News > News Archive > 3rd Generation PBS 8P Cylinderhead

I am pleased to announce the availability of a new version of the long running PBS 8P cylinder head.  The last generation used a combustion chamber very similar to the original A112 cylinder head, and technically this design had reached a plateau as far as development goes.  All of the initial development work was performed on the A112 cylinder head, but as the chambers are identical, equal/better results were found with the PBS 8P head.

Here you can see the original combustion chamber alongside the "development" chamber based on the new FlowCone developments.  As there was little opportunity to use larger valves (31/27.5mm) the idea was to "optimise" the flow entry into the cylinder.  You will notice I used the word cylinder and not combustion chamber, because it is the efficiency of flow into the cylinder that is important, and combustion chamber is only there to facilitate different compression ratios.

By having more or less piston dome you could vary the compression ratio, but the dome itself was an obstruction to good flame front travel.

The new head design is all about delivering an organized, predictable flow into the cylinder.  Yes, this makes the "volume" of what is left of the "free space" in the head rather small (probably around 15cc.  If you used a flat top piston with this type of chamber you would probably have a 15:1 compression motor.  This is of course not realistic.

So the idea is to put the combustion chamber in the crown of the piston.  This promotes a flat combustion chamber, without any impediments to flame front travel, and promotes a quicker combustion process.

The area around each valve is shaped very much like a "cone", in that flow remains organized all the way into the cylinder.  There are no longer any "dead" areas within the combustion chamber.

Below is a chart of the difference in flow based on the new chamber design, as compared to the original A112 design.

As you can see the flow is greater at all valve lifts, but especially in the range from 4mm-9.5mm.  After 10mm the flow is still increased, but remains flat.  The final form/shape is a combition of FlowCone technology and manipulation of seat angles and ports shape.

 A new series of cylinder heads, incorporating these developments, is underway at the moment.

 

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