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    Producing Quality Computer Tools for Racers and Engine Builders since 1986






Piston Dome

There are 3 basic types of Pistons: Dome, Bowl and Flat

Dome Piston


Dome Top Piston
Dome Top Piston
The Dome Piston looks just like it sounds. Instead of a flat top it has a dome that looks like the top of a dome stadium.  Piston Dome refers to the amount of added volume on top of the piston compared to a flat top piston.  This added volume increases the Compression Ratio and therefore should increase performance.  However, depending on the shape of the combustion chamber in the head, highly domed pistons can create slow burning, inefficient combustion chambers.  The optimum tradeoff between higher compression ratio and dome/combustion chamber shape can only be determined by trial-and-error on a dyno.

Dome Pistons are also used in 2 stroke engines, mostly to deflect the inlet charge up toward the spark plug, and not let it flow directly to the exhaust ports.  (Note: Performance Trends Engine Simulation Software does not work with 2 stroke engines. But our some of our tools can, such as the Compression Ratio Calculator and Engine Log Book.  And our Dyno Datamite systems have dyno testes hundreds of 2 and 4 stroke engines.

Bowl Piston


Bowl Piston
Bowl Top Piston - Image courtesy of dieselpowermag.com
Bowl pistons typically are used to reduce compression ratio because of the added volume of the bowl to the combustion volume.  Because they reduce Compression Ratio, bowl pistons can be used in Turbo Charged or Super Charged engines to help avoid detonation (spark knock) under boosted conditions.  The extreme bowl shown is used in diesel engines, where the bowl is used to confine the diesel fuel spray for good, fast combustion.  A piston bowl can do the same for a spark ignition engine and make for a fast burning, compact combustion chamber.  


Flat Top Piston


Flat Top Piston
Flat Top Piston
The Flat Top Piston is just like it sounds; it has a flat top. These pistons are typically used in mass produced engines. They are easy to manufacture and this keeps the cost of the engines low.

Flat Top Piston with Valve Relief


Flat Top Piston with Valve Releif
Flat Top Piston with Valve Releif - Image courtesy of shop.rezlo.com
The Flat Top with Valve Relief is basically a Flat Top Piston but they have small amounts of material removed to keep the valves from hitting the piston when the intake and exhaust valves are opening or closing. This allows for higher compression ratios by allowing the piston to go higher into the cylinder head.

Programs that take the Piston Dome into account

We have 3 programs that work with the shape of the piston top directly, which affect compression ratio and combustion chamber shape.  These are our Engine Simulation programs: Engine Analyzer v3.4, Engine Analyzer Plus v3.4 and Engine Analyzer Pro v3.9.

And we have 2 other programs that take the Piston Dome into account when making calculations. Compression Ratio Calculator v2.3 calculates allows you to change the piston dome type to help figure out the Compression Ratio. And Engine Build Log Book v1.1 will document the type of pistons used and the dome type for future reference.