March 2010


We have received the Roof 101 cylinder head assembly from Charlie Yapp.

The quality of the castings and the machine work look very good.

We are starting our development program by flow testing the intake and exhaust ports on the new Roof 101 head.






These flow tests are conducted with the cylinder head as received from Charlie Yapp, no modifications.






This flow sheet is the stock Model A Ford intake valve & port to use as a comparison for the Roof 101 Cyclone flows.




















The intake flow results are the best flows we have seen on any Model A Ford head! The intake ports flow very smoothly, no turbulence.









The exhaust flow is with a stock valve and no port work.







The exhaust balance test shows that the exhaust port flows about 65% of the intake flow. This is perfect for a naturally aspirated gasoline burning engine of this type.

I recommend that no exhaust port work be done when using this head for high performance street or hill climbs, where a broad torque curve is necessary.



This head will deliver a lot of horsepower over a wide RPM range.


The next step in our development program will be to look at the valve train geometry and rocker arm ratio.