The 1131's will yeild 9.25 to 9.4:1, depending on deck clearance, and assuming the heads end up at 71cc's. With the block milled to 10.150, you will have .012 deck clearance and 9.4:1. This is how we build 'em. The higher compression works due to the better quench. Price is probably about $85/set. But, I don't use these since we have a better hypereutectic piston that specs out the same for only $120/set.

The 1130's are a low compression piston. With a 19cc dish, if they are installed at the same .012 deck clearance with 71cc heads, you'll have 8.80:1. With a stock 10.17deck, you would have 8.48:1. Whoopty do. Plus they are more expensive at $175/set. Once again though, there is a Hypereutectic alternative for the same cost.

You can pick up .22 compression by milling the heads to 68 cc in the above scenarios.

The pistons can be sourced through many of the large warehouses, or you can drop us a line for help tracking 'em down.
Rob

 

I did the math with the TRW piston ( 2291) and with it's 1.776 comp height, a 70 cc chamber, and a 10cc head gasket volume, a 10.17 deck. It works out to a 10.5 to 1 comp ratio. This is also using a 5 cc volume for the valve reliefs, and the volume for the bore clearance to the ring lands. Deck clearance would be .010 with a 10.17 deck

 

The ccs for the L2291F pistons are like -9.2cc for the valve reliefs. They sit about .020 down in a stock block.

 

Even with the piston .020 down the hole, the comp ratio works out to 9.66. Mill the deck to zero and this will make it an even 10 to 1. Use steel shim gaskets ( .020 ) and this will get you 10.5 to 1.

 

Rob, whose hypers are you using ? Can you give us some part numbers and pin heights ? What are you setting the ring gaps to on the engines with the hyper pistons ? Most of the hyper pistons I've seen ( KB's ) look very good. But unfourtunately, they have, undeservedly I think, gotten a poor reputation in my area. Too many guys didn't read the instructions and ran the same ring end gap that they always had....and there were some scuffs. Anyway, the piston I want us all to avoid is the silvolite 1139. With its 1.66 pin height, it will give you something less than 8 to 1. Sadly, this is the piston most rebuild kits come with unless you ask for something better. DF

 

yes im also interested in the hyper pistons you are running, who makes them? where can they be bought? im still lost as to where i can buy the silvolites as well and what they cost

 

Compression heights are 1.759 or 1.760 depending on which piston it is. Still shorter than I would like, hence my reference to milling the block a bit to get the quench up, but not near the problem with the 1.660CHT pistons like DF mentions.

Silvolites, as I mentioned, last time we sold some they were about $85/set, and can be ordered from any major parts warehouse. "76"-the big rebuilder parts warehouses will typically not sell to individuals, only to business. Hence, the Silvolites may be in stock in a warehouse near you, but you would have to order them through your machine shop, the local NAPA or other parts store, etc. We order them from our local warehouse EPW.

I don't use many KB pistons, unless they have a compression height/cc combo that isn't available elsewhere. For the price, I'll upgrade to a Forged if possible. DF is correct, they are generally very relible though, as long as the rings are done right. KB's have a different silicone ratio that requires the special top ring gaps. None of the other Hyper pistons we use require any special ring gaps at all. Have been using them for years, on street/truck/mild stip applications without one problem.

The Hypers we use are made by a little shop in Missouri that does all their pistons on new CNC machines. They only make about 20,000 pistons a day, for many applications. Real nice pieces though. Now, you don't want me to divulge this "little" secret company do you? ('')
Can you guess who?

Basically, there are two pistons available: both with 1.759CHT. Flat top one has four valve reliefs with 10-11cc's. The dish piston has smaller valve reliefs and is about -13cc net. They do take slightly different ring packages from each other though. I have these figures in my copmression ratio calculator on this computer, but not the part numbers. Sorry, that's at work.