Does Your Skyline Shuffle?

[SIHethers]

Mark

I agree with what you say completely but is compressor stall not also in fact a consequence of trying to get the compressor to operate at the left of the surge line. My understanding was that compressors stall when they go way beyond the surge line, so mild surge you can drive through (as shown on my log above, which was at WOT), but when severe enough (such as running without a dump valve and going WOT to closed throttle) the compressor stalls.

I think we're all talking about the same physical process but using slightly different terminology to explain it. You see I would say that one turbo spooling quicker than the other causing it to stall (as it isn't spinning fast enough to sustain the pressure ratio generated by the other turbo at its current airflow), is exactly because you drive the slower spooling turbo across its surge line? To me, stall is a consequence of surge.

Forgetting the semantics of it, do you think different preloads on the two turbo actuators could cause this? I would have thought it could as the tighter actuated turbo will spool a little quicker. I suppose it would really only occur if one had too little preload and the other normal, rather than one normal and the other above-normal preload. So where the "Differential Exhaust Gas Flow Theory" results in higher absolute turbine flow in one turbo resulting in quicker spool and stall, the "Differential Wastegate Preload Theory" results in equivalent absolute gas flow, but lower relative turbine flow in one turbo (due to wastegate bypass of exhaust gas). The net result is the same

I think these technical discussions are what make a good forum so lets keep having them

[ExScoobyT]

Its not down to the wastegate pre-load as the shuffle occurs at just around atmos pressure (in the manifold). Pressure at the compressor exducer will be only just above atmos, maybe 1-2PSI and the wastegates are still shut at this point......

[SIHethers]

ExScoobyT

I agree that the DEGT would cause it so balancing this will help, but I'm also trying to tease out other possible explanations, as I'm sure you'll agree that this may not be the only cause.

What I'm sure of is that just having AFMs does not cause this, but there has to be an underlying mechanical issue also. Undoubtedly the AFM reversions you get with compressor stall/surge will make it worse so switching to d-jetro, for example, will help mask the symptoms. Moving to bigger twins will probably help due to slower overall spool-up so reducing the likelihood of such an imbalance developing. Mapping tweaks to lower start duty and slow spool will also help.

[SIHethers]

Originally Posted by ExScoobyT

Its not down to the wastegate pre-load as the shuffle occurs at just around atmos pressure (in the manifold). Pressure at the compressor exducer will be only just above atmos, maybe 1-2PSI and the wastegates are still shut at this point......

Very true, one of the wastegates would have to be open a fraction at low boost for the DWPT to occur (which isn't common, but not unheard of).

What mapping tweaks specifically would you employ to control this?

[whoflungdung]

I must say that after pairing the afm's together, the shuffle was noticeably better
This was almost a year ago
Since then the car has laid in my (soon to be ex) friends paintshop!!!
Tony said that it would need mapping again, due to the pairing of the afm's
So until they get it back again, which should be soon (a month or so)
We wont know the outcome of my car
And I say this with meaning, as I believe each car can be different
My car shuffles from memory around 70mph, and its horrible
And not always will it pull through on full throttle
The joys of tuning

"The Count of Shuffle"

John

[SIHethers]

Originally Posted by whoflungdung

I must say that after pairing the afm's together, the shuffle was noticeably better

That's an interesting thought. I, luckily, am not plagued by the shuffles (yet) but with some GT-SS set to go on this may become a problem. In particular my AFMs do read differently, typically the rear AFM reads low on boost but high on the overrun. I'd sort of put this down to different inlet tract shapes affecting AFM flow distribution, particularly as I'd expect the rear three cylinders to flow more if anything. In addition I had assumed that the 2 AFM voltages were averaged by the ecu before applying fueling, seeing as they feed a common plenum, but I've heard murmurs that they may dictate fuelling to the front and rear 3 cylinders separately. Does anyone know this with certainty?

Is this the herald of impending shuffle when I fit my new quicker spooling turbos?

[ExScoobyT]

AFMs don`t cause the problem. The lead item is one compressor flowing marginally more than the other due to different turbine flows. This can be picked up on the AFM signal of course and depending on the mapping can make it worse once its started. Deleting the AFMs drops the pressure loss on the low pressure side perhaps making pressure ratios on each compressor more equal. You also dont see the small load changes at the MAP in the manifold so position on the ECU map does not dance around.

Mapping wise, its a case of making sure the fuel & ignition map are failry flat in this region so that small changes in load don`t result in changing AFR & timing (thus driving differential flow over the turbine). Also making sure you don`t go too lean to course partial burns that you may not feel as misfires but again drives different flows in the turbines.

HKS `fix` is the balance pipe accross the exhaust manifolds which aim to equalize exhaust pressure pre-turbine and hence promote equal flow.

