Shift Points

I chose 52.5 mph over the stock 41 mph because it lets 3rd gear rev a little higher under slight/mid acceleration. This means you will accelerate more quickly with less throttle input (i.e., throttle response is improved), because you're letting the engine's revs pull more strongly in the lower gear.

OEM set the value lower for smoother shifts and better MPG.

Don't forget to change your WOT mph and WOT rpm settings. You need to figure out what RPM you wanna rev to, and then figure out what speed that is. Cam and #140 V-springs....I'm guessing 6400rpms?

Man, that's high. I cringed a little when mine broke 6k. I guess if your valve train is built for it... enjoy!

dont tell anyone, but i was doing some WOT scans with the 3.25" pulley. I set RPM limit for 6k for now and man does it pull up top. 6.4k is what zzp recommends with the mods.

I gotta get that wideband installed cause tuning without it is a bunch of back n forth guesstimation work. so far so good, tho, but i want to tune this thing to perfection.

I wish i could rename this thread shift points and pressure. But anyways

Please help me understand why so many transmission tunes turn the shift pressures down. How does this affect performance and longevity of the machine? Thank you   

A good tune shouldn't turn the shift pressures down, at or near WOT. The reason is clutches are less likely to slip under higher fluid pressures. Of course, you don't need 96% shifts going 25 mph with 8% throttle, nor would you want this - shifts would be jerky, and you may hear transmission whine from the pump. I like a blend from lower pressures with less throttle to max at WOT.

The risk is breaking hard parts, but that's why TM exists. I would much rather use full pressures with a little TM to soften things out than lower pressure with zero TM. Our hard parts are pretty robust unless you are making lots of torque, or running a crazy firm shift tune.

There are some areas in my shift table where I could not get the ultra-quick shifts at low throttle without jerkiness, so I lowered pressure to smooth things out. I did this only in the very low throttle % fields.

Here are my Shift Pressures....

2nd Base

5
5
5
5
6
8
12
19
22
24
27.5
30.8
35.2
39.59
44
47.3
49.5
51.7
56.59
58.91
61.22
63.53
65.83
68.14
70.45
80.05
82.59
85.13
87.66
96
96
96
96

3rd Base

4
4
4
4
4
6
11.5
16.75
19.91
23.05
27.41
29.59
32.91
36.2
39.5
42.8
45
47.2
51.81
54.13
56.44
58.75
61.06
59.72
72.27
75
80
85
96
96
96
96
96

4th Gear is bone stock cause who races with 4th gear? I tuned 4th once.....once

Thanks, Scott. I am going to check yours out later compared to mine.

yall with 1-2 and 2-3 0.01 shift times are crazy. I was running .05 and it felt terrible. I had .25 for 3-4 and it felt great. so i changed my 1-2 and 2-3 to be ~.25 and its so much better!

i am curious to see how shift pressure affects this too.

Definitely feeling a little more comfortable tweaking the trans tune. This is the first time i've messed with it since posting in this thread.

charlieRobinson wrote:

y'all with 1-2 and 2-3  0.01 shift times are crazy. I was running .05 and it felt terrible. I had .25 for 3-4 and it felt great. so i changed my 1-2 and 2-3 to be ~.25 and its so much better!

You have to remember one thing....a "skewed" MAF tune will adversely affect how the trans shifts as well. I'm not saying that yours is bad, cause I have no clue, I'm just sayin. I'm willing to bet, though, that your lower end of the MAF scale is way too high. This would cause "bang" shifts at low throttle conditions.
Shift Time really shouldn't affect how hard the trans shifts, just how fast. If the PCM thinks the trans needs more pressure because of the amount of air it thinks the engine is taking in at a certain TP%, it will bang into gear. This also might be what you were referring to in your above post about lowering pressures and what-not when raising HP.

My trans is nice and firm, no bangs. In fact, at low throttle, you can barely feel it shift, even with Shift Times at .05-.01.

believe it or not, the bottom end of my MAF values are nearly stock. the first handful of cells are stock and only go up like .0001 from there. My fuel trims are + or -2 at almost all times under normal throttle conditions right now.

I put a little more juice up top, tho.

Not bad for a narrowband noob tune, huh!?

