Any reason why not?

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Valvebounce

Valvebounce

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Just out of curiousity, is there any reason why one couldn't use 5.2 Magnum pistons, in an LA 318?

Magnums are next to non existant in my part of the world. But I was mindlessly surfing and I came across a set of Magnum pistons with a 1.755 comp height. (Flat tops too)
Now I've heard that 'teens suffer from pistons being way down the hole as a major component of their general low performance malaise. So surely fitting a taller slug would go a long way toward helping things along?
PLus at under $150 a set they're plenty easier on the pocket that the KB167's that everyone always recommends. For people with tight budgets (Like me) it makes good economic sence.

Or is there something I' m missing?
 
I've read of people using those pistons without having any troubles but haven't done it myself.

What is your desired compression ratio?

Before you choose your pistons. do whatever you plan to do with your heads. when they are finished measure the chambers and how far your stock pistons are down the bore.

It's all well and good to save $200 on pistons as long as you don't have to spend twice as much on decking the block and a brand new set of shorter pushrods to compensate!
 
Ah yes, I forgot the rings are different on the magnums.
Out of morbid curiousity, I went round the the workshop, and measured up the comp height of the .040 over slugs that came with my super low buck 318 build. Near as I can tell, they're 1.662". That'd have the compression ratio so low you'd almost be able to start the engine with a hand crank! lol I was hoping to cut the decks, but with a comp height that low, new slugs are starting to sound worthwhile.............
 
Just to be sure, I'd check the piston weights to be sure you won't have an imbalance. Both the 5.2 & the 318 are internally balanced engines.
 
This engine had been balanced by whomever built it last time. I have a pretty sensitive digital scale. So I'd make sure new pistons weighed the same as the ones that come out. Might be a bit more "fun" if I need to add weight though. Weren't magnum slugs lighter than LA's? (Or was that just the cranks and rods?
 
Isn't there a difference in the rods small end width between LA & Magnum?
 
273 said:
Isn't there a difference in the rods small end width between LA & Magnum?
Click to expand...
The magnum rods are the same width big end and small end. As long as the piston and ring combo fall within acceptable weight you're good.
 
skrews said:
The magnum rods are the same width big end and small end. As long as the piston and ring combo fall within acceptable weight you're good.
Click to expand...


I don't think that's right. IIRC the pin ends are narrower on a Magnum so the LA width pin end needs to be narrowed a little.
 
My honest opinion is that the KB167 is popular for very good reason.
 
moper said:
I don't think that's right. IIRC the pin ends are narrower on a Magnum so the LA width pin end needs to be narrowed a little.
Click to expand...
Pin end width on a magnum .933", big end .933". LA pin end 1.21", .933" big end. The problem might be the pin end of an LA rod may not fit a magnum piston (too wide). Wish I had one here to measure.
 
Ouch, thats quite a difference.
Does anyone have one to measure? I wonder what the internal clearance between the pin bosses is on a Magnum piston is? Since the O.D. of both pistons is the same, the space may be the same too?
 
skrews said:
Pin end width on a magnum .933", big end .933". LA pin end 1.21", .933" big end. The problem might be the pin end of an LA rod may not fit a magnum piston (too wide). Wish I had one here to measure.
Click to expand...

This is correct-The LA rod will NOT fit between the pin bosses on the underside of a Magnum style piston. I just used a set of really nice Magnum rods in an LA build. Wanna hear the weird part? Visually you'd swear the Magnum rod was going to be lighter. Nope. They weighed exactly the same, down to the last gram. J.Rob
 
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