[tirebird]

Wow you guys are great. First, Mark you, of course, win the bet. It is a #289 block 4-bolt block. However, because of the TransAm hood scoop, it has an aluminum Corvette intake manifold, #3963589.

I, like many of you, would love to solve the mystery of my and probably dozen of other #289 4 bolt engines with #291 heads. Even Alvin Colvin, the author of "Chevrolet by the Numbers", had a correction on his website for his Chevy bible regarding the #289, ” Some blocks have 4-bolt mains...several 4-bolt main blocks have been found."

Why did the Tonowanda plant use this block for warranty replacements and not the #512? It's an intellectual exercise that has no practical application. But, like all mysteries, it would be fun to know the answer.

Bill, you ask a good question. I've always used Mobil 1 in all my previous cars; a 63 Stingray and a 69 Z28 with a DZ302. I think it's the best oil to control wear, to keep the engine clean, and to prevent damage during high engine speeds and/or with high temperatures. I've seen high mileage, even abused engines taken apart that used Mobil 1 during their lifetime and was impressed with how little wear they've suffered. And, wear is what, most of all, I want to prevent with this rare block and heads.

Now, even with that said, the engine builder echoed what I've heard from other experts, that the Mobil 1 is so slippery it may be the reason so many people have oil consumption problems, with oil slipping past the oil control rings and the valve seals and guides. But, other than consumption issues and, of course the expense, I don't think I'm damaging my engine by using Mobil 1.

I've replaced the valve seals and I've decided that may be the extent of my rebuilding. If I do any work on the car this winter, it will be only to the heads for valve guides, hardened seats, and a general stuff. Thanks again everyone.

John