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Old 11-21-2017, 12:27 AM   #1
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Default Teach your old Chevy new tricks?

This time of year gives some time to go a bit deeper into some of the oddities of our vans, and this is another step into trying to determine why the 4 speed Chevies get hot, primarily transmissions, on long climbs. Lots of things make incremental improvements, like big coolers, two core radiator, add on electric fans, etc, but none of them really seem to address the root causes, I think.

I have been digging everywhere I could to find out what is different between the later model 6 speed and the four speed models like we have. Nothing stood out beyond the transmission change. We have found with our van that it tended not to get hot climbing mountains in high gear, but would get very hot climbing in lower gears in other places. Since the major part of the heat in a transmission comes from the torque converter when it is unlocked, I started looking for specs, or a way to test, when the torque converter was locked.

I did find a "tuner" which also did the trans settings as well as engine settings, tire size, drivetrain settings, etc. and finally decided just to get it it see what was up. The tuner piggybacks on the factory program, so you can change just what you want and leave the rest as is, so easier than a start from scratch programmer.

The first thing I did was read our existing program.

Here is the data table for the "normal" mode, which is basically the one you get most of the time, unless cruise or tow/haul are on.



This is the same thing when in tow haul mode



They basically show what the shiftpoints are in mph based on TPS reading and the gear in use and similar for the converter locking and unlocking.

What these table show, it appears is that the 4 speed transmission rarely has the converter locked under the conditions we see when climbing in other than 4th gear. For instance, we were able to climb to 12K feet in Rocky Mountain Nat Park in 3rd or 2nd gear within the 35mph speed limit, but there is no time that the converter would be locked. No wonder we got hot, even with the addon cooling stuff.

Compare those table above to what they have programmed to cool the transmission if it get too hot.



The converter is basically locked all the time, except in low gear.

To me, this made it pretty clear it was time to try to figure out what kind of changes could be made to the tables to keep the converter locked more of the time to prevent excessive heating.

I did go to a local high performance transmission shop to ask if the trans could handle locking more of the time, and they said no problem.

Next post will start to look at what I think can be done successfully to reduce heat, while keeping decent driveability.
Attached Images
File Type: jpg GM factory settings normal.jpg (109.7 KB, 128 views)
File Type: jpg GM factory settings Tow haul.jpg (110.7 KB, 101 views)
File Type: jpg GM factory settings hot.jpg (110.9 KB, 100 views)
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Old 11-21-2017, 12:40 AM   #2
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The tuner manufacturer keeps a library of user tunes on their website, and lots of folks have posted their results, including stock tune programs.

There was nothing for 6 speed vans, but I did find one for a 6 speed 2015 Silverado pickup, which should be similar to the vans, as the older 4 speed pickups matched our van program.

Here are same tables for the 6 speed for normal and tow haul.









Without going into detail, it gets pretty clear that the 6 speeds have the converters locked a lot of the time, and at much lower speeds and gears, than the 4 speeds. This is another piece of evidence that the 4 speeds should probably have the converters locked under the high heat generating conditions.
Attached Images
File Type: jpg 2015 6speed normal shift points.jpg (186.5 KB, 100 views)
File Type: jpg 2015 6 speed normal TTC.jpg (171.8 KB, 99 views)
File Type: jpg 2015 6speed tow haul shift points.jpg (193.0 KB, 99 views)
File Type: jpg 2015 6speed tow haul TTC.jpg (184.5 KB, 100 views)
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Old 11-21-2017, 12:48 AM   #3
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Wow... this is good knowledge.

Maybe you can concoct an electronic manual-automatic transmission controller?

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Old 11-21-2017, 12:52 AM   #4
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Again without a lot of details, here is what I have currently put together for normal and tow/haul for our van, and loaded it into the PCM.





All I really did was chose what I thought I would want for shift points, up and down and put them in, and then made the torque converter apply 2mph higher than shift up, and the torque converter release 2mph higher than the shift down settings. There are some areas in the low throttle area where this doesn't apply because of some practicality issues.
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File Type: jpg Tune 4 normal.jpg (109.7 KB, 101 views)
File Type: jpg Tune 4 tow haul.jpg (103.0 KB, 100 views)
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Old 11-21-2017, 12:56 AM   #5
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The above stuff is where I currently am at. The normal program was driven today and seemed to work very well for driveability. Of course it is not as radical as the tow/haul because it won't be used for the big climbs. The tow haul really won't get a good test until we get to mountains, but I hope to get it out soon to see how if does for driveability on the flatter roads around here.

All comments, questions, and suggestions are encouraged, as this it really uncharted ground for me at this point
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Old 11-21-2017, 02:44 AM   #6
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I'm in!

It will be very interesting to see how this works out. For me it's really important as I'm in the Rockies regularly and like the idea of pulling over and changing the tune when its needed.
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Old 11-21-2017, 03:45 AM   #7
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The hotrod shops can sell you a gizmo that you can use to dial in the exact parameters of all the engine functions -- from the turbo wastegate psi to the fuel-oxygen mixture ratio... to shifting points. The wonders of electronically controlled engines.
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Old 11-21-2017, 02:39 PM   #8
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Originally Posted by BBQ View Post
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The hotrod shops can sell you a gizmo that you can use to dial in the exact parameters of all the engine functions -- from the turbo wastegate psi to the fuel-oxygen mixture ratio... to shifting points. The wonders of electronically controlled engines.
Yeah, there are a lot of different methods around, although I think they are changing a bit over time. Most that I found now days seem to have a premade program, or programs that you can switch, and piggy back onto the factory program like this one does. Others are pure hot rod programs that don't piggyback and are true standalones. I have had several of them in the past that I put on my old Dodge Challenger when I turboes and fuel injected it. The standalones often allow tuning on the fly, which is really cool, but can be very hazardous to parts if you mess up.

This tuner appears to totally rewrite the entire program each time you make a change, so there could be no on the fly with this one.

You can still get some "trimmers" for some things like timing and mixture, but most of them I have seen just uses some electronics to send a bogus signal from a sensor to a factory PCM to get a different output.

One good thing is that a lot of the "tuner" shops around now have this kind of tuner, so if you knew what changes were necessary, all you would do would be to tell them or give them a printout of what you wanted. My guess is that it would cost maybe $200 or so. Probably take an hour or two tops. That's less than hiring a radiator change, and way less than adding a bunch of coolers and fans, so might be the least expensive change that could be done easily. I don't have a shop license for the tuner, and it costs $100 for each extra vehicle I license, so that would be the only cost I would have in doing another vehicle.
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Old 11-21-2017, 04:09 PM   #9
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I, too, look forward to the results of your real world tests.
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Old 11-21-2017, 04:50 PM   #10
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When I was trying to figure out where to put the shiftpoints and lockups, I discovered I needed a good chart for what the rpm is at the various speeds and in different gears. I put together this spreadsheet to make it easier to visualize what was going on. This is a screenshot jpg, but if anyone wants the spreadsheet I will add it. For your tire size, as ours are oversize, just go to Tire Rack and get the revs/mile for your tires from the specs tab for them, and divide it by our 657 revs/mile. Then multiply that answer times the rpm numbers in the table. I think it will be about 3-4% different.

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File Type: jpg Van rpm vs gear spreadsheet screenshot.jpg (90.2 KB, 89 views)
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