I think its a little of both. The oil line that feeds the head at least on my 350 is very small and I have seen people do away with them and use larger braided steel line instead to improve flow. They are also jetted very lean stock and so run hot a rejet and pipe will help it run cooler. The top end on my 350 was completly garbage and I replaced it with stuff from an xr as its better. I have put a lot of miles on it since and have had no problems. I think the previous owner ran it low on oil or somthing the cam and rockers were eating one another real bad.