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racprops · 03-19-2021, 06:55 AM

My research and comparing the 6 and 8 speed transmissions seem to show they are mainly needed and work best with the newer baby engines…where you NEED to have many gears to keep these little engines at their power range, where a big engine have a wider and stronger power range.

Then there is a reported problem with these transmissions of shifting way too much and in a factory PCM not going into say 8th until reaching something like 67MPG, and how to set up a gear selector on my column and granted the aftermarket trans controller might allow more manual control it is still a costly complex setup.

Sadly NONE of any of these 2 newer multigear transmissions have enough a lower final over drive gears, they are 65, or .67 to do what I want. The only way to fully use such as I see it means finding impossible to get super low rear end gears..like 2:24 or 2:45 sets. The lowest gear that is factory is a 3.08 and it still means that at 85 MPH I will still be running over 2000RPMs. My target is 1500 to 1800RPMs.

Thus for me the costs of something like $3000.00 plus even using used transmissions out of a junk yard…is not worth it. And add in the costs of the special rear end gear sets mainly again only used and rebuilding the rear end at a cost close to $1000.00.

Sadly the costs of the Gear Vender’s over drive is even more, like around $3000.00 installed, which will take a lot of miles driving with the improved MPG if you can even get such with a stock engine to pay off the cost.

With my 4L80E I can just buy a PCM from a 90s Van that had a 4L80e and with the US Gear just flip a switch and go from the high range to the overdrive low range, and this can be done in all four gears of the 4L80 so I do get 8 gears so I can select the best mountain climbing gear.

With the finding of this US Gear overdrive I end up a little higher than my original plan using an old Borg Warner devoiced Overdrive which added up to be .47, with the US Gear’s ratio of .80 none the less I am still running a .56 final gear ratio running the 4L80s own .75 overdrive so the two together comes out at this figure. This still is .11 below a 8L80 at about ¼ the cost of swapping one it.

I figure I will never really pay off all my current engine/drive line costs, but than I needed an engine and at least I will feel less guilty IF I can get near the same MPG I can get on the road in my 03 Crown Vic…

So in my case I found that I can stick to a stock 4 speed auto, and just add a second over drive to get much lower final gearing and hopefully great MPG thanks to a much lower engine RPMs with any 383 BUILT for high torque starting at 1000RPMs.

I can do this using an old US Gears Dual Range Overdrive hooked up to a 4L80E transmission. This rebuilt 4L80E came out of a motor home and is extra heavy duty.

First will be testing the new engine after break in, testing the Lean Burn Cruse program with an 87 Camaro TPI intake system, testing adding extra EGR, water injection and perhaps a propane injection system and some other wild stuff. A few of the other things I believe will improve my MPG.

Once I have done everything to get the most MPG and figure out the max MPG for the engine’s best RPMs I can then rebuild my rear end with it chosen final gears with a posi-traction carrier, which is also nearly impossible to find for the low 2.45 gear sets. There are only two gear carriers for the GM rear ends, there is a low number carrier which I believe covers 2.20 to 3.08 and these are very rear with a posi, then 3.08 up to 4.50 with posi carriers.

And again because of the fact of the stock rear end is howling it NEEDS rebuilding so once done I will have a bullet proof rebuilt driveline.

This baby will be like new and ready to cruse.

The frustrating thing is up until 2016 and the Express Van with the 2.8 turbocharged Diesel and the 2020 small gasoline engine both running the new 8 speed transmissions, 29/30MPG in a van was unheard of pipe dream…one only I had…until now…

AT least THEY prove that that old BS about you cannot get such MPG pushing a BOX though the air has been proven wrong!!!

03-19-2021, 06:55 AM	#24 (permalink)
racprops Master EcoModder Join Date: Oct 2009 Location: Phoenix AZ Posts: 799 Thanks: 4 Thanked 66 Times in 58 Posts	My research and comparing the 6 and 8 speed transmissions seem to show they are mainly needed and work best with the newer baby engines…where you NEED to have many gears to keep these little engines at their power range, where a big engine have a wider and stronger power range. Then there is a reported problem with these transmissions of shifting way too much and in a factory PCM not going into say 8th until reaching something like 67MPG, and how to set up a gear selector on my column and granted the aftermarket trans controller might allow more manual control it is still a costly complex setup. Sadly NONE of any of these 2 newer multigear transmissions have enough a lower final over drive gears, they are 65, or .67 to do what I want. The only way to fully use such as I see it means finding impossible to get super low rear end gears..like 2:24 or 2:45 sets. The lowest gear that is factory is a 3.08 and it still means that at 85 MPH I will still be running over 2000RPMs. My target is 1500 to 1800RPMs. Thus for me the costs of something like $3000.00 plus even using used transmissions out of a junk yard…is not worth it. And add in the costs of the special rear end gear sets mainly again only used and rebuilding the rear end at a cost close to $1000.00. Sadly the costs of the Gear Vender’s over drive is even more, like around $3000.00 installed, which will take a lot of miles driving with the improved MPG if you can even get such with a stock engine to pay off the cost. With my 4L80E I can just buy a PCM from a 90s Van that had a 4L80e and with the US Gear just flip a switch and go from the high range to the overdrive low range, and this can be done in all four gears of the 4L80 so I do get 8 gears so I can select the best mountain climbing gear. With the finding of this US Gear overdrive I end up a little higher than my original plan using an old Borg Warner devoiced Overdrive which added up to be .47, with the US Gear’s ratio of .80 none the less I am still running a .56 final gear ratio running the 4L80s own .75 overdrive so the two together comes out at this figure. This still is .11 below a 8L80 at about ¼ the cost of swapping one it. I figure I will never really pay off all my current engine/drive line costs, but than I needed an engine and at least I will feel less guilty IF I can get near the same MPG I can get on the road in my 03 Crown Vic… So in my case I found that I can stick to a stock 4 speed auto, and just add a second over drive to get much lower final gearing and hopefully great MPG thanks to a much lower engine RPMs with any 383 BUILT for high torque starting at 1000RPMs. I can do this using an old US Gears Dual Range Overdrive hooked up to a 4L80E transmission. This rebuilt 4L80E came out of a motor home and is extra heavy duty. First will be testing the new engine after break in, testing the Lean Burn Cruse program with an 87 Camaro TPI intake system, testing adding extra EGR, water injection and perhaps a propane injection system and some other wild stuff. A few of the other things I believe will improve my MPG. Once I have done everything to get the most MPG and figure out the max MPG for the engine’s best RPMs I can then rebuild my rear end with it chosen final gears with a posi-traction carrier, which is also nearly impossible to find for the low 2.45 gear sets. There are only two gear carriers for the GM rear ends, there is a low number carrier which I believe covers 2.20 to 3.08 and these are very rear with a posi, then 3.08 up to 4.50 with posi carriers. And again because of the fact of the stock rear end is howling it NEEDS rebuilding so once done I will have a bullet proof rebuilt driveline. This baby will be like new and ready to cruse. The frustrating thing is up until 2016 and the Express Van with the 2.8 turbocharged Diesel and the 2020 small gasoline engine both running the new 8 speed transmissions, 29/30MPG in a van was unheard of pipe dream…one only I had…until now… AT least THEY prove that that old BS about you cannot get such MPG pushing a BOX though the air has been proven wrong!!!