L89 Nova???????

[92646]

Why did they still use closed chamber heads in 1970? The open chamber heads had been around for awhile. It made more power and got better results with the smog regulations. In 1971 did they use an open chamber head with a closed chamber piston to lower the compression?
Mark Sheppard

[Chevy454]

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Why did they still use closed chamber heads in 1970? The open chamber heads had been around for awhile. It made more power and got better results with the smog regulations. In 1971 did they use an open chamber head with a closed chamber piston to lower the compression?

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I'm not sure it necessarily made more power apples-apples...today's Pro Stock engines aren't open chambered, quite the opposite...tiny, tiny chambers with a huge quench area. With an open chamber, to get any kind of compression you're talking a BIG dome, which means more weight in the piston, which means a heavier pin, which means a heavier rod, which means a heavier counterweight...that's a lot of *heavier* components, and these engines were already struggling with rods/bolts living as it was. Anyway, that's enough rambling from me...

IIRC, the 074s (L88, ZL1, '71 LS6) I believe were the only open chamber production BBC stuff...top shelf stuff indeed, but old technology as well.