Angle of attack for a rod/piston in a cylinder

I am looking to stroke an inline Ford 6 cylinder. A friend once used chevy rods in a 240 to DE-STROKE it for higher RPM's.
Is there a way to determine the best rod length/piston pin position/stroke, to achieve maximum RPM without too much cylinder wall stress? Looking from the crank end as it rotates, it appears as it reaches maximum outboard swing, it causes stress on the cylinder wall as the piston starts up the cylinder. I want to find best rod length when stroking an engine, to achieve max RPM without too much stress on cylinder walls. For now I am simply looking at theory and possible over-the-counter parts options. Throwing things out of balance and throwing pistons through the block are my main concerns.


Gold Member

It really depends on the design of the piston, wrist pin location, crank clearance, and cylinder block. I ran full race stuff and didn't care what the ratio was (as long as there were 8 rods and 8 pistons 1:1 ratio), because it was getting rebuilt pretty soon, and the block, pistons, crank were all designed to work together.

A little more stroke will probably be no issue, but when you get near the limits, clearances to the block, cam, rods, etc.. will all need to change. 200 six cylinders aren't all that common these days. I'd talk to a machine shop that has worked on these that may know what (not) to do. They may have knowledge of known weak points/strong points in that engine.

Ranger Mike

Science Advisor
Gold Member
changing to a diffrent connectiong rod will only build you headaches. YOU can not destroke an engine doing this. the only way to change the stroke is to weld on the crankshaft rod journal to increase stroke or offset grind the rod journal to destroke it. rod length change will NOT change the stroke.
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Okay guys, I really do understand how the stroke of an engine is increased or decreased...REALLY! I guess my question was stated poorly. With the change in stroke the angle at which the rod approaches the cylinder wall on its way up changes. Too much angle and excessive side stress is placed on the wall...if the rod does not hit the block. The piston also is stressed more. I was wondering if any formulas are available to find a ballpark figure for a given stroke (throw), as it relates to bore. The cylinder skirt, rod shape, and other things must be considered, but if a formula can get one close, maybe a few headaches can be avoided before building. I am not an engineer, but I am very familiar with "measure twice, cut once." Thanks for info so far.

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