I can see that if he were maybe doing some slip on mufflers but the fact that he did a full header change, with a very free flowing exhaust... I would tune that every time if it were me.

 

Would make little to no difference if you are not adding more air to the intake side, you can"t exhaust more than you intake. He clearly stated everything else was stock for now and wanted to know if tuning or other mods were REQUIRED just to change exhaust, and the simple answer is NO for strictly an exhaust change.

 

I tuned my bike ($400 TTS kit and sweat equity in my case) when completely stock and noticed a significant improvement in power, drivability, sound, and fun. It just cooled the bike down and livened it up as well as fixed an annoying surge. The tuner was worth every penny as I could set up the bike how I like it to run. So yes a tune provides noticeable gains. But the question is "is a tune necessary". You won't hurt anything by just adding slip-ons or an exhaust unless the exhaust system has O2 bungs in the wrong place or has significant reversion, so in that sense a tuner is not necessary. But if you want to get the most fun out of the bike and only the best will do for you, a tuner is necessary, regardless of modifications. That's a subjective call, however.

In my case, adding slips-ons improved the sound and adding an AF improved the look and feel but neither provided performance gains that I could notice less than 4500 RPM at near WOT. The tune improved performance in all RPMs and driving conditions, however.

You won't hurt anything but your wallet by changing the filter either (in that sense not necessary), but you just may not enjoy the ride.

In either case, just install the exhaust and/or filter for looks and sound and see how she rides, and just ride. Many riders are happy with the performance.

 

Close for closed loop cruising but....

The way I understand it is that its not a perfect world and there are practical technology limits. Since there is no practical way currently to measure AFR directly, the ECU uses a number of sensors to make a pretty good guess of how much and when to squirt fuel to achieve its target AFR for the load, rpm, fuel type, and throttle conditions (among others like temperature). The engine is basically an air pump and the ECU's guess is mostly based on the volumetric efficiency (VE) of that air pump given the throttle opening, load, and rpm. Anything that effects the VE (intake or exhaust restrictions or changes in their tune for example) affects the actual AFR mix being achieved. The ECU may be thinking its hitting the target AFR, but is off somewhat because its calculations are based on now incorrect VE data.

The HD engine VE is limited more by the A/C than exhaust, so changes in A/C have more of a tendency to impact the VE. In a steady state (cruise) condition, the O2 sensors provide a decent indication of AFR, but during transitions in load and throttle as well as for wide open throttle, the ECU wants to target a AFR outside of the O2 sensor measurement range so it does not use O2 sensor input, it simply guesses based on VE, throttle, rpm, load.

Whether it makes a difference to your seat of pants or not is a subjective call and, unless you are running full throttle (racing) most of the time, you won't be hurting anything as the ECU has enough adaptability range to set cruising AFR to the factory cruising target (whether the factory target is right for you or not is another topic).

That ECU is a sophisticated and complex unit, it certainly has plenty of smarts.

What tuners do, effectively, is measure the VE for your motor and correct the ECU VE tables (so called calibrating the VE). Tuners also change target AFRs and timing based on experience, but most of the work goes into the VE measurement under all loads and RPMs and then double checking that the tuner's adjustments results in the desired AFR and power curve.

 

well i have no expierence with harley tuning, i have been tuning forced induction cars for a few years. If its anything close, the factory o2 sensors have a lot to do with the drivabilty of the bike. If they are wideband o2 sensor then they will always control the drivabitly under any load(like i said i dont know). If the tuning is close to what im expierenced with, if you are using a PC III/V or something equivalent they would replace one of the o2's with a wideband sensor during tuning, that would show them the afr from idle to redline and tune the afr based on that (which is accurate). Then once they have a map the PC would be over riding the factory tuning. Thats how the self tuning kits work as well. You replace the factory o2 with a wideband sensor, you have a target afr and the computer plugs in the numbers for the mapping. Not as detailed tuning that you would get on a dyno with someone tuning but it works.

 

I still don't see how a reasonable exhaust mod changes what the O2 sensor reads. The combustion chamber exhaust gases will have a certain amount of oxygen present when they reach the O2 sensors, which is LONG before they reach the muffler body or the rest of the muffler pipe. That's why it's important to have the O2 sensors near, very near, the mounting flange on the exhaust port. They read the exhaust IMMEDIATELY after it's expelled from the combustion chamber. Immediately.

What happens after that does not interest the O2 sensor in the least. How can it? The exhaust is way downstream of the O2 sensor in milliseconds. So, the O2 sensors read the exhaust, tries to keep it at stoich (14.7:1) so the catalytic converter can function properly and signals the ECM accordingly.

