Someone here was asking about these, and I found this old document on them. It raised a general question for me. Is ONLY swapping a cam (and in this case intake from dual plane to single or vice versa) acceptable to change idle characteristics of an engine? I was always under the impression that cams were match to other parts of an engine, and therefore should not be swapped without additional changes such as valves. Am I not necessarily right, and is it more about converter and gears? The chart below didn't align properly but on left is 380hp and right 300hp, but the only change from the 360/300hp and 360/380hp was single plane intake and the cam. I had the 300hp version and it was very impressive and smooth idle with stock converter.


Mopar Performance Magnum V-8 Crate Motors
Feature 360/380 360/300
Assembly part number P5249499 P5249498
Compression ratio 9.5:1 (advertised), 8.7:1 (JTE nominal)
Cylinder heads Cast-iron, 18-degree valve angle high-swirl intake ports, combustion chambers
Intake valves 1.925-inch diameter, 5/16-inch stems
Exhaust valves 1.625-inch diameter, 5/16-inch stems
Rocker arms Ball-stud pivot, 1.6:1
Camshaft Hydraulic roller tappet
part number P4876348, without lifters P5249663, with lifters
application MP replacement '89 OE 360
duration 288/292 degrees 274/264 degrees
lift 0.501/0.513 inch 0.385/0.401 inch
Valvesprings High-performance, 1.42-inch diameter
Valve seals Banded Viton rubber, static
Retainers Chrome-moly steel, 7.5-degree plunge angle
Oil pan Center sump, 5-quart capacity (with filter)
Intake manifold Single plane Dual plane
M1 aluminum, square-bore carb pattern with provisions for
multiport injection
Ignition system Mopar Performance electronic kit vacuum-advance distributor
Valve covers Cast-aluminum, black-wrinkle
Fuel Premium only Best available grade