Slush-a-matic or Manual-matic?
If you are thinking about upgrading or converting your project to a late model automatic one important thing to consider is control over the shift points. What I am referring to is when it shifts or doesn't shift and how firm do you want that shift to be.
If you are anything like me a total control freak and perfectionist then you will probably not be happy with a stock shifting slush box automatic and could spend months trying to perfect the shifting pattern on a after-market programmable controller.
These very reasons are why for most of my hot rodding years I have preferred manual gearboxes on my street driven cars. In 2009 I bought one of the very last Pontiac muscle cars sold the G8 GXP with the LS3 engine and of course a 6 speed manual. They offered a really cool 6 speed automatic with a manual mode available but I prefer that full control. If I want to down shift at 120mph no problem.
The problem is as we get older we learn to appreciate the conveniences of an automatic.
First thing that drove me to automatics was my knee is not as flexible as it was 20 years ago and working a clutch in stop and go traffic is no easy task on a daily bases, so as always I was looking for a better solution. After reviewing the electronic controlled transmissions most auto makers have been installing for the past 20 years I discovered that they can be controlled entirely by manual mode if you bypass the factory controller and simply actuate the solenoids to select the desired gear.
The second thing I discovered was that no one was making a simple low cost box to do this and at that time the few available (as is today) were expensive because they were designed to be programmed for automatic shifting based on input from multiple sensors and from you. This lead me to develop a simple low cost MANUAL ONLY box theMagnaShift TCM806. I built it with the features that I was personally looking for, manual gear selection with simple buttons or a paddle shifter and a torque converter control button. I also discovered that line pressure on the electronic transmissions could be adjusted on the fly as you drive. What this means is no more shift kits required to get a firm shift. With a simple knob you can crank up the pressure when you want to shift firm and lower it when you are daily driving to save wear and tear on the drive-train.
Now here is one of the cool secretes most people don't realize on the GM 4L series transmissions you can lock that torque converter any time you like in 2nd , 3rd and 4th gear, so between locked torque converter and actual gear ratio's its almost like having 7 forward gears.
So the conclusion here is if you have the time to waste on trying to perfect the automated shifting then maybe a fully programmable controller is exactly what you need. But if you want it to shift when and where you want and a simple plug and play box then the full manual controller is the solution. No pushing a clutch pedal but with full control like a manual gearbox.
How many Gears are enough?
Decades past in the early days of the automatic transmission there were primarily 2 and 3 forward speeds. Since the early 1990's most US auto makers started making 4 speed automatics and more recently 5 and 6 speed automatics. Some European companies are even making 7 and 8 speed automatics.
So how many gears do you need? Lets first look at some real data; the early 3 speeds had two lower gears for accelerating and then the top gear 3rd was a 1:1 ratio. Under most circumstances in a average car or light truck that is adequate for acceleration and responsiveness. The 4th gear was added in the 90's as a overdrive to assist in gas mileage, but it also achieves other things like lowering the noise level of the engine and by running a lower RPM usually extends the life of the engine and other rotating devices (alternators, air-conditioning compressors, etc.). With the newer 5 and 6 speed transmissions some now have additional ratio's (gears) in between first and the direct drive gear. This can provide additional acceleration for low torque high revving engines, but it can also be a nuisance for daily driving if you have a larger engine that makes plenty of torque.
In most 6 speed transmissions the 5th and 6th gear are overdrive and from all of my experience driving and owning cars with 6 speeds that extra over drive ratio is only useful when you are doing a long trip and/or cruising at highway speeds in excess of 65MPH.
Over the past few years I have had many people ask about installing a GM 6L80 in their older project cars. Unfortunately these 6 speed transmissions were built with a internal TCM (Transmission Control Module) and are not easy to adapt to a older vehicle without the factory ECM and BCM that is programmed to function with this transmission.
I look at the number of gears in transmissions like the number of cylinders in a engine sure you can build 10 and 12 cylinder engines, but it has been proven time and time again that a V-8 can make more horse power per pound than most 10 or 12 cylinder engines and at a fraction of the cost.
I suggest you stick with the GM 4L60E or 4L80E models which can be bought and built at a much more reasonable price and are easy to incorporate into almost any make or model of car or truck. These transmission provide the 2 lower gears, a direct drive (3rd) and then a overdrive (4th). You also get the advantage of a lockable torque converter that improves gas mileage and provides dramatically different performance when compared to the older 2 or 3 speed automatics.
So the moral of this story is if you are building a car with a performance engine and don't plan to drive it often on higher speed highways then don't waste money and time on a heavier, multi speed overdrive. Instead spend that money on something more useful and more fun. If your looking for something to brag about then show off your intelligence and explain to the guy that went with the 6 speed why you opted for the 4 speed.