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Race it, Don't rice it!
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YES. A bigger bore will net more flow for the same head. The bore allows more air space around the valve head.
The bigger the valve the more it'll change and the better the head to begin makes the bore size less sensitive.
 

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Most sbc heads are tested on a 4.06 bore Your 4.03 bore will flow less than tested flow numbers. Chad Spieir is our best qualified member to explain everything about head flow. He does the programming for "Profiler".
 

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Yes the larger the bore the better the flow past the valve into the cylinder. A great comparison as an algology to this is seen with the Harley Davidson marriage to the under square bore diameter to stroke. Even the exotic 4 valves per head design of the new M8 does not produce the horsepower of similar sized, crammed, and compressioned competitor’s engines. I first got into this back in the 1990’s with the Fueling 4 valve head on the Evo motor where I found these head’s did not produce the expected power gains for the flow area increase. Rethinking the problem and setting up flow bench tests established that flow was more limited by bore diameter than port sizing and valve curtain area. There are things that can help like canted valves but under it all for otherwise comparable designs a larger bore offers less restriction to intake flow. Of course a blower goes a long way to overcome such restrictions.

Bogie
 
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