A lot of people forget, those numbers achieved (290HP) were from cherry picked dyno runs from multitudes of engines being ran in an ice-cold dyno cell; no accessories, optimal tune-up, and open-exhaust. IAT's and Coolant Temps, would have also been optimal.
A mechanical fan alone, can draw around 30-hp @ 5,000 RPM (Clutch is OPTIMAL, little to no difference vs. electric). Modern alternator and mechanical water pump, 12-HP @ 5,000 RPM. Coolant temperature, 140* increased to 200*, pulls another 10-HP (1-HP + loss per 10*). Adding to that last note, in a car, under a hood, this would negatively affect the IAT temperatures and further loss of power would occur. Manifolds vs. Headers, 20-HP +/- entire curve. Cheap muffler (OEM) vs. Good muffler, 10-HP +/- entire curve.
That's 80-hp, that's why it was a 'wow' moment in 1972 when going from Gross to Net figures. Minimal power loss from compression, most of the damage from more realistic power-measuring. Could you imagine if they measured RWHP!? 390 HP 440 six-pack, 300 rwhp. You see why Gross ratings were favored. In 1972, the 440 'high performance' net figures were down rated @ 290 HP from 375 +/- HP Gross. The cars were heavier, power was down slightly (few percent with CR drop), so it's pretty obvious why perceived performance was lower.
IQ52 took a pretty much bone-stock 78' 440 (7.8:1 CR), added headers and an Eddy carb, made 300 HP at the crank / 430 ft/lbs of torque off idle. . . . . next step, 387 HP / 450 ft/lbs from a .509 MP cam, M1 intake, and 850 carb. ..... 450 HP after switching over to some ported Iron heads, no other changes. HP per $ is really tough to beat - - - - Don't try that with a Poly. That's why it may be better to do budget-upgrades, upgrades that 'free up' HP and spend the real money on building a 440 instead if you want power.
