A4 WOT Shifting Issue

[MSCLCAR]

I posted this over on LS1tech, but I haven't gotten a response yet. So either I'm not asking the right questions, or all the smart guys aren't on that board today....

I finally got around to logging a WOT run after my Yank SS3200 install. I only picked up 2/10ths at the track, ALL in the 60', and I lost ~ 2mph. So I knew something was amiss. Anyway, what I found was this:

I have the car set to shift @ 6700, DFCO @ 6800, but the car never hits that target. It shifted at 6500 1-2, and at 6200 2-3. The 1-2 shift hit the MPH limit, so that most likely explains that (more later) but the 2-3 was 6mph under the shift point, so that one really puzzles me.

At 5600rpm in 1st, the MAF is pulling 35.2 lb & the dyn cyl air is .7 g/cyl. Then both start to fall off up to 6450rpm where everything flattens out until it hits 37mph & shifts (at 6500). At that point the MAF is around 38lb but the air dips down to ~.65 g/cyl. In 2nd when it shifts at 6200rpm, the MAF is at 36.4, the cyl air is .68, and the mph is 66.

I wound it out in 3rd & again about 6500 everything started to fall off.

EVERY table is set to make it shift @ 6700rpm, 37mph 1-2 (raising that) & 72mph 2-3. So waht gives? All I can think is that maybe I need to do the SD tuning & re-scale my MAF tables accordingly. (actually, a friend - Racehead - thought that might be my problem). I have never messed with that stuff.

Any ideas? ??? I need some help figuring this out if I'm going to run an 11 sec cam-only 1/4 mile. (I'm at 12.29 now)

Thanks!
Mark

[MNR-0]

Set your shift points according to the cams power band. If it falls over after 6400RPM you want to hold it as long as the power stays above what the next gear shift would extend down to. The stock cam falls over at 6000RPM so theresd not much point in holding it with a stock converter much past 6200RPM. in 1st, the tractive effort far outwieghs any power losses up till 6500RPM or so, so I woudl shift there (on a stocker). Without specs. on your cam it is difficult to speculate where YOU should be shifting.

[MSCLCAR]

Good response, except that wasn't the answer I needed. I have dynoed my car a lot so I know where my power band is with my setup. It peaks around 6300 & stays flat out to 6700. (I have a Hot Cam, 1.8 rockers, an LSX intake, ported TB, PPC coated 1 3/4" headers, etc)

What I need to know is why would my car NOT shift where all the tables tell it to?

Is there some hidden secret shift table that I am unaware of? I set all the WOT shift vs rpm & mph tables. I bumped the rev limiter 100 rpm above the shift points. What am I missing?

Is the PCM reading some intake air volumn parameter & using that in some algorythm to adjust the shift points? Or some other reading?

Something is going on behind the scenes here that I am not looking at. What could possibly make the tranny shift at a point OTHER than what the shift tables says?

[MNR-0]

OK. Tell me your tyre size, wheel diameter, diff ratio and tranny revs per mile.

[MSCLCAR]

OK. Tell me your tyre size, wheel diameter, diff ratio and tranny revs per mile.

I run 315/35/17 Nittos with 4.11s in my 9". All of that is entered properly too.

But tranny revs per mile? I don't think I've ever bothered to work that out. I believe the tires have a circumf of about 81".....and there are 63,360" in a mile....so that's 782 revolutions per mile for the tires......in which gear?

[MNR-0]

I run 315/35/17 Nittos with 4.11s in my 9". All of that is entered properly too.

But tranny revs per mile? I don't think I've ever bothered to work that out. I believe the tires have a circumf of about 81".....and there are 63,360" in a mile....so that's 782 revolutions per mile for the tires......in which gear?

Gear independant. The tranny revs per mile is a common fark-up with workshops and GM. Check in the Speedometer section.

This is what it should read:

Tyre size
25.08

Gear Ratio
4.11

VSS Pulses/Mile
132192.166560838

VSS Pulses/Rev
40.0000

VSS Output pulses/Mile
10020

Trans Revs/Mile
3230.51770074874
(25.66)



What does yours say?

[MSCLCAR]

Hey, THANKS! I never heard of this problem before. My speedo tables were WAY off. The only ones right were the ones I entered....gear ratio & tire size. The VSS Pules/Mile & Trans Rev/ Mile were off quite a bit, and the VSS Output Pulses/Mile wasn't even close. I'll go see what that does. I may owe you a beer!

[MSCLCAR]

Or not. those numbers were not even close to what should be in there. My speedo read double what it should. Thanks for trying. You did get me looking in the right area (I think).

I went out & measured the Nittos. Turns out they are 1/4" taller than my old GoodYear GSCs were. And the custom Predator tune had entered 4.10 gears (like a 10 or 12 bolt would be), where a 9" is actually 4.11. So I changed all that, and my numbers moved by about 5-10%. We'll see if that is what was causing my problem. I'm thinking it was.

[MNR-0]

Those tranny settings work for Holdens. But I heard from Chris recently that for US cars the calcs. could well be different. It depends on how the pulses are calculated and as I understand it GM employs 3 different techniques across the range of all their cars. Yours might be one fo those hard to guess ones and in that case you may well be on your own. Go with the stock speedo cal. and rescale from there. Just check the pulses make sense - it all revolves around the transmission pulses/mile.

Im sorry those calcs. were wrong for your car. Perhaps if you tell me what car you have, make, model and year and I can check a stock BIN.

Good luck.

[MSCLCAR]

Thanks for your help. Like I said, I think it pointed me in the right direction. Since I THOUGHT all that stuff was correct. And I have a 2000 WS6 Trans Am.

[MNR-0]

Luckily I found a stock 2000 WS6 from my VERY limited BIN library. After rescaling for your tyre size and diff ratio, this is what it comes out to. Note the VSS pulses are different. This would be one of the differences between your Pontiacs and our Holdens. Plug it in and give it a go. Can't hurt - that is, if its not already fixed.

Tyre size
25.08

Gear Ratio
4.11

VSS Pulses/Mile
132210.820374183

VSS Pulses/Rev
40.0000

VSS Output pulses/Mile
4000

Trans Revs/Mile
3305.384253
(25.08)

[MSCLCAR]

Yeah, I agree, the main dif is the VSS Pulses/Mile. Mine is/was set at 4000. And as I said I went out & measured the tire height & plugged that in & it helped, but it still wasn't right. So I started messing with other things. What seems to have worked was setting the rpm shift points to 7000. Scary! Now the car shifts at 6800 1-2 & 6600+ 2-3. (so I dialed 1-2 down to 6900)

But, what this probably means is that one value or another in the speedo table is incorrect. (getting paranoid, he thinks to himself, ya know, you never actually checked those gears to verify they were 4.11s, you just bought & slapped em in....) More likely it is one of the other values. I'll go look at a couple stock tables & jimmyblues that I have on my laptop at home to see what theirs say.

Thanks again! Oh, and could ya learn how to spell TIRE, mate!? ;D