Building the Long Rod Nissan SR20VE Engine
By Mike Kojima and Chuck Johnson
We last left off our SR20VE engine repair job with Port flow Design fixing our head. Read about that here! Since our broken valve chopped up one of our pistons, we decided to go through the engine's bottom end at this time. Since we have been editorially discussing the effects of running a longer connecting rod at MotoIQ lately, what better place to try a longer connecting rod than our race motor! Check out Khiem Dinh’s excellent article on the subject here!
|Here is a chart showing the effect of a longer rod on piston acceleration over degrees of crank rotation.|
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.
|Here is another chart comparing the effect of rod length on piston acceleration over degrees of crank rotation.|
The stock SR20DE and H22 rods are very strong and are safe for extended use at up to 8000 rpm and for a low buck motor, they are perfectly adequate. However for our goal of a very bulletproof, inexpensive build we chose some H22 Prelude ESP rods from Eagle. Eagle ESP rods are forged from 4340 steel alloy with a high nickel and chromium content. The nickel and chromium give the steel a high tensile strength, high toughness and a much improved fatigue life over high carbon and chromoly steels.
|Another chart comparing piston velocity over degrees of crank rotation with the stroke to rod length ratio as the variable.|