I have removed the front half of the packing from a set in the past. Definitely louder and wasn’t unpleasant as far as the tone goes. Removing all of it probably would have sounded like hell though. As far as tuning. Probably, maybe,… I think a lot of guys have some idea that these things are finely engineered marvels of mechanical construction. They aren’t but a few clicks away from a lawn mower engine. You can change more than you think. “Optimal” tuning is a thing but if you have one pretty close, and change a muffler you aren’t going to melt the thing down or send a piston through your ball sack. Yes, I have tuning experience on many different platforms. Not just HD. Your mileage may vary I suppose..

 

I am in the minority here. You can do what you want and all remains within the factory settings UNTIL your changes trigger the engine light. That means your changes have been big enough that the adjustable ranges built into the system can no longer maintain the programmed limits. Freeing up air flow in both intake and exhaust would cause a lean condition in the old days. Computer controlled engines can compensate up to the point that the limit of programmed enrichment is exceeded. Then the lean condition triggers the engine light. At that point, a retune would be a good idea.

 

and swapping mufflers cannot exceed the variables the ECM can handle…completely agree with ^^^^

 

Or removing them completely for that matter. You’ll change the characteristics of how the exhaust works for the engine so you’ll gain/lose hp/tq in the appropriate areas of load and RPM but you aren’t going to be doing any damage.

 

I'm no expert at tuning, but I have had a small amount of training (from DynoJet), and experience with my EFI bikes and a couple of friend's EFI bikes. I'll have to respectfully disagree...

Computer control doesn't apply to the open loop portions of the tune map. If you wait for an engine light from the closed loop portions of the map before a retune, you are most certainly way out of spec on the open loop portions of the tune map.

The closed loop portion (adjusted by the ECM w/ O2 sensor feedback) is mostly cruising areas of the map, and low load, lower rpm portions of the map.

The open loop portions of the map, operate outside the accuracy range of the narrow band OEM O2 sensors. Therefore the open loop portions of the map are in the high rpm, high load areas of the map. These critical open loop portions are controlled by algorithms based on the OEM configuration of the engine, and are not adjusted by the computer & O2 sensor feedback.

If you increase airflow, only the closed loop areas are computer adjusted, and the open loop are going to be leaner. Depending on the amount of change, and the riding style of the bike's operator, some open loop areas could get very lean....

If the bike is tuned for OEM, Stage I, Stage II, Stage III, etc, etc.... The tune not only changes the range of the closed loop operation, but also adjusts the AFR of the algorithms in the open loop sections.

IMHO, if you deviate a small amount from the state of tune, while you may not have the "optimum" tune for that bike, it should not harm anything.

But the farther from an OEM (or other stage) tune you stray, you can tax the closed loop adjusted portion and you definitely are pushing the open loop, non-adjusted portion. The more you stray, the more important your riding style affects the safety of the tune.

A bike tuned for racing, can still develop tune related issues in a Race type environment. We all know that a good street tune can be "tested" by a "ride it like you stole it" operator. Imagine how much that same tune would be "tested", if it started out already behind (lean) in the open loop, non-adjusted portions of the tune...?

FWIW....
On my EFI bikes, I always adjust for a change in airflow. It may just be a basic auto tune, dialing in the VE tables on a simple change. It will surely be a new map, and/or Dyno Tune for larger mods (cams, displacement, headwork, etc).

 

No expert on glass pack mufflers am I. Though I know a bit about fluid flows, acoustics, and other silly stuff.

It seems to me that the changes from simply removing the packing wouldn't be overly severe. If anything, it seems it should worsen flow. When new and tightly wrapped, the scoops in the main tube end right in the packing, so virtually no exhaust gasses go into the outer chamber, just sound waves. With the packing removed (or blown out), exhaust gasses now could go through those scoops and out into the outer chamber. This would start restricting flow, much like the water valve from Nikola Tesla.

