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.