PPK Changes VR v8

[hsv08]

Got a guy throwing in some 3.7 diff gears in his vr club and needs the ppk changed to suit.
On 11b v103 xdf the code is written as ppr and standard being 40, If this where changed by the percent difference this would alter what the pcm see wouldnt it?
Im used to working with vt onwards pcms.

afaik you will still need a jaycar module between the dash and pcm

and i will need to change the checksum to AA right?

[Jayme]

in the VR auto, the value in the bin does not affect the output to the dash. you dont even need to change the value of the ppk in the bin at all.... if you do, you need to rescale all of the shift tables....... rememebr the speed sensor is at the output shaft of the gearbox, not at the wheel, so diff ratio swaps do not affect the shift tables.......

eg: (values not to scale) before diff swap the pcm might shift at 40km'h which is really 30 pulses per second on the VSS, which ends up being 4000 rpm at the engine.
swap diff and it still shifts at what it thinks is 40km/hr, which is still 30 pulses per second, which is still 4000 rpm. it may be showing the wrong speed in the log, but it will shift at the correct rpm.

long story short, all you need to do is fix the dash with a speed corrector.

[Holden202T]

BUT! .......

if your car is now accelerating faster it might hit the rev limiter before the gear applies! in which case you might need to change the shift points by a few km's!

[hsv08]

Awesome thanks Jayme and holden202t,
So where did changing the PPK become nessasary?
I was always under the assumption that in order to correct the shift points the PPK needed to be changed by the percentage amount of the change in final drive?

[hsv08]

Also he was originally going to go 4.11 but as I was sure the code didn't allow more then a 22% change from standard I told him 3.7 would be about as far as the code would allow. He can't find 3.7s so he is going to go back 4.11 after I told him that the PPK won't need changing.
If they rpm remains the same at the shift point obviously the speed will be lower at the change correct?
Physically the car will drive as it was before except the likely hood of smashing the limited on quick changes?
Just want to be certain before I tell him the 4.11 are go.

[Holden202T]

yep thats right, you'll be cruising along at 100km's and it will be like 70km's really and when you do get to 100kms it will feel like the motors screaming

also keep in mind if you are running a stock tune, you will hit the top speed limiter a fair bit earlier than the stock setting..... which is probably only going to be an issue for racing or similar!

as for the 3.7's, they are hard to find in borgie size compared to 4.11!

[hsv08]

Ah got ya. Thanks for that. Yea those 4.11s will be some super short gears on the auto I'd imagine.

[VL400]

You may have already found it, in the 11P zip under calculations is a spreadsheet with a VSS setup calculator. The driveline ratio can be as low as 0.0194.

And you are correct with the standard rollout that 3.7 ratio is as far as the code can handle.

Edit: Dont change the trans ratio for the reasons above, but you can adjust the engine code ratio to as close as you can get. Wont make a huge difference though.

[hsv08]

So guy has put in his 4.11s in and driven on them. As per above he says the shifts are pretty normal but he hasn't open her up yet as the weather here has been crap.
He has noted though that the car doesn't seem to be changing into 1st gear until stationary when in drive.
I know with the vt's that the shift tables look at both rpm and kmh and based its shifting via these tables.
Would I tgis still be the same with the VR? I'm thinking that one variable is falling short of one of downshift tables not allowing it to drop 2-1 until stationary?

[Holden202T]

more than likely, it will revving higher at any points, so probably don't drop down enough till its almost stopped.