Some cars may be worse than others due to different flows in the exhaust manifold. I flowed & matched the throttle bodies, head & exhaust manifold and this defineately improved the issue to the point that it rarely happens on my car.....

Editted to add that the airflows are averaged to calculate load. The MAFS will read differently and I also put this down to different pressure drops pre and post compressor......

[SIHethers]

Yes, that all makes good sense.

Cheers!

[Mark@Abbey M/S]

Its not down to the wastegate pre-load as the shuffle occurs at just around atmos pressure (in the manifold). Pressure at the compressor exducer will be only just above atmos, maybe 1-2PSI and the wastegates are still shut at this point......

agree on this

Moving to bigger twins will probably help due to slower overall spool-up so reducing the likelihood of such an imbalance developing. Mapping tweaks to lower start duty and slow spool will also help

In my opinon the bigger the turbo,s the worse the shuffles will be as the turbo,s need more exhaust gas to spin them , we have very little trouble with shuffles on GT-ss , but removing the AFM,s is the best way to go , you can hear the shuffles but no hassle with driveabilty.

All the theory stuff holds no relevance to me, we seen , tried and worked around a lot of problems, thats where the dyno and years of experience come into reason.

And if you want to get rid of the shuffles 100% fit a single thay arent laggy just need to be specced 100% correctly....

[whoflungdung]

Well after a "YEAR" stuck in my ex friends bodyshop, my car went back to Abbey for the re-map......
Abbey Motorsport

The re-map was done with the afm's paired
The car was mapped at 1.2 bar producing 393 at the hubs if I am right?
So then you add whatever theory you are working with on top 20 to 27%???
And the torque was 347lbs/ft
Not really bothered about the figures, its just a very quick car(for me)

The car is much more user friendly now at a sustained steady pace
It does still shuffle, but nowhere near as violently as it did

Two thumbs up for the mapping and Abbey's professional approach to helping me sort this out

[Steve]

Oh I could go into one here!!!! I think the bottom line is that it all depends on your tuner!!! I have had my car for 9 years now and have “gone thro” most of em !

AFM’s, no AFM’s, Bigger or smaller Turbo’s, Hard pipe kits, Bigger Intercooler, all excuses have been used ! The way I “beat” it was to tell my tuner in no uncertain terms that I didn’t want any Turbo shuffle on or off boost and as far as I am aware it can be “tuned” out with the correct hardware. Now running sweetly but, yes it all took time. Also, don’t go along the line of “this is what we do for all our customers” WE ARE NOT ALL THE SAME and use our cars for different purposes and we all drive differently! My car is now (as it should have been long ago) set up as a track car more than a road car, BUT I still want to be able to use it on the road comfortably. Again, speak to them, tell them what YOU want and pay accordingly!!!! As I say it has taken me (and my tuner I am now with) the pat 3 years to get the car the way I want it.

Good luck and open another bank account for the new loan!!!

[drive]

after i bought a pair of hks gtrs turbos for my gtr i went againts everyones advise and still proceded to fit them onto my car. mark at abbey told me not to fit them, and i sooooooooooooo wish i never had done. the car was very unplesent to drive, very noisy and i lasted about 500miles before i jus had to change them. i fitted a pair of garrett turbos and although it does still slightly shuffle its hardly noticable now.
i have lernt one important thing about modding cars and that is ALWAYS seek advise before you go and throw a load of money at your car

[anthonymcgrath]

mine does a bit of chuff chuff if I put my foot on the gas then ease off but usually only above 70mph really. If I come off gas (ie: gearchange) it just makes the usual bov sound. I'm just on stock tubs.

[sethrichmond]

Originally Posted by ExScoobyT

Its not down to the wastegate pre-load as the shuffle occurs at just around atmos pressure (in the manifold). Pressure at the compressor exducer will be only just above atmos, maybe 1-2PSI and the wastegates are still shut at this point......

my r33 is fully built 2.8 with new gt2860-10's.
just laid down 600whp at 16psi
gigantic cams, tomei 290degree with 11.(something) lift
aem standalone no MAF's

sounds like darth vader... i like it.
surges under part throttle boost. (still tuning)

one turbo has the oem wastegate actuator and one is a new garret. (had tech difficulties with the 2nd garret actuator.)
i'll change out the oem actuator this week. i expect it to help the part-throttle surge. if it cures the shuffles that would be interesting.


would connecting the 2 intake pipes (precompressor) help? it seems like it would balance the airflow?

[paul cawson]

I have managed to fix my shuffle it was quite bad but now the car does not do it at all. I have changed the induction system from Ms to Apexi and both MAFs. Also running a different MAP and injectors. I will put the old induction system back on to see if it starts again.