Harley-Davidson Air-cooled Twin Cam 110™ engine. Did You Know?

The Harley-Davidson CVO Road Glide Custom model(FLTRXSE) is equipped with an air cooled 110″ Twin Cam engine (most of rest the lineup uses a 103″.) Anachronistic engine? Yes, for sure, but Harley fans are attached to air cooled engines and don’t want their bikes (EPA permitting) to be equipped with a radiator.

Summer heat, triple digit temperatures, stalled in traffic. So, how does Harley succeed at avoiding its air cooled powerful engine (122 lb-ft torque) to melt under your seat?

With a function called “Rear Cylinder Cut Out” system introduced in 2008. Taking in account that the rear engine cylinders always running hotter because not receiving as much air flow as the front one, the “RCC” is conceived to try to equalize the difference of temperature by shutting off fuel and spark to the back cylinder if the motor idles for more than 3 seconds above 288°F. Below 275 F normal operation resumes. Until 2009 RCC was actuated by a cable and since then by the throttle-by-wire technology. Many cars use this technology of cylinder deactivation with the objective of saving fuel. Not the main preoccupation of bikers with their motorcycles. Just interested by more power… (picture @ harley-davidson. Written with assistance Popular Mechanics)

11 Responses to “Harley-Davidson Air-cooled Twin Cam 110™ engine. Did You Know?”

  1. 1 BILL Jul 25th, 2012 at 9:55 am

    the temp control has been used on EFI harleys since 03

  2. 2 mario Jul 25th, 2012 at 2:56 pm


  3. 3 Ronnie Jul 25th, 2012 at 3:37 pm

    Bill. Not since 03 on a 110″. There was no 110″!

  4. 4 Maytag Jul 25th, 2012 at 4:55 pm

    Does this mean the long-rumored water cooled model won’t arrive as a 2013 CVO model? Or a marketing trick by H-D to try to sell remaining 2012’s before the H2O models arrive? Hmmmmmmmmmm……….

  5. 5 fxrocket Jul 25th, 2012 at 9:15 pm

    Engine Idle Temperature Management System aka EITMS aka RCC can also be turn on and off on 09 models with throttle grip sensors… simply turn ignition to on and roll your grip foward watching your cruise light … green means on and if you roll it again foward red mean off … if you live in the Desert like i do id leave it on

  6. 6 Jul 26th, 2012 at 5:14 am

    I have an ’08 103ci Ultra with a few goodies dynoed with FBW that doe the same without cables.

    But an aluminum engine should not reach 275 degrees.

    Boss Hawg

  7. 7 alansharp Jul 26th, 2012 at 8:09 am

    wot H/P does 110 put out??? lots of heat not a tot of H/P…………..

  8. 8 Doc Jul 26th, 2012 at 4:59 pm

    You bagger guys get all the bells and whistles! I still have to watch out to not catch my pants on fire with my pipes! Choppers por vida!

  9. 9 Jeff Jul 30th, 2012 at 2:45 pm

    ha! ha! Doc, I’m with you on that one. Most of my jeans have shreds and holes on the inside of the lower right leg from my pipes! That leaves the already burnt and purple scarred skin of the right calve very venerable to new injury while stopped in traffic……but it’s worth it.

  10. 10 Jul 31st, 2012 at 8:29 pm

    Right after the 2007 HD motorcycles were introduced the issue of high engine heat and poor throttle response showed up. Nightrider with its background and experience in fuel injection systems was able to quickly identify the HD supplied narrow band O2 sensors and the OEM EFI operating in closed loop mode as a significant source of the complaints. Even Harley-Davidson recognized that there was an issue and put out an EFI download to improve the situation for FLH’s. But this HD supplied upgrade did little to address the real cause of the issue. Harley-Davidson was unable to do much more than it did for the FLH’s because of Government EPA regulations and most Dealers had little idea what the real problem was or how to correct it. The most common fix “sold” to riders was a Stage 1 download, SE Race Tuner or installing a PowerCommander or similar “black box” upgrades. None of these upgrades was overly successful at reducing temperature because they never addressed the real cause of the situation which is the ECU operating in closed loop mode. Eventually some of the “black box” aftermarket companies started supplying O2 Eliminators for the 2007 bikes. The O2 eliminators would reduce the heat, but most riders saw large drops in fuel mileage. When the O2 sensor is disconnected from the EFI, the engine is forced to run at an overly rich 12:1 fuel ratio in many circumstances. This is an overly rich fuel mixture that drops gas mileage and can result in excessive carbon buildup in the engine.
    What was needed is a Wide Band O2 sensor upgrade for the 07 HD’s that would allow the rider or mechanic to set an appropriate AFR for the engine and the way it is ridden. Under most circumstances, the more appropriate AFR is in the 13.5-13.0:1 range. This AFR helps keep engines cooler, provides good throttle response and does not severely impact gas mileage.

    Without getting into the heavy technical details, replacing narrow band O2 sensors with a wide band O2 sensor is a lot more complex than just taking the NBO2 out of the exhaust and installing the WBO2 sensor. Narrow band O2 sensor basically only understand a single AFR, 14.7:1. This is a good AFR for gas mileage and water cooled engines. But 14.7:1 AFR produces the highest exhaust temperatures, which is not good for air cooled engines or motorcycles. A Wide Band sensor is able to accurately report on air fuel ratios from 10:1 to 20:1. This makes them ideal for performance and pollution controlled engines. But wide band sensors require special electronic circuitry to process the signals from the sensor and they also produce different voltages than the NBO2 sensor. A narrow band O2 sensor puts out a signal of 0-1 Volts where the wide band sensor electronics puts out a signal of 0-5 Volts, making it seem incompatible with the Delphi ECU.

    But this incompatibility between WBO2 and NBO2 sensors can be overcome with some additional electronics. Nightrider identified and successfully tested ways to upgrade from the OEM HD NBO2 sensor to a wide band O2 sensor. Along the way, some the operating characteristics of the HD engines EFI system were captured by data logging instrumentation. These EFI operating characteristics explained many of the issues that riders see on their motorcycles. It was also established that the WBO2 sensor upgrade would be compatible with all HD Stage 1/2 downloads, HD supplied engine upgrades (103, 110CID), SE Race Tuner, and aftermarket tuning aids like PowerCommander, Fuel Pak, TFI and other devices without requiring the use of an O2 eliminator.

    Installing the LC1 Wide Band O2 sensor upgrade and setting it for a 13.5:1 or 13.0:1 air fuel ratio dramatically lowers engine heat and will reduce the instances that the engine goes into high heat/parade duty mode. Because we have seen stock 96CID engines go into high heat mode in 10 minutes of idling in the shade. This means that the OEM HD engines are “on the edge” when it comes to their ability to keep cool. We believe this marginal cooling ability is very critical for HD 110 CVO engines and HD 110CID engine upgrades due to known issues with scored/scuffed cylinder walls occurring. There is also a high probability that this situation is also occurring on the HD Stage 2 103 Big Bore upgrades.


  11. 11 Aug 3rd, 2012 at 10:33 am

    the new stuff just gets on my nerves and so do new the hog chapter snoots.. might as well buy a honda, it has more american made parts on it

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