S8 Turbos on A8 4.0T, will it fit/work?
09-17-2016, 08:57 AM
#1
AudiWorld Super User
Thread Starter
S8 Turbos on A8 4.0T, will it fit/work?
Looking at a set of S8 turbos. Anyone know if these will just drop into my A8 4.0T?
Next question will be to APR to see if their Stage III software will run them.
After driving an RS7 yesterday I realized that I want to stay in an A8, but I do not want to pay now for an S8 Plus or change the car at all for that matter. I have become quite accustomed to my setup and really like my car given how little I owe on it. So looking to upgrade the turbos after losing to a heavily blown E55 wagon last night.
Next question will be to APR to see if their Stage III software will run them.
After driving an RS7 yesterday I realized that I want to stay in an A8, but I do not want to pay now for an S8 Plus or change the car at all for that matter. I have become quite accustomed to my setup and really like my car given how little I owe on it. So looking to upgrade the turbos after losing to a heavily blown E55 wagon last night.
Last edited by DirtyVegasTT; 09-17-2016 at 11:17 AM.
09-17-2016, 11:26 AM
#2
AudiWorld Super User
No shame in losing to an E55. 
Those came factory with a supercharged V8 with 493hp, assuming it's the model I believe. They were pulling mid 12's from the factory and a pulley swap puts them into the 11's very cheaply. There's always a faster car, be careful you don't ruin a good thing in the quest for being #1.
Those came factory with a supercharged V8 with 493hp, assuming it's the model I believe. They were pulling mid 12's from the factory and a pulley swap puts them into the 11's very cheaply. There's always a faster car, be careful you don't ruin a good thing in the quest for being #1.
09-17-2016, 12:04 PM
#3
AudiWorld Super User
Thread Starter
No shame in losing to an E55. Those came factory with a supercharged V8 with 493hp, assuming it's the model I believe. They were pulling mid 12's from the factory and a pulley swap puts them into the 11's very cheaply. There's always a faster car, be careful you don't ruin a good thing in the quest for being #1.
Those came factory with a supercharged V8 with 493hp, assuming it's the model I believe. They were pulling mid 12's from the factory and a pulley swap puts them into the 11's very cheaply. There's always a faster car, be careful you don't ruin a good thing in the quest for being #1.Last edited by DirtyVegasTT; 09-17-2016 at 12:43 PM.
09-17-2016, 03:10 PM
#4
AudiWorld Super User
I would pull the related parts diagrams from EKTA and look at part numbers at critical points for A8 4.0T vs. S8--head pipes, gasket at turbos (as partly an indirect clue since turbos do vary), anything on exhaust manifold at bolt up points (which I think is all heavily integrated now IIRC), etc. My WAG is plug and play pretty much, but no first person info. From memory I'm thinking the turbo's are all integrated now with manifold, so you may want to check that--to look at whole manifold bolt up. Design and high level differences were summarized in the 4.0T SSP publication as I recall--which covered the S8 and RS7 variations too.
If needed, I have the S8 side donor and could snap pics of any specific question areas after you poke some at parts, EKTA slides, etc. RS7 vs. S7 should give you pretty similar comparo if any posts there. Also remember the air boxes in S8 are twinned (unlike RS7) but I'm guessing that doesn't affect it. I would still be looking carefully at how the pressurized side is piped/ducted. If a delta, could be any RS7 part number variances bridge that gap.
If needed, I have the S8 side donor and could snap pics of any specific question areas after you poke some at parts, EKTA slides, etc. RS7 vs. S7 should give you pretty similar comparo if any posts there. Also remember the air boxes in S8 are twinned (unlike RS7) but I'm guessing that doesn't affect it. I would still be looking carefully at how the pressurized side is piped/ducted. If a delta, could be any RS7 part number variances bridge that gap.
09-17-2016, 03:27 PM
#5
AudiWorld Super User
Thread Starter
S6 and S7 guys drop in RS7 turbos, which are a direct bolt on from what I understand for C7 cars. I was hoping the same would apply to our D4. You're right about checking the hardware around it. I will see what my local shop and APR says first before trying to figure all that out myself.
Last edited by DirtyVegasTT; 09-17-2016 at 03:30 PM.
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09S5 (07-10-2021)
09-17-2016, 06:42 PM
#6
AudiWorld Super User
Wondering how this would affect the transmission. Can the A8's transmission safely handle the extra torque generated by the S8 turbos? If it's OK handling the additional pressure from chip programs, then maybe, but....
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09S5 (07-10-2021)
09-17-2016, 06:45 PM
#7
AudiWorld Super User
Thread Starter
I think our 4.0T has the same tranny as in the S8 and RS7. Those guys race and launch their cars with mods + 100 octane all the time. I've seen some 800+ HP RS7 race on the stock transmission as well I think.
Last edited by DirtyVegasTT; 09-17-2016 at 06:51 PM.
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09-19-2016, 07:26 AM
#9
AudiWorld Super User
I would not just assume it is the same tranny without more research. Sure, "same" = the ZF 8 speed generically. But even on ZF's (somewhat) marketing oriented site it shows 9 different flavors with 5 different torque ratings. Also, even in the same car/body you can find different torque rating ones being used depending on the motor, at least on prior gen Audis when I have looked into it. It's not to say, it won't work or be okay, but rather not something just to assume the other direction either.
You start with the basic nameplate to at least figure out which model/class it is within the overall 8 speed group. On a ZF always underneath where you can see it pretty easily, though on any of the newer big Audis you often have to pull a noise/aero panel to see it. For OP's purpose, looking at basic model and rating may be enough since it gives upper bounds for torque tranny was rated to handle for a given application. Then the three digit codes on it get you down to the more specific fitment if you want to pursue further. Historically Audi has also used different gear ratios in a given model depending on the motor. With turbo's though I think that has lessened. It doesn't affect the torque tranny can handle generally, but does affect acceleration and fuel economy. Thus on a D3 the S8, 4.2 and W12 all had different ratios. S8 was lowest geared and W12 highest. And without it BTW, pretty obvious to me in that generation W12 would have taken it rather than be closer to tied. D3 W12 was also right near the limit of torque that model of (six speed) ZF tranny could handle as an example of why to check. In turn I think Bentley's blown W12 used a different specific model to deal with added torque. I don't recall info about these areas offhand for D4.
You start with the basic nameplate to at least figure out which model/class it is within the overall 8 speed group. On a ZF always underneath where you can see it pretty easily, though on any of the newer big Audis you often have to pull a noise/aero panel to see it. For OP's purpose, looking at basic model and rating may be enough since it gives upper bounds for torque tranny was rated to handle for a given application. Then the three digit codes on it get you down to the more specific fitment if you want to pursue further. Historically Audi has also used different gear ratios in a given model depending on the motor. With turbo's though I think that has lessened. It doesn't affect the torque tranny can handle generally, but does affect acceleration and fuel economy. Thus on a D3 the S8, 4.2 and W12 all had different ratios. S8 was lowest geared and W12 highest. And without it BTW, pretty obvious to me in that generation W12 would have taken it rather than be closer to tied. D3 W12 was also right near the limit of torque that model of (six speed) ZF tranny could handle as an example of why to check. In turn I think Bentley's blown W12 used a different specific model to deal with added torque. I don't recall info about these areas offhand for D4.
Last edited by MP4.2+6.0; 09-19-2016 at 08:01 AM.
09-19-2016, 08:33 AM
#10
AudiWorld Super User
It seems the A8 4.0T and S8 ZF 8-speed transmissions have the same gear ratio set-ups (at least for 2015 & 2016), but I still think there could be some internal differences between the two.