1972 307 cam selection... HELP!

[MikeB]

Originally Posted by 68Stepbed

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.

I don't know if the 307 was built to get rid of parts, or simply to make more torque than a base 283 in the new longer, wider, heavier cars.

All 283 blocks were small journal, and all 307 blocks were medium journal, right? I guess the raw block castings could have been machined for larger main bores. But the real question is how would GM have changed the casting number in a leftover block that was cast for a 283?

Also, the 307 crank was a different animal. It had lighter counterweights than the 327 crank. Again, it could have been the same raw casting but just machined differently. It would be interesting to talk to a Chevy powertrain engineer from back in the late 60s.

I think you overestimate the number of 302 engines produced. I mean, they were available only in the Camaro Z28, and only for 3 years. Whereas 283 and 327 engines were available in virtually any car or truck. I'd bet there were easily 50 times more 327s sold than 302s during those years. When I was a kid slobbering over hot new Chevys that I couldn't afford, I would see dozens of 327 emblems every day, even in 4-door sedans. Z-28 302 emblems? MAYBE a couple per month.


***I love your stepside!

[BigBird05]

GM only keep on hand 2 or 3 days of block castings. They never stock pile them.

[68Stepbed]

Originally Posted by MikeB

I don't know if the 307 was built to get rid of parts, or simply to make more torque than a base 283 in the new longer, wider, heavier cars.

All 283 blocks were small journal, and all 307 blocks were medium journal, right? I guess the raw block castings could have been machined for larger main bores. But the real question is how would GM have changed the casting number in a leftover block that was cast for a 283?

Also, the 307 crank was a different animal. It had lighter counterweights than the 327 crank. Again, it could have been the same raw casting but just machined differently. It would be interesting to talk to a Chevy powertrain engineer from back in the late 60s.

I think you overestimate the number of 302 engines produced. I mean, they were available only in the Camaro Z28, and only for 3 years. Whereas 283 and 327 engines were available in virtually any car or truck. I'd bet there were easily 50 times more 327s sold than 302s during those years. When I was a kid slobbering over hot new Chevys that I couldn't afford, I would see dozens of 327 emblems every day, even in 4-door sedans. Z-28 302 emblems? MAYBE a couple per month.


***I love your stepside!

At a certain point, they ditched the 3.00" 283 crank, and most likely just went into production to make the 307 because it was cheap, and they already had the machines setup to cast and machine them, so they continued producing them.

The pre-62 283s were small journal, but the 62-68 283s were medium journal, just like the 327s.

The 307 crank was just balanced different for the 307 piston weight. Smaller piston= less weight

As for production numbers of the 302, SCCA requirements said the engine had to be in a "production" car and meet a certain sales requirement. They only made the minimal requirements in the Z/28 Camaro. However, race teams had quite a few spare engines laying around as they experimented different induction systems, ignition systems, etc. to gain an edge on the competition, along with replacing blown engines before the next race.

As for sales, the 327 was the mainstay for a few years, and since most hot rodders of the day were more about drag racing than road racing, the all new "350 SS" Camaro, then the 396 equipped Camaros caught all the limelight. The Z/28 versions weren't popular with drag racers. The little 302 made impressive horsepower, but torque was limited since it was a high winding road race engine designed to turn 8000rpm(race version at least) on long straights at speed.

Thank you!

[MikeB]

Originally Posted by 68Stepbed

The pre-62 283s were small journal, but the 62-68 283s were medium journal, just like the 327s.

Actually, medium journal cranks were not used in the 327 until 1968. And I think all 283s were small journal. Google it. (For those who aren't sure what we're talking about, I say "medium journal" because only the 400 had what is referred to as "large journals".)

Originally Posted by 68Stepbed

The 307 crank was just balanced different for the 307 piston weight. Smaller piston= less weight

Correct. Several years ago I built a 327 using a 350 block and 307 crank. The shop that balanced it had to add Mallory metal to a few counterweights.

Originally Posted by 68Stepbed

The little 302 made impressive horsepower, but torque was limited since it was a high winding road race engine designed to turn 8000rpm (race version at least) on long straights at speed.

Exactly. A buddy of mine had a late 60s Z28 back in the day, and said it was a rocket ship, but not great as a daily driver. The race versions used dual quads on a cross ram manifold and reportedly made over 500hp(!) on an engine dyno when it was tested by Smokey Yunick.
https://www.jalopyjournal.com/forum/...8#post-6908697
There's another story out there saying Holman-Moody got similar numbers.