Shift table adjustment???

[C2500]

Looking to do some modifications to the shift table on my 94 c2500 with a 4l60e trans.
I want to get the mph up from 1st to 2nd and 2nd to 3rd. Right now it shifts into 2nd at 15mph if my foot is in it or not and into 3rd at 28 or so...
Here is one of the tables I found but I have no idea what to change and how to do it so I need some
help and plain English please..
Thanks12838

[dave w]

If you post your gear ratio and tire size I will post a "tuned" shift table.

dave w

[Kitch]

Hi, I saw your PM and I've just had to remind myself what I'd previously done.
I like to plot my existing curve on a graph so I can visually see whats happening and when. I mark on the graph my current TCC engage, release and shift points (it's easier to graph just one gear at a time otherwise the graph can get confusing).
I use the info from the TCC/Engage and release thresholds and the upshift/downshift MPH vs TPS tables, then from a TunerPro log I manually plot my actual throttle position and MPH onto the graph, generally when I log I try and drive in the MPH and TP area I want to change so I can get some data to plot on the graph. Once I have that I look at moving the shift point or TCC engage points to suit and it can be a little trial and error.
In my Yukon I had my TCC lock in third at 30MPH when lightly cruising but as soon as I had any more than light acceleration the TCC would release, this allowed the engine to pick up a few revs on light acceleration and made it feel more responsive to me.
I also played with the shift point under load when driving uphill and once again I just had it down shift sooner under moderate TP increase and this really woke the truck up.
That worked for me but it may depend on how you use your vehicle as that might not be ideal in other situations.
I do remember thinking I got more real world noticeable drivability improvements from tuning the shift and TCC points than I did from tuning the engine.
Be careful with big shift point changes, you don't want to downshift to 1st at 60MPH or anything like that.

I've just changed from a 46mm TBI unit back to an ultimate TBI modded unit and I've just had to look at tweaking my shifts points because of the slight increase TP% with the smaller stock TBI throttle blades.

[dktool]

Looking to do some modifications to the shift table on my 94 c2500 with a 4l60e trans.
I want to get the mph up from 1st to 2nd and 2nd to 3rd. Right now it shifts into 2nd at 15mph if my foot is in it or not and into 3rd at 28 or so...
Here is one of the tables I found but I have no idea what to change and how to do it so I need some
help and plain English please..
Thanks12838

That table is about as "plain english" as it gets, as you're driving (or do a log) look at the TPS % and the speed it shifts, my experience is that it will correspond very closely.

At full throttle your 1st to 2nd shift speed should be right at 30 mph, if your hitting 2nd at 18 mph regardless of throttle position you have some bigger issues.

[Kitch]

Seeing how I'm currently working on adjusting my TCC lockup and shift points on my van today, here's the changes I've made since I posted the previous graph.

I made the change because I wanted the TCC to release in 3rd gear as I accelerated up and onramp, the release of the TCC feels like mildly shifting down a gear and it just gets the engine RPMing a bit sooner, than if it was bogged down by the TCC being engaged.
Hopefully you can see from the graph how this can work.

You mightn't want to play with TCC engage/release point much but the same principles can apply to shift points.

Even if Dave sends you a revised shift table it can still be interesting to look at them on a graph and overlay your actual throttle possition % vs MPH over it.

[C2500]

Thanks guys, Dave is going to send me a tuned shift table.
Kitch did you make the graph?? I like your idea about the release of lock up.

[dave w]

Sample "Tuned" Normal Up Shift / Down Shift and Normal TCC Lock / TCC Unlock for tire size 265/75R/16 (31.6") with 3.42 gears. (shift firmness setting 2 / engine idle RPM = 850 / stall = 1500 RPM / Minimum RPM TCC Lock = 1500 RPM)

SAMPLE ONLY, this is not the "Tuned Shifting" sent to C2500.

"Tuned" = Excel Spreadsheet Calculated.

dave w

[lionelhutz]

Attached is an example of the type of shift curves I use.

You want the shift speed to be lower than the speed the truck would reach if you manually held that gear and throttle position.

If throttle position doesn't affect the shift speed then you likely have bigger problems.

[Fast355]

I use BlueCats software to tune the transmission.

[dave w]

I use BlueCats software to tune the transmission. attached ???????

dave w

[Kitch]

Yep, I just made the base graph up on my iMac using a program called "Numbers" but thats because I'm hopeless with Excel.
Dave's spreadsheet calculated settings sound cool and everyones suggestions will be better than the stock ones.
If you want to see visually how it works plotting it out on a graph can help you understand it better. Then if you need to you can tweak it a little more to suit your vehicle and driving style.

[lionelhutz]

BlueCats seems to create OK upshift curves, but I was not impressed with the downshift curves. After an upshift, you have to use a lot of throttle to get a downshift again.

I do use a similar curve shape, but I make mine even more aggressive ramping up to the maximum shift speed even quicker.

I didn't do much with the 3-4 or 4-3 curves in the example I posted, but they can be made the same shape as the other curves.

I first figured out that curve shape by driving with 1st and 2nd manually selected and noting the speed reached at 12.5%, 25%, 37% and 43% throttle. I dropped a little speed so it would actually shift and put the values into the curves. Once I fit the rest of the curve, that shape was pretty much what came out. I put the downshift curves just under the upshift curves. The closer they get, the quicker it will start kicking down when getting into the throttle.

[Fast355]

BlueCats seems to create OK upshift curves, but I was not impressed with the downshift curves. After an upshift, you have to use a lot of throttle to get a downshift again.

