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GM Torque

nick mcintire
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nick mcintire Enthusiast

nick mcintire

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Posted

How does GM figure Torque?  At the flywheel or the rear axle.

The sierra 1500 with 6.2 engine has 460 lbs of torque, which has the 3.23 rear axle.

How many lbs of torque does the 6.2 engine with the Max Tow Package have which has the 3.42 rear axle.

Gangly Senior Enthusiast

Gangly

Posted
Posted

GM uses an engine dynometer to gather engine HP and TQ.  However, GM is very conservative with their numbers and the engines will usually outperform the measured and calculated test results in the real world.  The LT1 from the mid 90's to the LS motors that ran through the late 2000's were notorious for being under rated and outperforming their factory numbers.

  • 2 weeks later...
Transient Senior Enthusiast

Transient

Posted
Posted

GM, and most of not all other manufacturers utilize SAE testing to determine the hotelier and torque ratings of its engines. As others have said, it's at the flywheel and not the rear axle. As another person said, GM has been known to understate the numbers. That could be because they went with the lowest numbers achieved at time of testing. I use to have a supercharged Cobalt SS (engine code LSJ). GM said that engine produced 205hp/200tq. I dynoed the car and it was a little more than that. I actuality got it into the 130 MPH Club on the Bonneville Salt Flats in showroom stock condition with an average speed of 131mph by running 4th gear all the way to ten limiter (which was 134mph at 6,500 rpm).

 

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swathdiver Senior Enthusiast

swathdiver

Posted
Posted
On 3/11/2021 at 11:18 PM, nick mcintire said:

How does GM figure Torque?  At the flywheel or the rear axle.

The sierra 1500 with 6.2 engine has 460 lbs of torque, which has the 3.23 rear axle.

How many lbs of torque does the 6.2 engine with the Max Tow Package have which has the 3.42 rear axle.

You can figure this out with a formula on an excel spreadsheet.  

 

My truck puts down about 689 foot pounds of torque at 2000 rpms in 6th gear.  A 6.2 with 3.73 gears in my generation puts down about 980 ft lbs in 6th at 2000 rpms.

Transient Senior Enthusiast

Transient

Posted
Posted
You can figure this out with a formula on an excel spreadsheet.  
 
My truck puts down about 689 foot pounds of torque at 2000 rpms in 6th gear.  A 6.2 with 3.73 gears in my generation puts down about 980 ft lbs in 6th at 2000 rpms.
I can't find a calculator that considers rear axle gearing, but I did find these formulas.

Torque = (Horsepower * 5252) / RPM
Horsepower = (Torque * RPM) / 5252
RPM = (Horsepower * 5252) / Torque


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aliveguy5 Enthusiast

aliveguy5

Posted
Posted

I think I get what you are asking for... How do you calculate the torque multiplication that the gearing and gears will give you. I don't have this answer either but I'd be very interested as I feel the 6.2 is even beefier than what they say as well. 

redwngr Senior Enthusiast

redwngr

Posted
Posted (edited)

When going through a gearset, (transmission, differential etc) the ratio of the torque in/out is the opposite of the ratio of the speed in/out.  Both are calculated by the number of teeth in the gearsets -- but are sometimes expressed as the ratio of in/out speeds instead.

 

 

So, if the output speed is lower, the output torque will be higher. (in 1st gear, the output torque is higher than in second gear)

If the output speed is higher (as in an overdrive gear) the output torque will be lower.

 

Every time power goes thru a gearset, some of the power is lost (converted to heat and noise). 

Since gearsets don't have 'slip' the power loss is be observed as a reduction in torque. (if there is torque measuring sensors on the input and output sides of the gearset)

 

HP out = HP in x efficiency

torque out = torque in x speed  ratio x efficiency

speed out = speed in x gear ratio 

 

Edited by redwngr
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swathdiver Senior Enthusiast

swathdiver

Posted
Posted
3 hours ago, aliveguy5 said:

I think I get what you are asking for... How do you calculate the torque multiplication that the gearing and gears will give you. I don't have this answer either but I'd be very interested as I feel the 6.2 is even beefier than what they say as well. 

You multiply the final drive ratio in the given gear with the known torque value at the desired RPMS.

 

An LC9 makes 302 ft lbs of torque at 2000 rpms.  The final drive ratio of the truck (gear ratio multiplied by axle ratio) is simply multiplied by the torque value.

 

6L80 6th gear ratio is .667 and the axle ratio is 3.42 which results in a final drive ratio of 2.28.  So we multiply 2.28 by 302 and get 689.

Gangly Senior Enthusiast

Gangly

Posted
Posted (edited)
3 hours ago, redwngr said:

When going through a gearset, (transmission, differential etc) the ratio of the torque in/out is the opposite of the ratio of the speed in/out.  Both are calculated by the number of teeth in the gearsets -- but are sometimes expressed as the ratio of in/out speeds instead.

 

 

So, if the output speed is lower, the output torque will be higher. (in 1st gear, the output torque is higher than in second gear)

If the output speed is higher (as in an overdrive gear) the output torque will be lower.

 

Every time power goes thru a gearset, some of the power is lost (converted to heat and noise). 

Since gearsets don't have 'slip' the power loss is be observed as a reduction in torque. (if there is torque measuring sensors on the input and output sides of the gearset)

 

HP out = HP in x efficiency

torque out = torque in x speed  ratio x efficiency

speed out = speed in x gear ratio 

 

Your efficiency comes down to frictional losses, as described above as heat and noise, as well as the energy required to maintain rotation of said mass.  

 

Also, the ratio is calculated by the number of teeth on the gear set as mentioned above, but more specifically the ratio of the circumferences (circular pitch) of the matching teeth gearsets.  Its a small difference, but important.

 

Very accurate and great answer!

Edited by Gangly

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