Pros and cons of open or closed loop exhaust. I am new to Harley's and was curious abou this topic. Looking at true duals on my 2013 ultra classic. I just wanted some input from y'all.

 

Exhaust isn't open or closed loop. Unless you mean does it have 02 sensor bungs?

The term refers to your ECM using the 02 sensors for feedback on the A/F ratio. Closed loop means it is using the sensors to read A/F (air/fuel) ratio. Open loop it is not using the sensors for reference, but just using the inputted A/F ratio from the calibration.

Normally your bike uses closed loop at idle and "normal" conditions. WOT (wide open throttle) goes into open loop and just dumps fuel in with no 02 sensor feedback.

 

Say what????????

 

Thanks for the explanation. I am an old dirt bike rider that now has an ultra classic. Just wanted some information and the forum came through. Thanks again.

 

As stated, open or closed loop do not refer to exhaust.

If your question is about exhausts.....

True duals are separate pipes for each cylinder.

The other option (stock exhaust) is called a 2-1-2, where the pipes from each cylinder connect with a "crossover" chamber/ pipe then go on separate paths.

Then there's the 2 into one exhausts

You may be confusing these different pipe configurations with the open/closed loop terminology.

It is generally believed that 2-1-2 exhausts will give you a little better bottom end torque over a true dual, and the 2 into 1 as the best performance...

 

Thanks.

 

ok, so "open Loop" the ECM provides fuel to pre-determined maps.

the ECM will decide that at X rpms it will provide a fuel pulse width of Y and ignition timing advance of Z, regardless of other conditions.


cold idle is one of these, where on start up the motor may surge to 1600 rpms ( or so) while it warms up.
Another may be when the throttle is suddenly opened- at which time the vacuum in the intake drops and fuel may be added to prevent a stumble and to increase intake velocity and rpms. this occurs for a short period as the vacuum returns to normal the ECM will return to closed loop

this is an example of the ECM doing what it is programmed to do based on sensor input...air density, temperature etc.

Closed Loop, the O2 sensors are telling the ECM constantly if the motor is running rich or lean, and the ECM corrects to achieve the best* mixture possible. This is based on actual conditions, motor load, temperatures, air density, throttle position etc.

*The Devil is in the details- the "best" mixture may be programmed to prioritize exhaust emissions over performance.


Tuning a motor is very tricky- too rich and performance is compromised- incomplete burn and the resulting fouling and gas in the oil etc.

Too lean and the motor may misfire- leading to raw hydrocarbons ( HC) dumped out the tailpipe or pinging and damage to the combustion chamber.


I personally did not consider the EFI Harleys until they incorporated o2 sensors and closed loop operation into 2007 ( about 20 years after the automotive world- and years after Buell incorporated modern EFI on the Harley Sportster style motor)

I run a 2009- I use a tuning compensation method which retains closed loop operation, which is probably about 90% of the time I am riding.

Pipes have been explained above- on 2010+ 50 State models, there is a catalytic converter in the header.

Some change headers or remove the cat ( search for tutorial) to achieve better flow potential.

On the large touring bike, the advantages of a 2 into 1 over the 2-1-2 are not as obvious, the large volume of the 2-1-2 headers and mufflers are good for power.
On a smaller chassis such as the Dyna, the 2-1-2 has less overall volume and the same motor is usually spec'd to make about 3 HP less with that exhaust.
On a Dyna a 2/1 would give a more obvious performance gain.

My FXR was a cop bike and came with an "unusual" full touring size exhaust system for the extra power potential- I've run a supertrapp 2/1 on that since 1990


Mike

 

A lot of information to consider. I am thinking about a stage one upgrade

 

buy a set of fl-vied-10 from nightrider.com and be done with it until you put cams or bump the compression.