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@Dammit
Bore and stroke - the standard 3.4 engine has a 96mm bore, and the Lokasil liners are an open-deck design which ovalise over time.
They can be fitted with reinforcement rings, but a better solution is to machine them out and replace with Nikasil liners, and whilst you're there close the deck.
And, if you are machining out the liners and replacing them - why not go for a little extra displacement?
Initially I was going to use my existing 3.4 litre engine, but as development went on I was made an offer on a brand new 3.2 litre (Boxster S) block that was impossible to refuse. The 3.2 is identical to the 3.4 in every dimension that mattered for me, and the new 100mm liners combined with the 3.4 crank yielded 3.7 litres. Martin decided to build a 3.7 for his existing early 996 coupe, and a 3.9 (using a 996.2 3.6 litre bottom end) for his new project car, a 996.1 C4 converted to RWD.
New 100mm pistons matched to the new bores:
And three fresh engine blocks waiting to be built up:
We need to finalise our con-rod dimensions and get them ordered, then we can assemble an engine and run it up on the dyno.
We're so very close now - but there's still so much to do.