirely due to the .63 exhaust housing on the t300s combined with the t04s wheel which pumps more air at low shaft speed than an equivalent GT spec wheel. I'm not interested in changing anything on my car to work around it as it only happens at partial throttle highish revs as mentioned earlier (basically what i would describe as the no mans land between having a go and cruising). Simple work around is either get off the gas and get back on it, or give it more gas, as it's due to the compressor trying to push more air past the butterfly than it can flow. In your case the stock bov is more than likely masking it somewhat as it has the bypass. If you blocked it off completely it would be worse.

The r34 rear housing mentioned by manwhore will fix the issue (well i'm 99% certain) whether it then moves the point of surge further up the rev range with a different amount of throttle is anyones guess, particularly with a high flow.

Too many dots cubes.....

Edited June 27, 2007 by BHDave

[benl1981]

BHDave - the surge is quite noticeable - so you think an r34 housing with the larger volume may reduce this a lot!?

Cheers

[BHDave]

It's quite likely. It also assumes you have an r33 spec rear housing (likely). I think it may be worth while talking to GCG about it as they have the experience. But more than likely they will come up with a similar solution, namely, reduce the turbos ability to push air at moderate load with low throttle openings. They are also likely to be able to tell you whether that will have an effect somewhere else (other than the obvious raised boost threshold)

[benl1981]

Yeah I've spoken to them quite a bit and shown them pics of my turbo before I installed it. They can't see anything wrong with the specs.

I know it has an R33 exhaust housing..so yeah maybe the R34 one would reduce this effect. Might be the easiest solution - just machining off the cg30 housing as opposed to changing wheels..

[benl1981]

I found a vacuum hose that wasn't connected - the one just after the AFM off the rubber intake pipe that connects to the solenoid. My solenoid isnt used ( always closed) but I usually connect it up to close the system. This hose was just dangling there..

Will check tomorrow to see if it makes a difference..probably not.

[benl1981]

Problem still there so definately a turbo isssue..

[benl1981]

Anyone know how to tell a BB VG30 turbo from non-BB?

Is the exhaust housing from a non-BB not useable on a R33 turbo?

Thanks

[Cubes]

The BB looks like a regular RB20/RB25 style turbo.

The non-bb looks like a VLT style.

[Cubes]

I really am a little concerned you may be barking up the wrong tree.

Another that has experienced the same issue but more severe; a large longer inlet pipe sorted the issue.

http://www.skylinesaustralia.com/forums/in...5074&st=40#

Have a good look at what the problem is before you go out and waste money making your turbo more laggy for no good reason....

Part throttle constant acceleration, boost starts to build and then begins surging. Turbo match related and quite common with big turbo's. GT35r's on rb30 sohc's see a little compressor surge under this circumstance.

Surge/jerk as you back off the throttle after accelerating IS afm reversion. No doubt about it.

HKS EIDS FTW. Nengun - $137 delivered.

The HKS EIDS has been developed to buffer dramatic airflow meter signal fluctuations. By buffering these fluctuations the EIDS prevents engine stalling or stumbling associated with sudden imbalances in air/fuel ratio of airflow meter-equipped vehicles that utilize atmosphere venting blow-off valves.

[Hardman69]

Sounds like classic compressor surge to Me. I've seen a couple of guys mount the AFM between the I/C and the throttle body - that would prevent any air flowing backwards through the AFM, but it won't stop the surging. I'd suggest looking into a (second) pre-I/C Blow-off valve (plumb-back of course!) that'll bleed-off pressure with only a small pressure differential between intake manifold & compressor exit. That'll vent the pressure peaks & smooth/reduce the surge pulsing.

Short of getting some precision compressor/housing machining done to move the surge line, backing off the boost at low rpm is the only real way to eliminate it. My Turbo is prone to surge at 0.5bar at 2,500rpm, 0.65bar @3k, 0.8bar @3.5k, etc. etc. It's called a stall/surge line. get used to it.

