Actually, we did not really choose this engine to run in Classic B; it came down to a group default engines which were off-the-shelf, reasonably made and had spares available in good supply.  The other important factor was that the engine could be extensively and successfully modified without changing the inlet and transfer timing too much, simplifying modification.   The lineage of the engine line was well known and previous offerings of BB 25 from OS had performed very well.

We also tested the OS 25 AX, GMS 25 S2000, ASP 25 XL (Magnum 25 XL in the USA) and ASP 25 S (Magnum 25 XLS in the USA), Enya 25 SS AlChro, Enya 25 SS/D and Irvine 25 Mk III.

All the engines tested were suitable for running in Classic B but the top performers, after similar modifications, were the Irvine 25 III, OS 25FX, Enya 25 SS AlChro, and GMS 25 S2000.  The ASP 25S (Magnum 25XLS) shows considerable early promise and has yet to be fully tested.

The ASP (Magnum) 25 XL and the Enya 25SS/D did not perform well because of mechanical design problems, and the performance of the OS 25 AX was somewhat stunted by OS leaving the boost port out of the design and choking off the engine’s torque at the required operational revs.

Development then concentrated mainly on the OS 25FX, with some examples of the GMS 25, Irvine 25 and Magnum 25 XLS being produced.  Whatever development proved advantageous on the OS simply flowed through to the other engines anyway. 

Modifications to produce the ultimate OS 25 were applied to the GMS and this proved very fruitful, creating a very robust but cheap to produce BTR 25.  Unfortunately all the development undertaken with the GMS BTR may be in vain, as the manufacturer has ceased production of this line of engines.

At one stage in 2009 we thought we had been dealt a major blow when OS announced the withdrawal of the 25FX in favour of the constipated 25AX.  After considerable protests from R/C combat end-users in the USA and T/R C/L users in Australia, and also due to the release of Magnum’s strikingly similar 25FX clone (the so-called 25XLS), OS relented and reintroduced the FX, albeit at a new, higher price of US$130/engine.

Take a look at the modifications we made.