Does Your Skyline Shuffle?

[rasonline]

Are stock GTR's known to shuffle?

[R32 Combat]

I can't see why AFM's not working 100% would make any difference to turbo shuffle.

I can't see why cams would make any difference either.

I think you might have one turbo that has a slightly higher resistance than the other.

[mantamac]

From memory: Before Dung Boys car went for mapping, whilst on the sensor check screen on the PFC, one AFM was giving a slightly different voltage to the other. At the time I thought this may be because the car needed mapping,or because one of the induction pipes was shorter and more direct than the other, and I discounted it as being a problem that mapping couldn't cure.
If in theory one turbo is more efficient that the other and one and one of the MAF sensors is reading differently to the other. The more efficient MAF may be fitted to the more efficient turbo, and this might be another reason for getting shuffle.
I will check the voltages today whilst removing the heatsheild as Abbey Motorsport suggested. If the voltages are in fact different, I will swap them round and road test the car. I'll let everyone know how we got on later. It will be a nice cheap fix if it helps reduce the Whoflung Shimmy a little.

Mac.

[Tony@Abbey M/S]

Originally Posted by R32 Combat

I can't see why AFM's not working 100% would make any difference to turbo shuffle.

I can't see why cams would make any difference either.

I think you might have one turbo that has a slightly higher resistance than the other.

AFM,s will make a difference because they control fuelling and timing for 3 cylinders which in turn affect the efficiency of those cylinders. Less than perhaps the efficiency on the other 3 cylinders. This causes an imbalance in the air movement and could lead to "shuffle" exageration.

The cams also can make a difference because harmonics can come into the equation.Surely you have seen a n/a engine on a pr of sidedraughts ,even unloaded they get to the point were the "cammy" nature of the engine blows fuel back out of the trumpets.Now if this happens at a bad point on the RB26 it accentuates the so called "shuffle"

Now the imbalance of the the turbos,I think in this case, you have hit the nail on the head.I once had a mildly tuned car with a pair of rebuilt plain bearing turbos that shuffled like mad.We spent a considerable amount of time trying to cure it one way or another and we did make it 90% better with f.con pro and some mods to the "Y" piece on the turbo outlet.We then removed the turbos and air powered them and measured that they had an approx imbalance of 20%. New turbos,back to old management, problem cured!!!.

Tony

[Jim27]

Well my car was chuff-chuff-chuffing at idle. Not sure if this was shuffle or not but it sounded quite 'Darth Vader'ish with the noise coming out of the air filters. There was a 1-2 second pause between each chuff.

I replaced the old atmos BOV with factory recircs and cleaned the AFMs with enough brake cleaner to dissolve a small child and the silly chuffers had stopped.....

[R32 Combat]

Cams, yes, I could see the issue, but johns turbos should run ok with STD cams. You could lessen the effect with difference cams, but thats not solving the issue at its source.



I still don't understand the AFM point.

How can 1 AFM control the fuelling/timing on 3 cylinders when the air its metered had met up with the air from AFM 2?

[Howsie]

Originally Posted by Abbey M/S

IT WAS MAPPED BY ABBEY (DAN0H) so he should know what he is doing......but it was mapped on a dyno not the road so there.....



thats not the shuffles that is the boost pressure being dumped from the turbo,s. All skylines do this when they have non std air filters fitted.

The shuffles is when the car will not pull though a certain revs area due to the AFM voltage ocisllating so badly the air fuel mixture and ignition readings are unstable and the car will not accelarate. Normal it is the BIGGER twin set up,s that are worse at this than small twins.

John you have a E-mail answering your questions. But I feel the S/H blowers may be the problem...

Well done for defining it Mark. Some people have no idea.

[Tony@Abbey M/S]

Originally Posted by R32 Combat

Cams, yes, I could see the issue, but johns turbos should run ok with STD cams. You could lessen the effect with difference cams, but thats not solving the issue at its source.



I still don't understand the AFM point.

How can 1 AFM control the fuelling/timing on 3 cylinders when the air its metered had met up with the air from AFM 2?

That is exactly the point.One is working harder than the other,irrespective of where the air finishes up. One is connected to the part of the ecu that manages the front 3 cylinders,one connects to the part of the ecu that managesthe rear 3 cylinders.
I did not say the car in question should not run correctly on standard cams,all I said was that different cams could affect the outcome.
Not rocket science and Ive been there, done that.

[Pikey]

The air an AFM is metering is being sucked in from the turbo fed by the front 3 / back 3 cylinders, so it does make sense that the afms control the relevant front/back cylinders

[R32 Combat]

Ok.

[mantamac]

Update is: Whoflungdung rolled the stone back over his door and stayed in the Bear Cave today.
I will get to see the car on monday. I'll take a few pictures of the readings the AFM's give on the Power FC.
It is nice to have a few other opinions rather than just my own.

Mac.

[IanH]

On lifting off from say 1/4 throttle to only 1/8th throttle mine shows AFM voltage and Inj Duty figure fluctuate during the "Pan-pipes" (inj shows 5%-15% extra duty) but it still pushes through (although I usually just take my foot off and start again). I'm using a Tial BOV (new piping meant no recirc option available) which I would have thought is my particular area but having read this it could be turbo related

[Milko]

My 92' GTR with HKS Metal Flow, Trust downpipes, cat bypass and singlebox cat back has no shuffle at all, but the 94' GTR I just bought, which has aftermarket filters, cat back and some kind of dump valves, shuffles in 3rd, 4th and 5th at part throttle, its not stopping it pulling so I wouldnt consider it that bad, feels more like a misfire, it may even be a misfire, but you can hear the shuffle going from one turbo to the other......

[keith]

I have had a good few skylines now,anytime that I have experienced turbo shuffle when running 400+ bhp my tuner has been able to sort it out everytime with a tweak to the ecu,plus they have always been mapped on the road.

Keith

[Cord]

Shuffle is common on GT-RS's but can usually be all but elimanted by careful mapping and use of a balance bar manifold.

I've never experienced shuffle on GT-SS's that wasn't curable with a bit of careful mapping. Maybe the car isn't pulling the exact same loads sites on the dyno as the road and needs a fine tune tweak on the road (not having a pop at the mapper, just a possibility) or there is a problem with one of the turbo's that is causing an imbalance.

Dumping the AFM's is an option, but i don't think it's needed in this case.