RedLS6

Maybe they did, and just re-did the internals slightly. It sure does look like an existing ZF case on the outside, at least from the limited cad angles we have available now. I've been impressed with GM's transmission engineering more often than not. On the flip side I'm not sure if this new box has any joint ZF-Porsche patents, which may preclude its licensing elsewhere, in an unmodified form.

They might have increased the torque capacity considering a 400-ft-lb N/A Porsche versus a twin-turbo 5.5, and also modified the gear spread to account for the torque curve differences and to keep the engine closer to its sweet spot for partial load economy.

A modded TT 5.5 is going to potentially make serious power and torque. Hope these boxes are tough enough to survive at the strip.

JoesC5

While it's true that the 608 HP V8 in the 918 has 398 lb-ft of ICE torque, it also has a 156 HP electric motor also feeding a large amount of torque through the transaxle to the rear wheels. The ZF DCT is not limited to 400 lb-ft of input torque

According to Porsche...."Maximum torque calculated on the crankshaft in 7th gear(combined)....944 lb-ft".

RedLS6

That's a good point. It's torque capacity is very likely higher than 400 ft-lb in first gear, the question is how much.

That 944 figure is in 7th gear, quoted above. The 1st gear torque rating may be significantly lower. Take a look at how the 918 hybrid powertrain works. Starting out from a launch, power is sent to all four wheels in the lower gears, and then power is gradually diverted away from the front wheels and more towards the rear wheels. By 147mph, 100% of its power goes to the rear wheels.

In 7th gear, this is the 944 ft-lb equivalent.

In 3rd gear, it's 787 ft-lb equivalent.

Below that, they claim a minimum of 590 ft-lb but they're a little vague as to how and where this torque is generated, although the implication is 800rpm-5000rpm.

Consider also that the DCT likely has its maximum input torque specced by gear, and that 7th is likely the highest, with 1st gear possibly being the lowest.

It's not an exact science trying to guess its real 1st gear torque rating from what Porsche publishes, but I'd guess it's good for more than 590 ft-lb in first gear, maybe even as high as 650 or 700 ft-lb. That's my back-of-the-envelope guess..... it's certainly probable it can hold more, which it would likely need to do for the C8.

Maybe you can google around and find a more solid estimate or published data.

JoesC5

The power to the front wheels has nothing to do with the torque capacity of the 918's DCT, as the front 129 HP electric motor(and it's gearbox) is powered 100% by the on board battery.

The 918's DCT is supplied power by both the 608 HP ICE and by a separate(from the front wheels) 156 HP electric motor(powered by the onboard battery).

The way you structured your post was to imply that the ZF DCT ONLY had to contend with the 400 lb-ft of torque supplied solely by the 608 HP ICE, but in reality, it has to handle the torque from both the 608 HP ICE and the 156 HP electric motor(combined).

As of now, we have no idea what the torque of GM's 5.5L V8 will be thus we have no idea as to whether the DCT that GM has selected to use will handle that torque "out of the parts bin" or if it will be required to be upgraded from what Porsche's requirements are for the 918.

thebishman

These exhaust ‘farts’ as you call them are not an intrinsic design element of a DCT transmission, rather they are deliberate and artificial ‘noise’ generated by a small amount of fuel being dumped into the engine whilst the exhaust valves is open iirc. I may well be wrong on where/when the fuel is being artificially added by the ECU, but it’s a manipulated sound by the manufacturer. If it wasn’t written into the ECU/TCU ‘code’, it wouldn’t occur.

Bish

RedLS6

You're missing the fact that, as the power to the front wheels is decreased to zero, the power to the rear wheels is increased. That's where it impacts the DCT. The DCT sees a variable input torque versus speed, and they can lower the torque seen in the lower gears. The 944 ft-lb is very likely not the input rating in first gear. Actual crank torque at launch in the critical first gear will be much lower.


If that's all you read from it, then you're probably just looking for nits to pick. The way you structured your post was to imply that the ZF DCT is good for 944 ft-lb. Neither of us know the real number, but we can make educated guesses. At the end of the day, we can probably all learn something by building on the material we do post, instead of nitpicking apart each detail looking for an argument. Kinda like it was pointed out a while back that the transmission isn't going to be a Tremec 9007.

Shaka

WRC cars have had an injector and a spark plug in the intake before the compressor for years for an instant spool up. Those items can be purchased after market.. http://www.racecar-engineering.com/r...nd-wrc-turbos/

NoOne

Partially. If you read the article I posted regarding it there is a reason it is done to help smooth out the shifts. There is a reason behind it, it is deliberate but it is not meant to create an artificial noise.

JoesC5

You are missing the point that the torque passed through the DCT is the combined torque of BOTH the ICE and the crankshaft mounted electric motor.

That combined torque is considerably more than the 400 lb-ft you wanted to pass off as being the capacity of the 918's DCT.

I'm guessing that the combined torque of both the ICE and the electric motor in the 918 is around 755 lb-ft and that the 918's DCT can handle that amount of torque in 1st gear.

The Tremec M7 used in the C7 Z06 is rated at 635 lb-ft of input torque, yet that same transmission is used in the C7 ZR1 with it's 720 lb-ft of engine torque.

JerriVette

Do Ferrari 458 s fart?

Lamborghini huracan?

BMW M5 ?

Mclaren?

Non turbo versions don't fart...

It's the turbo..not the dct...