But I did not know that. Thanks for telling me.  

I spend lots (most) of time driving in 4th gear, since my TCC lock-up is disabled. There's actually some good power accessible in 4th without the TCC. I don't race there, but it's nice to have the low and mid throttle response.

charlieRobinson wrote:

believe it or not, the bottom end of my MAF values are nearly stock. the first handful of cells are stock and only go up like .0001 from there. My fuel trims are + or -2 at almost all times under normal throttle conditions right now

I'm sure it is, but even a good tune on a stock 3800 lowers the lower end of the MAF table. I don't reach
3g/sec until 2125Hz. Stock is 4.4g/sec at that point.....

no way! did not know that.

Just GMs way of making sure we stay rich?

I guess. That sort of makes sense with the mush trans tune. If you ever noticed, at idle and cruise, STFT is always at least -2%. If you get that flattened out, you can raise line pressures and trans torque.

Not following the connection between fuel trims and shift behavior. I've never noticed any effect on shifts from adjusting fuel tables.

AA wrote:

Not following the connection between fuel trims and shift behavior. I've never noticed any effect on shifts from adjusting fuel tables.

The trans relies on the MAF readings to adjust trans torque and line pressures. If the MAF is skewed, it can cause mush and/or bang shifts. Have you ever had a bad MAF and the car slammed into gear? Maybe not so much on the older cars, but even 2000-up GM's will throw Traction and Stability lights for a bad MAF before it throws an SES light. It's because the trans is looking for the correct torque values, and the MAF is in the equation.

This is also why throwing a CAI on a car can cause the trans to shift harder.....it skews what the MAF thinks is incoming

Oh okay, guess I didn't notice that when the MAF was disconnected - must have been more focused on the rough idle. Makes sense though. Seems like your fuel trims would need to be way off before it became noticeable.

Unplugging the MAF won't affect it really. Well, it will, but not as bad as just a skewed MAF. When you unplug the MAF sensor, the PCM no longer expects to see readings from it, and runs off of base calibrations (VE). It's when the PCM sees readings from the MAF that aren't true that really screws it up. When this happens, it's still seeing TP, MAP, O2, etc, but the readings reported by the MAF are wrong, and throw off all the tables. Basically, the PCM believes the MAF more than any other sensor, which is why the engine can run like such garbage if it's wrong....

Interesting. I was going to say. During VE tuning with stock transmission tune, i didnt notice any irregular shifts or jerkiness.

Good info!
Thank you

Abaddon wrote:

charlieRobinson wrote:

believe it or not, the bottom end of my MAF values are nearly stock. the first handful of cells are stock and only go up like .0001 from there. My fuel trims are + or -2 at almost all times under normal throttle conditions right now

I'm sure it is, but even a good tune on a stock 3800 lowers the lower end of the MAF table. I don't reach
3g/sec until 2125Hz. Stock is 4.4g/sec at that point.....

I show stock 2125Hz is factory set for .521lbs/Min anyone else with HPT show this for MAF airflow vs output frequency?

I tested out of math in college but my programming and high school experiences proved to me that I suck at math. so, this might not be right..
4.4g/sec = 264g/min
264g/min = .582lb/min

your PCM thinks it's sucking in .582lbs/min at 2125Hz, I do believe. My stock 99 is tuned for .521lbs/min or 3.94g/sec at 2125Hz.


 

Well, you've adjusted your tables though, right?

2125Hz is pretty much idle. There's no reason to be using that much juice a idle. You're just wasting fuel. Wait until you see the N* MAF table....I have it if/when you need it btw

Abaddon wrote:

Well, you've adjusted your tables though, right?

2125Hz is pretty much idle. There's no reason to be using that much juice a idle. You're just wasting fuel. Wait until you see the N* MAF table....I have it if/when you need it btw

That is the stock value for my 99 PCM. So youre saying I should turn it down? By how much?

Yeah, man... i gotta get that stuff together.

i gotta get the pulley off the snout so i can polish the snout properly. then get gen V and LIM gaskets then i should be good to rock n roll.

charlieRobinson wrote:

That is the stock value for my 99 PCM. So youre saying I should turn it down? By how much?

At this point, I'd just wait until you get the N* hooked up....