the drivetrain question no one could answer:-)

[ravenp]

Okay, trying to get my head around this stuff. Any help would be appreciated.

Please fill in the blanks..

1. A4 w/3.08's ... at WOT shifts around 5500rpm.

2. Swap in 3.42's, leave PCM alone... at WOT car shifts at a _______ rpm(where blank = lower or higher).

3. Swap in a pcm from a y87 car, at WOT shifts around 5500rpm's.
_________________________________________

Same scenario, but on a dyno.

1. A4 with 3.08's makes max torque at 3900 rpm.

2. Swap in 3.42's, leave pcm alone... torque curve moves _____ (where blank equals up, down or not at all), and max torque rpm moves _____ (where blank equals up, down or not at all).

3. Swap in pcm from y87 car, torque curve moves _____ (where blank equals up, down or not at all), and max torque rpm moves _____ (where blank equals up, down or not at all).
_____________________________________________

What is the optimal shift point relative to your max torque rpm for WOT racing? (working on the assumption that our cars are tuned for fuel economy.

Thanks

[ November 21, 2003: Message edited by: ravenp ]</p>

[ravenp]

anyone? [img]smile.gif[/img]

[ravenp]

hello? no one even with an opinion?
do i need to add some drama to my post? soem controversy? pi$$ing match with a moderator or something like that?? :D

[ravenp]

I dare someone to answer my question [img]smile.gif[/img] [img]graemlins/crybaby.gif[/img]

[John_D.]

<blockquote>quote:</font><hr>Originally posted by ravenp:
1. A4 w/3.08's ... at WOT shifts around 5500rpm.

2. Swap in 3.42's, leave PCM alone... at WOT car shifts at a _______ rpm.

_________________________________________

Same scenario, but on a dyno.

1. A4 with 3.08's makes max torque at 3900 rpm.

2. Swap in 3.42's, leave pcm alone... torque curve moves _____ (where blank equals up, down or not at all), and max torque rpm moves _____ (where blank equals up, down or not at all).

3. Swap in pcm from y87 car, torque curve moves _____ (where blank equals up, down or not at all), and max torque rpm moves _____ (where blank equals up, down or not at all).
_____________________________________________

What is the optimal shift point relative to your max torque rpm for WOT racing?<hr></blockquote>

All good questions... I was waiting for somebody else to post... But since nobody is, I'll take a shot at it. Maybe that will get the ball rolling.


For your first question - shift points - a lot of people say the car shifts at a lower rpm, because the pcm shifts based on vehicle speed, not rpm. At first this makes sense, because now the pcm thinks the car is going faster than it really is... But... If the pcm is reading the vehicle speed from the transmission, or even from a 3-channel abs sensor -- that is forward of the gear change -- so the rpms of the tailshaft/driveshaft have not changed in relation to the rpms of the engine. So it seems to me the tranny would shift at the same engine rpms as before.

Question 2, about the torque curve. I believe the torque curve would still fall at the same place. The different gearing is going to provide more leverage to the wheels, but the upramp/downramp of the curve will still happen at the same rpms, and the peak would still be at the same rpms. If the dyno did not take the gear ratio into account, then the whole line moves up on the scale, but with the same curvature. I'm pretty sure they usually factor your gear ratio into the dyno parameters though. I don't think a pcm change would affect the torque numbers in any case.

Question 3 - about optimal shift point.... Imagine a dyno graph with a vertical line drawn down from the shift point rpm. And find the point where the rpms drop to after a shift. Pull a vertical line down from there too. The most area under the curve, would be the ideal. So if you shift late, the area is small, because you didn't stay centered under the peak. Same if you shift early. The best point would roughly center the rpm range under the peak... Most area under the curve, depending on the shape of the upramp and downramp.

(sometimes I can't resist a dare...) :D

[ November 21, 2003: Message edited by: John_D. ]</p>

[ravenp]

Thanks for answering John.

Regarding the shift points though... i could swear i've read people changing gears but not reprogramming/swapping in a new pcm and having messed up shift points costing them good ET's.

Am i mistaken?

[cb1101]

My shift points are the same...i never reprogrammed the computer but my 1-2 shift is around 5500. The only thing that changed that I noticed was the mph..it was off by a few mph at 60..I think some people say like it is a 10% difference?? not sure

[ravenp]

Okay, so here's another question... if the pcm controls the shift points, and you don't change the pcm(or reprogram it), then visually it'll still shift at the same spot right? ... but the question is, are the rpm's now in sync with the tach or are they off too...?

They should be off right?

[HAZ-Matt]

<blockquote>quote:</font><hr>Originally posted by ravenp:
Thanks for answering John.

Regarding the shift points though... i could swear i've read people changing gears but not reprogramming/swapping in a new pcm and having messed up shift points costing them good ET's.

Am i mistaken?<hr></blockquote>

That is in fact what several people have claimed. If there is a difference that is not due to the drivers relearning how to launch the car, it might be that the 3.08 cars are programmed to shift at a lower rpm than the 3.42 cars. So even though the car is shifting at the same speed that the PCM is reading after the gear swap, it is still at a different spot than it would be using the 3.42 gear program.

This is speculation on my part. I'm just trying to reconcile the conflicting data that we have. We know that the PCM shifts by mph reading, not rpm reading... but we also know that the mph reading is generated by measuring the rpm of the tailshaft/driveshaft... that should lead us to believe that it is shifting at the same engine speed as before... but we have the reports that the car is not as fast until it is programmed as a 3.42 equiped car.

Possibilities:
1. Perception of gear swappers is wrong.
2. Shift points are not at the same engine speed for 3.08/3.42 cars.
3. Our understanding of how the PCM measures vehicle speed and shifts is flawed.

EDIT: I want to knwo where people have gotten their shift point data from. I think a lot of people that have quoted shift point data have gotten it from looking at their tach. I do not think we have seen any reliable data in that regard. If I am mistaken, please point me to something credible regarding the location of stock shift points.

[ November 24, 2003: Message edited by: HAZ-Matt ]</p>

[ravenp]

Well, I never autotapped my car before the swap, but i did after....with a y87 pcm and according to the pcm, my car shifted at 5500... which was pretty close to the tac.

[awesomeame]

is there a way in autotap enhanced to tell at what rpm the gear change takes place? i've never looked since i've got an m5...

--matt

[95Batmobile]

<blockquote>quote:</font><hr>Originally posted by cb1101:
My shift points are the same...i never reprogrammed the computer but my 1-2 shift is around 5500. The only thing that changed that I noticed was the mph..it was off by a few mph at 60..I think some people say like it is a 10% difference?? not sure<hr></blockquote>

3.23 to 3.73 and my shifts are the same too.
if my speedo reads 70mph right now I'm really going 61.
I don't know if they will be the same after I fix my speedometer though, I'll let you know soon enough.

[HAZ-Matt]

<blockquote>quote:</font><hr>Originally posted by ravenp:
Well, I never autotapped my car before the swap, but i did after....with a y87 pcm and according to the pcm, my car shifted at 5500... which was pretty close to the tac.<hr></blockquote>

1-2 or 2-3, or both?

[ravenp]

I'll check the atap logs when I get home, but I think we shut it down before i hit 3rd, so definitely the 1-2, i'll confirm the 2-3.

[John_D.]

I'm usually in the mid 5800's before my rpms drop after a shift change, in my 3.42/y87 car.