I'm thinking of getting my old YS engine out and doing a rebuild. I'd like to use the original 72cc heads (actually i have 2 sets), but lower the compression to something like 9.2 or 9.5 to 1. Anyone have any experience with pistons for that? I've talked to a few machine shops, most reccomend hyper pistons due to the forged "slap" and cold oil use. I'm not really in favor of cast pistons. I've heard good things about Speed-pro, Sealed Power and good/bad about Keith Black. Any other thoughts on that?
Don  

Don - I think it all comes down to two factors.
1.What do you want to do with the engine?  
2.How much money do you want to spend?  

When hyperatic (I didnt spell that right) pistons break they crack up. If that happens a lot happens.  But these pistons are fine if you are not really going to be running nitrious or anything crazy.

When Forged pistons break they melt. You can salvage the engine.

It comes down to what you want to do with the engine.  

Speed-Pro, Sealed Power, TRW or Keith Black - All are reputable companies, You will be happy with any and or all.  

If it were me I would do a kit from TRW.

Have you had the block and crank checked?  Do that first because you need to know about brearings and piston/ring size.  
I'm pretty sure TRW sells an entire rebuild kit.

Let's build you an engine. What do you want the end result to be?

John  

I've built several chevy engines in the last few years but haven't done a poncho since about 1978. This is going in a '69 GTO, i want it to use the stock Th400 converter and make 400-425 hp. What i'm looking at is KB hyper pistons, about 9.5 to 1 ($275) Comp Cams 268XE ($225), new seals/springs ($100) in my '69 72cc heads (they only have 47,000 miles on them) Edelbrock performer-have, 750 QJet-have, pertronix conversion kit-have. I have not mag'd the block yet, crank is std thus far but i'll need to mic it. Estimate .030-040 bore on the cylinders. Eagle full floating rods ($675), no stroker. Not interested in nitrous, or forced induction. A fairly powerfull cruiser for the GTO, i have a '69 RS camaro to blast the 1/4 in. lol. Those thoughts are what is leading me to the hyper KB pistons, if not those then i'll use the TRW forged (+150 over the KB's). Fel-Pro perma-torque gasket set($100) I doubt if it will ever see above 5500rpm. I'm not buying anything until i do the crank work & block work. Just floating my ideas by some other folks & see if i'm in the ball park. My machine shop is estimating about $500 for block work, including polish of the crank assuning no turning required. I'm thinking i might be able to build it for around $2000 + machine work?? Also converting the heads to BBC studs or poly-locks for adjustable valve train. Thanks for your time, I appreciate it.
Don