over bore for Ford 711M or "L" block

[Jerry Poole]

I have been doing research on the maximum over bore that would safely work with the blocks listed above. My research indicates that the absolute "safe" overbore for each of these blocks would be 83.5MM. I have seen a Lotus Twin Cam for sale on EBay with an overbore of 85MM using the "L" block? Could anyone on the forum provide any information or insight on this topic. Thanks for your time and consideration. Jerry

[mdwracer]

The "L" block was a Ford block developed for Lotus with thicker casting provisions. The Lotus engine building book or the Dave Bean catalog should more detailed info on max overbore.
Mike W

[DanW]

I have the Dave Bean book with the info on the L blocks. A stamping of "LA" or "LAA" indicates the most desirable blocks for boring oversize. I can scan the pages and email to you if you PM me your email address.

Some general info on Kent blocks from the Cortina folk:
http://www.lotus-cortina.com/library/block/blocks.htm

From Bean's Lotus Elan handbook:

"The 701M casting version with the large letter "L" cast at the motor mount pads had thicker cylinder walls, were sonically tested and further graded after machining.

The grades were stamped on the front right corner of the block with "LB" - most production road Elans,

"LA" occaisionally found in standard road twincams but usually went to English race engine builders, they could be bored to 85mm

"LAA" - went to Fords RS programs.

Dan