I have a question for the board. Which is better for a normally aspirated street engine, say ~450HP. The reason I ask, is that I have read some posts about forged piston slap. I think this is caused initially by temperature variations on forged pistons. Once things heat up, the slap goes away? I know forged are recommended for nitrous and supercharged applications, but for the kind of HP I am referring to, is there a compelling reason to go with forged?
Do all forged pistons slap?

I guess it depends on how you arrive at 450 hp. If it's a 540" motor, a HE piston would be just fine. If you're making this power with a 327, your piston requirements will be different.

Okay. But what bout piston slap. I am considering rebuilding my 327 and am worried about forged pistons making unnecessary noise.
My combo will be ~400hp

onova's pretty much right, I think. I'm running a 375-400 hp 355, and opted for the hypers to save a little cash, and avoid the extra wear (and noise)...but if I were making another 50 to 100 hp, or EVER running any nitrous, it would be worth the expense, and any increase in wear, to go with forged. Since I'm kinda pushing the octane requirement/CR ceiling, I mighta been wiser to go with forged even at the hp level I'm at - no problems so far, though. Lots of people go with forged just because of the unknown, and a little extra peace of mind. It's mostly a little noise on warmup, a little wear, and a couple hundred bucks (a drop in the bucket once your going to the effort of replacing the pistons - even if that's ALL you're doing).

Alligator - If you're getting there with nitrous, go forged (or have any thought of ever using it). Otherwise, hypers would probably live fine (if you're not riding the edge of detonation).

But it is cheap insurance, and the noise is only on warmup. If you don't run it in REALLY cold weather, I wouldn't worry about it (the noise and wear).

With you being in RI, and it does get rather chilly in the winter time, if the car is driven daily, and the stated hp is max, I'd go for the HE pistons. I agree with others here, but, after a few 10K miles, the soft alum piston slapping when cold will gouge the cylinder wall. See GM and their modular engines, i.e., 5.3L, 6.0L, cold slapping and ask any new truck owner.

Just my 2 cts.

Thanks for all the replies! I suspect the HE pistons would work fine for my application.
Do forged pistons not last as long as HE or Cast?
Being performance oriented, I guess it depends on the driver...

Because of the increased clearance at startup, forged WILL wear faster...but how much depends a lot on conditions. Like Everett said, if you run it daily in the winter - you may well have an issue. If it's primarily a pleasure vehicle, or one that you only use in nice weather...then it's less of an issue.

If you wanna use it day in and day out, in all seasons, stick with hyper. If you wanna run nitrous - definitely forged. Otherwise, it's kind of a toss-up. If you don't put a lot of miles on it, and don't run it in the winter, forged will be fine. If you aren't gonna bump the power, run nitrous, or flirt with the limits of detonation, hypereutectic will work fine. In the middle ground, lean whichever way you feel most comfortable.

fwiw, my srp forged pistons run at .002-.0025 clearance. i've never noticed any piston slap, even on a cold northwest day. i think loose fitting forged pistons are getting fewer and fewer, due to more modern alloys possibly. imo, go with a good forged piston, the security is nice, especially if you get the nitrous bug (yeah, that never happens ;) ). i believe the hypereutectics are heavier as well. also, i know people have had good luck with them, but i also know guys, and have heard of a lot of people that have had problems with them, and thats reason enough for me to stay away. for a couple hundred bucks you could have a set of forged srp's, that are great pistons. if were me, if nitrous could be in the future, get a good forged piston (actually what i did), and if N/A is the way it will stay, in the horsepower range your talking, go with a lightweight forged. just my .02

I also have the SRP forged pistons w/ tight tolerances, and have never heard piston slap. I live in San Diego, so cold winter isnt a problem, but i like them.

Run forged. I learned the hard way. It really doesn't have so much to do with the power level as it does the pistons ability to live with detonation.

New forged pistons typically have a much tighter clearances than the old forged oned did, so piston slap and other not-so-great side effects of running a forged piston are basically a thing of the past. Unless you get a cheap, old technology forged piston.