What does cubic inches have to do with horsepower? More torque, yes, but not horsepower. The heads, cam, and induction are going to dictate the horsepower capability
The cubic inches will only dictate where that peak horsepower occurs. If a larger motor makes significantly more horsepower than a smaller motor, there is a problem with the valvetrain not being stable enough to allow the smaller motor to rpm like it should. That never happens, right?
These particular motors we are discussing are not max effort race motors.
They are are hot street/strip, mild bracket type motors.
None of them is making "maximum" use of the heads, and my experience has been with that type of build, the cubes make more power.
Oem 440 4bbl motors are rated at 40 more hp than a 383 4bbl, with the same heads & cam.
The cubic inches aren't what makes the extra power. There are other differences that contribute to a power gain that are relative to the additional cubic inches. The factory horsepower ratings have never been considered trustworthy, but let's give them the benefit of the doubt. Would a larger bore help the cylinder head breathe better? In most cases, yes. So, the .070" difference in bore size would give the 440 an advantage. Maybe not 40hp, but an advantage no less. Also, The horsepower ratings were only 400 rpm apart, and all else being the same, there should be more of a spread than that for almost 80 cubic inches. Compression ratios were not very accurate, so that's another variable. And finally, considering that the 440 was an upgrade in many cars, customers were not going to spend extra money for the upgrade unless the numbers were impressive. Marketing does tend to make results biased to the sellers advantage.
Mopar Performance crate hemis are another example. The 426 and 472 are basically the same except for the stroke/cubes, with the 426 rated at 465hp and the 472 at 525hp.
Sorry, but the 472 has quite a bit more camshaft than the 426, which would allow it to carry the torque curve to a higher rpm, which = more horsepower. Rpm not cubic inches.
I built two very similar street strip RB motors years ago, a 446 and a 493. Both had rpm heads that were prepped the same, and flowed within a couple cfm of each other.
Both had Holley sd intake manifolds with 850dp carbs. Both were tested with the same 2" hooker headers. Both had cams from the same lobe family, and both used 1.5 rockers.
Both were right about 10:1cr.
The 446 cam was 254/254-110 in at 106, the 493 cam was 250-254-112, in at 108.
Desktop dyno said the 446 would actually make more power than the 493(which is when I decided that it was pretty much worthless for determining how to build bb mopars with modest flowing std port heads).
The actual dyno had the 493 making about 45-50hp more than the 446, along with a bunch of extra TQ.
This is pretty typical of a build that likely has valvetrain issues. Let me guess, they both had Harland Sharp rockers just bolted to the cast in stands. If you can't carry the torque curve on a smaller motor because the valvetrain becomes unstable, it doesn't have a chance of making more horsepower. Because, say it with me now, rpm makes horsepower! Diesel trucks have pretty small horsepower numbers, but they make enough torque to pull enormous loads. Why? They don't rev high enough to make a lot of hp.
The desktop dyno is simply a calculator that uses mechanical formulas to determine a result. It can't account for inefficiencies or deficiencies in the actual motor, or incorrect data input. A Mopar motor is still an air pump, just like any other internal combustion engine, and the same formulas still apply.
This is what I find is more typical with that type of build. The hp/ci doesn't change all that much, and more cubes just nets more horsepower.
When the hp peak is at a fairly conservative rpm, if you start higher(more torque), you end higher.
If the hp/ci doesn't change with differences in cubic inch, then there is definitely a problem. The cylinder head, camshaft, and induction has the ability to move a certain amount of air, based on effiency and cross sectional area. A formula one motor, that turns over 15,000 rpm with roughly 280 cubic inches, has a very high hp/ci ratio, but if the cubic inches were increased, that ratio would drop drastically, because the rpm would fall as well. The same thing with Pro Stock engines. I realize they are highly refined race engines, but the mathematical rules still apply.
I would say the big crate engine builders(R-M, Shafiroff, etc)must agree, since the displacements just keep going up, and the hp along with it.
As always, your results may vary.
What are R-M and Shafiroff building? A pile of big block Chevys with really good heads. That means either rev it to the moon, or increase the cubic inches to get the power at a lower RPM. A bigger port is going to need a bigger valve since it is the biggest restriction in the port anyway. That adds weight to the valvetrain, which is harder to control at higher rpm without exotic parts. Anyone who is willing to spend the money for those parts is going to want a custom build, not a crate motor.
Again, if I had peak power at 5600 with 505ci, and a 242/248 HYDRAULIC roller, why is a 446ci motor with a 242/248 SOLID roller peaking at the same rpm? Oh, and let's not forget the half a point of compression and the high rise single plane manifold the 446 had.
