compression ratio 400ci

[mossman]

Does anybody know the stock compression ratio on a 400ci motor?  Does anybody know what kind of pistons they ran from the factory?  Dished?  How much -cc?

[VileZambonie]

What year and application?

[Captkaos]

8.3:1 was the factory ratio, the pistons were cast, and dished.  Don't remember the CC.

[mossman]

Not sure of year.  I think it came out of a blazer.  Thanks captkaos.  You don't happen to know the cc of the combustion chamber from the factory?  The reason I am asking all these questions is I want to run a 60cc head and I don't want to have too high compression to run on the street.

[fitz]

Don't forget the heads on a 400 need steam holes.

[eventhorizon66]

Use this to determine your compression ratio.

http://www.kb-silvolite.com/calc.php?action=comp

If if was 8.3:1, as Capt said, the stock 400 would probably be a 76cc combustion chamber with a 22cc dish piston (assuming .025" deck clearance, .04" gasket thickness).  Bolting a 60cc head (with no other changes) on this engine would raise the CR to 9.5:1.

[Captkaos]

All 400's that I have ever messed with had 76cc chambers, nothing you could put on them will bump the high enough to worry about.

[choptop]

If I remember right, the last small block I built had 76cc heads and flat top pistons, and I think the compression ration was 9.2 to 1 or somewhere in that area. I had a chart that would tell you what the estimated compression ration would be with various combinations, but I cantt find it now

[mossman]

Thanks for all the info guys.  Does anybody know how to measure the cc of a dished piston?  Will a piston have that marked on them somewhere?  Thanks again.

[HAULIN IT]

Moss, The simplest/most accurate is to get a piece of Plexiglas/lexan (if the pistons are still in the engine, cut into a circle a little smaller than the bore), where ever the top of the dish is needs to have a notch cut in the piece to fill, grease the piston around the flat area & stick down your plate. You will need some sort of dispensing item (a chemist burett, is best...a large syringe will do) preferably in cc's (or some conversion will be needed). Fill the dispenser up with water, kerosene, alcohol, ect. to a certain number (hopefully 30cc or more to avoid re-filling), then fill the dish up until the liquid has the area full...subtract the amount from your first number, this is your cc of the dish. If using a dispenser smaller that the dish, refilling will be needed & now you would be adding (the refilling leads to room for slight errors). I have never seen a marking on a piston as to a cc of a dish. Hope this helps...any other questions, Just ask, Lorne     

[VileZambonie]

I bring the piston to tdc and raise the deck level. I use a large syringe with atf and fill it until it's level with the deck surface.