2Cs - Misc

[David Lockhart]

To add to several of the recent posts RE 2Cs, some misc thoughts/data from my experiences.

The question has been asked, how much power is enough/needed - how much more is needed?  If you have enough power, and it is consistent, quiet, friendly, smooth, reliable, cheap, etc - you don't need more.  However, having too much power (haven't found it yet myself) allows several things - milder cams, smaller carbs, lower compression, richer needle setting, lower nitro, milder porting, milder tuned exhaust systems, etc - all of which are essentially trading "extra" power for something else that is nice to have - ie, cheaper, quieter, consistency, more linear response, more torque, etc.

With 2Cs, I've posted before how the exhaust system can have a huge influence on not only the peak power of the engine, but also on the midrange running characteristics.  Tuning the exhaust for peak power usually has some nasty side effects - non-linear throttle and rich/lean spots in the mid-range being the biggest nasties.  The old "traditional approach" to mitigate the nasties was to test many combinations of props, plugs, compression, nitro, oil, pipe lengths, pipe designs, and port timing on the engine itself.  The point in time when the "average" pattern flier probably knew the most about the "traditional approach" was probably in the mid to late 1980s - piped 2C 60s were propped between 13,000 to 16,000 RPM on the ground (10-11.5" diameters and 7-9" pitches), and the tune length of the pipe (diverging/converging cone type, mufflers were rarely used) was 13-15" (plug to baffle).  After the introduction of turnaround and noise limits, and just prior to the 4Cs becoming dominant, 10,000-12,000 RPM (11-13" diameters, 9-12" pitches) and 17-20" (diverging/converging cone type, and baffle type, still no mufflers) were the norm for 2Cs.  A couple 2C guys on the fringe were running even bigger props, with longer pipes, and lower RPM.  My personal setup at that point (1992) was a Webra Race 61 LS w/ Dynamix using a CF pipe set at 22" and turning an APC 13-13N at about 9,500 - not a friendly setup - few aside from myself could set the needle, but the power was awesome, and whisper quiet.

Today, the "traditional" approach to tuning a 2C still works, AND, some new approaches exist - the OS EFI system and the MC carb system.  The "traditional" approach today includes tuning the engine not only for peak power, but for peak power at a lower RPM and with linear throttle response as well - and relative to the mid/late 1980s, the average pattern flier knows substantially less about 2C tuning.  All three systems will yield the same amount of peak power - EFI and MC do not yield more top end power.  However, when the goal is peak power AND a smooth midrange - it is easier to achieve that goal using EFI or MC - the "traditional" approach requires substantial 2C knowledge and/or experimentation.  Very often the "traditional" approach sacrifices a little bit of peak power to get the smooth midrange (and retain some flexibility/consistency) and it is for that reason that the average EFI or MC setup produces a tiny bit more power than the std carb (traditional setup).  The "best" 2C setup, IMHO, is going to be one that is "traditionally" setup with the addition of EFI or MC, to allow very fine tuning and more consistency and flexibility (with regards to changing weather, props, fuel, etc).  A very poorly setup 2C is not going to become wonderful with the addition of EFI or MC.

Aside - in my experience from running the OS140 EFIs and 140 RX - the EFI system has a "sweet" spot - it wants to be propped between about 7,700 and 8,300 RPM on the ground which will yield about 8,300 to 9,000 RPM in the air - if the 140 EFI is setup outside of that range, the power drops substantially.  OTOH, an OS140RX can be tuned to run extremely well from 7,400 up to 8,800.  I've not found a 2 plug head to provide more power or a lower idle - but the needle setting becomes less critical.  And while Shadel piston/sleeve is a great weight saver (40 grams), I've not found it to produce any more power.  And if the engine ever gets hot on the ground, the stock setup (ringed) idles a little better (never noticed a difference in the air tho).

Regards,

Dave Lockhart
DaveL322 at comcast.net
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