This is about as close to anything useful I have found so far. When Jerry does his testing we will know for sure...
I haven't made an actual A > B swap to compare effects, but I think it's probably a case of "people tend to see what they want to see". Curt Bergeson CC'd a few common castings and found 79.1 cc (4.83") for the 848, which is the smallest chamber by a small margin. Other common heads: 850 = 86.2 (5.26"), 570 = 95.5 (5.83").
A worst to best comparison on a 235.5" stock motor: if the engine had 7.25:1 CR with a 570 head, its total chamber volume (including deck, gasket etc.) is 6.28". Swapping an 848 head subtracts 1" (5.83 - 4.83) for 5.28". The new static CR is 8.43:1, a very substantial increase, the largest gain for any chamber size-derived swap. A bigger engine or one with a higher CR will have a greater increase.
In round numbers, raising the CR from 7.25 to 8.43 picks up about 5.6% efficiency, and perhaps worth 7% in power.
For a cam with 50° ABDC closing, the DCR numbers:
the 570 head 6.40:1, 122 psi gauge pressure, about 32 hp @ 1,000 RPM
the 848 head 7.42:1, 148 psi gauge pressure, about 40 hp @ 1,000 RPM.
As you know, besides a head swap and (limited) head and block milling, the only remaining avenue to really high compression is a domed piston, $$$.
I got that from a friend on the internet. No idea myself. Looking forward to Jerrys tests.
The reason the 848 is so important to the 261 is not for the gruntvalue=max. Its because real 261 heads are very hard to come by, and the 848 was the most produced modify-able head.
