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Longer connecting rods will reduce the mean piston speed, but just barely.


One can play with the stroke/rod game, but when you figure out what can be used at maximum (in relation to where to put the piston pin), you'll find there isn't that much difference.


The real gain comes in using a much lighter and stiffer piston. With the long strokes typical of the British lumps, anything you can to reduce rotating weight will mean longer life of the block itself. With the 4cyl TR engines, the block, for the very best engine builder, is becoming the Achilles heal and he's done everything to take weight out of the rotating assembly.


Here is an example I made years ago:


Same engine, 7200rpm peak. 136mm long connecting rod to a 145mm long connecting rod.


Peak piston speed (FPM):
136mm: 5685 FPM @ 76 degrees crank rotation.
145mm: 5661.2 FPM @ 76.5 degrees crank rotation




Here is the real reason why you put longer connecting rods in. This for a 1296cc Spitfire engine:


Edited by hoffman900
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