Transmission Tuning Tutorial - Page 3 - CamaroZ28.Com Message Board


Computer Diagnostics and Tuning Technical discussion on diagnostics and programming of the F-body computers

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Old 02-28-2007, 11:36 AM   #31  
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A word of caution about line pressure and shift kits.

Chevy High Performance published a tech article (http://www.chevyhiperformance.com/te...ertrain_module) about custom PCM tuning and they consulted with the owner of PCMFORLESS.COM on the subject. The article wrote that increasing line pressure on transmissions with shift kits and/or other modifications that increased the line pressure mechanically can result in blown seals and other broken transmission internals due to excessive line pressure.

At least one custom transmission builder's warranty policy stated the warranty would be void if the PCM's line pressure tables were not stock and there was a component failure.

Of course, the only expertise I have in the 4L60E is breaking them with my heavy right foot. Lol.
Thanks for the word of caution. I am going to keep mine stock.
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Old 02-28-2007, 11:40 AM   #32  
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Looks like I am going to just stay with my B&M shift kit for now. I did a search for shift kits and people who have used B&M like them and people who use Transgo like them. They like them each so much there willing to argue over it. LOL
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Old 02-28-2007, 12:03 PM   #33  
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Filling in the rest is best accomplished by starting with a factory table and tweaking it by driving the car. I actually started from the performance shift table from a F-body, copied it over to the normal shift table and worked from that. The performance shift profile was more like what I wanted.

Of course, you're running a non-stock gear ratio. You will need to scale the stock values appropriately. In the past, I started by figuring out how much to scale by dividing the old ratio by the new ratio. For example, which i upgraded from factory 3.08 gears in my Impala to 3.73: 3.08 / 3.73 = 0.82573726541554959785522788203753. OK, we don't need THAT much precision, let's trim it down to .826.

Now, if the first line in your original shift table is:

11 19 29 11 11 27

...you would multiple each value by 0.826, which, when rounded off, gives you:

9 16 24 9 9 22

Do this for every value in the table. You can easily do this with Tunercat by selecting the whole table, right clicking, select 'Scale', then enter .826.

No guarantees this will get you exactly what you want, but its a great place to start. Drive and tune, drive and tune. I think I went through about 15 program iterations to dial in my Impala transmission *exactly* the way I wanted it.

I'd like to hear from other experts on this, but I am not sure increasing the max line pressure to 120 psi actually does anything. I'm going to start a new thread about this though.
Is there any way I could get a copy of that f-body performance table you have?
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Old 02-28-2007, 12:13 PM   #34  
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Check out my write-up on the performance mode switch mod for 94-95 LT1s under the Technical Info section at http://www.trifectaperformance.com. It has a copy of both the normal and performance mode shift tables for a 1995 Pontiac Trans Am. Looks like it was from a car with a 2.73 ratio differential.
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Old 02-28-2007, 01:08 PM   #35  
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Check out my write-up on the performance mode switch mod for 94-95 LT1s under the Technical Info section at http://www.trifectaperformance.com. It has a copy of both the normal and performance mode shift tables for a 1995 Pontiac Trans Am. Looks like it was from a car with a 2.73 ratio differential.
Thanks, there is alot of info on that page. I have alot of reading to do.
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Old 03-01-2007, 12:43 PM   #36  
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Line Pressure Offset vs. TPS% vs Gear (Normal/Perf/Manual)
This gets very complicated from here. I was checking some of mine and alot of them max out. Does your PCM always use this offset or does something trigger the offset? And if it always uses it why can't you just zero all of these that way the PCM will just use what you have set in the max line pressure 0-64MPH?
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Old 03-01-2007, 12:49 PM   #37  
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The base pressure tables are gear agnostic. If the transmission needs a pressure adjustment depending on what gear it was in (which apparently the factory thought it did), there'd need to be a table like this, to be used in conjunction with the base pressure table.
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Old 03-01-2007, 11:03 PM   #38  
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So how should I go about changing this table to work with the shift points that I have now? Could I do it the same way I did the shift tables?
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Old 03-01-2007, 11:08 PM   #39  
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Are you referring to the base pressure table or the line pressure offset table? I'll assume the former since that table is related to the vehicle speed.

I don't have a good answer for that one. I might suggest hunting around for two calibrations from the same vehicle that had different gear ratios from the factory and see what the factory did differently.
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Old 03-02-2007, 09:14 AM   #40  
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Are you referring to the base pressure table or the line pressure offset table? I'll assume the former since that table is related to the vehicle speed.

