the bore centers and v angle are the same as the LA and magnum engines, so they could keep some of the tooling. Other than that, it's a new motor. They have less dome in them so they can keep the chamber hotter, which helps emissions. Where they actually make their power is with the way the valves are angled. It allows a straighter shot into the cylinder for the intake charge, and a straighter path out for the exhaust. They are fired by coil packs instead of a distributor, and each coil fires a plug on its cylinder, and one that is 180 around the crank from it's cylinder. One plug it fires is on compression, the other on exhaust. That way if a coil pack fails, each cylinder has at least one plug still firing. They also run two rocker shafts per head, like both previous generation Hemis did. Beyond the v angle and bore centers, and the bell housing bolt pattern, there is nothing common between a new Hemi and a Magnum or LA engine.
Magnum heads can be swapped to an LA engine, but LA heads will not work on a Magnum block. The Magnums oil the rockers through the pushrods like a smallblock Chevy. The LA heads oil them through the rocker shaft pedestals.
The second generation 426 Hemi had a unique block. You can't bolt Hemi heads on a B (383, 400) or RB (Raised-deck B, the 413 and 440) block, nor can you bolt wedge heads on a Hemi block. They also used a unique input shaft on the manual transmission.
The first generation Hemi blocks are actually quite similar to the 383 block.
I guess the new generation Hemi can really be woken up with a cam. You will run out of valve-to-piston clearance before you max out the airflow while adding valve lift. You can also buy a kit, or a whole motor, from Indy Cylinder Head, that strokes the 5.7L (345 C.I.) out to 426 inches, and the 6.1L (apx 370 C.I.) out to 440 inches.
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Today's Featured Article - Timing Your Magneto Ignition Tractor - by Chris Pratt. If you have done major engine work or restored your tractor, chances are you removed the magneto and spark plug wires and eventually reached the point where you had to put it all back together and make it run. On our first cosmetic restoration, not having a manual, we carefully marked the wires, taped the magneto in the position it came off, and were careful not to turn the engine over while we had these components off. We thought we could get by with this since the engine ran perfectly and would not need any internal work. After the cleanup and painting was done, we began reassembly and finally came to t
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