Pistons: forged vs cast

[harleyguy]

Hi Mike
My question is regarding forged vs cast pistons (1550). I know forged will sustain higher rpm. My concern is that forged have a larger piston to cyl wall clearance than cast due mainly to higher expansion rate. Will the forged setup have a much higher oil consumption rate, and would engine lifespan be shortend: mainly cyl wall wear. If so by how much? I believe the se forged pistons use chrome top ring. Also, would synthetic vs regular 20/50 have any effect?

[Mike]

Technically the forgings would have higher oil consumption but in reality we've not observed this (or it's such a small amount as not to be seen). True of cylinder wall wear as well. I prefer the castings just for the tighter fit (and that H-D coats them and they tend to be lighter). This should translate into more stable ring to cylinder wall contact and better seal due to less piston rock. As you noted it should also extend life of both parts due to less impact during rockover. The lifespan difference between the two hasn't been established because of the applications dictating which to use. By definition, engines requiring the use of forgings typ. see much more stress and will have shorter life span than a more mildly built/ridden application that can use cast pistons. We use chrome top ring in both applications. The synthetic will help reduce wear and promote longevity in either application. The decision of which to use is based upon the motors expected operating range and how often and long it's expected to run in the upper rpms (stroke/rod ratio also plays a role in big cubic inch applications). 9 out of 10 street aplications are fine with castings. If your going to be drag racing, then forgings will be a safer bet.
Thanks, mike