Originally Posted by
nashrcracer
one of the guys that came up with the had it figured at 7.95 when the 21.5 was 4.2 but with 27t motors you have difference in a rpm vs torque blank. like the roar stock has more rpm and the co27 has more torque just figure out how many rpm it turns at 8 volts and back track that in the equation. it's harder to find that happy medium in that range of the design being brushed as a real good prepped 27t will beat a 17.5 with no speedo timing. I would say start in the 9.0fdr yes way the fit up there. and that should be about right.
Ok, thanks.
Has anyone actually tested a 21.5 against a 25.5 with the recommended FRD's? I ran VTA last year with a 21.5. We allowed timing but no boost. I was using 30 degrees of timing and was geared at about 5.1. I was surprised to see that with no timing, I need to gear it up to 4.9 to equal a 25.5 at 4.0. If this holds true, the 25.5 should be faster than I thought it would be as I thought my 21.5 at 5.1 was pretty quick.
We have adopted these rules for this season.