AYLOR ENGINEERING
Building Hi Performance Racing Kawasaki Triples since 1978

690 Polaris Blvd. SE
Rio Rancho, New Mexico 87124
(505) 896-4699
(505) 410-8064 (mobile)
 johnayleng@aol.com

 

 

What are "Squish Heads" or what is a "Squish Band"
 
 Basically the name "squish" is just a description of having the fuel mixture "squished" towards the center of the combustion chamber. There are a couple of reasons that you want this to happen. First it causes turbulence which makes for a more combustible mixture, but more so, to help prevent detonation.
 
 But before we get into the mechanics, I want to define pre-ignition and detonation. They get interchanged a lot, but are two totally different things.
 
 Pre-ignition is the fuel mixture igniting from a "hot spot" in the combustion chamber, the two usual causes are built up carbon deposits and the sparkplug being too hot of a heat range.
 
 Detonation is the fuel mixture being ignited by the heat and pressure in the combustion chamber, usually at the outer edge of the piston. When that combustion "event" collides with the ignited fuel from the sparkplug you get the "marbles in a can sound" from the motor. Detonation is very hard on the bearings as the loads on the bearings are greatly increased. Also the action of the collision of flame fronts, strips off the thin boundary layer of mixture (about .020" thick) that actually protects the metal parts from the intense heat. Signs of detonation are the aluminum parts are pitted, and usually metal flakes on the spark plug. In bad cases a hole will actually be burned through the top of the piston.

And now to "squish" bands.

To decrease the chance of Detonation, what is needed is to "push" the fuel mixture away from the outer edges of the piston and also use the boundary layer to our advantage.

 
 The squish angle is the degree of angle difference between the angle of the piston dome and the angle of the combustion chamber. If a piston dome angle is 13 degrees, then the head angle can be from 14 to about 17 degrees depending on what the motor usage is. The smaller the angle the faster the MSV (mean squish velocity).
 
 Next there is squish width, which is set (basically) by the percent of the area of the combustion chamber. This can be anywhere from 20% to 70% again, depending on the motors usage. But usually ending up around 40 to 50%.  The higher the motor is loaded, the wider the squish width.
 
 Finally the squish clearance. This is the clearance between the piston dome and the head. Now we are back to the boundary layer. If we reduce the squish clearance to around .040" the cool boundary layers on the combustion chamber and piston dome intersects creating a cool area around the edge of the piston preventing heat from igniting the mixture, thus preventing detonation. The clearance is dependant on a few factors, including "stretch" of the rod at higher rpm's.
 
Modifying older head designs allow the stock compression ratio on today's pump gas, and higher compression with race fuel. It also promotes better combustion and more power.
 

Head Designs
 

 

 Next comes the total redesigning of the combustion chamber. Though the H2 head is a decent design, it still is doesn't have a squish band. The S series and H1 heads are a terrible design, with the spark plug in deep pocket.
 
 Newer design combustion chambers are spherical , or versions of top hat design. These bring the plug closer to the piston for a shorter flame travel distance, and a more open chamber for a larger pressure area on the piston dome. The H1R and H2R used a version of the top hat design.
 
 Of these two newer designs, I prefer the top hat design, as I like to keep the spark plug very close to the piston. So for very high performance motor I weld fill the chambers and re-machine the chambers.  E series plugs are necessary.
 
 Modifying stock heads for correct CC's and adding a squish band $55.00 per head.
 
 Please call or E mail for pricing for weld fill and reshaping to a top hat design.
 
Home