Well, first off there's no such thing as a "10:1 piston" anymore than there's such thing as an 8:1 piston. It's all relevent to SEVREAL factors, A) the bore & stroke of the engne, or basically the "displacement" of the engine, B) The TYPE of piston being used, whether it's a dish, an inverted dome, a flat top, a dome, etc., AND more importantly the compression height and positive or negative displacement of the piston top. For instance; a domed piston is obviously going to have a positive displacement which compresses the air into a smaller area thus increasing the compression, and a dish or inverted dome piston has a negative displacement causing a larger area between the piston top and the combustion chamber to compress les air thus lowering the comression ratio. You also have to factor-in the valve relief area. A piston with large, deep valve reliefs is obviously going to have more of a negative displacement than a piston that has very small valve reliefs, or no valve reliefs at all. And last but not least. C) the combustion chamber size of the heads. ALL of these play a role in determining what the comprsion ration will end-up being.

You will never know what type of pistons you’ll be using or what size chambers in the heads you need until you establish what compression ratio you want to end-up with first. Of course there are a zillion variables on this, and 10 zillion guys that will say that they run something different, but as a GENERAL rule of thumb, on a stock engine with cast iron heads that you want to run regular gas in (87 octane), you want to stay around the 8.5:1 or so area, unless you have a computer system with a knock sensor to control timing to prevent detonation. You can run a little more compression in that engine if you want to run higher octane gas.

If it is a performance engine with cast iron heads and running premium fuel (91 – 93 octane), you don’t really want to get above 10:1. You’d be better off running between 9:1 and 9.5:1 which will allow you to run full timing rather than having to back it off to prevent detonation (pinging) and making the engine “lazy” by not utilizing full timing.

If it has aluminum heads and you are running premium fuel, you can bump it up to the 10:1 to the 10.5:1 area, but you don’t really want to exceed that area by much or you’ll have detonation problems. A "general" rule of thumb is that with aluminum heads you can bump your compression up by about 1 full point over what you shoukd run with cast iron heads. This is simply because aluminum heads cool much faster between combustion cycles which helps keep detonation a bit more under control. Yes, some people run more compression, and so do we sometimes on some engines on pump gas, but it depends on things like the cam profile, and the type of car it is. You really want to stay below about 10:1 though on any typical street performance engine running typical premium pump gas.

Once you know what compression area you are shooting for, THEN you can begin looking at what heads & pistons you want to run. One brand or model of head may only be offered with a certain sized combustion chamber, such as 64cc. Well then, you’ll have to look for pistons that obtain the compression ratio you’re targeting with that combustion chamber size. Cubic inches, the bore diameter, and the stroke all play a role in it. Piston manufacturers do provide basic tables that show what kind of static compression you’ll end-up with for an engine of a given size, using a particular piston of theirs with a given combustion chamber size in the head. One piston will yield several compression ratios using several sized chambers. In other words; a flat top piston that makes 10:1 compression with a 74cc chamber might make 12.5:1 compression with a 64cc chamber. You REALLY have to be careful when choosing the right piston / head combo for any given sized engine.

When you run into this, by using the tables & graphs piston manufacturers provide for quick reference you can look to see what other piston they offer to lower the compression to what you’re looking for using the combustion chamber size your heads have (or are planning on choosing for your build). They’ll most likely offer a dished piston that will make 10:1 or so with the 64cc chambers. Again, you want to be REALLY careful when laying out what you want to run to get the desired compression you’re looking for BEFORE you go buying anything. Assuming you already know what size engine you're building, you MUST also know what chambers the heads that you want to run have to then find a piston that best suits your target compression.

Sometimes you’ll run into situations where you simply can’t get a piston to obtain the compression ratio you’re looking for with the combustion chamber size your heads have, so you’ll have to see if that head manufacturer offers a head with another chamber size. Sometimes they do, but sometimes they don't. We run into this all the time with strokers and blown engines. The more stroke you add, the more the compression goes up. You can only get a piston with a dish just so deep before you run out of area for a dish any deeper to get you a low enough compression for a blown application. Also, sometimes you can't get a head with a large enough combustion chamber so you run into the same scenario. This means you need to run a shorter connecting rod and then find a piston with a different compression height that allows more area to lower the compression or to allow for a deeper dish.

This is all part of setting up an engine so it runs properly that a lot of guys just don’t do, or know how to do, and why a lot of guys run into troubles and wonder why they blow head gaskets, or they can't time it properly because it pings from having too much compression, or runs like a complete turd because it doesn't have enough compression.

You have to take EVERYTHING into consideration BEFORE you buy any parts, and do a LOT of research on what parts are available with given chamber sizes, pistons types (with domes, flat tops, dishes, various compression heights, etc.) for a given bore / stroke / cubic inch size engine, and for how it is going to be set-up (stock, high performance, race, blown, nitroused, etc.) so you can gather all of the correct parts to get you the desired compression you’re looking for. It’s not about whether you WANT to run a flat top, dish or domed pistons. It’s a matter of what you HAVE to run to obtain your target compresion ratio. You need to know what you want to run first, (type of fuel, compression needed that runs best with that fuel, etc.) and then look at ALL of the parts available to see what kind of combo you can come-up with to get you what you want.