ok. what the hell are the advantages/disadvantages of the various types of pistons. flat top, dished, domed, hollow domed, solid dome, etc etc etc. i have no idea what the differences are. i want to buy some for my future 400. thanks rick

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Rick
90 Camaro RS 305 TBI
400 on the way!!

 

hard to explaine flat tops, i'll call them middle of the road pistons and after you read what the others are you'll see where flat tops fall in to place. dished increases the volumn resulting in lower compression ratio, domed decreases chamber volumn increasing compression ratios, hollow dome reduces weight of the piston. there are a lot of other factors to consider, wrist pin location, rod length, cc size of the heads, quality of the gas you run.

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-=ICON MOTORSPORTS=-

 

There are basically two types of pistons that are manufactured in different configurations (fat top, dish/reverse dome and dome). Cast pistons and forged pistons are the two “types” manufactured.

Cast pistons are either stock replacement with a 12% silicon/silicone aluminum alloy or aftermarket hypereutectic. The hypereutectic pistons have a higher, 18% silicon aluminum alloy. The hypers’ are a good performance upgrade over standard cast. The higher silicon alloy is much stronger and will take more abuse. It also acts as a heat barrier that resists thermal expansion. Both of these pistons are made by pouring the molten alloy into a mold and allowing it to cool.

Forged pistons are made by forcing the aluminum alloy into a mold with a press. This creates a piston with a very dense molecular composition. Forged pistons will sustain even more abuse than the hyper’s. The drawback to forged is a required larger piston/cylinder clearance. Because they are denser than cast, they expand more. There are a couple lines of forged pistons that have a different alloy with a high silicon content. The JE srp line uses this alloy and can be run as tight as .002”. The standard forged piston clearances will vary between .004 to .008” which creates a noticeable piston slap until they reach running temperature.

The flat top piston is the most common. Back in the days where 103 octane gas was available and cylinder head combustion chambers were on the "large side", domed pistons were used to increase compression ratio. They are not really needed anymore. The closed chambered, smaller head combustion chambers and flat top pistons can achieve up to 11/1 with ease.

Domed pistons also have undesirable effects on the combustion process. The dome has a tendency to interfere with this process and the homogenization of the fuel/air mixture is not very efficient.

A dished piston has a "dish" cut into it at varying depths and configurations. The dishes are either cut into the piston top with tooling or shaped with the mold. They can be a standard dish that will encompass the entire piston top or shaped into a "D"/half dish or a reverse dome. The standard dish is the least desirable and it does not propagate combustion as efficiently as the later two. The reverse dome dish is the best from a combustion efficiency standpoint. The homogenization of the fuel/air mixture is greater because of the shape and taper (reverse dome) of the dish.

When you select a piston, you need to know what head you will be using, your induction, rpm/peak hp and what your desired static compression is.

Mike