8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

5.0 V10 50v biturbo - 571 bhp
welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Fri Mar 26, 2021 10:13 am

I'd be grateful for a bit of help on this. I need to gather some information.

If someone has either a C6 or C7 S6/S7/RS6/RS7 in the air for any reason, could you please measure the overall length of the gearbox from bellhousing mounting flange to the output shaft flange, and also the overall length of the prop-shaft to the rear axle, again measured between the coupling flanges?

The ZF 8HP has a splined output shaft, so it would need a different or modified prop-shaft.

Thanks in advance for your help.

Nick

Jim Haseltine
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by Jim Haseltine » Sat Mar 27, 2021 10:16 am

I tried yesterday afternoon but my car now isn't high enough for me to take accurate measurements and the front UV joint heat shield is back on too - something I don't want to take off a third time. A couple of weeks back when the car was higher and I had the engine dropped it would have been easy(ier) but manipulating a tape measure when there was only an inch or so between my face and the bottom of the car was a non-starter - sorry. Don't think I'll have to lift the car any higher again before I'm finished with this job but if that happens I'll see what I can do.

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Sat Mar 27, 2021 11:51 am

Thanks anyway Jim. I don't have a good solution to the propshaft problem, I'll just work something out when I get there, but leaving myself flexibility and options will help.

It would be wonderful if the RS7 propshaft would just drop straight in, but that may be too much to hope for.

Of course I may just have to have to have a custom shaft made.

Now the rear diff......

k1llertech
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by k1llertech » Sat Mar 27, 2021 6:41 pm

Hey welwynnick, looking forward to your updates. I'm searching everywhere for such info. I'm not a technical person, but I really hope you can make it. I talked with some mechanics, and their only concern is with the TCU and the ECU. From their prospective the fitting is not such a big deal.

Stay safe.

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Sat Mar 27, 2021 7:05 pm

k1llertech wrote:
Sat Mar 27, 2021 6:41 pm
I talked with some mechanics, and their only concern is with the TCU and the ECU.
If that was the extent of the problem, I think someone would have done this by now. I heard that someone did it with a BMW, but he used one of the aftermarket TCUs.

I have a long list of challenges ahead, and though I've already overcome some of them, what worries me is what I haven't thought about.

As an example, there are about 4000 different versions of the 8HP, and how do we know which one to use?

But if your mechanics know more than I do, I'd appreciate all the help I can get. I doubt if I can do it all myself.

Nick

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Sun Apr 11, 2021 12:36 pm

One of the mechanical hurdles that has to be overcome is the rear axle. Since Audis have the front differential in the gearbox, the final drive will be whatever is in the gearbox, and the final drive ratio with it. I don't think you can change the crown wheel.

Unfortunately, the 8HP generally has a different final drive ratio to any of the 6HP transmissions that it replaces. You can't really expect the centre diff to accommodate the speed difference; I think it would overheat and wear out in pretty short order.

Therefore you really need the rear differential from the same doner car as the gearbox. And that will inevitably be somewhat different to the RS6 C6 rear axle. That will need some proper mechanical engineering for the mounting yoke. As with many things, there is at least a lot of commonality with VAG drive shaft flanges. They're 6 x 115mm for many cars from my A5 2.0 manual to the ZF 8HP.

Nick

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Fri May 28, 2021 5:19 pm

For the record I thought I'd list the advantages with using the 8HP over the 6HP. It's stating the obvious, but it's quite a good list:

Good reliability
High torque capacity
High efficiency
Low first gear
High top gear
Close ratios
Quick gear shifts
Smooth gear shifts
Shared architecture
Improved performance
Reduced fuel consumption
Reduced emissions

These are the integration problems that I think I have solutions for:

Which doner car
Bellhousing
Flywheel
Starter motor
Front drive shafts
Mechanical control
Electrical power
Cooling

And these are the integration problems that I don't have solutions for:

Rear differential
Transmission mount
Prop-shaft
Parking lock
Electronic control
Security
Space

And these are the differences that I'm just going to ignore for now:

Stop/start control
Automated neutral
Dashboard display
Diagnostics

Nick

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Sat May 29, 2021 5:44 pm

Up to now it's all been a bit academic as I don't own an RS6. However, I don't think tinkering with the gearbox on the car would be very easy, so I'm taking a different approach, so I can build up some confidence before actually making the plunge.

I'm going about things the wrong way round by proving the easy solutions before tackling the difficult things, but I've committed myself now. I've bought an 8 speed gearbox to play with. It's from a low mileage write-off and seems to be in good condition.

Sadly I couldn't do a trial fit in my A5 when I was replacing the clutch. I'm pretty sure some quattro versions of the A4 and A5 use the 6HP box, and if the 8HP would fit in there, I think it would go anywhere. Now I have a nagging doubt, as it's a big transmission.

