Yes, I did a search....a whole lot of searches!

What is the ldeal rod/stroke ratio and can anyone get technical on this?
Why is the LS r/s ratio not good? Do you need to shorten the rod to make it better?

 

1.75

 

um, okay....let me reprase, I don't know a dman thing about Rod/stroke ratios....who, what, when, where, why and how.

 

Rod to stroke ratio is a comparison of how long the rod is to the stroke . . . .

Basically, the higher the number (shorter stroke, longer rod), the lower the sidewall stresses, since the crank angle is less severe. But too high a r/s ratio, you end up with a very short stroke & little to no low-end power. 1.75 is considered the best compromise for a street-driven car.

The B18 engines have a r/s ratio of somewhere around 1.58, I believe. So good torque, but crank angles are somewhat severe & can limit high-rpm reliability. Their longer stroke also means piston speeds are going to be high. So to answer your question, it would take a longer rod & matching crank to improve the r/s ratio on the B18 (destroking it into . . . . a B16!! - 1.74 r/s ratio). This is the reason for putting a B17 crank into a B20 (reducing displacement), it shortens the stroke to provide a good r/s ratio.

I think that's the gist of it, but feel free to correct me if I've misstated something.

You can find a lot of information regarding this over on www.theoldone.com . Just don't get sucked into the hype over Endyn unless you know what you're doing. But there is good information over there.

 

Okay, then has anyone tried destroking the block and increasing piston size to compensate?

The stock B16's R/S is 1.74?

 

YOu can overbore slightly, but too much and you run into serious heat problems.

 

It seems most of the Subreu engines I have seen specs for follow that idea. Large bore, small stroke, with nice rod lenght.

Longer rod also allows more dwell time at TDC and BDC....plus lower piston acceleration speeds(not so sure about the acceleration thing.

I would think more longer dwell time would benifit a high revving motor. It would allow more time to fill and scavange the cylinder.




[Modified by HXMan, 11:17 PM 11/8/2001]