Does a Porsche engine fit?

Yes it does! But it’s not easy. This question was just asked on the gt40s.com forum, so I thought I’d write a more long-form answer here.

My drivetrain is from a 2004 Porsche 911 GT3. It’s a 996 Porsche in Porsche-speak, a naturally aspirated engine which can be traced back to the LeMans-winning GT1 Porsche and beyond. The block is known as the “Mezger” engine and it’s proven so durable that it’s even being deployed in the new 991 GT3 coming out this year. It’s also used on the 996 and 997 Turbo or GT2 (also a turbo) models. For this project, you likely can’t do a turbo engine though, because the exhaust routing will be very hard without major chassis modifications. But I wanted a high-revving naturally aspirated engine anyway. Redline should safely be in the low 9k.

Overall, this is not a project for the weary. I’m pretty sure that if I had used an LS engine I’d be done with my build by now. I have spent an incredible amount of time on perusing parts diagrams, electronics schematics, sourcing Porsche pieces, sourcing Porsche pieces which dealers don’t sell (like engine harness connectors), fitting metric stuff to SAE, fabricating brackets for rerouted stuff, designing and building a custom ECU harness, etc. I’ve had a blast doing this though and have learned a ton of stuff though, so I don’t regret this choice one bit. It was a personal challenge and I knew it wouldn’t be easy going in.

Here are a few points on what needs to happen:

  1. From what I can tell, my chassis required some modification, but not extensive rework to fit this slightly wider engine. I also have two steel upright mounts for the front of the engine onto which the stock front engine brace is mounted. (Note that in a 911 the “front” of the engine is in the rearmost part of the car)
  2. There’s no adapter plate to join engine and transmission, which does necessitate some chassis cross-bracing.
  3. The transmission housing does require modification because the bolt pattern on the engine isn’t perfectly square. GBox can do this when they do the setup/cleanup/inversion.
  4. I made a bracket to hold the transmission in the rear, so now the drivetrain is mounted on the front of the engine and near the rear of the transmission, which is the same basic setup of stock 911 to my knowledge.
  5. I took a number of things off the engine like the power steering pump and the A/C compressor. That required a new belt which I had to use some connections to get a Cup car part.
  6. You can’t use the stock oil tank and have to plumb in an external one. Not that hard other than finding the right size of tank to fit in the chassis
  7. With no turbos exhaust routing is ok, though I haven’t done this yet. Passenger side is trickier since the cylinders are further back, but it should be fine. The stock exhaust diameter is well within the size of open space. If it does become and issue, I can redesign the adapter plate mounts for more clearance.

That’s the major mechanical stuff which is all fairly solvable, though of course time-consuming. Electronics is by far the hardest part. But I enjoy that, so it’s ok for me. It’s literally fun to me, so maybe I’m a little nuts.

You will need to work with a motorsports provider on sourcing a programmable ECU and designing a harness which is hours and hours of meticulous Excel work. Or you of course can pay someone, but my goal was to learn and it’s been fun. I’ve worked with Neel Vasavada from Apex Speed Tech who sold me the ECU and has helped me design the harness. You can see a few of the design threads here:

The last two are good examples of trying to understand Porsche diagrams and me learning about how different pieces work, like a Hall effect vs magnetic speed sensor. The ECU harness is about 120 connections and I’m now about 98% done with the design with maybe 20-30% of it built. You can see the rat’s nest in the photos below as I had it in the car to check some wire lengths.

Here are some pics of how it all looks. Sorry for the bad light. My camera clearly sucks.

Engine compartment layout
Engine compartment layout
Engine compartment close-up
Engine compartment close-up
Engine compartment close-up 2
Engine compartment close-up 2


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2 thoughts on “Does a Porsche engine fit?

  1. Unbelievable stuff! This is truly an inspiring story. I guess it puts my confusion about how to wire a floor lamp into its proper context.
    Please start work on “cold fusion” next…it can’t be any harder than designing your own wiring harness for this vehicle.
    Keep us posted.

    Julien

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