I also have had considerable experience with the Byron kits and OS91's. I have not had ANY luck when using the small head in the Byrons....period.

I only tried it in 3 of his planes, F16, Mig 15 and the Bullet. All had overheating problems until the large head was installed. An in-flight (BVM) was used on all of them and extra Castor run in the fuel too....

I have found it hard enough to get them to run cool with the large head----4000+ ft altitude most of the time.....Dennis must have the velvet touch to make it work without them......

I am now following "Jackjets" style and adding 6 to 8 oz of Castor to each gallon of fuel for the Byron fans and am having better luck keeping them running with a lot less overheating problems.

Just my experiences....

Rod Springer