Choosing an engine for your Porsche
The Porsche 996 engine, the M96, has a variety of ways it can be damaged that will require a full rebuild. Unfortunately, the M96 is a difficult and expensive engine to rebuild, with many undocumented special assembly steps, special tools needed, and expensive parts that need to be replaced every time the engine is taken apart. We would not recommend the home mechanic attempt to rebuild the M96 themselves.
We should mention that Porsche is now offering rebuilt short block M96 engines through their dealers, for around $6,000 to $8,000. If your engine heads are still good, you could swap the short block yourself, or have a shop install it for you. Also, there are a few companies that will rebuild these engines and sell them as a complete drop in, though they are not cheap. The cost of a new engine can easily exceed the value of the car. We would not recommend buying a used M96 engine, since it is hard to verify the condition without disassembly.
It's worth pointing out that if you are not excited to take on a project like an engine swap or rebuild, but just want your Porsche fixed, there are options. A shop will have a much easier time replacing an M96 with a rebuilt one than swapping in a different engine. The Porsche 996 has become a lot cheaper and selling your car with a damaged engine and buying one in good condition may be your best option.
If you want to sell your Porsche with a damaged engine or no engine, contact us. we can help find a buyer for your car.
Chevy LS3 Engine Swap
Swapping the engine for a Chevy LS3 is a project that can be done in your own garage with normal tools. It is my goal to assist anyone that wants to take on this project and remove as much guesswork as possible. Mechanically, it is not a difficult project. There is minimal cutting for clearance required, but with the right parts, the engine can just bolt in. The actual process of dropping the engine and transmission, removing the M96 engine and adding the LS3 engine, and lifting it back into the car, could be done in a weekend.
Currently, the cooling hoses, exhaust fabrication, and A/C lines are the majority of the work getting the engine running and ready to drive. These are areas of future development to make bolt in kits available. These are good projects to have a local shop help with, but you can do them yourself. See the relevant web pages for more advice on these areas.
The wiring can easily be the most difficult and time consuming part of an LS3 engine swap. You have a lot of options depending on your budget, goals, and level of skill. See the Choosing a Wiring Harness page for more details.
LS3 E-Rod Crate Motor
Buying a crate motor from Chevy Performance is the easiest option for a great engine, especially if you need emissions documentation where you live.
Buying an engine from a junkyard can be a great way to find an LS engine for cheap. I will often refer to the LS3 on this site, but there are actually a ton of options in the LS family of engines that will work great to swap in a Porsche. There are a wide variety of cars that can with some variant of an LS engine, but some will need more changes than others.
The biggest and most relevant difference in engines to look for is whether it has a 58X reluctor wheel or 24X reluctor wheel. A reluctor wheel is a toothed wheel on the crankshaft that a sensor detects to measure RPM and crank position. The bottom end of the engine needs to be taken apart to change it. Unless you plan on completely rebuilding your engine, you will have a much easier time getting an engine with the correct reluctor wheel.
You want a 58X reluctor wheel wheel for this engine swap, because it will match the Porsche tachometer signal. This means you can splice into the LS crank position sensor (CPS) and get the tachometer on the dash to read correctly.
A 24X reluctor wheel has proven problematic. There is currently no off the shelf solution to convert the signal. There is a also a difference in CPS voltage, 12V for the 24X and 5V for the 58X. Supposedly, the E40 ECU can be programmed to output the correct signal, but it will be 12V and need to be reduced to work. This currently an area for more research because a lot of people want to use these engines. I hope to find a reliable solution in the future.
Iron Block or Aluminum
Either engine block will work fine in a Porsche swap. An aluminum block LS3 will actually be about 50 lb lighter than the Porsche M96 engine. I would recommend aluminum if can afford it and are going to be naturally aspirated. An iron block LS engine weighs about 100 lb more than the aluminum block and that means it will be about 50 lb heavier than the M96. If you plan on turbocharging or supercharging your LS and making big power, the iron block is stronger and might be worth the weight penalty.
Basically, you want a car intake manifold, not a truck one. The stock LS3 intake manifold will only have an 1/8" to 1/4" clearance between it and the top of the engine bay. That is after removing the fuel rail crossover, intake manifold cover, and the sound dampening from the engine bay. If you buy an engine from a truck, you are going to have to swap it because it is too tall.
Some aftermarket intake manifolds will clear, like the FAST 90 and 92, but anything taller than stock will not work. You are better off getting your stock manifold ported and spending your money elsewhere.