Quote:
Originally Posted by blykins
I'd like to see where you got your info on the Windsor oiling restrictions. I always knew that there was a possible issue with Cleveland blocks, thus the need to bush the lifter bores, run external oil lines, etc. But as far as Windsors are concerned, 302s/331s/347s are dialed up pretty high without problem, as well as some 357s/393s/408s that I've seen. 6000 rpm seems *extremely* conservative as I've spun them a lot higher than that. |
I have read lots of comments in books, magazines, and on the net where people claim the 3" main journals are too large to handle high rpms. They say it about the 385 series as well as the Windsor. The block's oils system is not the problem.
If you compare a SB main journal of 2-1/4" vs the 351W at 3", A SB turning 10,000 rpm would have the same journal suface speed as a 351W turning 7,500 rpm.
The surface speed shear thins the
oil. The viscousity goes down with the shear rate in the bearing. Anyway this is what I had assumed was the issue with the comments that the 3" journal limits the rpm. The other day I read an artical describing the problem as one of centrifugal forces. They explained that the
oil spinning in the bearing generates a centrifugal force that is trying to push the oil back into the block against the oil pump that trying to feed the bearing. They recomended keeping oil pressures high for high rpm applications, with 60 psi as the minimum. The FE with its 2-3/4" main has always ran very high oil pressures to survive high rpm use.
I know the shear thinning is real, and the centrifugal theory makes sense, as well. If the centrifugal force reduces the rate that the oil is flowing into the bearing, then the oil in the bearing will be subjected to the shearing longer and that increases temp and reduces viscosity. Certainly these two things would have a sinergistic affect taking you towards the fairlure point.
What I don't know, is exactly where the real world limits are. I know people who are spinning 408W to 7500 rpm drag racing. That same engine may not take that same rpm on a circle track, where it would stay at those rpms much longer. Perhaps they can turn even more, this is what I have been trying to sort out. I see comments saying they can turn 8000 rpm all day others saying do not go over 6000. I don't know what the limits actually are. I never built one, never owned one, never saw one fail. It is all research at this point, for me.
I did see one stroker kit that had 2-3/4" main journals with extra thick bearing shells. I have seen this with the SB 400 Chevy for years. I know some circle track guys who run the smaller 350 main journal by turning down the 400 crank. They also claim this allows higher rpms.