8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

[VaudiGR]

That's good news Nick.

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[VaudiGR]

Any updates here?

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[welwynnick]

Sorry, no, not much progress.

I didn't think there seemed to be much interest.

Nick

[VaudiGR]

Oh I'm interested!
If there was a complete way for the bentley box to be mounted and electronically accepted in the rs6 I'd probably go for it if it was affordable.

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[welwynnick]

I think there's probably a way to do it, and its relatively affordable. If you do an eBay search for Bentley Continental GT gearbox you get a few 8 speeds for around £3000-5000, some of which can be offset by selling the 6 speed.

You could spread the net and look for Bentayga, RS6 C8, SQ7, RSQ8, Urus, Cayenne or Urus boxes, and they might fit if you use their front drive shafts. I don't know about the bell housing or transmission selector, yet, though. That's why I suggest the 2013-2018 Conti GT box.

There is still the problem of the prop shaft and the rear axle to solve.

Even if the worst comes to the worst and it needs an after-market TCU, that's not the end of the World, and I'm not sure it will come to that. At the very least the 8HP TCU would have to be re-programmed with the RS6 chassis number, in order to allow the engine to start, and I think several companies can do that now.

There's very good reason to do this, and lots of motivation, but there are other things to do as well....

Nick

[VaudiGR]

In your own time Nick, there is no rush. Ideally a box that could fit without issues and then a TCU that can be programmed is the perfect scenario. Going aftermarket with the tcu would not be nice IMO as keeping everything stock is better

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[welwynnick]

No progress on my side I'm afraid (other cars to look after), but I couldn't help noticing the launch of the Dodge Challenger SRT Demon 170. Literally, in fact, with wheels in the air. With more boost, lots of drivetrain mods and E85 fuel it generates 1025bhp and 1281 Nm. With semi-slick drag radials and a perfect drag strip, Dodge claim 0-60 in 1.66 sec and a quarter mile in 8.91 sec, peaking at 2.0g. Great achievement, but so what?

Gearboxes are usually specified by their input torque capacity. But the output capacity becomes important for 4WD vehicles and commercial vehicles, as the back wheels don't act as a torque-limiting clutch like they do in a lighter car. Although it's only RWD, the Demon 170 still has enough torque and grip to accelerate a heavy car at 2.0g. The gearbox is rather between an irresistible force and an immoveable object. Otherwise reliable transmissions often break when launching on a sticky drag strip.

Dodge must have noticed customers modifying their previous Hellcat / Demon / Durango with a lot more power and torque, and that the stock ZF 8HP90 gearbox actually survived. The Demon 170 has a heavily modified engine and transmission. In the engine, only the original camshaft remains, everything else is upgraded, and the prop-shaft, differential and half shafts are all heavily strengthened. This is a production road car that will inevitably get thrashed mercilessly at the drag strip, after all.

But as far as I can tell, the only change to the gearbox is a bigger output flange. The 8HP90/95 must be stronger than ZF claim, and much stronger than the 6HP26/28.

Nick

[VaudiGR]

Nick, I have my car at the Shop ready for your input. Where do I pay ?

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[Sam16510273849]

Can't believe this thread is nearly three years old, and there's little progress in replacing the 6 speed ZF gearbox with the 8 speed.

So to those who have been saying this forum has been quiet of late, I'll try to liven it up and have a go at fitting the 8 speed box.

I have a feeling that you're going to need some patience, though.

Nick

I own an S6 V10 and was considering this swap, not only for performance, but efficiency as well. I spend most of my time on the highway and having the rpm bellow 2000 would be nice. The 8 speed from the C7.5 A6/A7 mated to the 3.0TFSI is currently top of my list. I've been looking at the bell housing bolt patterns and they seem pretty similar. I noticed you didn't go for it, so any pointers/info/tips I should know in case I decide to do it? A tuned 3.0T makes very similar, if not more, power than the S6's V10, so I'm not worried about it not handling the torque.

[welwynnick]

The bolt pattern is the same, but you would need at least a bellhousing adapter, a modified prop-shaft, LHS front drive-shaft and a different rear differential.

[VaudiGR]

Oh so rear differential also needs changing. What about the electronics though?

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[welwynnick]

The rear differential has to match the front differential, and the 6HP and 8HP have different final drive ratios on the front diff.

The electronics are inside the transmission, and the electrical interface is the same as the 6HP, but the 8HP would have to be programmed with your chassis number.

[VaudiGR]

Would there be communication since the age of the 2 transmission is different?ie dash would only show 6 gears while the 8hp has 8

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[welwynnick]

They both use CANBUS comms which have standardised data and physical interface.

[VaudiGR]

That's grand. Ticks another box!

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