1972 307 cam selection... HELP!

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Originally Posted by MikeB

Are you sure about that? It assumes 327 or 350 blocks were used for the 307. Or that 307 blocks had thicker cylinder walls than all other blocks.

At Mortec.com I found 8 casting numbers for 307 blocks. But not a single one of them is used for 327 or 350.

I guess a 307 block with zero core shift could take a +.125 bore, but who knows how much flex there might be in the cylinder walls?

I'd do a max overbore of .060" on a 307, just like I did with the 283 back in the day to get 292 cubes. That was back when the 301 was popular, but a machinist convinced me to stick with +.060". I doubt the power difference between 292 and 301 was even measurable. And heck, a 292 would probably last longer than a 301 with thin cylinder walls.

Many people don't like it when I tell them this, but the 307 was a culmination of GM getting rid of stock. With the popularity of the SCCA Trans Am series, and the 5.0L engine size limit, GM used the 327 block (4.00" bore) and used the steel 283 crank (3.00" stroke) to make a 302. That left a multitude of 283 blocks (3.875" bore) and 327 cranks (3.25" stroke). They were put together, and with a set of wheezy heads, they were thrown into base and low option modeled cars and trucks.

The early 283 blocks (pre-62) could actually be safely bored +.155. The later blocks could only be taken to +.125

The biggest difference in 327 & 350 blocks were bearing sizes. The 350 cranks had larger main journals, which is why people don't destroke 350's with 327 cranks. It can be done, but with custom 3.25" cranks with the larger 350 journals.