Sealed Power Piston Question

[MrFurious]

Anyone know what size (in cc's) the dish is on the Sealed Power 362NP pistons? Trying to figure out what kind of compression ratio they'll give me, but nobody lists the dish volume. HELLO! :(:

[SwampRat]

I also couldn't find any specs for those pistons either, but it probably wouldn't of mattered, not only I have found but have read that dish volumes/dome volumes are usually underrated to prevent "excessive compression surprises" as Dave Vizard puts it...

Is there no other options out there for a better dish to lower your compression? That piston looks like a great way to kill quench and hurt torque and efficiency along the way...

[MrFurious]

Yeah, the deck clearance works out to around 0.035" which is far from good. MadDog advertises them as having a 9:1 CR, but I'd still like to be around 9.5:1 with the stock heads. If I go with the Eddy heads they won't even come close to working. I have no desire to spend $650 for a set of Ross pistons, and so far that's the only set I've found that have a decent quench height and compression ratio.

A piston with a 1.608" compression height and a 22cc dish combined with a 0.032" thick gasket and stock heads will give you a 9.55:1 CR and 0.040" quench height. Slap some Eddy heads on top of the same pistons and have a 10:1 CR. Imagine that! A piston that would work with both stock and Edelbrock heads, offers a good compression ratio that will run on pump gas, and has a good quench height.

Now someone call KB and tell them to start making them so I can stop bitchin. 8)

[Rogue Racer]

The dish in these pistons generally measure between 26 and 27cc.

[MrFurious]

Thanks RR. As I figured the CR with that big of a dish would be on the low side. Stock heads with a 0.021" thick gasket comes out to 8.9:1 with a 0.056" quench height. Eddy heads with the same gasket come out to 9.23:1. I guess if you shaved the stock heads enough to get to a 54cc chamber and took 0.010" off the deck you could get to 9.4:1 and a have a slightly tighter quench, but that's a lot of wasted money on machining if your block and heads don't actually need it.

[Rogue Racer]

Furious -
Depends what you mean when you say "don't really need it". From the figures you supplied, you will have .077" total piston to head clearance. My experience with the 360s shows that the less deck clearance, the better (more power and torque). The limit is probably in the .035" range before you run into clearance problems.

My figures show a 360 with 57cc combustion chamber (optimistic number; most are 60 cc) and .077" deck clearance with a 27 cc dished piston is 8.2 to 1 compression ratio. I'm not sure where you are getting a .021" gasket. I haven't seen any brand that is significantly less than .040". If you cut the block to zero deck clearance, with a .040" gasket, a 57 cc combustion chamber and a 27cc dished piston, the compression ratio is still only 9.0 to 1. That extra point of compression will be worth 1% or 1 1/2% horsepower in the engine and that should caluculate out to be over 20 hp. If your combustion chambers are really closer to 60 cc, which is likely if the heads have not bee surfaced, then the actual compression ratio will still be under 9.0 to 1 even with a zero deck. When face with all these numbers and facts to deal with, I would say the block really does need surfacing, and it has nothing to do with sealing. The money and effort spent getting the block close to zero deck is cheap considering the power advantage. You can object all you want about the manifold not fitting, push rods too short and all that stuff, but those are minor problems to solve.

[MrFurious]

Yes there's ways to make them work to get the CR you want, but that's not my point. My point is that no one currently offers an off-the-shelf piston that will give an optimum quench height (.035 to .040") or decent CR (9.0 to 9.5:1) without having to have major machining work done.

As for shaving the decks 0.035" to get a zero deck height (and having to do the same on the intake side of the heads), I shouldn't have to if the people designing the pistons did their jobs right.

BTW, you can get the 0.021" head gaskets through Summit. They're SCE copper gaskets if I remember right. They also offer a 0.032" one as well.

[SwampRat]

But you won't find the piston manufacturers doing their jobs right anytime, pretty much any piston is made to be at the least .020-.025 below the "blueprint" deck height.

[Rogue Racer]

Jim-

Correct. Nobody makes a suitable piston at a price that fits the picture and budget of a rebuild.

I had not considered the SCE gaskets, but you are correct about them. I had my mind stuck on composite rebuilders' gaskets that come from Fel-Pro, ROL, Victor-Reinz, Corteco, etc.

Rebuilders' pistons are one-size-fits-all designed. So they cut the compression height to makesure there are NO problems with that one-off block that happens to be out-of-spec and to make up for any increased compression from the overbore. They want to eliminate the time needed to check stuff by pre-assembling.