I do use a similar curve shape, but I make mine even more aggressive ramping up to the maximum shift speed even quicker.

I didn't do much with the 3-4 or 4-3 curves in the example I posted, but they can be made the same shape as the other curves.

I first figured out that curve shape by driving with 1st and 2nd manually selected and noting the speed reached at 12.5%, 25%, 37% and 43% throttle. I dropped a little speed so it would actually shift and put the values into the curves. Once I fit the rest of the curve, that shape was pretty much what came out. I put the downshift curves just under the upshift curves. The closer they get, the quicker it will start kicking down when getting into the throttle.

That is the cool thing with Blucats. You can play with all the settings and make the upshifts and downshift more or less aggressive and space them closer or farther apart.

[lionelhutz]

You can't change the overall shape of the curves. Upshifts are always S curves and downshifts are always exponential curves. So, there is never a good match between the upshift and corresponding downshift curves.

[Fast355]

You can't change the overall shape of the curves. Upshifts are always S curves and downshifts are always exponential curves. So, there is never a good match between the upshift and corresponding downshift curves.

I disagree, you can definitely change the shape of the curves. There are adjustments for up and downshift, as well as for the throttle body size.

[lionelhutz]

I disagree, you can definitely change the shape of the curves. There are adjustments for up and downshift, as well as for the throttle body size.


Whatever. I didn't say you can't change the curves, i said you can't change the overall shape of the curves. Do you do understand what a general curve shape like exponential or s-shaped is?

[Fast355]

Whatever. I didn't say you can't change the curves, i said you can't change the overall shape of the curves. Do you do understand what a general curve shape like exponential or s-shaped is?

I understand the differences and have an Excel file I setup to graph the shift points so you can easily see the changes. I have had the Excel file since long before I found Blucats. I have been fixing GMs shift table disasters for 14 years. Never did like GMs sluggish 2-1 downshift tables on anything. My point is yes you can change the shape of the curves both up and down by playing with the blue cats software settings. I have made Blucats downshifts so aggressive it feels like you put the weight of a feather on the pedal at cruising speed and it double downshifts.

[Fast355]

Here is proof of what I am saying. Graphed the multipliers used in Bluecats to adjust the shifting. You just have to understand what the different settings do to the shifting. The lower the factor, the less S-shape, the higher the factor the more. Raise the Down to take away that linear curve shape in the center of the downshift. If you graph any pair of upshift/downshift for a given setup you will see they are shaped exactly like the graph of multipliers.

[Fast355]

Here is yet another result of playing with the settings. Basically it is straight line linear shift mapping more throttle, more speed in a straight line. All depends on how you setup it up. Using the graphing function in Excel can be very helpful in other ways as well.

[lionelhutz]

LOL, you have a rather odd definition of a feathers extra press on the throttle. I tried LOTS of combinations and the downshift curves were always at least 20% apart meaning at least 20% more throttle past the 1st downshift is required to get to the 2nd downshift. But then, anything that kicks down before WOT is typically better than GM. At any rate, it would make no sense to have the downshift curves right on top of each other so close that 2 downshifts occur with almost the same extra pedal movement.

I did try lots of settings and found that the factor around 2-2.5 and the up around 8-10 started making what I consider decent performance upshift curves. But, those values caused the downshift curves to be spread quite far away requiring a LOT more throttle to get a downshift again once the upshift occurred. So, for me it'd work fine for the upshift curves, but I'd re-do the 30% to 100% part of the downshift curves.

I think you could put in some factors to make a granny upshifting table where the downshifts would happen aggressively with little extra throttle. But what is the point when the upshift table sucks?

[lionelhutz]

Proof? Well if you want to make stupid curve shapes then sure....

[Fast355]

Proof? Well if you want to make stupid curve shapes then sure....

The curves I made are extreme cases just to show what the software can do. That being said you can easily find a happy medium. I find lower factors, negative offset and higher upshift and downshift numbers create a very nice performance oriented upshift and downshift mapping. Around 1.10 factor, -15 offset, +5 upshift and +10 downshift will be fairly aggressive. In fact it is what I use for my Haul A$$ tune in the Express van. Going off the numbers from my old 3.73 gears at 70 mph my cruising TPS was about 18%. My shift tables were setup so that it shifts into OD at 64 mph @ 19% TPS and at 70 mph @ 25% TPS. Holding 70 mph, downshift to 3rd is 35% TPS, downshift to 2nd is 70%. At 60 mph the downshifts are spaced tighter. I cruise at 60 at about 12% TPS. At 12% TPS I go into OD at 56 mph. At 60 mph the 4-3 downshift is 25% TPS and the 3-2 downshift is 56%. The old 350 makes enough torque in my setup I try my best to keep it out of 2nd unless I just want to get around someone. My normal acceleration is around 1/3 throttle which brings the MAP to about 95 KPA. At 35% throttle 1-2 shift was 33 mph, 2-3 shift 55 mph, 3-4 80 mph. Under heavier throttle where I enter PE at 60% throttle, 1-2 is 49 mph, 2-3 is 77 mph, 3-4 is 115 mph. Point is you can play with the settings and get it to shift just about anyway you want it to much more easily that trying to take a stab at it by hand. It also has helpful limits that prevent it from stack shifting or overlapping TCC settings.

[lionelhutz]

I found negative offsets make a poor upshift curve which doesn't match what the car wants.

[Fast355]

I found negative offsets make a poor upshift curve which doesn't match what the car wants.

I din't really mess with cars but my Express van, my Tahoe, my brother suburban, my buddies 97 6.0L swapped C1500 and my coworkers 99 K1500 with a 5.3 swap all like it.