This is a subject that I've never thought about, but can make for some good read. From what you've said, if it's true, then my take would be that the standard person that doesn't know anything can make this type of statement about tighter clearances and be halfa$$ right. Me? I don't think they are tighter, but I do think that the machining process of parts and blocks is tighter and more accurate with the use of computers, lazers, etc. so that componets are more square and all. Now if you take all your bearing clearances and tighen them up, there will be lots of friction and heat going on within the motor that you could cook some fries with the oil it'd be so hot. So I think Detroit has them where they need to be and have had plenty of years to do the homework on tolerances to seal a motor yet allow friction to be at a minimum.