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Internal differences between M96.20 and M96.21

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A few months ago I got lucky and picked up two non running Boxster engines for little money. One M96.21 (2.7 L) with a failed IMS and piston / valve collision. The other 2.5 had a dropped sleeve that had resulted in a shattered piston on #1.

In order to be able to "mix-and-match" remaining good parts I am trying to figure out (beyond part numbers from PET) what the real differences are in terms of basic internals between these two engines.

From comparing / measuring, I believe the following parts are identical:

- Case halves

- Heads with valves and valve covers

- Connecting rods and bearings, wrist pins etc.

- IMS to exhaust cam chains

- Chain guides, tensioners etc.

Slightly different (but interchangable) are:

- Crank carrier; the main bearings are mirror images 2.5 vs. 2.7, but offsets and angles are the same. Also the 2.7 has a different design for the chain that runs from crank to IMS shaft; gear vs. double row of teeth.

- IMS shaft, for the same reason as the cranks are different.

So AFAIK, the only real difference is in the pistons.

Kind of important to have this reconfirmed before mixing-and-matching parts...

The forum's input would be very welcome.


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