Engine Torque vs Gearbox Torque
Thread Starter
Intermediate
Joined: Dec 2006
Posts: 48
Likes: 0
From: New Orleans Lousiana
Engine Torque vs Gearbox Torque
Whats the difference?
GM rates thier current lineup of hydramatics for both engine torque and gearbox torque, with gearbox torque being MUCH higher than engine torque specs.
For example:
4L70:
400 ft/lbs ET
670 ft/lbs GT
4L85:
460 ft/lbs ET
885 ft/lbs GT
6L80
439 ft/lbs ET
664 ft/lbs GT
Sometimes GM puts engines in front of transmissions that exceed the max engine torque #'s but are still well under the max gearbox torque numbers. The 4T65 is a good example imo. Rated at 280 ET / 400 GT, the engine is both in front of the 280 ft/lbs 3.8L s/c engine and the 5.3L LS4 wich puts out 315 ft/lbs torque IIRC.
My guess would be engine torque is the max the transmission is typically used with while the gearbox torque is the max the transmission can physically handle? Or am I completely missing the point? If I'm right, that 4L70 would be lovely for the C3
BTW, all these numbers are direct from GM's site.
GM rates thier current lineup of hydramatics for both engine torque and gearbox torque, with gearbox torque being MUCH higher than engine torque specs.
For example:
4L70:
400 ft/lbs ET
670 ft/lbs GT
4L85:
460 ft/lbs ET
885 ft/lbs GT
6L80
439 ft/lbs ET
664 ft/lbs GT
Sometimes GM puts engines in front of transmissions that exceed the max engine torque #'s but are still well under the max gearbox torque numbers. The 4T65 is a good example imo. Rated at 280 ET / 400 GT, the engine is both in front of the 280 ft/lbs 3.8L s/c engine and the 5.3L LS4 wich puts out 315 ft/lbs torque IIRC.
My guess would be engine torque is the max the transmission is typically used with while the gearbox torque is the max the transmission can physically handle? Or am I completely missing the point? If I'm right, that 4L70 would be lovely for the C3
BTW, all these numbers are direct from GM's site.
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
i really have no idea, but those GT numbers look they are in the range of torque multiplication of a torque converter. maybe the GT values are multiplied by the TC and then reduced by gear losses . . . ??? . . . just guessing
Thread Starter
Intermediate
Joined: Dec 2006
Posts: 48
Likes: 0
From: New Orleans Lousiana
So theoretically, could you run a higher torque engine than specced with a low multiplication converter and still be in the 'safe zone' as long as you stayed under max GT? How would you determine the mutiplication of a TC (higher stall speeds = higher multipliers)?
I wont be doing this, but this is pretty interesting since I was under the impression that TC's didnt increase torque THAT much. I have a LOT to learn about transmissions
I wont be doing this, but this is pretty interesting since I was under the impression that TC's didnt increase torque THAT much. I have a LOT to learn about transmissions
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Manufacturer should tell you what the multiplication ratio is since it depends on the turbine and stator that they use. This multiplication is why it's called a torque converter instead of a fluid clutch. Early automatics, like the Dynaflow, used a fluid clutch and a four-speed automatic. The 1st gear was extra low since the coupling didn't multiply torque.
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
but - don't always believe everything the mfg tell's you on torque multiplication!
see this:
http://www.converter.com/torqueratio.htm
"They (compertitors) also advertise STR’s (STALL TORQUE RATIO) of 2.7, 2.9, 3.0, 3.2, etc. this is pure BS."
"The formula for STR is EXACT OUTPUT TORQUE ÷ EXACT INPUT TORQUE = STR. This requires a known power source and a data recovery system."
"...the stock torque converter you took out of your car has a STR of 1.9-1.94"
see this:
http://www.converter.com/torqueratio.htm
"They (compertitors) also advertise STR’s (STALL TORQUE RATIO) of 2.7, 2.9, 3.0, 3.2, etc. this is pure BS."
"The formula for STR is EXACT OUTPUT TORQUE ÷ EXACT INPUT TORQUE = STR. This requires a known power source and a data recovery system."
"...the stock torque converter you took out of your car has a STR of 1.9-1.94"
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
