For all of you Gear-Heads out there;
We just finished the design work on a custom set of pistons for the
Magnum 360 engine. Anyone who has gone through the struggles of a rebuild on
the 360 knows how hard it is to find a set of pistons for it. Currently the
only options available are the OE style replacement pistons sold by
Silvolite, Federal Mogul or Sterling. These pistons were designed with the
large engine rebuilder in mind (lower compression height). If you chose to
go the High Performance route, you could buy custom forged pistons like
Ross. The problems with the forged pistons is that they are generally made
for the early A-engine and you ended up with a CR of 11:1. Also the forged
slugs are generally a race piston and don't hold up on the street (generally
40,000 miles is about all you get out of them). Dodge doesn't even sell
oversize pistons for the Magnum (.020 or .030 overbore). The Magnum head
combustion chamber is actually a beautiful double quench head averaging
about 62 CC's (very small chamber). Unfortunately, Dodge chose to run the
pistons an average of .050 down in the bores. When you add the thickness of
the head gasket, you don't develop the squish that you need to create the
turbulence for a fast burn. We have been working with Keith Black (a
division of Silvolite) to come up with a piston for these engines. We
started with a slug used for the 327 Chevy (4 inch bore). The top of the
piston (compression height) was set based on the block being decked .020 in
(pistons are flush with the top of the block). The pistons have been notched
for valve clearance up to .650 lift. The dish is a "Double D" arrangement so
the quench can be utilized. The pistons are cast Hypereutectics so they run
tight in the bores and they are grooved so the rods can be either full float
or pressed. We set the dish volume so that a CR between 9-10:1 could be
achieved based on gaskets chosen, surface cut on the heads and block (don't
need any higher in a truck engine driven on the street). The ring lands are
standard 5/64, 5/64, 3/16 so almost any ring combination can be run (not
metric like the factory). The only drawback that I can see is that the
pistons are heavier then the factory so a balance is in order. Dome
thickness minimum is about .220 inch so they should be durable. The first
set is going in the engine we are building up. I am real excited about this.
We are still negotiating with KB on how to market them, but more than
likely, you will be able to buy from anyone that handles the KB pistons.
Like I said, I am real excited about this, because we put a lot of work into
it and the folks at KB were willing to help. This should benefit anyone
contemplating a rebuild or an engine buildup.
Frank
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:16:35 EDT