How a reasonable exhaust mod (done correctly) can alter O2 sensor readings is beyond me.

Now, and this is IMPORTANT: If you go from factory exhaust, or from a set of slip-ons, to a fire-breathing, pavement cracking set of 2 into 1 exhaust? THAT can change your AFR. It can. For real. I don't wanna get into it right now, but it can change what's going on, on the intake side, enough to need a re-map. But people that do that hardly ever change JUST the exhaust. They're usually changing intake and exhaust. But I gotta cover my **** here.

Reasonable exhaust mods? Nah.

 

StretBobTony;

Nothing is as simple in the real world, there is more technical info over in the EFI tuning forum. At the risk of oversimplification:

The HD engine environment is a different beast, a more severe sensor environment that can compromise sensor accuracy and life, but the general principles are the same. There is also two systems that use different terms; the old AFR based and the newer lambda based.

O2 sensors don't measure AFR directly but if they are set up right and you know your fuel, you can do some math and derive AFR. The stock HD O2 sensors are narrow band switching type, very accurate but over a relatively narrow range. Some tuners use (as well as the auto tune modules) broadband sensors, which are the same technology as narrowband sensors but also pump some ions in to provide additional measurement range. They are accurate when used as the manufacture suggests, but in practice not accuracy enough out of the narrowband sensor range to do better than simply making an educated guess based on VE and loading and closed loop narrowband sensor information. There are other advantages, however. The much more expensive wideband sensors used by some dyno tuners are a different technology and have the capability, when used properly, to provide a more accurate AFR indication.

When the dyno operator is setting up the stock delphi ECU they watch the AFR with a calibrated wideband sensor, then calibrate the VE tables and adjust the AFR targets to get the AFR target the operator wants for each operating condition (RPM and load). Tuning WOT is simple, its getting everyday street riding (idle to cruise, transitions, cold/hot starts, decel enrichment) right that takes time.

BTW, the PCIII/PCV won't use O2 sensors in operation (they are disconnected). The dyno operator simply steps through rpm and loads and sets up the PC module to adjust the ECU provided fuel to one that provides the operator desired AFR (as measured by a probe or bung based sensor). Thus these can be tuned fairly quickly as there is only one parameter to adjust and the dynojet software steps the operator through without the need for much thinking. The delphi ECU has two adjustable parameters (VE table and target AFR) to set fueling, so it takes a bit more time to get right.... the results are better, however. But the best is the worst enemy of good enough.

 

The point I was trying to make is that we should worry more about open loop damage than closed loop as the ECU has some AFR feed back when operating closed loop and will adjust for perhaps a 20% VE mismatch. It does not adjust for mismatches open loop directly. The ECU applies some closed loop adjustments to the open loop, however.

You are right in that you really have to screw up an HD exhaust system to affect the O2 sensor, mostly because the HD exhaust is so short anyway that its not very good to begin with. You can't think in the same terms as a car exhaust where the relative tuning pipe legnth is long. Making a bad system worse is just another bad system.

The exhaust is so short that some "reasonable" systems allow outside air to revert back up the pipe and mix with the exhaust even before it reaches the O2 sensors (at some rpm and load harmonic effects). I know its hard to believe, but it happens. Some reasonable systems put the O2 sensor in a different spot than stock which causes some differences.

 

No, it's not hard to believe. That's where we get decel popping. When outside air mixes with hot exhaust gases and unburnt fuel. It's like fanning a fire -- More air, more heat = Ignition inside the pipes. It doesn't happen that much with stock exhaust because, 1) The stock system is so quiet you can't hear it even if it does and, 2) The stock system is so restrictive that outside air can't get in.

It's tough to tell people NOT to put a tuner on their bike. If you tell them TO put one on, you can't go wrong. Afterall, it's their money. If you tell them NOT to put one one, then you're taking several risks. You don't know what kind of system they put on, whether it's on right or not, what else they've done to the bike, how the bike will react, whether they'll catch an adverse reaction in time, etc, ad nauseam.

Which is why I went the 'safe' route with slip-ons only. I'm still worried that I might have loosened/damaged the header studs/nuts when I was pounding the crap out of my stock muffler bodies to remove them. But I'm watching them and haven't seen/heard anything remarkable yet. I think.

I just wanted my bike to sound like a Harley, that's all. I didn't like that it sounded like it was in a swimming pool. Sounded like crap. I think the V&H Twin Slash look better, too. The stockers looked like a couple sewer pipes hanging off the end.

Right now, I'm not interested in going fast. If I wanted 'fast' I'd buy a big watch and a cheap motorcycle.

 

I figured they were narrowband sensors. Thank you for your input.