AMC Pistons; Forged have downsides too , Cast has advantages ...

[biljoh@xxxxxxxxxxxx]

   Did some research on the net and read the links posted by others in this thread.  Seems to me that the major advantage of a forged piston over the cast variety is the ability of a forged piston to withstand detonation, and you know after reading the facts that's about the only one. 
 Now weigh THAT against the downsides:  
   Forged pistons are harder to maintain tolerances with when produced/"forged", meaning that out of a set of pistons there can be differences in weights-now this is just what I have read on the net and am not sure "why"- but, I read that they are more inconsistent. In addition they are Heavier than cast aluminum in all but the most trick expensive sets, because they have thicker side skirts, wich means you may have to re-balance your rotating assembly(correct me if I interpreted this wrong) meaning even more costly rebuilds.

 Another disadvantage is the price: 
 I did a little thumbing through the summit catalog and discovered that even the "POPULAR" brand forged pistons start @ $600.00 and from there they just go up exponentially depending on who you get them from. Nothing for AMC is even in there. I paid 198.00 for my cast aluminum reinforced +.030 10.25:01 Badgers OEM replacements. It comes down to cost VS. advantages and the intended use of the motor.

 Another disadvantage with forged, They are NOT as bullet proof as you might think:
    Cast aluminum pistons weak point is the ring lands and tops are prone to damage when subjected to detonation or extreme heat, if you don't have detonation you won't have a problem with them, if you don't overheat your motor or run very lean causing extreme combustion heat you won't have a problem, they don't just break own their own after a year or 2, it takes certain conditions within the motor to do it.  Forged has a distinct advantage here as they are much stronger in this area, but you also pay for this strength with other weaknesses. As stated above they are typically heavier due to the extra thickness of the forging. The side skirts go through greater thermal expansion than cast, and therefore the majority of forged pistons fit with much greater clearance (they fit more loosely) in the cylinder bore when the motor is cold to allow for the greater expansion as the pistons reach operating temperature. 
   Now you can have problems with the piston rocking in the cylinders when the engine is cold or until the pistons expand sufficiently to tighten up the clearance in the bores. This means noisy operation and increased ring and bore wear if the bores arent machined correctly for the expansion factor of forged pistons and less power. In extreme cases the emgine can use oil, contaminating the combustion process and REDUCING horespower. Is all that WORTH the extra money just for detonation insurance? I am not so sure!
Another disadvantage:
 Cast pistons will break on top but forged pistons are more likely to develop cracks or failures to the skirts because of the greater expansion inherent to their designs.

  Cast pistons can be fit tighter in the cylinder bore and can sometimes make MORE power than forged pistons from better, more consistant sealing of the cylinder and thus have less ring and bore wear. Detonation can be controlled quite easily on a mild performance motor such as the 10.25 :01 compression 343 I am building; fat fuel mixtures, controlled engine temps, and common sense timing settings will insure there are no problems, and I read that Nitrous shots up to 100 Horsepower are safe when the above precautions are adhered to, but that when approaching 200 and 300 horsepower shots forged pistons are mandatory. 11 12 and 13 : 1, compression motors will be happier with forged pistons because of the extra strength. 

So for a mild street performance motor that might take a "trip to the strip" every now and then cast is fine.  For a serious strip motor using very high horsepower to cubic inch ratios, lots of nitrous or supercharging, forged pistons make much more sense and justify the cost and inherent quirks associated with them.

  Hyperutectic pistons are a compromise, and were developed to combine the advantages of cast and forged in a single piston. In a nutshell they are almost as strong as forged but can be fitted tighter into the cylinder bore as they dont have as much expansion, so they don't give up the advatages of cast but they are prone to detonation damage.

  It's true you get what you pay for, but do you really "need" what your paying for.

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