Today, dollar for dollar, is the 318 faster than the 340 ???

Dave_J said
As far as shrouding the valves between a 318 and a 340, how much is 3.2% less bore diameter really in effect?

If the compression ratio, heads, valve size, cam, intake, exhaust were all the same exactly:
A 340 with 22 more cubic inches at 85% volumetric efficiency is 18.7 HP.

This is based on a 318 Police 4bb @ 165 HP. The 340 with higher CR, bigger valves and hotter cam makes 275 HP, 110 more horses. But, this is NOT an equal comparison.
Many of us have built a 318 with 9.5:1, 2.02 X heads, 340 resto cam, larger 340 size intake and headers.
Except the headers, 'WORKED' iron logs, my 65 B-Cuda 318 (0.030 over) 9.5:1 CR, with ported X heads, a DC Purple 272 cam, Sanborn Oil mods, a 904 (2800 stall and shift kit) and 3.55 SG would slowly walk on my friends stock 340 Duster with 4 speed and 3.55 SG. I'd have him by a door in the 1/4 mile time after time.
My B-Cuda weighed 100 more pounds.

YEPPER, a 340 is FAR superior to a teen. I will leave them to their cult followers. :mob:

.
A modified 318 Beats a Stock 340. I can see that happening.
Rework the 340 heads and put the same cam in it that you put in the 318 and I guarantee the 340 will walk the dog on the 318.
Cost would be the same between the two Motors. I'm talking about the cost to do the heads in to put a cam in it.

Yes it's fun to modify a 318 and see if it will outperform a 340. But in the end you want the 340 even if it cost a little more. So keep looking for those 340 blocks.
Personally I think the 360 or the 5.9 Magnum is the way to go nowadays.