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Forged v. cast pistons

1K views 5 replies 5 participants last post by  cragdweller 
#1 ·
I am planning an engine rebuild for my 88 RC w/318 and was wondering if anyone can answer the forged v. cast piston question for me. What are the pro/con for each? And I am also wondering what is the best Carb/Intake compromise for street and offroad use?
 
#2 ·
Forged if it'll be severe duty, forced induction, turbo etc.  Older cast is weaker, but modern cast (hypereutectic) is pretty formidable.  The cast expands less so the bore-to-piston gap can be tighter.
 
#3 ·
There are some pluses for cast. GM loves to use cast even in 500hp with forged or titanium rods, so that says something.

Reason is less emissions and slight power increase due to a tighter bore. Cast doesn't expand so much , so they can run a tighter better sealing bore.

Since the forged requires a looser cold tolerance, they slap more until they warm up and seal.

They can handle higher cylinder pressures, but very few truck builds make those kind of pressures. Lot of vehicles come from the factory these days, including trucks, with 400hp/10:1CR+ and cast pistons.

In between the 2 are various grades of hypereutectic cast, and usually sufficient for all but the 1%'ers.
 
#4 ·
Don't forget detonation resistance...forged being better.
 
#6 ·
For a 318, go with a nice set of KB hypers.
 
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