The Howler .604 cuin. spark ignition motor was produced in small numbers by the Bone Tool & Gauge Co. of Detroit, Michigan during the years 1946 and 1947. In many respects its design followed the “standard” formula for big-bore racing engines of the period – twin ball-race shaft, ringed baffle piston, cross-flow loop scavenging, automotive timer. However, the Howler could not be considered to be a true "racing" model.

The Howler was unique in one respect - as far as I’m aware, it was the only model engine ever produced anywhere in the world which relied entirely upon sub-piston induction for its operational air supply. The fuel was admitted quite separately through a crankshaft front rotary valve and mixed with the air in the crankcase.

The Howler was designed by an individual named H. E. Fowler. It was developed for the US military during the latter stages of WW2 to power a small model helicopter that could be deployed by downed US airmen to assist rescuers in locating them. The Bone Tool & Gauge Co. apparently tooled up to manufacture these engines in quantity at $50.00 apiece, but the contract was terminated at the conclusion of the war. In order to recover at least part of their investment, the manufacturers thereupon decided to see if the engine could be marketed as a model airplane powerplant – a not-illogical decision.

The selling price of these post-war model aero units was set at $34.95 – a substantial figure by 1946 standards. Unfortunately, the engine proved to be an under-performer in a racing context; an unwarrantably over-designed unit in a sport flying context; and an uncompetitively-priced engine in either context. As a result, it failed in the marketplace – only some 300 examples ended up being manufactured.  

A full review and analysis of this very unusual design will appear on this website in due course.