It's Better To Give A 327 or 350 A Loving Home

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B_: I am considering rebuilding my 307ci and I need to know if it is possible to bore it out safely to 4.000" or 4.030"? If I do this, can I use 327 heads and pistons? Do the stock 307 heads have smaller valves to clear the smaller bore?

JD: No and yes. To bore a 307ci to 4.000" you would need to bore it .125". This would leave you with either paper thin walls (which would crack soon) or water jackets where your bores used to be. If you want a 4" bore, use a '68 or later 327ci or 350ci block with your crank to make a 327. Make sure to rebalance the crank as the 327 pistons will be heavier. As for valve size, they are small; not just to clear the bores but because the 307 was never intended to be a performance engine, hence the 2-barrel.

S_: Before you do anything with a 307, check to see if the iron it's cast from is any good. Look for a "10" and "20" cast into the front of the block under the timing cover. If you don't see both a "10" and "20", the block is cast from low grade iron and should be considered a paperweight. The 307's had small valves because they were an economy engine, not because they wouldn't fit. The 2.02/1.60 valves should clear a 283/307 bore, but not a 305 bore unless you are using Trick Flow heads. The 262/267engines are truly hopeless in the "Big Valve" department.

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Archivist: Tom Wilson


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