We researched economical ways to do this by perusing the rod dimensions from other motors. We did not want to order custom rods for cost and timing reasons so we figured we could find a rod/bearing combo that was close and work with that. We ended up settling on the rods from a Honda H22 Prelude motor. The H22 rod is 5.630” long vs the stock SR20’s length of 5.365”. This would give a stroke to rod length ratio of 1.66:1 vs the stock 1.58:1. Not a huge difference but one that we could probably find measurable results from.
Here is another chart of piston displacement in bore over degrees of crank rotation, rod length being the variable. The big end of the Prelude rod was 2.008" in diameter and the pin end was 0.866", both of which are identical to the SR20's rod. The main difference was the rod width, the Prelude was 0.938” wide vs the SR20’s 0.894”. We could make the H22 rod work by narrowing each side of the rod’s big end by 0.022”. When looking at the Prelude rod bearing, we realized that its shell thickness was the same as the SR20’s and that it was narrow enough to not overhang the rod even after we machined its width thinner. In addition, the undercut radii on each end of the SR20 rod journals allowed the H22 bearing to fit into place without any interference issues. Add the fact that there are many H22 performance bearing options and we were sold on the Prelude rod.

I'm looking at possibly using the NA20 head on a z24 (or any other) bottom end with a Z series rocker cover.

From what i get from it is its good for NA applications but maybe not for turbo applications due to the chamber design, I believe you would want an open chamber head to get the flow right. My question is if the combustion chamber was opened up CNC'd could this be used for turbo application and cure some of the faults of the naps Z heads (Running bigger valves / cam etc). Worst case scenario, the roller rockers could possibly be used in the Z head.

For the life of me i cant seem to find any info on the NA20 and what bottom end it uses. It looks to be using the z24 bottom end from visuals.

Does anyone have any info on this NA20 head and it's compatibility with the Lseries or Z series bottom ends ?

Cheers