8 cylinder front engine iconic vehicle
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By Zirconocene
This is a little bit of a thought experiment for a project I'm thinking about. Hopefully some of the brains on here can help educate me.

Supposing that you had an automatic transmission hooked up directly to a 32V motor, like you might find in a 911 or a Boxster, how much would you need to worry about thrust bearing failure? Would you still want to spend some calories on clamping things to the degree needed when a torque tube is involved?

By worf
Yes and no.

Remember there are two leading causes of TBF: Shaft migration in the clamps and improper (post-factory) installation.

So, the former isn’t an issue, but the latter is an issue.

You’d probably still need *a* flex plate I think…
By Hey_Allen
Just in the matter of it being a thought exercise...

Since the transmission is either a Mercedes design or at least based on one, I have a little actual experience working with one directly attached to an engine.
The flex plate and torque converter tend to self center in their forward-aft positioning, assuming that you have the torque converter properly splined into the front of the transmission before mating the transmission with the engine.

Once the bell housing bolts are tight, it was only a matter of spinning the converter until the first pair lined up, then turning the engine 120 degrees for each of the remaining pairs.
The torque converter was pulled slightly out of the front of the transmission as the bolts were tightened to secure it to the flex plate, but then stayed put at that depth over the operating life of the engine.

If never heard any concerns about thrust bearings on the MB om617 diesels, or the m103, m116, and m117 gas engines that I'd worked with that used the 722.3 transmissions that 928 transmissions appear to be based on.
By Zirconocene
I haven't spent nearly as much time thinking about the transmission as I have the engine side of the drivetrain, and given my systems understanding of the (to me) hairier parts of the engine, I'm in a totally unknown space with thinking about this.

My sense of things was that, as @worf said, getting rid of the TT shaft would eliminate part of the issue. What I am working to understand is if there are other forces that would impart the same kind of effect, just over a shorter range. So, for example, would there be some stress put into whatever get attached to on the transaxle that might end up with the same kind of damage as is seen with a TT.

If I'm catching what's being thrown, a flex plate will help mitigate these kinds of issues, with the same caveat as exists with a TT: good, solid connections that don't move between the engine and the trans. To be honest, I probably need to go stare at PET some more and think about what a more direct connection between the engine and trans would look like. A super short, splined...something?

I'm pretty out of my depth here, but paddling furiously.

By worf
Zirconocene wrote: Wed Sep 21, 2022 7:30 pm I'm pretty out of my depth here, but paddling furiously.
This all begs the question of just WTF are you trying to build? :)

You want to mount a 928 engine and trans in a Corvette? A reverse LS-swap to throw a big bird at the LS-swap guys? :)
By worf
Zirconocene wrote: Thu Sep 22, 2022 1:31 pm In a Cayman :rockon:

Figured out how to run the transaxle with it flipped around?
By Zirconocene
A couple/few things I have running through my brain as I think about this, along with some background.

I bought a "spare" S4 engine and trans with the idea of transplanting them into my car, or as insurance for the day that thing go seriously south.

Within near the same time period I also couldn't resist buying a project Cayman with a broken engine. I don't know what's broken in the engine yet, there are other projects that need project-ing. I'm assuming a broken connecting rod bolt started things off, and then who knows what happened, but this is pure speculation.

So options I'm thinking about:

1) find a new Porsche 6 cylinder engine, preferably something that's an upgrade. That's $$$
2) find a Subaru engine and figure out how to add boost to get it to Cayman power numbers (or higher). That's less $$ for the engine, but I don't know squat about building a boosted engine
3) figure out how to make this S4 engine work

Right now I'm focusing on #3 because I think it would be sort of awesome. This page makes me think it could work: https://sites.google.com/view/boxsterv8swap/home

However, I'm trying to think through potential issues, which is where the TBF thing came from, as the Cayman is a Tiptronic model (which will present its own set of issues). Some open questions in my brain:

- what does an engine cradle look like that let's me keep AC in the car?
- how low can an engine cradle go to wrap around/under the alternator and AC compressor and tie into the original Cayman engine mount point?
- would the Cayman engine support need some reinforcement (in the flexible bits) for the heavier engine?
- how to handle the intake? The stock S4 intake is really tall. I've reached out to Sterling about some experience with ITBs, as a potential route to a lower overall height.
- Could I use the Tiptronic and, if so, how could I make that work with some pretty different engine characteristics to what it's programmed for?
- Can I use the spare S4 auto trans directly on the motor and call life good?

It's sort of important that the car remain automatic, as it's intended for my wife but the easy button would be to buy a new Porsche motor; there's a few available on eBay. While that would have its own set of appealing learning opportunities, that route would have far fewer that I could also (potentially) port over to my proper 928s. This would include the (almost assuredly necessary) aftermarket ECU to handle the motor and feed the right signals back to the original DME).

Probably more than you wanted to know, but I'll take any insight you might have.

By hernanca
Thinking a long way back to when I went pretty deep into exploring a V8 powered 914 (there's a cool one known as "Alien" aka 918-S with a 16v 928 motor in it and Pascha interior), I recall two big issues:

1) protrusion of the front of the motor into the seating area (some incarnations stretched the rear of the 914 and I remember trying to figure out how much angling of the half shafts was acceptable to buy as much room as possible) and

2) chassis twist from the v8 torque

Measurements will inform you about #1 and you should look into Cayman chassis reinforcement techniques for #2.

Agree, it would be cool if it could be accomplished!
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