Reading things on packing mufflers from several manufacturers seems to bear this out. All reporting power loss from an unpacked muffler. Not huge reductions, but real. Small enough to be dubious of detection by the classic butt dyno.

I agree with Hattitude that while you're likely to get away with it, you also could put yourself far enough outside optimal operation that it causes minor problems like a stumble or intermittent backfire or such. Would you "need" to fix it with a retune? Probably not. Using my old TC88, I suspect it was tuned, and to the straight pipes it had when I bought it. When I put stock pipes on it it ran just fine, save for an intermittent "sneeze" through the intake when running low rpms and working the throttle quite a bit (fire road riding and the like). It didn't do that with the straight pipes. Though it's a worthy question if I ever could have detected it with those loud pipes. It was never enough of a problem that I bothered to address it. I just lived with it, knowing it would sneeze sometimes.

 

In the old days carburetors injected fuel based on how much air went through them, adding fuel if more air flowed. Fuel injected engines really don't do that as the volumetric efficiency is measured and programmed based on the factory equipment. If you could actually make a meaningful difference in airflow (bigger cylinder heads, camshaft), it would result in far more difference in AFR in a fuel injected engine than the same one with a carburetor.

The reality about changing mufflers and air cleaners is that they don't make a meaningful difference in those things. If they did, the computer would be unable to compensate for altitude, atmospheric pressure, temperature, and even a dirty air filter, all of which make a much bigger difference than what (or if) you have a muffler installed.

People think just because they hear more noise that they've done something that makes a difference but if you actually look at the fuel trims, it's noise at best. Because unlike a carb, the EFI adds fuel based on measuring the combustion process, not the amount of air passing through the throttle body.

 

If carburetors adapted well, there would be no need for mixture control in light planes. Lean issues in carbureted engines is real especially with exhaust changes. I believe open loop is primarily for cold start and warm up. Most OWNERS don't beat their bikes during warm up and closed loop takes over after warm up. If it is specifically locked out under some conditions, such as wide open throttle, I was unaware of that. However there should be power enrichment programmed into high power requests.

 

Most switch to open loop above 3000 or 3500 RPM and above a certain manifold air pressure or throttle position. WOT and high rpm are open loop even after warm up. Closed loop is mainly active at idle and under low load cruising conditions.

 

The O2 sensors are either heated, or unheated and warmed up by exhaust gases. They do need to warm up to operate properly...

OEM narrow band O2 sensors, fully warmed up, still only accurately cover an AFR range of 14.3:1 to 15.2:1. That's why the warm up tables in a tune, only affect portions of a tune map covered by O2 sensor feedback. When the bike is up to operational temperature, there are still areas of the map that require an AFR richer than 14.3:1 (high load, high RPM), and do not have closed loop monitoring or adjustment. If a tune map cell calls for an AFR richer than 14.3 (or maybe 14.4, I forget) the tune automatically switches from closed loop to open loop.

On an OEM ECM tune, the closed loop portion never covers all areas of the tune map. It only covers that narrow band O2 sensor range which is just a portion of the tune map (mostly cruise). On a tune map for a highly modified engine, that range covers even a smaller portion of the tune map.

You can run a DynoJet Target tune, Thundermax ECM, or a couple other aftermarket modules that will change to wide band O2 sensors, and once warmed up, the entire tune map is in closed loop, and has O2 sensor feedback and adjustment.

There are some "issues" with running wide band O2 sensors for the entire tune map, the biggest being that wide band O2 sensors respond slower than narrow band sensors. In fact a lot of racers and other people with really high performance engines would rather run complete open loop tunes due limitations with O2 sensor feedback.

All this was to say that on a fully warmed up OEM ECM tune/engine, there are still open loop portions in the areas where AFR can be critical if not properly adjusted. It doesn't take someone to "beat" on their bikes to be in these map areas. Sometimes just normal riding will put you into these areas and push your bike with a lean tune condition, ie: Two up touring with a bunch of luggage, going uphill at altitude.