Upgrade engine and pistons

[jhdeval]

I am going to try this here.

I am in the machine phase right now.

I am having my block cleaned and decked. Same with the head. I have the crank, rods and block being line honed. Cylinders are being honed. Camshaft is being ground to a more aggressive setup with new lifters/push rods.

I am eying a set of over sized valves and 318 springs.

My question is what valve cc should I shoot for? My other question is do I need to replace the pistons or will cast pistons handle the higher compression?

 

[grumpuscreature]

What compression? most slants wind up with the pistons around .250" below the deck and are lucky to have 7.5 to 1 compression. Cutting .100" off the head will get this almost to 9 to 1. Cast pistons will be fine until you add boost or nitrous, so it boils down to what you want to do with your slant. You really need to get the top of the piston closer to the deck than it is right now. That is not going to happen with 225 rods and replacement pistons. If I ever build another one, I would bore it to 3.5" with forged 2.2 Turbo pistons and 198 slant rods. This gets the compression near 9.5 to 1 without milling the head or deck. There is enough metal in the cylinder walls for this much overbore and that is about as big as you can get with readily available head gaskets. You can get the pistons and K1 H beam rods from Campbell Enterprises and when the new found power becomes boring you are ready for boost or nitrous.

 

[jhdeval]

I am shooting for 9.5 to 10:1. I am prepared to have the deck or head lowered and I have spoken to my machine shop. Which is what sparked this question. The need to know what I am looking for so they can shave off what is needed to get there.

 

[BillGrissom]

I think most modern non-turbo cars come with cast aluminum pistons and compression around 9.5:1, so shouldn't be a problem. Slant pistons appear more rugged than most current designs. They changed to short, stubby pistons with minimal skirts and top rings further up to minimize drag and quenching. Forged pistons require more clearance since the metal expands more, and consequently have more piston slap and such. They aren't the best choice in a daily driver.