My 47 truck has a 30 over 302 .268 duration .456 lift comp cam with a Holley 4 barrel and dual exhaust, stock iron mid 70s exhaust manifolds, and a 3.08 rear gear and C4 auto tranny.
It runs pretty well and has a sweet spot for the hiway at 60-65 mph at about 2000-2200 rpm.
It's a 74 block with D2 heads.
I'd like to get a little more power, but I'm wondering if there's some things I could change without digging into the engine. Things like the exhaust manifolds for shorty headers, or maybe change the rear gear to something like a 3.5 to 3.7 ratio. The 3.08 seems to me to be a ratio made for fuel economy, not performance. Is it even worth doing anything else without changing the ratio?
Are the heads junk? Would E7s or GT40s make a difference or would they be strangled by the rear gear?
Thanks for your thoughts.

 

D2 heads have small chambers(58cc) so your compression is pretty good but they also have small valves and don't flow particularly well so GT40 heads and headers of some type would really improve HP output.

 

The gear swap will do far more for acceleration than anything you can do to the engine, short of a full rebuild combined with better heads. I just went from 3.55's to 4.10's in my 96 E150 van and the difference in getting up and goin is amazing.