Tom Lieb recently talked with EngineLabs about rod side clearance, and the belief that it determines the oil flow exiting the connecting rods and that excessive side clearance cannot be tolerated. As EngineLabs points out (and Tom reinforces), this is an engine building myth that people still believe.
We also thought it would be a good idea to get a perspective from a crankshaft and connecting rod manufacturer, so we spoke to Tom Lieb, owner of Scat Enterprises. Lieb knows quite a bit about the subject with over 50 years of experience. As soon as we broached the subject that connecting rod side clearance established oil flow, he laughed and replied – ‘Yeah, all those guys are off base. Side clearance means nothing (when it comes to oil flow).’ Instead, Lieb supported the position that the restriction to oil leakage through the mains and rods is the bearing clearance.
He also made a great point that journal circumference is another variable in this discussion. There is a huge difference in circumference when comparing a big-block 429/460 Ford rod journal at 2.50 inches versus the 1.850-inch journal used on many small-block race engines. The circumference for a 2.50-inch bearing is a massive 7.85 inches compared to the smaller journal’s 5.81-inch measurement. That’s a difference of 26-percent, with the larger circumference offering more area for the oil to escape.
Read the full article here.