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From: Bob O.
Remote Name: 220.127.116.11
Date: February 21, 2003
So all I'm getting are "What are you up to?" and "Why would you even THINK of it?". So here's why. I've recently come to realize that the poly engine had one absolutely unique feature: its volumetric efficiency. If the Mopar figures as found in the Plymouth factory manual are to be believed, torque of the poly 318 was 345 lb.ft. Now, take torque and divide it by cubes, then multiply this by 151, and you get brake mean effective pressure (bmep). Try it for your self: bmep for the poly 318 is 164 psi. (Again, that's the figure Plymouth give). That is near to the theoretical limit for an unsupercharged engine (and that's with the old log-type exhaust manifolds too) and is very close to the 426 hemi's bmep of 173psi, which had all those performance-designed components. The bmep figure purely reflects breathing efficiency (proportional use of the charge coming into the engine), and is a product of the head, as opposed to the block, which just needs to suck/blow as rapidly as possible without flying into little pieces. The poly block doesn't really have much going for it, and in fact is poor at shedding heat, not especially strong, weighs an incredible amount, and needs custom-made pistons and cams for any performance application. So if that poly head could be mated to the LA block, like say a Mopar Performance 360, then that might be quite an incredible engine. In theory it ought to take CR's in the 10+:1 range on 92 octane without a problem. Now I cannot imagine that if it was possible, someone wouldn't have tried it already, but I just thought I'd ask. That's all. And yes, I do realize that the intake manifold might be quite an interesting exercise...... exactly how good is that POR-15 stuff?