Lynn,

  Do you know how short the intake actually was and I presume this was a

 13B fueled by a carburetor dynoed by Drummond ?..............

 

The engine is a 12A with a Weber and 38MM chokes. A 13B would be about 10% better.

The sheet is from Daryls computer dyno. He did some passes for Tracy years ago using his injection control unit.

 

That particular intake is still on the engine in my shop. It looks just like any aftermarket 12-A intake but he has them made from his design. His runners are very small about the same size as a stock Mazda intake. It uses a stock manifold gasket. I think most aftermarket stuff has the runners too big, and also there is not enough meat to go bigger if you need to use hogged out 6 port end irons or turbo end irons for some applications. We are limited to 38MM chokes in a 48 IDF Weber so going bigger just costs low end torque.  If forced to guess, I would say about 8 inches from flange to flange.

 

The smaller runners keep the velocity high and help torque over a wider range of RPM. Probably not a problem in aircraft, once you get the runner length right. Bigger runners move best power up the RPM range, and make tuning more important.  

 

Lynn E. Hanover