[Stan Weiss]

Originally Posted by Tim Corcoran

I am going with a 4.181 bore and 4.25 stroke. There are a few reasons why I would prefer not to go to a 4.5 stroke. With my heads having a 71cc combustion chamber it would bring my static compression way too high, of course I could of ordered dished pistons to get my compression down. A longs stroke like 4.5 puts additional stress on the crank and the block, I don't want to push my luck with an OEM block. Longer the stroke the faster the piston speed thus shorter ring and bore life, I already have increased piston speed using 6.8 rods that's a tradeoff for less side loading on the cylinder wall and better cylinder filling since it dwells longer at TDC. If I were building a monster engine with an aftermarket block I'm not sure even then I would go with that large of a stroke. Many have done it with good results in my opinion it's not the best choice for me. I'm not going for max power I'm trying to stay in the low 10 second range for a reliable long lasting bracket engine and I don't want to put in a cage and window net.

Tom,
While increasing the rod length does change the piston velocity curve, where in the velocity curve are you looking at when you say velocity has increased? Peak velocity is actually reduced as you length the rod. You also move the point of peak velocity and where the rod and crank journal are at 90 degrees to each other farther ATDC.

Stan