Thinking outside the box
OK, you're trying to do this two different ways:
Initially, you compare the SB Mopar to the SB Chevy.
There are a lot of reasons why small block Mopars SHOULD have outrun Chevy V8 small blocks over the years... To name a few:
Superior design features, like:
Valves centered in the cylinder (Chevys are not)
Larger diameter lifters (better valve actuation)
Longer rods (better cylinder filling)
Usually, bigger valves
18-degree valve angle STOCK (Chevys were 23-degree, I believe)
Bigger bore (Chevy never had a 4.040" bore like a 340, without siamesed bores)
Shaft-mounted rockers
"Cool fuel" (Thermoquads)
Better automatic transmissions
I'm sure there are a lot more reasons; I just can't think of them right now.
Then you start comparing it to the late model LS motors...
Someone suggested that I should be comparing the LS heads to a late Hemi head... and I would except they won't work on my 360... and, that's what I am directing this discussion towards; 318/340/360 motors.
The LS heads won't bolt on a Small Block Chevy either.
First off, the LS motors are the top of the heap as far as small block motors go, like it or not. If GM could manage to put one in a car anyone wanted to buy, it would be more obvious.
The newer production stuff also has the advantage of better ring technology (less drag), and machining tolerances that your local guy is never going to beat. Also remember that the ports on these heads are only required to flow air, whereas old school small blocks have to flow air and fuel.
I think you're on to something with the weight issue, and there are a bunch of supposed advantages that the Mopars have that aren't really advantages....Like...
Gigantic heavy lifters. I suppose they might give "better valve actuation", but the brand X cars are actuating their valves just fine. Valvetrain weight is a huge concern for RPM production (which is how small blocks make power). Racers fret over Ti retainers and beehive springs to save
grams, and we're stuck with these lifters that way
ounces more.
I don't really think the shaft rockers are an advantage. You can spin stud mount rockers really high without trouble (in my SB Ford, I ran 7/16 stud mounts 8000 RPM in NMRA Pure Street competition *without* stud girdles). Stud rockers have a big advantage in that its cheaper and easier for them to improve what the factory gave them than it is for us.
Valvetrain Angle; Well, that's an advantage, as it can move air more easily, but it can only move the air that gets in, and the problems with Mopar heads are widely known...same thing applies to big valves.
Thermoquads? If I want to make power, I'll go for a Holley every time, cool fuel or not.
As you mentioned, rotating assembly weight is also a huge problem. There are huge gains to be had in dropping weight here.
Lets not forget exhaust, either. The A body wasn't designed with a V8 in mind, so the header options aren't as good as they are for most GM and Ford stuff.
Timing control is hugely important for power production, and WTF is with the distributor on these small block Mopars? Whose idea was it to set that up?
I think a lot of this has to do with the fact that Chevy (and Ford) put a lot of priority on their small block design. GM invented it after all. (and this is doubly true of the LS motors), whereas in the 60s Chrysler was concentrating on the big block stuff.
Don't get me wrong, I love my Mopar, but I'm not going to be in denial about its limitations.