Either way it's fine...I don't care as I believe GM engineers can rid us of this fart noise of VW GTI s and Audi s4 s...

Audis s5 that had a dct in its last generation never darted with the v8 non turbo.

At least that's my opinion...

Ridiculous sound for kids..

Although GM has flames shooting out the
LT5 zr1....so it's all I. Good fun I guess..

NY09C6

That really is an undesirable sound. Reminds me of a kids Honda with a fart can.

RedLS6

Nope, I stated the above TWICE, in post #243 and again in post #246. What do you think "as the power to the front wheels is decreased, the power to the rear wheels is increased" means? It means that there is an electric motor supplying aux power to the rear wheels, and its torque increases as the front drive torque decreases. Jeezus. I'm not sure I can make it any simpler for you.

And, I actually agreed with you in post #243, in the very first sentence.

Reading comprehension escapes you. Next time I post I'll make sure to dumb it down for ya, as you seem unable to grasp concepts from sentences, only strings of words.

RedLS6

Your guess is based on wrong assumptions. You are trying to add the peak IC engine torque with your guessed peak rear electric motor engine torque, and these peaks occur at different RPMs and are not additive.

Furthermore, Porsche's equivalent crankshaft torque is the torque a conventional ICE would need to produce to equal the combined torque of all four drive wheels.....including the ICE, the rear electric motor, and the front system. It's not actually the torque present on the crank.

Your post was phrased to imply that the full 944 ft-lb (or 787 ft-lb 3rd gear) goes through the DCT. It doesnt.

The equivalent crankshaft torque isn't what goes through the crank and therefore the DCT. And in third gear, this "equivalent" combined torque is 787 ft-lb, considering the entire system, front and rear. And you're saying the ICE and Rear motor alone are worth 755 ft-lb of that 787 (which the 787 is probably lower still, in first gear)?.

dcbingaman

Don't forget that GM does a LOT of CAD studies to determine what will fit. Further, they provide the transmission companies with Interface Control Documents (ICD's) for conformance to what GM needs. Supplier Mgt. no doubt has forced Corvette Engineering to compete the bid for the transmission, so it is possible, (even likely), that GM has CAD renderings of BOTH the ZF unit and the Tremec unit in their chassis, with envelope and mount points specified BY GM. For that reason I think it could be either a ZF unit OR a Tremec unit, depending on cost, schedule and a host of other factors. I don't think one leaked CAD drawing is the last word on this subject.

I do think the box shown in the leaked CAD drawing is a ZF DCT - too many coincidental features for it not to be, so.....clearly ZF is a candidate provider. I guess we'll know when GM is ready to tell us.

ltomn

Mr. Bingaman, I am inclined to disagree with you on one important point; that of one CAD drawing being the "tell all" of the transmission story. My understanding is that the details of the new ME car have been settled for quite some time and the choice of a transmission certainly is not a minor one and, as such, was an early decision. In fact this has been settled for so long that some of the mules we are seeing are likely models that will not be released until much later in the vehicle life (2021-2022). One point of notice to support that theory is a post in another thread about testing acceleration at GM Michigan test grounds. eyedeekay said he believed he saw the front wheels slipping. That can be read several ways but certainly one is: it is the electric motor version, which has been said to power the front wheels, overpowering the front end.

All this does is suggest that we have wild imaginations but those imaginations all revolve around our personal knowledge of a situation. Some more informed then others. However, I am inclined to believe that the ZF transmission has been chosen and will be in the cars in 2020.

Bikerjulio

I'd tend to agree that the transmission decision was made some time ago. We don't know the date on that CAD and for all we know it could be a few years old. The interesting thing is that C&D and others were saying "Tremec" as far back as 2016, which has been confirmed by one of the "insiders" here as well. The only evidence for ZF seems to be that CAD. So the ZF theory comes down to how much faith one has that it represents the current setup.

https://www.caranddriver.com/news/ev...h-transmission

ltomn

Read the post by Skank on the other thread about DCT transmissions:

https://www.corvetteforum.com/forums...post1597504080

Bikerjulio

I did already thanks. It's interesting. It's possible. But it's all speculation. I'd agree that in the event that RWS is offered in the C8, then it's likely going to be ZF.

dcbingaman

You may well be right, but a lot of stuff gets created on CAD that never gets built. My issue with a leaked CAD file is its age and provenance - we just don't know where it came from or how old it is. Is it truly the current "electronic mockup", or is it an early configuration that landed "on the cutting room floor". We won't know until GM tells us.

There are at least two journalist stories (Car & Driver in 2016 and Don Sherman's 2018 article in Hagerty Auto news) that say it is definitively a Tremec DCT. Sherman has had a pretty good record of predicting Corvette developments and is an insider's insider in Detroit, so I don't think we can discount his account easily.

I do agree that they picked the transmission a while ago and that the mules sound like they have both a small block Chevy OHV engine (LT2 ??) and a DCT. I don't see evidence of both a base and an advanced model being tested, but I do agree with Bikerjulio that there are distinctive parting lines in the roof indicating that one model may be a coupe with a removable targa top, while the second may be a Ferrari 488 GTS "Spyder" type with a retracting hard-top. Again, we will see when GM is ready to show us.

dcbingaman

With Porsche's mark-up, I'd bet GM's cost for these in quantity is about 50% of this or $3500, about the same as their cost for a 8L90 automatic transmission. This may be a no-brianer.