What compression ratio was/is your 3L running at?
Longer duration thrives on higher CR (and vice versa)
I'm sure that played a large part in how effective they were!
Also I bet with a real UIM your HP figures would have skyrocketed. Running large 35mm valves with those tiny SH UIM ports.
Why would a larger lower suddenly make a big difference when the upper is the piece already restricting the airflow? (I.E. If the lower is already larger then the upper. How does making the lower larger help if the upper stays the same? It's (LIM) not suddenly getting any more airflow.)
IMO the 5HP jump was mainly (3+) from the DH upper alone. The extra EH on the heads probably made up the last 1 or 2HP. The lower likely didn't account for much; if anything.
