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Discussion Starter #1 (Edited)
Hellcat auto transmission (8HP90) max torque rating

I know on paper the 8 speed automatic transmission (8HP90) is rated at 663 lb-ft of torque. I also know other cars like Rolls-Royce and Bentley use the same transmission in some of their cars.


The Birkin Edition Bentley Mulsanne makes 512 PS (377 kW; 505 hp)@4200 rpm, 1,020 N·m (752 lb·ft)@1750 rpm

It's only 505 hp, but 752 lb-ft of torque and the Bentley is almost a 6000 lb car. Same transmission as the Hellcat.

8HP90

I think this new 8 speed transmission can handle a little more than the basic specs would suggest.



What is the real torque limit?


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That's a great question! I think owners who put REAL drag slicks on the car will soon find the limits. The 10.85 pass was done with Nitto 555 DR's 305 35 20's DRAG RADIALS!!!
I think repeated launches with Real tires will burn up the clutches or worse...
Imagine the replacement cost once it's out of warranty!
6spd for me!! Clutches are cheap in COMPARRISON to a new automatic trans.
 

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Discussion Starter #3
That's a great question! I think owners who put REAL drag slicks on the car will soon find the limits. The 10.85 pass was done with Nitto 555 DR's 305 35 20's DRAG RADIALS!!!
I think repeated launches with Real tires will burn up the clutches or worse...
Imagine the replacement cost once it's out of warranty!
6spd for me!! Clutches are cheap in COMPARRISON to a new automatic trans.
I think you missed the point of my post.

I feel the paper specs of the 8 speed transmission is underrated.

Concept, your comments are strange and random.


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I think you missed the point of my post.

I feel the paper specs of the 8 speed transmission is underrated.

Concept, your comments are strange and random.


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I understand your post totally and tried to respond in the second line of mine with my opinion.
Putting SLICKS on a car multiplies the torque and while you can't get the accual rating when it breaks I'm CERTAIN they WILL break under those conditions after Repeated passes.
The input shafts have been snapping off 6cyl trucks with the 8spd who's too say that can't happen?
Sorry I didn't buy the auto I bought the stick because I feared the long term repair bills. Not too mention the stick is a more enjoyable experience FOR ME.
I am curious however about the limitations and if they are accually underrated
 

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I'm not even sure how they come up with these ratings in the first place. The old Warner T-10 4-speed with 2.88 low gear was only rated at 300 lb-ft yet this tranny lived behind many big blocks some making almost double that torque.
 

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Personally I think the clutches in the M6 cars will have a lot harder time living long lives than the A8 transmission. The automatic is already locked up in first gear at the starting line and the only thing really taking a beating is the torque converter which usually holds up well if ATF temperatures are kept under control.
 

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Edit: Never mind, my post was redundant. On paper, yes, 663TQ. What can it actually hold, no idea.
 

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My guess? Bentley probably used/selected the trans as it fit their engineering/packaging requirements and modified it's internals to meet their performance specs. Sort of what DCX did with the NAG1 which Merc provided. Hasn't Dodge typically rated their "gear" at full load engine HP/torque? And remember, those "torque" ratings, right, wrong, speculation are usually quoted at the input shaft? Don't gear ratios change the equations. Plus factor in duty cycle and environment.
 
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Tim K said this was a beefed up variant of the 8HP90, with ~30% higher TQ capacity. I'm guessing the true TQ capacity of this particular variant is at least 800 lb-ft.

This is similar to the different levels of the TR6060. The version used in the Viper, Hellcat, GT500, ZL1, etc. is heavier duty than the variant used in the 392 Challenger.

Sorry to use the ZL1, but it's a good example of upgrade trans documentation for the higher perf models:

"A new Tremec TR-6060 MG9 six-speed transmission has a stronger output shaft, a more robust rear housing, and an additional mainshaft roller bearing to provide 30-percent more torque capacity than the manual transmission used in the Camaro SS."

"The ZL1’s automatic is a Hydra-Matic 6L90 six-speed with additional clutch plates, a strengthened output shaft, and the extra planetary pinion gears needed to ensure survival..."
 
