Randy Molkentine

I am in the process of getting a 383 together for summer and had a question. What dish should I get the piston? It will be naturally aspirated, with stock ported heads. The heads have been cleaned once but hardly cut. The chambers also had very little taken out of them. I want to run 93 pump, and it will be sprayed occasionally. Can someone recommend a which piston to go with it. 6'' rods and cc306 cam. Thanks for any input.
Randy

BadAssed93Z

thats a lot of cam for stock heads.

but any how i would go with a flat top piston, maybe like a 4cc dish for valve clearance.

make sure when you buy them you get them for a 6 inch rod.

Randy Molkentine

The stock heads are ported alot!! My engine builder thought compression would be to high with a flat top piston. I was thinking between -4 and -20cc dish. But this is my first stroker so any ideas are helpful

chicken man

whats up randy?Long time no see?I still have your stuff hooper will give it to you. Nick

Dave88LX

Flat top piston with stock heads? Do you have any idea what the Compression ratio will be?

Go with the 16CC SRP's.

Prorac1

depending how many thousandths in the hole the stockers are, the stock pistons are flat top with 4 valve reliefs, with stock heads. and stock comp is around 10.5-1. if i remember correctaly with ported and shaved stock heads and stock STYLE pistons wont comp be up to around 11-1 because of the extra stroke. Hope this helps, prorac1

97WS6SCharged

A 16cc dish and ~58cc heads should give you near stock compression, possibly a tiny bit more or less depending upon deck height.

A flat top piston will yield closer to 12:1 compression.

Dave88LX

Have you run it through a compression calc yet?

Bore: 4.030
Stroke: 3.75
Conn Rod Length: 6
Cyl Head Vol: 53 (Was 54, now 53 due to milling the heads .006 to clean-up)
Deck Height: 0 (zero deck)
Head Gasket Bore: 4.125 (Fel Pro 1074 for reference)
Head Gasket Thickness: .039
Piston-Wall Clearance: .003 (SRP specs .0025-.0035)
Top Ring Land Height: .25 (Approx, not going to make a big diff.)
Dish Volume: 16cc (Inverted Dome)
Compression Ratio: 11.102:1

I should be running 11.265:1, if I pop the piston out .005", and run a gasket with a bore of .080", if the SCE ProSeal will work.

But, if you run a flat top with 5cc valve reliefs at 0 deck:

Bore: 4.030
Stroke: 3.75
Conn Rod Length: 6
Cyl Head Vol: 53 (Was 54, now 53 due to milling the heads .006)
Deck Height: 0 (5 out of the hole)
Head Gasket Bore: 4.125
Head Gasket Thickness: .039
Piston-Wall Clearance: .003 (SRP specs .0025-.0035)
Top Ring Land Height: .25
Dish Volume: -5
Compression Ratio: 12.77:1

Seeems a weee bit high to me...

97WS6SCharged

Nope, I didn't run mine through a compression calc. I'm pretty sure that stock LT1 heads are 58 CCs though, not 54cc. I agree that 12.77:1 is too high for a street car. The 11:1 with the 16cc dish should work just fine though.

Randy Molkentine

I think I am going to go with the -16cc dish srp forged. Thats what I figured with the flat tops, to much compression. Thanks for the input and now I am sure about the -16cc. Thats the piston I was going to go with! LT1 heads are 54cc if they are ported they are bigger but mine are milled so I figure they cancel each other out so I have to be right around 54cc still. Thanks for the advice!

rskrause

The correct static CR will be dependent on the cam used. The method to determine this is based on the desired dynamic compression ratio. For an LT1 you should aim for ~8:1 DCR. This will allow you to determine what pistons you need. If you need help, I can run the numbers for you.

Rich Krause

Randy Molkentine

It would be appreciated as that is way over my head!!

TCAL95Z

I'm building a forged 383 and I just bought the SRP-16cc pistons but I have LT4 heads that are 54cc. Just look up one of the compression ratio calculators or call SRP direct. I spoke with them a couple times and they are helpful. I went with their Extrem duty pistons

Randy Molkentine

The piston i am looking at is the 138103 srp part #

rskrause

Assuming zero deck (flat part of piston crown flush with block deck), and the FelPro #1074 gasket the DCR with the CC306 would be 8.25:1 with a -16cc piston. This is a little high for 93 octane, but close. So, it looks like you did pretty good just guesstimating it! You might want to consider a -0.010" deck. This would lower DCR to 8.06:1 but would also increase the quench to the upper limit of what is desireable. The general opinion is that quench should be not >0.045". However, I question that to a point when I consider that the stock LT1, which runs pretty good for a high CR motor on pump gas, has a quench of ~0.075". If it were me, I think I'd go 0.005" or 0.010" down in the hole with the -16cc pistons to lower the DCR just a tad.

Rich Krause