My motor a 455 Oldsmobile in my 66 has been smoking pretty bad on the highway and was wondering if anyone could help me out. If I am just cruising around back roads not going too fast no problem no smoke. But when I hit the highway and start doing highway speeds comes the grayish smoke. Especially when I get on it and I let off the gas the smoke is horrible. Oil consumption of course is going up now. I had the thing rebuilt two years ago with new pistons and rings etc. My question is what would be the best way to go about figuring what the problem and where the smoke is coming from, bottom end or top end. Rings? Valve seals? Any help, advice, ideas would be greatly appreciated.

Easiest way I know to determine whats going on is to do a cylinder leak down test. This is where each cyl is put at TDC on the compression stroke, air is pumped into the cylinder and if pressure drops listen for hissing from the crankcase, indicates a ring problem. There is a chance the rubber boot covering the valve stem has failed, which means just working on the heads. Pull your plugs to see which one(s) have fouled to get an idea of the location. Hope this helps

I second the leakdown test. This is the best way to determine how well your engine is sealing and where the leaks are.