AT vs MT WHP difference

[86TOYO2k17]

Originally Posted by UNREAL

I was under the same impression that an AT can handle way more power... Unfortunately that isn't entirely true, nor the facts are very positive at all...

Our AT is called A960e, it is used in the IS250 and several other cars, and the max torque it can handle is 300nm/221ft⋅lb Only!*
The other issue is that the options to beef it up is almost none existing.



Reference
* https://www.gt86.org.uk/forums/forum...rbox-strength/
(go to the post by a member named Leeky)

Sent from my ONEPLUS A6000 using Tapatalk

I am fully aware of the transmission and capabilities,
The MT is rated is at about 185ft lbs but many people handle much more with out issue. same with the AT rated at 220ft lbs but people are running 300ft lbs no problem. What its rated at and what it can actually handle are far different. and many different factors contribute to this. which means its also rated at 35ft lbs more then the MTs. Which is a good amount of power when applied at higher rpm.

Also plenty of options to upgrade/Beef it up, SSP makes clutch packs that will handle 400 ft lbs, also numerous valve bodies and a high stall torque converter. Many other companies like IPT also make things for our transmission like valve bodies and even a fully built trans ready to go. A trans cooler is another easy good option that will help extend the life of the transmission when making more power and driving it harder.

I installed a custom made transmission cooler and i installed ssp stage 2 valve body. it handled 220ft lbs no problem before those and now even easier after.

[Goingnowherefast]

Originally Posted by JDM4E

The question was: why - and even if - AT drops power at hi-rpm, and where the AT loses power when the transmission is locked. It was a genuine technical question.

I'll try to tackle this. Worth noting that I'm not specialized in transmissions per say, but there is a lot of overlap with my area of engineering. From a technical standpoint, there two main reason why a traditional planetary automatic transmission will always have some efficiency losses even when it's locked:

1. In order to lubricate and to create sufficient hydraulic line pressure to energize the clutches and brakes, an oil pump is required. This is usually driven off the torque converter which is driven off the engine, and thus will have inherit losses, just as any accessory driven off the engine does.

2. Transmissions that use wet clutches (like the automatic in the twins) will have drag losses caused by the shearing of oil between rotating (but open) clutch plates. In this sense, DCT's have the advantage in that they only have one open clutch at a time, where as a traditional automatic could have 2-4 open at any given time depending on the gear selection.

Additionally, in practice AT's aren't truly "locked" a whole lot. This is to improve shift quality, durability, and NVH. Of course, any slippage will result in a power loss and it generates a considerable amount of heat. Tell me if you guys have any questions or something is unclear.

[86TOYO2k17]

Originally Posted by Goingnowherefast

I'll try to tackle this. Worth noting that I'm not specialized in transmissions per say, but there is a lot of overlap with my area of engineering. From a technical standpoint, there two main reason why a traditional planetary automatic transmission will always have some efficiency losses even when it's locked:

1. In order to lubricate and to create sufficient hydraulic line pressure to energize the clutches and brakes, an oil pump is required. This is usually driven off the torque converter which is driven off the engine, and thus will have inherit losses, just as any accessory driven off the engine does.

2. Transmissions that use wet clutches (like the automatic in the twins) will have drag losses caused by the shearing of oil between rotating (but open) clutch plates. In this sense, DCT's have the advantage in that they only have one open clutch at a time, where as a traditional automatic could have 2-4 open at any given time depending on the gear selection.

Additionally, in practice AT's aren't truly "locked" a whole lot. This is to improve shift quality, durability, and NVH. Of course, any slippage will result in a power loss and it generates a considerable amount of heat. Tell me if you guys have any questions or something is unclear.

This doesn’t answer the question. We know why the AT has an extra 2% drivetrain loss across the entire powerband, we don’t know why it has a much steeper/quicker drop off in power after 6900rpm vs an MT but an almost identical (but 2%) lower powerband all the way up to 6900rpm.

I have a feeling this may intentional in the ECU tune and/or TCU programming to help smooth out the shift and/or help save the clutch packs.
And I think based on personal experience how my car feels that this can be entirely tuned out as my car continues to pull hard all the way to redline (7500rpm now) with no noticeable drop off and my tuner has done many things to change how the AT works in the tune.

