narrowing rods

Ken_Parkman wrote: .........BTW those 340 Mopars did work amazingly well for such a miserable design. ..........

Now that hurts.

Ken_Parkman wrote: I've used a small surface grinder with a magnetic table to narrow rods - very easy.   I know you asked us not to try to push you away, but rod length is essentially meaningless for performance. A lot of successful EMC engines have used very short rods, and they were all about torque and power both. But for sure the destroke will kill power and torque roughly linearly with the cubic inche loss. Having shorter pushrods is more important for performance, one of the reasons race engines have gone to shorter deck heights and therefore shorter connecting rods and rod ratios. Absolutely everything else is more imprtant than connecting rod length.

Connecting rod length does make a difference. You guys keep siting examples of engines that are essentially "white paper" designs.  While it is true that given a clean design to start with, you can take advantage of the inherent advantages of short decks when everything else in the engine is manipulated to be optimum with that.  On a modified production engine design in an application that has entirely different parameters of efficiency than a Pro Stock engine, you can use the long rod to an advantage as long as you know what it characteristically changes in the operation of the engine. 

de-stroking reduces torque because of a much more basic principal - a shorter crank to be pushed on.
Torque is a measure of pounds of force against a length or distance. Reduce that distance but keep the force the same, you reduce torque.
It's really quite that simple - and the reason tractors are long-stroke engines. TORQUE comes from longer strokes.
Even if you keep compression the same and the same peak combustion pressures, less stroke= less torque. To keep the same torque with less stroke, you'd need to increase the combustion pressures or the force pushing on the crankpin - via larger piston, whatever.

If I push on a breaker bar with 200 pounds of force and that bar is 1 foot long, that's 200 pound/feet. Reduce that bar to 6" and I've cut the torque in half, I no longer have the same mechanical advantage.
Folks building climbers as opposed to racers, or rock crawlers, or who want a pulling tractor................
I'll put my long-stroke F20 rated at only 19.xx hp against any other 19 hp engine as far as torque - I'll kill 'em with the torque. I can lug it until I can count the cylinders firing and it will keep moving.
In a turtle contest, the long stroke engines win every time.

Science DOES count.


Edited by billd - Jun/16/2009 at 4:21pm

Class Guy wrote: Connecting rod length does make a difference. You guys keep siting examples of engines that are essentially "white paper" designs.  While it is true that given a clean design to start with, you can take advantage of the inherent advantages of short decks when everything else in the engine is manipulated to be optimum with that.  On a modified production engine design in an application that has entirely different parameters of efficiency than a Pro Stock engine, you can use the long rod to an advantage as long as you know what it characteristically changes in the operation of the engine.    As for the comment that short strokes kill torque, that is as incorrect as is this discussion about rod lengths.

Way I understand it, the rods job is to connect the crank to the piston.......Well, some of these guys build engines........and you are arguing with them?????