I think what is missing is that a motor is a package, and while airflow in the heads can indicate how much hp the cylinder head can
support, it doesn’t necessarily match the motor’s output. Compare a stock 5.9 making 245/330 to a 300 hp crate motor with 340 exhaust (reference the below article) making 315/409. The crate motor is fundamentally a stock 5.9 with a different intake, and the difference in induction made a whopping 70 hp and 74 lb-ft difference, and moved the rpm band up about 500 rpm. Just from adding a better flowing intake. Then put a bigger cam in it and drop a single plane intake on it (e.g. the 380 hp crate motor), and now it makes 400 hp, all with the same heads. But on the 380hp motor, the heads are probably maxed and would need to be swapped out or ported to go higher. At the same time, a G3 hemi with a much smaller cam will probably make the same hp, be much more civilized and has the potential to go much higher than a Magnum, all because the better flowing heads can support it.
Not saying everyone needs more, just saying that the
potential in a G3 is far above what a Magnum has to offer, even with some high end cylinder heads like Dr J's on it.
The 1998 5.9 was rated at 245 hp @ 4,000 rpm and 335 ft·lbs @ 3,250 rpm. The 2015 truck 5.7 is rated at 395 hp @ 5600 rpm and 410 lb-ft @ 3950 rpm. The 300 hp crate motor used in the "famous" exhaust test made a peak of 327 hp @ 4600 rpm and 425.5 lb-ft @ 3700 rpm with TTI exhaust in
this article, and a 380 hp test made 409 hp @ 5,400 rpm and 439.5 ft-lb @ 4,100 rpm in
this article.
Yes the truck 5.7 makes its hp 1600 rpm higher, but the torque peak is only 700 rpm higher, and if you dump the kegger intake on the Magnum, all the sudden the difference is 1000 rpm for hp and 250 rpm for torque. And if we are talking about adding a cam for more power and rpm, the kegger becomes a real issue forcing you to buy a different intake (which is even more expensive if you want to keep the EFI). The truck 5.7 does a pretty good job of keeping up with the 380hp crater motor, with a much smaller cam and no headers. Now compare that 380 hp crate motor to an SRT 6.4 and all of the sudden the G3 is bigger everywhere, but it does it with a smaller cam and still has the potential to grow while the 380 hp crate motor needs more cylinder head before it can go anywhere.
For reference the car (6M) 5.7 is rated at 375 hp @ 5150 rpm and 410 lb-ft @ 4300 rpm. The 6.4 in a 2011 SRT8 was rated at 470 hp @ 6000 rpm and 470 lb-ft @ 4200 rpm, 100 rpm lower than the 5.7 and only 100 rpm higher than the 380 hp crate motor. It should be noted that the 6.4 has an active intake, though.
None of this is meant to imply that a Magnum isn’t worth swapping, or the potential is inadequate. Just thoughts and points of discussion.
