I'm about to order an oili pump for my brother's 355.
we're rebuilding it currently, and I was wondering if I should get a slightly higher volume pump. Ive read that if bearing clearances are a little on the loose side, a high volume pump is good. I'm not sure on the clearances yet, but Ive read in order to measure the rear main bore, I need to torque down the pump.
Should I get a standard volume, or upgrade to a 10% or 25% increased volume pump? Would extra flow with clearances on the tighter side hurt anything? Also, with the stock pan, would I have to worry about running the sump dry with a 10% or 25% increase?
Thanks.

 

I've gone with the Melling 10% pump, and it's good with clearances in the 0.0025-0.0030" range. That's the ideal range for performance builds anyway.

 

i used a big block oil pump that is converted 4 small block use. i ordered off jegs i think its made by GM performance parts. i never have low oil pressure

 

+1

The BBC pump is approx 30% higher volume than stock.

High volume pumps produce higher pressures at idle and low RPM, then bypass more oil at higher RPM.
This takes a little more engine power to pump the extra volume, but is not significant.

Oil pumps bypass the oil back to the pick-up tube, so if you empty your oil pan, then it means something else is wrong there.

I have heard this myth before. I think it originated with some engine building shops not wanting to warranty performance engine builds that had high volume pumps and came back with bearing damage.
This story has fooled a lot of people.

If you're pumping too much oil to the top of the cylinder heads in relation to the drain-back capability (drains blocked), then you can indeed run the pan dry. This is extremely rare and generally only happens in racing where high lateral G-forces are involved. They usually run dry-sump systems that avoid this possibility.