I was reading something the other day that said nascar engines run as little as .001 on bearings and those engines spin 9000+ for hours at a time. Also, used to know an old guy that built many circle track engines. He once told me he sets all bearing clearace to .002, when the overlayment wears off there at .0025. Interesting stuff.
You are correct. They also have 1.88 rod journals, as well as mains under 2.0. They have some of the most precisely machined and engineered parts in the world, run oil about the weight of water, with LOTS of friction modifiers in it and also run at a more or less steady rpm for 500 miles or so. When the motors come down after a 500 mile race, the bearings, rods and usually the crank are junk from the intense heat. Tight clearance also equals HIGH heat in both the oil and the bearing. The cranks are machined perfectly and micropolished to a 2 or less microinchess RA. And even though the motors don't make huge power, they run very expensive, high quality steel rods. Why?......because rods deform at both TDC and BDC elongating the hole an changing bearing clearance. Cheap rods deform MORE. Cheap heavy cranks also deform. So comparing a CUP motor to your run of the mill performance motor, is about like comparing a Pro-Stock motor to the one in your minivan. Guys who try and apply cutting edge racing technology to their motor with run of the mill, Chinese made parts are ASKING for trouble. Makes no difference if it checks perfect in the shop. It will NOT be when it's running. THIS is the part guys don't get. .....So, can you run a motor tight and it live? yes sir, but you better have some damn good parts and that list doesn't include $1500 rotating assemblys
