Calculating Rod Length

[NUT-CSE]

Could someone help me on this as im getting quite confused with it. If i were to use a CA20 crank in a CA18 block with stock CA18 pistons what would be the rod length required to suit this setup??

How would i go about working out this??

[float_6969]

You can use the stock CA rod, but you've got to get custom pistons made that move the wrist pin up 4mm, IIRC.

[ceniack]

what would the displacement of this motor be? and would it be square, over square, or under square?

[NUT-CSE]

float - i dont want to go custom pistons, im just playing around with numbers and combinations tryin to figure out what rod length would be needed and maybe find that length rod from another motor.

ceniack - It would be 1904cc, CA19DET!!

[float_6969]

the problem w/using the stock pistons and shortening the rods is you're getting the rod ratio down so low you're going to loose the rev-ability of the motor. You're also going to get A LOT of side loading on the pistons. Lengthening the rod ratio would be better, but can't really be done with the limited confines of the CA block. You could try putting the CA18 crank in the CA20 block and with some custom rods would yeild you a GREAT rod ratio, but the CA20 block doesn't have all of the webbing that the CA18 block does, and will require some other machining and creative metal work as well.

You basically need to find a piston that has the wrist pin 4mm higher than the CA does. That will allow you to use the CA18 Rods and the CA20 crank.