Recent RC Model Engine Dyno Tid-Bits

Head Button Configuration:

Recent experimentation has indicated that using a squish band with the total area sloped inward at 1 1/2 degrees had a tenancy to reduce the low/mid range of the smaller engines. With the 3.5cc engines, a squish band shaped so that the outer 50% is flat and the inner 1/2 has a 1 1/2-degree inward angle, has proven to be much better in low/mid-range output. There is an increased tendency to detonate with part of the band flat, but is much more preferable to a lack of low/mid-range power. With 50% having the angled squish, the detonation is tolerable. On engines larger than the 3.5, you can get away with the full angled squish band. On the 7.5cc engines, it appears that some flat (maybe 25-30%) is advantageous.

Recent Tuned Exhaust Findings:

The 3.5cc engines running high nitro can gain substantial performance (both high RPM and high torque) using the CMB muffled pipe with the silencer can cut off and the stinger shortened to 3/8". The stinger should be drilled out to .280". There is a weld ridge (hidden inside) at the junction of the stinger and the rear cone.

The 7.5cc engines running high nitro can get high performance from the Irwin Nitro pipe.

New Picco EXR Drum Engines:

The Picco EXR Drum engines seem to be improved considerably by looking at the total duration of open time of the rotor. The rotor closes at 65 degrees atdc, which I believe is close to optimum for our use. The opening is later than I believe optimum. A total open duration of 215 degrees is probably closer to optimum. The Engine Analysis Program is an invaluable tool to understand and manipulate data as it relates to engine tuning subjects.

Carb Findings:

I was contacted a couple months ago by an expert engine tuner, who specializes in flow optimization for a broad range of racing applications. He indicated that he owns an expensive and "state of the art" flow bench and would like to try to optimize one of my carbs. After talking to him at length, I sent one to him for his MAGIC. I really didn't know what to expect. I ran the carb on the bench and inspected the atomization at full throttle with a high intensity light. I compared to the stock carb and found that there was over 50% increase in mist coverage within the carb. There were blank spots with the stock carb and the optimized carb had full coverage. At the pond, I found that the engine had a "different sound"! Not only that, but I gained 4+ mph with my 3.5cc Roadrunner. That is a HUGE gain. I raced it this past weekend at Celina, Ohio and the boat was AWESOME.

I have made an arrangement with the flow expert to offer serious racers the opportunity to get their carb optimized. It isn't cheap, but he spends over 3 hours on each carb. If you are interested in having your carb(s) optimized, send them to me along with an order form. The cost is $50.00 plus shipping. There will be some delay in getting your carb back to you, so plan ahead. He can only do so many and I have sent him ALL my carbs, as have my associates.

Marty Davis



ENGINE Analysis Software for the Serious RC Competitor



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