Yes one of the things to watch for is oil sheer. Other obvious things are sidewall loading, dynamic compression, mechanical advantage, exhaust gas rarefaction and inversion, blowdown, cam events, swirl, etc.
Long rods cause the piston to have a slower velocity around TDC and faster around BDC, so you need to look carefully at your exhaust ports and blowdown event otherwise you can lose some power pumping out the exhaust gases. Tend to give a higher peak power and can sustain higher revs because of a lower piston acceleration and less strain on the low end mechanicals.
Short rods give you a better angle in relation to the crank pin for mechanical advantage, but you will need stronger mechanicals as a result. They put a fair amount of stress on the cylinder walls. Blowdown timing is typically earlier and you will need nice big exhaust ports so that the slower piston speed is still enough to pump out the residual gas.
The "senior" probably looked at the ratio and decided it was either outside the 1.6 to 1.9 limits, or if he was after a short RR outside the 1.6 to 1.8 limits.
"She gave me a look only a mother could give a child."
Last edited by Wally : 02-28-2006 at 03:37 AM.