All:
I've wanted to check for a long time but in my quest for rings which were off the shelf and such I discovered the 93 GM 4.6L Northstar V8 has the same bore. Turns out it also used a 22mm wrist pin and the compression height of the piston is nearly identical, from what I recall less than 0.010" shorter.
I recently bought a set of replacement Northstar pistons at 0.5mm oversized when I had the chance to buy singles as most often they come in sets. The piston was within 10 grams (heavier) of the stock HCX piston, so that will be easily taken back to the factory HCX weight without hurting anything. Or if you left it, it would result in shifting balance factor lower. These are flat tops so compression would go up a shade. I purchased two of them for $56.
Things to note:
1. The oil return slots are not at skirt but over above pin as similar to the new pistons in many engines such as the twincam HD. I think I would mill some oil return holes in the skirt area for safety sake on oil control, but should not be necessary.
2. width between bosses on piston is near identical to HCX piston and tang on skirt does not interfere with counterweight nor would you expect it too as overall height of piston is nearly identical.
3. This piston has the advantage of retaining the factory low expansion rate of a hi silicon hypereutectic aluminum casting so it will be quieter, last longer, etc.
4. The factory Northstar ring package is a steel chrome plated top ring and a napier second ring. If one wanted to drop to a moly faced ring that is very easy to do.
5. This piston is a robust design and more than capable of anything this engine would throw at it, all in all a nice set up.
6. I have not checked the alignment of the valve reliefs but with the stock cams and near zero overlap who cares as they are not even close to being an issue.
My intention is to sleeve my original cases at the left hand main bearing again, bore the cylinders 0.020" over and fit these pistons in and get #307 back with to a numbers matching status, so while it may take a while these are my intentions.
I just think this is great news as I don't like the 2618 top fuel type race piston for use on the street and I doubt we could find a 4035 piston available unless of course it was for a early North Star application. The 4035 alloy can be fit tighter but not as tight as the casting. To top it off this is a HUGE savings vs. custom pistons.
For the record I measured one of my stock bore pistons which was or had been coated on the crown with a ceramic from swain at 506 grams w/o the wrist pin keepers and rings. The +0.5mm piston i purchased was an Enginetech P30581. The Enginetech was 515.6 grams. I'd like to have purchased a set from Federal Mogul or Mahle but I'd have to have bought 8 of them and I figured I'd never use the other 6 unless of course other members needed a set. So when I had the chance to buy singles at $28 I jumped on them.
