318 pistons revisited

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needsaresto

needsaresto

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I have brought this up before. Please excuse my memory...

318 magnum truck pistons. I think factory cast pistons have a comp height of 1.88 (could be wrong here). It just makes sense to me to use a cast piston for a street engine and these have really great comp height. So whats different about the magnum rods? Different pin size?


My question is; can they be used in an LA engine/rod combo? Maybe with some grinding/resizing to the little end of the rod? What are the issues around this? Whats the work around for the average guy at home? Or do I need magnum rods? Will they work on the LA crank? Can I use the 3.8 connecting rod?

So many questions,so little time...
 
magnum rods are narrower on the small end....pin size the same at .984

magnum rods should be able to be used on LA piston...

but LA rods would need to be narrowed to be used on magnum pistons...
 
After some further searching (about 2 days worth on the net!) I found reference to a 318 cast piston that is supposed to yield 9:1 compression.

P4529419

Could be an old #?


Cant find it in my Mopar performance catalogue. I'll call the dealer tommorow and see if thier parts guy can tell me anything.

Does anyone know about this piston?
 
Just found it!. Aproximately 1.77. I think that's the same as the 68-69 318 piston.
 
i put the kb167s in a 318. they were nice they sat .010" in the hole. with head combo and gasket i was using it ran the compression at 9.7568:1. The guy i sold the engine to said he dynoed it and got descent numbers somewhere between 300 and 340 hp. they were real nice pistons.
 
needsaresto said:
Just found it!. Aproximately 1.77. I think that's the same as the 68-69 318 piston.
Click to expand...

According to my books, that's the height for the early 273. Sorry, I don't have data on the Magnum piston. The 67-69 318 was 1.759 from the same source. These pistons have 4 valve reliefs cut into them. Compression of the the 318 of that era was 9.2:1.
The other way to raise compression is to reduce the volume of the combustion chamber. Milling the heads is one way to do this. It may be cheaper to get heads off of a 66 or 67 273 or 67 318 (57 cc). In 68, the heads were enlarged to 60 cc and remained this way through the end of 74 production. At one point, Mopar was touting using the Fast-burn heads of 85 & 86 for 318 build ups where stock valve size needed to be retained. These heads have 62.6 cc chambers. These heads, with no change in the piston, caused compression to rise from 8.4:1 to 9:1.
Hope this is helpful
 
You are right about the 5.2 pistons. The height is 1.77". With the rods, all 5.2 and 5.9 rods use pressed pins. So unless you have a press and a fixture for mounting the piston/rod a machine shop will have to mounth the pistons onto the rods...or you could get aftermarket full floaters.
 
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