Calculating rod length

Hi guys.

Need to calculate rod length for our motor. I know thanks to a few informed sources it's a derivation involving deck height, stroke and pin height, it may involve more, so i'm asking for all the engine builders out there for their input?

The motor we have is standard deck, and the pistons for arguments sake we are going to get is 1.094 pin, with the 4.25" stroke crank.

Thanks

Joe

 

try here,.some good calculators...

http://www.wallaceracing.com/rod-length-calc.php

 

Bottom dead center volume / Top dead center volume = compression ratio

 

everyone has their own way of doing things, and there is always a formula out there for people to use as well. i ran into this very problem some time ago, and was told 2 different ways to get the correct rod length. i tried both of them, and got 2 different answers. i ended up CC'ing the motor with an adjustable rod to get the desired compression i wanted. once i got the compression i wanted i just sent the rod out and had my new set made to that length. i just cut an old rod in 1/2, and took out 3/4" or so to give me some room to work with. you will need left, and right handed threads on opposing ends, and you can adjust the rod to whatever length you want. once you get the correct length, just tighten down the lock nuts on each side and there you have it. it would work like the barrel valve on your injector if you know what i mean. hope this helps

 

I have used the adjustable rod length method. However the easiest way is to give your piston manufacturer the engine specs and the compression you desire with a head gsk thickness and they will make the pistons and tell you what rod length you need to order.