gvx

With fuel mileage in mind for a daily driver. Some shop talk about compression height with longer rods and a short compression height. What is the trade off with long rod, short comp height as opposed to shorter rod and tall comp height. The advantages I see is less cylinder side load, less friction, and the narrower rings even less friction. Now what are the disadvantages to the longer rod length? Will the short comp height piston suffer from any reliability problems?

butler

More piston rock, scuffed skirts.

speedtigger

iTrader: (16)

This ^ and improved upper RPM performance. Generally speaking a short rod engine will have a lower and peakier torque curve where a long rod engine will peak higher and have a broader torque curve. Short rod motors tend to prefer a wider LCA cam where a long rod motor tends to prefer a narrower LCA cam. These are general rules and each combination is unique.
Also, short rod motors will have higher piston speeds and shorter dwell times at TDC.

chrisfrost

iTrader: (8)

the way I understand it is with shorter "stroke" You have faster piton speeds , higher rod ratio so the piston actually is at TDC longer thus allowing more ignition timing creating more power . The example I know of uses a long rod with a short stroke and a pretty large bore . Hot Rod magazine an article called "The 350 Chevy should have made" . 2 physics, engineering , or geometry wizzes take a sm 400 bore it .030 over (4.155") and a 307/327 crank (3.25") stroke , Ford 300-6 cyl rods (6.209") , aluminum 58cc heads , special L&E pistons with pin loc higher up on the pistons ,,,,,,a quadrajet, LT's on pump 87oct made 435lb.ft. and 412 hp with a stock cam no detonation ,,,,,,,good article