Rod to Stroke Ratio and Connecting Rod Angle?

John

If you don't have plans for the Moldex 4.4 crank, I still would like to see you use it, so here is my last effort.

With the pistons you currently have now (20cc dish) they will end up deep in the hole with little or no quench.

Put the heads on the block and scribe the cylinder bore on the deck side of the heads.
Then bring the spark plug wall side of the combustion chamber out towards the scribe line including the area around the valves.
This should increase the chamber volume closer to 68 cc.

Get the inexpensive Eagle 6.8 inch BBC rods which will yield a rod to stroke ratio of 1.545.
Have a set of Spherical dish pistons made with 35 cc dish with a compression height that will let you zero deck them. (Somewhere less than 1.57)
You will have 10.5:1 static compression (.040 head gasket) with quench and 523 stump pulling cu. in.

Use The TA-290 cam either flat tappet or roller.
Have something different on the street.

You should have no problem selling the rods and pistons you presently have.

Paul

 

The counter weights will no doubt hit the bottom of the piston.

 

Yes, the standard piston will hit the counter weights, but if you are doing a custom piston with a higher pin height, 1.5ish versus 1.975,
then a piston that is .250 shorter on the skirt should clear the counter weights.

 

Everything I've read over the past couple years basically says that the main things for durability are rod angle and piston velocity along with overall balance and harmonics.

I have an "Engine Masters" from 2006 that has a section explaining the basics for crankshaft issues such as crank deflection, balancing, and lightening the rotating mass. It also has a section about rods including finding the right ratio, material, and rod failures and what causes them.

If you can't find a copy let me know and I can scan and e-mail the sections to you.