View single post by Esprit2
 Posted: 03-22-2015 07:01 am
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Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 289
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Good, they're more fun above 4500 rpm anyway.

The 104/107 cam combination is the same as was used in the 912 HC. I've not driven that combination, but I have twin 104 cams in one otherwise pretty stock 907, and twin Dave Smith DS2 cams in a hotrod 2.2 907, and both will happily scream right past redline. If the internals are built for it, the cams will pull 8000 rpm. The 107 cam... not so much. But the exhaust cam is less of a factor in determining the engine's personality, and the 104/107 combination is still pretty sporty.

Do you know if the Bedford crank is cross-drilled? The non cross-drilled crank isn't prone to running bearings at first flog. But the cross-drilled crank with the bearing shells that go with it are more durable if you're going to be using it's capability regularly. My 2.2 has a cross-drilled crank, but my two 2.0s are non cross drilled. Lotus Elite, Eclat & Excel (LC) were considered more civilized, and got non cross drilled cranks. The Esprit S1-S2, the Excel SE, and Turbo 910 were considered more boy-racer, and got cross-drilled cranks.

The 190 psi 'COLD' is high for 9.5:1. Lotus specified 190 psi 'HOT' for the 10.9:1 CR... but don't complain, higher is better.

If the cylinder head has been skim cut for flatness (.020" max allowed for the 907), the result would have been about a half a point increase in compression ratio (9.5:1 becomes 10.0:1).

On the other hand, the modern composite head gasket's crushed thickness is about 0.020" more than the original gasket, so it lowers the compression by a similar amount.

Tim

Last edited on 03-22-2015 07:27 am by Esprit2