A few more bits of info from engine builders-



From Darin Morgan (was at Reher-Morrison now I believe BES)

"A cast iron block with cast iron heads will make more power than any other combination.
A cast iron block with aluminum heads will make less power.
An aluminum block with aluminum heads will make even less power."



From Larry Meaux (pipemax creator)

"a back-to-back Dyno test on SBC
cast-iron Bowtie Block -vs- alum Block
everything exactly the same, just blocks were swapped
there was 30 HP difference at 600 rpm/sec

another back-to-back Big Block Chevy test = approx 40 HP

another back-to-back SS Hemi test on Cylinder Heads only
with cast-iron -vs- aluminum = 12 HP more w/cast-iron
same flow numbers + port vol CC's

i did another similar test with my own personal SBC dyno test engine
..on the small block Chevy, it was a solid 8+ HP gain with
cast-iron over aluminum head.

the above were actual Dyno tests,
for theoretical HP/TQ differences between alum -vs- iron Blocks
by using FlowBench CFM Numbers -vs- what HP the different
block materials made on the Dyno =>

the results were=> for the same Flow CFM numbers,
i have yet to see an aluminum block engine make
the same HP/TQ that the cast-iron Block engine makes.

so far in all my Data,
the cast-iron Block always 100.0 % PerCent of time
makes more HP/TQ than an aluminum block

since Heat=HP/TQ
i think most of it might have been lost
to aluminum block acting like one big Heat-Sink
and some of it to ring blowby cfm w/alum.