I don't have a good answer for that one. I might suggest hunting around for two calibrations from the same vehicle that had different gear ratios from the factory and see what the factory did differently.
I am referring to the Line Pressure Offset vs. TPS% vs Gear (Normal/Perf/Manual). I am following the tutorial above. I went through it step by step changing everything up to this table. Should I just leave the pressure table alone? It seems that the pressure spots would change being I changed where the shift points are. Also I was looking at my stock tune and one I got from PCM's for less and the one from PCM's for less has me maxing out at 120 with that Line Pressure Offset vs. TPS% vs Gear (Normal/Perf/Manual). The stock tune is subtracting pressure in this table as PCM's for less is adding. Whats with that? Could you try to explain for me please? Thanks.
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Old 03-02-2007, 09:42 AM   #41  
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I am referring to the Line Pressure Offset vs. TPS% vs Gear (Normal/Perf/Manual). I am following the tutorial above. I went through it step by step changing everything up to this table. Should I just leave the pressure table alone? It seems that the pressure spots would change being I changed where the shift points are. Also I was looking at my stock tune and one I got from PCM's for less and the one from PCM's for less has me maxing out at 120 with that Line Pressure Offset vs. TPS% vs Gear (Normal/Perf/Manual). The stock tune is subtracting pressure in this table as PCM's for less is adding. Whats with that? Could you try to explain for me please? Thanks.
I can probably shed some light on this once I'm back from vacation, but heading out the door. so you'll have your answer by monday at the latest, and if earlier I'll delete my worthless post(this one).
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Old 03-02-2007, 11:17 AM   #42  
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I can probably shed some light on this once I'm back from vacation, but heading out the door. so you'll have your answer by monday at the latest, and if earlier I'll delete my worthless post(this one).
I'll be waiting!
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Old 03-02-2007, 11:19 AM   #43  
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Is there a way I can post my tables?
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Old 03-02-2007, 10:48 PM   #44  
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I can't explain why the stock tune subtracts line pressure in some cases but I assume the GM engineers did it for good reason!
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Old 03-07-2007, 09:08 PM   #45  
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I'll be waiting!
Ok, after looking over a couple of tunes, including one by pcm4less for my tranny I came to a few conclusions.
They completely left alone the "Line pressure modifier in WOT vs RPM" table and instead resorted to modifying the other tables to increase line pressure so it would reach the new 120psi maximum.

They also left alone the "Line pressure mod vs %TPS vs Trans temp xxxx" tables which are effectively meant to keep your transmission from self-destructing due to temperature.

The Main Line Pressure 0-64 and 64-128mph tables are one of the two step method I am seeing as used to increase the line pressure on the "performance" transmission modifications to make the most of them. But the 0-60 and 60-128 tables seem to be just the start. and instead of using the "Line Pressure modifier in WOT vs. RPM" tables (either because it doesn't work, or otherwise unknown to me) it seems the prefered method is the "Line Pressure Offset (psi) Vs. %TPS Vs. Gear"
Which is really a much better way of doing it, as the 1st->2nd shift is probably the most important.

This table on mine was heavily modded by the tuner, and I haven't touched it. but I must say it does the trick, and like I mentioned before, my transmission hasn't suffered from it, in fact the firmer shifts are probably extending it's lifespan. The most important thing of note, is that the modifier is set to "95" which will probably ensure it is maxed out at 120psi from 62.5% TPS to 100 in every gear to ensure pressure is set as high as it can. 0-25% TPS are zero'd in every gear. Honestly this makes sense if you are familiar with kickdown linkage on old transmissions, a lot of drag racers would just wire their kickdown linkage full on, since it wasn't used on the street and they wanted every shift at maximum pressure it made sense to do that. the rest of the table is slightly scaled as shown here.....pasted below that is the stock settings for a '94 camaro for reference.

0 0 0
0 0 0
0 0 0
0 0 0
12 12 12
24 24 24
36 36 36
48 48 48
59 59 59
72 72 72
84 84 84
95 95 95
95 95 95
95 95 95
95 95 95
95 95 95
95 95 95


0 0 -10
0 -2 -2
-2 -10 -8
-4 -8 -8
-4 -6 -2
0 -7 -4
-1 -9 -3
-4 -14 -10
-1 -15 -11
-2 -16 -12
0 -15 -13
0 -12 -10
0 -15 -1
0 -11 6
0 -13 6
0 -11 6
0 -11 6


You could probably get away with leaving your 0-64 and 64-128 tables alone and just do your main adjustments with these tables. I'd assume that the WOT table does nothing since it is zero'd out and my tranny still reports full line pressure at WOT.
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