This should be fairly obvious, but i've only seen a handful of pistons up close in reality, so:
I have a 350 with unknown origins (010 block, 2 bolt main), apparently the heads have been "reworked" (993's, whoopie... heche en mexico)
anyway, just got a head off, and i'm looking at the pistons, and I assume a dished factory style would be a "large" dish, while what I see looks like a flat-top... Before I go buy a dial caliper to check the bore, i'd just like to know if I have a flat top piston (and assume it's a non-stock piece) or if it's just a plane jane dish....
Thanks

 

It's got a slight dish. Flat-tops are flat on top, except for the valve reliefs.

 

Stock dished pistion.

 

huh, i'll be damned, I figured a dished would have a larger dish...
The combustion chamber on the 993s looks just tiny, maybe it was milled.... oh well, I need more power than 993s can provide anyway....
For sale : 993 heads

 

Partial dished. Full dished won't have any valve reliefs in the dish.

But, they are stock-looking '87-later pistons.

 

really???
I thought this motor came from a '78 Impala, or something I thought would be completely smog and useless except for the block basically... But the valve reliefs made me think twice...


Would there be a P/N stamped on the underside of the piston perhaps to get an exact dish size?
Would an 010 block have a roller cam, or is that too old of a block id#? (in case it is a later block and not from a '78?)

Thanks

 

If you want to know the dish size, you can set it up in a stand and CC it with a burette. You can also work some plasticine into the dish and reliefs, trim it smooth, peel it off and drop it into a graduated cylinder.

An 010 block isn't a factory roller block. You can even see that in your picture.

If you want to see a fully dished piston like five7kid mentions, take a look at any factory 400 piston. They're like soup bowls.

 

It's probably a GM crate engine since the heads were made in mexico. There is a thread floating around, some one did measure the dish or found specs on it.

 

Sounds like a good shortblock to add ported 305 HO heads to. Boost the flow and the sick compression ratio.

 

this a a GM Hecko e mexico goodwrench crate motor. the cr is 7.8:1 with a .038" gasket.

 

Exactly why you should switch to some HO 305 heads.

 

This is destined to be a fairly high buck 383 motor for my brother, probably some trick flow heads or AFR, i'm looking for low end grunt mainly. I don't think 416 heads will go on this one, but my next 355 will have them...

 

I've seen them many times. They're about -12cc worth of dish. Also check the deck clearance. Most sit at the typical .025" in the hole at TDC but some (I'm told- never seen it myself) sit significantly further down- .050 or more.

Compression ratio with those pistons (stock 4.000" bore), 993 heads and a typical Fel Pro .039" head gasket will be a rather dismal 8.0:1. The factory rates them officially at 8.5:1 but it's not that high in reality and the factory uses a much thinner steel shim head gasket.

A swap to 64cc heads and a GMPP composite head gasket (.028") will get you up in the low 9s for compression. A Vortec head swap would be a good example of this- it would get you the compression plus a lot better flow than the 993s.

 

If you're building a 383 you probably won't be using those pistons anyway.

 

Exactly Ape.
I just thought if they were decent, then I might keep the block and pistons for myself, and have my brother use a "worse" shape block for his 383.
For a 383, do I need pistons, crank *and* rods, or can I reuse the 350 rods? or do I need the 400 rods?
Thanks

 

Full dished piston

 

You can use 350 pistons and 5.565" 400 rods, or you can use 383 pistons and 5.7" rods from anything except a 400.

 

JE/SRP 4.06" x 1.25" CH -16cc dished forged alum. piston 388cid & 10:1 CR.
3.75" crank & 6.00" rods - topped with TPI vortec baseplate, and GMPP Fast Burn Alum Heads.