TBMSport GM 6L80/6L90 Six Speed Automatic Conversion Systems
Making the world's FIRST 4WD conversion of a 6 speed automatic into a vehicle that was not designed for it WITH FACTORY CRUISE CONTROL, Gear Hold, Traction/Launch Control and all original interior features fully functioning was no easy feat!
However, having successfully completed a 4L70E four speed automatic transmission to a 6L80E six speed automatic transmission in our project Trailblazer rewarded TBMSport with a tremendous accomplishment that we are now ready to share the benefits with you, the enthusiast.
While the world has come to embrace and offer solutions for installing GM's LSX engines into almost any vehicle, the differences between the 6L80/90E transmission and 4L60/65/70/80E transmissions have perplexed the aftermarket for several years and created a major void in the GM performance world. Concerns about installation fitment and functionality have discourage many from considering the swap as transmission alternative. Those who recognized, desired, embraced the 6L80/90E provided benefits were stuck with a handful of expensive and/or incomplete ECM/Harness solutions that were often only able to be installed as a full powertrain and harness system in pre-OBDII emission controlled vehicles. If enthusiasts had a late model OBDII EFI vehicle, such as our project Trailblazer, they were stuck with their 4 speed automatics or forced to lose accustomed functions such as cruise control. As a result of this, few have experienced the potential gains in performance, driving dynamic and fuel economy that this independent transmission swap can provide. Fewer have come to appreciate the overall bang-for-the-buck cost savings that makes this conversion a top MUST DO on any enthusiasts TO DO list.
All of that has now changed. The rules and assumptions of bang-for-the-buck performance vs. daily driveability compromise have been officially rewritten.
We now are TAKING ORDERS on Plug & Play systems for I6 ('08-09) and V8 ('07-09) GMT360 platform trucks (Ascender, Rainier, Envoy, Trailblazer, 9-7x, SSR), and '07-'09 GMT900 (Silverado, Sierra, Yukon, Suburban). Other LS based vehicles are being evaluated, so please provided us with your feedback.
6L80/90 TBSS LS2 Power Range Shifts
4L80 TBSS LS2 Power Range Shifts
4L70 TBSS LS2 Power Range Shifts
(Click Above Images)
The above charts demonstrate the usable power range of a stock Trailblazer SS with 4.10 gears with no other variation than the installed transmission: 6L80/90, 4L80, and 4L70. The graphs prove that acceleration with a 6 speed automatic, in an identically powered vehicle, will generate greater multiplied torque product to the wheel and shift into each gear at/or near the peak torque.
THINGS TO NOTE IN COMPARISON:
1) RPM when each gear shifts
2) How far below peak torque each shift puts the engine
3) RPM at given highway speed in O/D gear
4) As a rule of thumb, given the same power and axle ratio, the shorter a given transmission gear (i.e. 1st, 2nd, 3rd, etc) the sooner the vehicle will achieve it's given gear's maximum speed. For instance, a 6L80 will max out at a little above 30 MPH in 1st gear, but will achieve that speed sooner than in the 4L80. Additionally, the 6L80 will shift into it's peak torque curve at that speed to maintain momentum. By contrast the 4L70 will shift into 2nd well below it's peak torque and give that "lugging" feeling as it has fallen off of it's torque curve.
CONCLUSION: 6L80/90E Gear ratios multiply more torque per gear & overall useable, average torque. Other transmissions would require significantly more RPM torque band from the engine to match the output of the 6L80/90E and have and overall higher RPM at highway speeds.
"email@example.com" & "Speedo Video" Video Highlights: '08 GMC Sierra Quad Cab 5.3L, 4L60E w/4.10 converted to cammed("228/236 .588.601 112+2 or something like that"), LT, 6.2L, 6L80. Easily a 5200+lb truck.
1/8 8.512 @MPH 84.68 1/4 13.135 @MPH 106.42"
'08 GMC Sierra Quad Cab 5.3L, 4L60E w/4.10 converted to cammed("228/236 .588.601 112+2 or something like that"), LT, 6.2L, 6L80. Easily a 5200+lb truck
+Gain of up to 7% in acceleration times from transmission swap alone (MaxChevy.com 3/07)
+Superior torque capacity to 4L60/65/70E in stock form
+FOUR evenly spaced forward gear ratios (Less work required of engine)
-Best compromising solution when choosing to use widely available parts
-Best compromising solution when choosing NOT to change ANY other vehicle components
+Unmatched torque capacity
+Evenly spaced forward gear ratios
+Lots of cores & aftermarket performance parts
-Least torque multiplication. Installation often requires expensive changes to overall drivetrain (Camshaft, Torque Converter, Axle ratio) to maintain or gain performance. Swapping in this transmission WILL make your vehicle accelerate slower AND consume more fuel.
-Worst O/D gear ratio
-Can require rewiring and standalone control module
-Usually requires new/modification to crossmember
-Best solution when engine output currently or will potentially exceed 600 hp/tq
-Best upgrade solution for drag racing vehicle that sees limited pleasure street driving use
For the following reasons, TBMSport felt that it was necessary to rid the GMT360 platform of the 4 speed automatic transmission, known as the 4L65/4L70, with GM's latest and truly greatest 6 speed automatic transmission, the 6L80/6l90.
A) 4L65/70's just cannot repeatedly stand up to the power and weight of these vehicles under hard use. This will result in repeatedly rebuilding the transmission.
B) 4 speed autos drop the engine RPM out of its torque band during shifts, causing anything from too much shock to the gears/shafts, too much work load to the engine, to too much torque converter heat build up.
C) The new 6L80/90 comes from the factory behind engines making more power than GMT360's and vehicles weighing more than GMT360's
D) The 6L's are clutch trannys that automatically, with the computer control, adjust the clutches so you maintain the same consistent shifting as the clutches wears
E) For the most severe applications, the only upgrade necessary will be stronger clutch discs; which are available
F) The transmission swap cost is equal to or less than the cost of rebuilding the factory 4L65/70 (w/ torque converter) and will last longer
G) Keeping current axle gear ratios will result in improved acceleration and fuel economy
H) 4L80/85 transmissions are expensive, reduce 1st-3rd gear acceleration through less torque multiplication, (giving the impression of sapping a lot of overall engine power), and increase fuel consumption
I) To swap the 6L80/90 transmission into these means less money in the long run with other mods, from forced induction to cam to exhaust. Do a transmission mod ONCE.