ArmyVette

Check this out! This is my 3-4 shift speed line from my current PCM reading. Oh, 2004 Vette Couple with the A4 tranny.

%TPS 0 6 12 18 25 31 37 43 50 56 62 68 75 81 87 93 100
3-4: 22 22 26 32 40 46 52 80 203 203 203 203 203 203 203 203 203

Sorry if the columns aren't straight.

What I believe this chart indicates is: at 43% throttle and 80 mph, the car will shift from 3rd to 4th gear. But at 50% throttle and above, the car won't shift into 4th gear until 203 mph!! Of course, the car doesn't go that fast! (Top speed is 172 mph).

If I read this correctly, at WOT, this car won't shift into 4th gear.

Am I reading this chart correctly?? Does this chart make sense???

Any idea what the correct MPH settings should be at 50+ % TPS?

ataylors

iTrader: (2)

sounds right, I think you will do the 172 mph before 4th gear, also the overdrive clutch pack cannot handle WOT its designed to conserve fuel..

jimmyblue

iTrader: (11)

That looks heinous.

You can try out the shift & TCC tables I have in here,
though you'd have to make the 3.23 -> 3.42 correction?
Also my torque management scheme is a little bit unusual
and you probably want to leave that alone or figure out
what 'Vettes like, what with electronic throttle being in
there.

http://home.cfl.rr.com/jimmyblue/PCM_Trans_20040823.xls

ArmyVette

Most people I've talked to have their 2-3 WOT shift (100% TPS) set at around 85 or so. Not sure you can get to 172 in 3rd gear because of the redline. The tranny MUST shift into 4th to attain that speed. Also, many Vette owners doing high speed runs talk about the 3-4 shift occurring at around 130 MPH.

horist

sounds right... GM protecting the transmission... WOT 3-4 shifts are bad... trannies don't like them very much... so looks like GM is taking it 1 step further and just not allowing 4th gear at all during heavy acceleration...

I've modified my shift tables so that the car won't go into 4th gear unless i'm at >55mph (won't lock the converter in any gear other than 4th also) and will never go into 4th at >80% throttle ...

ArmyVette

I never thought about the potential tranny abuse at WOT 3-4 shifts. The higher MPH settings at >80% throttle is probably a good idea. Still have to address the 50% - 80% WOT speeds though.

BTW, JimmyBlue, I copied you tables to spreadsheets. Looks really good. I noticed that you've got the hot, performance, and cruise charts populated. Do you really use those values or is your SS just using the normal chart's values? Also, what's the top speed on your SS?

jimmyblue

iTrader: (11)

I populated the tables earlier but the Performance
isn't active; at one time I had hoper to find a way
to implement the "performance" switch but that
seems to be a no-go deal as it involves the BCM
telling the PCM to go do it and the F-body BCM
looks to have no such connection or intent.

I haven't had the road or the ***** to see what
top speed is, yet.

One thing I noticed is that the 3-4 shift is -not-
torque-managed from the factory. I felt this was
kind of dumb. So I put the same TM on it as the
others. Though I have yet to hit the 3-4 shift
under full power as that would be 125+ MPH.

Seems to me if you torque-managed the shift that
would be a nicer protection than balking it and
making you lift throttle. Though that is going to
protect it for sure.

ArmyVette

Though I have yet to hit the 3-4 shift under full power as that would be 125+ MPH.

OK, that's pretty close to what I'm thinking the 3-4 WOT shift point would be. Then I can just make some incremental adjustments from there.

I'll create a chart sometime later today and post it here and in Corvette Forum's Scan & Tune forum and see what comments I get on it.

Thanks, gang!