Powell Machine Magnum 5.9 360 roller cam regrind video
It could be a myth, but I don't think so.
I know in 1994 the 5.2 had 220 hp at 4400 rpm and 300 ft-lbs at 3200 rpm. That same year the 5.9 had 230 hp at 4000 rpm and 330 ft-lbs at 3200 rpm. Everything else on those engines is the same (heads, intake, exhaust, etc). Based on that it seems like the 5.2 has a slightly hotter cam. Peak power RPM is higher and only 10 hp lower, which isn't really a lot when we're talking about a 42 cid difference. We need someone to send Powell a 5.2 cam for comparison!
Here is what
@YY1 posted for numbers.
5.2 Magnum Hydraulic Roller 432/432 251/264 113CL
5.9 Magnum Hydraulic Roller 410/417 249/269 109CL
Here are the numbers I got from having a 2000 Ram 5.9 cam run through the Cam Doctor at Bullet Cams:
Duration @ 0.050: I/E 189*/194*
Lobe separation angle: 111*
Lift @ cam: I/E 0.273"/0.278"
Valve lift w/ 1.6 rockers: I/E 0.437”/0.445”
Not sure on the advertised duration numbers, but my 5.9 cam had more lift than both the 5.2 and the published 5.9 numbers.
One interesting point that YY1 made someplace (as I recall) is that the published valve lift numbers for the 5.9 match the cam lift numbers from my cam if you use a 1.5 rocker ratio. So it is possible that info like that was just done wrong, but the rest of it is correct. No sure, just pointing it out.
If we assume the advertised duration is correct on the numbers from YY1, the 5.9 cam is a couple of degrees smaller on the intake but larger on the exhaust and my lift number say both are taller on the 5.9 cam.
Based on that, I don't believe the 5.2 cam is better. Frankly, I think both are so small it wouldn't make much difference either way.
I have never heard anyone say the 5.2 has bigger valves, but for sure that's totally false. I would agree that no Magnum ever had a 1.88 intake valve. They were 1.92.
I pissed off the guy that was making a business out of Magnum swaps years ago because I didn't agree with Magnums having a 1.88 valve.
Here is just one example -
5.9 Magnum exhaust/intake combo help