[Cubes]

Hardman,

I've highlighted the areas of importance.

One of the things I notice on the map trace if you hit it in 2nd (or any gear >1st) and then back off - i.e. rev to about 4 or 5k and then back off the fot doesn't go straight back to the top - there is a slight delay. THen when it hits the top It shoots back down the vertical axis for a second or so even with the throttle closed.

Thanks

What ben is saying is your crusing along on boost, lets say up a hill. You then back off the throttle the boost guage reads neg vac, the bov releases, the pfc's map trace bounces to the top then quickly back down a little (this is when the car jerks forward) then back up to the top.

Bens surge (well it feels like a surge/jerk) isn't occuring when boosting; its occuring when you take your foot off the accelerator as a result the BOV does its recirc thing.

So in short.. No Ben isn't experiencing the traditional surge you have suggested. That being when accelerating and making boost.

I'll say it again; depending on driving conditions I am easily able to make a stock turbo'd Skyline do this little surge/jerk when jumping off the throttle.

[Hardman69]

Yeah, that part of it (what the hell is "fot" ?) I wasn't real sure about - I'm guessing that's just lagging air in the intake system getting pushed out backwards through the AFM ?

I've found my Hi-Flow turbo will start surging slightly (without stalling the compressor) at low-rpm and middling load, on small throttle openings. Plant the foot and it cleans up the airflow, cuts the surge.

I think there's TWO things going on here - compressor surge, and BOV recirc-blowback.

[BHDave]

You missed this bit cubes;

Also going up a hill in 4th gear hovering around 0-3psi you can see the dot flutcuating between about 3 or 4 load points in the vertical axis with a steady throttle opening.

Thanks

There are 2 issues, the throttle back off reversion isn't the important one as (unless it's causing the car to stall) it really has no effect on drivability, which is why i've generally addressed my responses to the on throttle surge issue as quoted.

[benl1981]

Yeah sorry Cubes. I do have an issue when holding a constant load also... i.e. around 0-3psi.

So a non-BB housing is not interchangeable to the rb25 turbo?..Does the VG30 non-bb turbo still have a 45V1 on the compressor housing..i.e. how can you tell?

Hardman69 - what sort of highflow do you have??

I would like to rectify this. I don't think the boost control will fully get rid of it..since the problem is very close to atmospheric pressure or at 2psi etc. The wastegate should be fully shut around this area.

Like hardman said - fully opening the throttle clears it up.

E.g hold a steady light throttle up a hill (promoting around 0-5 psi) and you will get reversion and a jerk. If you do the same thing but fully open the throttle from the start you won't get it.

When you change housings you still have to get new seals don't you. GCG reckoned that to put on a new wheel they had to put new seals in. ..they said anytime they dismatle a turbo..!

I would have thought the cartridge would be sealed though.

I wonder if the R34/vg30 housing would fix this issue.

Edited July 1, 2007 by benl1981

[Cubes]

E.g hold a steady light throttle up a hill (promoting around 0-5 psi) and you will get reversion and a jerk. If you do the same thing but fully open the throttle from the start you won't get it.

If you are holding a steady throttle, boost builds and while holding throttle it begins surging then yes that is compressor surge.

So what issue is difficult to live with?

The holding a steady throttle, boost builds and then starts surging 'while' holding that same throttle opening

OR

Accelerating on boost, reduce acceleration, BOV recirculates and you get the jerk and load points diving.

If its the later; don't mess with making the car laggier the only solution that will fix that issue is playing with inlet pipe dia and length, atmo bov, hks EIDS, or atmo bov + hks eids.

[Cubes]

You need the BB core VG30DET turbo.

http://www.mygen.com/users/dbruce/myz31/images/P7210029.JPG

You can see the different VLT Style dump design. The wastegate is integrated into the dump pipe.

I 'think' rad33 from SA had a couple of VG30DET BB turbo's that were stuffed and wanting to get rid of.

Well some one did..