rod ratio

[GARRICK.CLARK]

Quick question.
Is the con rod ratio on a 66 crank and standard con rods a good ratio.
I read some were that 1.68 is an ideal ratio.
and that that a longer rod can help in reducing piston scuffing .
On my motor with the AA piston kit I had to shorten the cylinders as they were too long, I also had to trim the piston crowns as they didn't match either.
Just wondering if my rod ratio is ok or if I need to look at sorting it next time its apart .
cheers.

[bj]

if you divide the rod length (in mm) by the stoke...this should be your rod ratio.

127/66 = 1.92 1.8/1.7l

131/71 = 1.85 2.0

137/69 = 1.985 stock type 1

there is a ton of opinions regarding rod ratio...do a search first and see what more experienced folks (than me) have to say.

my 2316cc (96x82 using 135mm rods) is a 1.67 ration...short...but not too short. all depends on what you're doing with the motor and how you want to assemble it.

BJ

[Piledriver]

Several of the "really high end" engine gurus/builders have repeatedly opined (I'm paraphrasing:)
...the correct rod "is the one that puts the pistons at the proper deck height", everything else is ~inconsequential.

The small bore Hondas are at a ~1.5:1 rod ratio.
Bigger bores have more issues with sideloads/wear at low rod ratios, but that's about the limit to the downside of short rods, a really short ratio will likely limit your max RPM in some fashion.

There are some theoretical benefits of the different setups, really short ratios boosting tq, really long rods allowing marginal heads to "work" at higher RPM, but I suspect anyone would be hard pressed to see a noticable difference on a dyno, even comparing extremes..