New impala motor/carburetor identication - Impala Tech
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post #1 of 2 (permalink) Old 12-24-2015, 04:44 PM Thread Starter
 
 
Join Date: Dec 2015
Location: Florida
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New impala motor/carburetor identication

I acquired a 1969 impala convertible and the previous owner had no information on the vehicle. I am trying to confirm the motor and carburetor based on casting numbers. The engine block has a the number 3970024 on the driver's side near the Bell housing. Based on my research the motor is a 307 CI. The carburetor has the number 9755S 1885. Which I've identified as a Carter/edelbrock 750 cfm. The car idles well but stalls under acceleration. Can this carburetor be jetted and tuned to work on the 307?
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post #2 of 2 (permalink) Old 12-24-2015, 06:09 PM
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Welcome to the Team Tip!

Not Easily. A 307 is 283 block (three and seven eighths of an inch bore size) with a crankshaft out of a 327 (3.250" stroke vs. the 3.000" stroke for a true 283). So it will rev as high as a 327 will. It just won't breath as well as a 327 or make as much power per cube due to the smaller bore.

Of course small is a relative term. Compared to a 305 the bores are huge, just no where as big as a 327 or a 350 (with their four inch bore size). Or no where as big as the SBC 400 that had a bore size of 4.125 inches. Bigger bore is better in the world of over square Chevy engines that rev higher to make more power strokes per minute.

Olds, Pontiac and Buicks (and Caddy as well) all have under square engines that have a stroke that measure longer than the engine bore is across to make more torque to move a heavier car, and to do so at much lower RPM so that you can enjoy your afternoon tea party in the back seat. These engines where rather large in displacement compared to other engines of the day which is why Caddy and Buicks where the engine of choice before the Chevy small block was created.

The problem as I see it is the carburetor's size (750 cfm) is too large for your displacement. That carb would be happier on top of a 454. Your engine is happiest with a carb of 500 cfm though if you are willing to spin it higher than your cam and gearing now allows you to do you could get by with a 600 or a 650 cfm sized carb.

Big Dave
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