20210318_120849.jpg

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Fri Jun 04, 2021 8:04 am

Well, there are lots of pieces to this puzzle, and I just got another one. I thought I'd try to find a scrap RS6 or S6 engine, but it turns out there aren't very many of them.

However I did find an R8 engine, and I've had to find some space in my shockingly cluttered garage.

It's not exactly what I was looking for, but the possibility of having an actual Lambo engine in an RS6 was intriguing. After all, they are the same engine, aren't they?

Nick

20210309_134755.jpg

rtd
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by rtd » Fri Jun 04, 2021 9:17 am

Supposedly the only similarity between both engines is the block. Everything else is different.


Sent from my iPhone using Tapatalk
Volvo XC90
C7 - RS6
C6 - RS6
B5 - RS4

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Sat Jun 05, 2021 4:30 pm

rtd wrote:
Fri Jun 04, 2021 9:17 am
Supposedly the only similarity between both engines is the block. Everything else is different.
What's your source of information? Here's a picture of the back of the R8 V10 engine:

R8 Engine Rear.jpg

And here's a picture of the back of the RS6 V10 engine:

RS6 Engine Rear.jpg

EDIT: Notice the R8 has the power steering pump in the bottom left corner, and the aperture for the front diff propshaft in the bottom right corner.
Last edited by welwynnick on Fri Dec 02, 2022 3:16 pm, edited 1 time in total.

don0301
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by don0301 » Sun Jun 06, 2021 10:42 am

Makes you wonder why Audi made a completely different block from the lambo one....then stamped a lambo bull on it.... :roll:
Ferrari 488 Spider
C6 RS6
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Nissan 200sx mk 2
Vauxhall Senator
Ford Sierra 1.8LX
Peugeot 205 1.9 GTi
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Vauxhall Astra 1.3
1st car Datsun 120 FII Lime green....yeah :shock:

Stiggles
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by Stiggles » Sun Jun 06, 2021 6:42 pm

don0301 wrote:
Sun Jun 06, 2021 10:42 am
Makes you wonder why Audi made a completely different block from the lambo one....then stamped a lambo bull on it.... :roll:

I'm pretty sure the block isn't the same as the 5.2 but the first gen 5.0 gallardo, but given the displacement difference and having seen countless pieces of information stating that the C6 RS6 shared minimal parts with any 5.2 Lamborghini/R8 I would say it's safe to assume the block is one of the few shared pieces

The oil pump has a bull stamp on it, but I don't know if that is used in any other engines

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Thu Sep 23, 2021 9:35 am

I'm pretty sure the block isn't the same as the 5.2 but the first gen 5.0 gallardo,
The 5.0 Gallardo block had a bore spacing of 88.0 mm, same as many Audi 4 and 5 cylinder engines.

All other Audi/ Lamborghini 90 degree V engines have a bore spacing of 90.0 mm, which includes the following:
3.2 V6
4.2 V8
5.0 V10 RS6
5.2 V10
Last edited by welwynnick on Thu Sep 23, 2021 9:36 am, edited 1 time in total.

welwynnick
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Re: 8 Speed ZF8hp from C7 RS7 and RS6 retrofit.

Post by welwynnick » Thu Sep 23, 2021 9:36 am

welwynnick wrote:
Fri Mar 26, 2021 10:13 am
I'd be grateful for a bit of help on this. I need to gather some information.
If someone has either a C6 or C7 S6/S7/RS6/RS7 in the air for any reason, could you please measure the overall length of the gearbox from bellhousing mounting flange to the output shaft flange, and also the overall length of the prop-shaft to the rear axle, again measured between the coupling flanges?
The ZF 8HP has a splined output shaft, so it would need a different or modified prop-shaft.
Thanks in advance for your help.
Nick
I can answer some of this myself now, having unearthed some useful information buried deep in the internet.

The length of the RS6 C6 prop-shaft is 1759 mm (GKN says 1583)
The length of the RS6 C7 prop-shaft is 1649 mm (GKN says 1649)
The length of the RS4 B7 prop-shaft is 1529 mm

That doesn't actually tell me whether I can or can't use the C7 prop, as there are other variables:
The C7 has a wheelbase of 2912 mm vs 2843 mm for the C6, so the C7 is 69mm longer.
The ZF 8HP box is probably longer than the 6HP, so the prop may need to be shorter.
The 8HP has a splined rather than flanged output, so the prop needs to be longer.
The C7 has a different rear diff, but I don't know what the effect of this is.

Although the RS6 C7 has a different prop Part No to other A6 auto models, it's the same length, which suggests the 'box is the same length as lower capacity versions of the 8HP.
In other respects the B7, C6 and C7 props are similar - the tube diameter is 70mm and the diff flange has a 6 x 86 PCD

I am still trying to fit the 8HP, but haven't made much progress recently. This isn't much, but it's a little bit of information that I'll need.

Does anyone know if it's possible to split the prop-shaft into two?

Nick
Last edited by welwynnick on Mon Jan 03, 2022 4:15 pm, edited 3 times in total.

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