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Old 08-05-2008, 12:39 PM   #1
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6 speed 4L80E

I'm doing some research on the 4L80E as I'm thinking of doing a 60E to 80E swap and came across the topic of a 6 speed 4L80E. I remember seeing this mentioned on an episode of HPTV and doing a search here I didn't find much other then its either done by software or there may be a different valve body required to make it work. Does anyone know anymore about this illusive 6 speed 4L80E setup? I'm wanting to know how its done and what kind of gear ratios result from it. If its just software then thats just a matter of changing the shift routine is it not? Any info is greatly appeciated.
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Old 08-05-2008, 07:32 PM   #2
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Re: 6 speed 4L80E

It's a valve body change plus a custom chip and an on dash controller.

Standard gear ratios for the 4L80E are the same as a TH400 plus an overdrive.

2.48
1.48
1.00
0.75

The 6 speed conversion splits 2 gears with the overdrive to give

2.48
1.86
1.48
1.11
1.00
0.75

Because the valve body is computer controlled with electric solenoids, the valve body swap is not cheap. The 6 speed conversion was most popular with trucks since it allowed the engine rpms to stay in the sweet spot by only dropping half a gear. Using OD as an extra gear isn't a true 6 speed since the OD gear is always small and weak. The OD gear is never a performance gear because of this.
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Old 08-05-2008, 08:02 PM   #3
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Re: 6 speed 4L80E

Interesting. So overdrive in the 4L80E is really that weak huh? It was kind of my understanding it would split the load and put less strain on the internals but maybe not. Is there any place online that has more info on this? I would like to see some pics of this setup if at all possible.
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Old 08-06-2008, 12:10 AM   #4
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Re: 6 speed 4L80E

All overdrives are weak because it needs a small gear driving a big gear. Automatic transmission OD is no different. OD is not designed for power. The final OD is designed for high speed, low rpm highway operation to cruise at a much lower rpm to save fuel. Splitting the gears with an OD still needs a small gear driving a big gear. In an automotive transmission, you just won't get a big enough small gear to take any abuse.

In a highway tractor, it's a little different. It's common for a big truck to have an 18 speed transmission but it doesn't really have 18 gears. It's really just a 5 speed with a high and low range for 10 gears plus an OD that can split all the gears to give a total of 18 gear ratios. The OD gears are in the back of the transmission and are separate from the main gears. They use 2 countershafts to increase the load strength on the output shaft. the only time you need to split a gear is when you need to change the engine rpm one or two hundred rpm. Running empty, you can start in low gear and go through to high in only 10 gears or less, not needing the OD gears at all.

The 4L80E 6 speed conversion is the same thing. The split gears is only needed when in a truck as a tow vehicle and you need to drop down half a gear when climbing a hill to keep the engine in a slightly higher rpm range until the rpms drop down again for another 1/2 gear split. In a lighter vehicle, the extra gears are not required because it doesn't need as much HP to move the lighter vehicle. Climbing a hill, it's unlikely it won't even drop out of high gear. When I towed my car through the mountains years ago with my 454SS pickup which has a 4L80E, the transmission never dropped out of OD at all going up the mountains.

A proper 6 speed tranny would be more like the 6L80E with a very low first gear. It would give good acceleration off the line with something like 3.23 gears in the diff and have an OD for high gear on the highway.

Trouble with most 6 speeds transmissions is they're not really a 6 speed. The T56 has the gear ratios of a 4 speed tranny and has 2 OD gears. Unless you cruise down the highway a lot, you'll probably never use the OD gears.
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Old 08-06-2008, 06:52 AM   #5
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Re: 6 speed 4L80E

I see what you're saying. I thought it was odd that such a thing as a 6 speed 4L80E conversion kit existed yet nobody seems to know much about them and I've never known anybody that used one. My only beef with the 80E is the tall first gear ratio but that can be overcome with a high stall converter. Thanks for the information.
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Old 08-08-2008, 09:38 PM   #6
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Re: 6 speed 4L80E

Quote:
All overdrives are weak because it needs a small gear driving a big gear. Automatic transmission OD is no different.

You realise that the same 2 planet assemblies are used for both under drive one to one and over drive right?

Planet assemblies consist of the sun gear planet gears and the ring gear.

Depending on how torque is routed each assembly has 6 ratios. 4 forward and 2 reverse.
The only thing that varies is which element of the planet set is static which is input and which is output.
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Old 08-08-2008, 09:38 PM
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