[Goingnowherefast]

Originally Posted by 86TOYO2k17

This doesn’t answer the question. We know why the AT has an extra 2% drivetrain loss across the entire powerband, we don’t know why it has a much steeper/quicker drop off in power after 6900rpm vs an MT but an almost identical (but 2%) lower powerband all the way up to 6900rpm.

I have a feeling this may intentional in the ECU tune and/or TCU programming to help smooth out the shift and/or help save the clutch packs.
And I think based on personal experience how my car feels that this can be entirely tuned out as my car continues to pull hard all the way to redline (7500rpm now) with no noticeable drop off and my tuner has done many things to change how the AT works in the tune.

The drag losses aren't going to be perfectly linear with engine RPM. That could be what you are questioning.

[86TOYO2k17]

Originally Posted by Goingnowherefast

The drag losses aren't going to be perfectly linear with engine RPM. That could be what you are questioning.

Comparing the two dyno graphs besides below about 3500RPM where torque converter isn’t fully locked, and above 6900rpm where for some reason the AT falls off drastically quicker, basically about to 2whp loss per 100rpm vs 1whp loss per 100rpm or about 10whp drop off at redline vs 5whp drop off at redline for MT after peak power. They are almost 100% identical between 3500-6900rpm minus an extra 2% drivetrain loss for the AT. So the question is why does the AT have such identical powerband curve up to peak power and make peak at same point (same exact engine should be exact same) but then falls off twice as quickly after 6900rpm compared to the MT. Only thing that would make sense to me is something in the tune/programming doing this intentionally for some reason and thus could be altered to not do this if desired.

[Goingnowherefast]

Originally Posted by 86TOYO2k17

Comparing the two dyno graphs besides below about 3500RPM where torque converter isn’t fully locked, and above 6900rpm where for some reason the AT falls off drastically quicker, basically about to 2whp loss per 100rpm vs 1whp loss per 100rpm or about 10whp drop off at redline vs 5whp drop off at redline for MT after peak power. They are almost 100% identical between 3500-6900rpm minus an extra 2% drivetrain loss for the AT. So the question is why does the AT have such identical powerband curve up to peak power and make peak at same point (same exact engine should be exact same) but then falls off twice as quickly after 6900rpm compared to the MT. Only thing that would make sense to me is something in the tune/programming doing this intentionally for some reason and thus could be altered to not do this if desired.

The most likely thing is that you simply can't have solid conclusions based on dyno data with very loose boundary conditions. You can change dyno results literally based on how tight you strap a car up.

Provided that, it's possible that there is some calibration changes to the automatic twins that explains the delta. It's no surprise that the AT owners have different expectations when purchasing a vehicle, so a different PT cal is likely used. Also, again, an even simpler answer is that at high engine speeds there is higher drag loss because of oil shearing combined with some micro-slip of the TCC as most OEM's use.

[86TOYO2k17]

Originally Posted by Goingnowherefast

The most likely thing is that you simply can't have solid conclusions based on dyno data with very loose boundary conditions. You can change dyno results literally based on how tight you strap a car up.

Provided that, it's possible that there is some calibration changes to the automatic twins that explains the delta. It's no surprise that the AT owners have different expectations when purchasing a vehicle, so a different PT cal is likely used. Also, again, an even simpler answer is that at high engine speeds there is higher drag loss because of oil shearing combined with some micro-slip of the TCC as most OEM's use.

Same day, same dyno, and the main thing being compared is the powerband curve being identical, up to peak power. Then beyond peak power for the last 4-500rpm AT drops off twice as quickly, we aren’t comparing so much what the exact drivetrain loss/difference is (which was basically 2% across entire band) or who makes more power, but the powerband curve which shouldn’t really change and doesn’t, until after peak power. Which if it was slip you would think this would happen and be noticeable at either peak torque and/or peak whp, not after the fact. also why people who are tuned with FI don’t experience this which if it was slip you would think the extra power would exacerbate the slip making it more pronounced not entirely covering it up.