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Discussion Starter #10
Tim K said this was a beefed up variant of the 8HP90, with ~30% higher TQ capacity. I'm guessing the true TQ capacity of this particular variant is at least 800 lb-ft.
Are you sure your not talking about the 8HP70. The 8HP70 8 speed auto is what is being used in the 392 cars. It is rated at 516 lb-ft on paper.


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Are you sure your not talking about the 8HP70. The 8HP70 8 speed auto is what is being used in the 392 cars. It is rated at 516 lb-ft on paper.


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I was referring to the 90. Whether it has been further upgraded over its base form is unknown, but it wouldn't surprise me - there is certainly precedent for this in other automotive applications like I cited above. I can just see SRT asking ZF for a super duty variant of the 90 to make sure it stays healthy in the Hellcat application. But pure speculation on my part.
 

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Torque-management may make these torque limits (somewhat) moot. With TM in place, they can arbitrarily limit the engine output in lower gears to whatever torque is needed to satisfy design limits.
 

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Discussion Starter #13 (Edited)
Torque-management may make these torque limits (somewhat) moot. With TM in place, they can arbitrarily limit the engine output in lower gears to whatever torque is needed to satisfy design limits.
Please explain Torque-Management. I am not familiar with what you are talking about.

The last transmission that I worked on was a 727 torqueflite.



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Discussion Starter #14 (Edited)
OK, I have done a little reading and correct me if I am wrong. The computer basically reduces power/torque automatically at the shift points to cushion the transmission.


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OK, I have done a little reading and correct me if I am wrong. The computer basically reduces power/torque automatically at the shift points to cushion the transmission.


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That is correct and throughout the entire rpm band.

663lbs-ft recommended torque input on paper. This is the maximum safe torque input for long term durability purposes.
 

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OK, I have done a little reading and correct me if I am wrong. The computer basically reduces power/torque automatically at the shift points to cushion the transmission.


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Application at shift points is just one aspect to TM. In a larger sense, it can be applied at any rpm or operating condition, as needed. For example, there can be a program in the engine computer that says to reduce maximum torque to x% in 1st gear, y% in 2nd gear, z% in 3rd gear, and then wide open in any gear higher.
 

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Discussion Starter #17
OK, thanks fellas. Pretty cool stuff

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Tim K said this was a beefed up variant of the 8HP90, with ~30% higher TQ capacity. I'm guessing the true TQ capacity of this particular variant is at least 800 lb-ft.

This is similar to the different levels of the TR6060. The version used in the Viper, Hellcat, GT500, ZL1, etc. is heavier duty than the variant used in the 392 Challenger.

Sorry to use the ZL1, but it's a good example of upgrade trans documentation for the higher perf models:

"A new Tremec TR-6060 MG9 six-speed transmission has a stronger output shaft, a more robust rear housing, and an additional mainshaft roller bearing to provide 30-percent more torque capacity than the manual transmission used in the Camaro SS."

"The ZL1’s automatic is a Hydra-Matic 6L90 six-speed with additional clutch plates, a strengthened output shaft, and the extra planetary pinion gears needed to ensure survival..."


I do not believe I ever made any such claims. I have not researched the 8 speeds a lot.
 

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Auto Transmissions rarely die from to much power... they die from heat. I put over 200 1/4 mile passes on a 46RE in a 2001 Dakota R/T spraying a 150 shot out of the hole with 28x10 Hoosiers.

No way the 46RE is as stout as the A8 in either the 392 cars or the Hellcat, yet it stood up to 500+ ft lbs of torque.

I changed the transmission fluid every 15k with Royal Purple.
 

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OK, I have done a little reading and correct me if I am wrong. The computer basically reduces power/torque automatically at the shift points to cushion the transmission.


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That is correct and throughout the entire rpm band.

663lbs-ft recommended torque input on paper. This is the maximum safe torque input for long term durability purposes.
I also think that Torque Management tables in the ECU is how Dodge manages the load on the drive train, as well as the driveability of the car (Difference between the "red key" and the "black key"). See the video below and look at about 2 min 15 seconds where the Dodge person driving says the Hellcat was designed for about 850 HP and detuned to 707 HP.
https://www.youtube.com/watch?v=ZwZt9FEh_lY
 
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