Author Topic: New generation of cylinder heads  (Read 3134 times)

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Offline Paul vander Heyden

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New generation of cylinder heads
« on: September 11, 2011, 06:39:42 PM »
In recent months I have been doing a lot of research on how to improve the combustion chamber of the Fiat and PBS style combustion chambers. 

This is the result.  The new chamber is quite different and can basically be described as two inverse, increasing radius cones.  In addition, the valve seat location has been moved .100 inch (2.5mm) closer to the surface of the head.  As well, the spark plug has been reposiitioned .100 inch (2.5mm) closer to the center of the combustion chamber.

The intake port now has a larger, short-side radius and is lightly larger than the internal diameter bore of the valve seat itself.  In addition the the 45 degree seat, there are important bottom cut and top cut angles that lead into and from the seat itself.  From the top cut the "chamber" arcs outward with an ever increasing radius until it reaches the deck surface of the head.

This outcome allows for a more organized entry of the air-flow, making the valve seat area into a "quasi" venturi, thereby enhancing pressure recovery into the cylinder and keeping the alrflow attached to the surface of the head. 

This type of chamber can be adapted to both Fiat (850/A!22) heads as well as PBS style cylinder head.  In flow bench testing intake flow increased by an average of 14% from 0.040 inch (1mm) to .500 inch (12.2mm).

I have already modified several origninal Fiat A112 castings (NOS) with this new combustion hcamber, and with flat top pistons (no dome) it works out to 12.5:1 compression.  For street applications at 10:1 it would require a piston with a small "hollow".  I can have these special ordered without any problem.  No dome would generally indicate better flame travel, less ignition advance, and overall lighter pistons.

If you would like additional information about these cylinder heads, you can contact me at

Offline biketesting

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Re: New generation of cylinder heads
« Reply #1 on: July 26, 2012, 01:12:11 AM »
That is amazing Paul. 14% increase in flow and no drop in compression. Sweet. I should not have sold my Abarth and bought a Mini ;)
What can I test for you?