What is the minimum and maximum rod and main clearance for a 6500 rpm BBC?

Is there any relationship between bearing clearance and oil weight?

Ask 10 people and get 10 different answers.

If the application was bracket racing I would say .003 on both. If the application was street with only a little racing I would say no less than .0025. I would run 10-40 oil for either.

The stock pump with the pink spring will get you 20-25 lbs pressure at idle and 55-60 running pressure with 10-40 oil with .003. Heavier oil more pressure but not a whole lot.

I have spun bearings at .0025 but not at .003 racing. If racing I would really want .0035 on the mains and .0032 on the rods. Not everyone wants them that loose. Just what works for me during my 30 years of playing with engines.

Generally, bearing clearances are specified as .001" of oil clearance per inch of journal diameter, as a starting place. Therefore a BBC would need about .002" on the rods and just under .003" for the mains In the "old days" engine builders would generally open the clearances further, then use higher viscocity oil.

Current technology dictates the use of tighter tolerances, along with using lower viscocity oil.