Your factory ECM has an understanding of the air flow through your motor. It uses that information, along with a target air/fuel ratio pulled from a table, to calculate how much fuel to inject.

So any time you make any changes that alter the airflow, the ECM's model of the airflow becomes incorrect, and therefore the amount of fuel injected is incorrect.

The ECM has a limited ability at some throttle positions and rpm's, mainly in the cruise range, to read the actual air/fuel ratio and make adjustments to the fueling. However, it doesn't work at higher rpm's and higher throttle settings.

The reason you're seeing so much debate on the subject is because there really isn't a lot of hard data out there on specific air cleaner/pipe combos that characterize how far off they throw things. So everything is just subjective and anecdotal.

I don't think that anyone will argue, though, that the bike will run better if you tune it after making changes that affect the air flow.

With respect to tuners, there are three basic approaches:

1. Piggy Back Tuners (Fuel Pak 1&2, Power Commander, Micro Tune, Dobeck, Cobra, etc) - these are devices that hang outside the factory ECM, intercepting and modifying signals coming and going, to "fool" the ECM and alter the fueling and in some cases ignition timing. The factory ECM doesn't even know it's there, as far as it's concerned it's operating a stock motor.
2. Flash tuners (Powervision, SEST/SEPST, TTS Mastertune, DirectLink, Fuel Pak 3, etc) - these are devices that give you access to the ECM's internal settings and tables that are used to control fueling and ignition. So basically, instead of fooling the ECM, you're actually teaching it what's going on. These devices also have some method by which you can log oxygen sensor data and feed that information back into the tune to make it better.
3. Replacement ECM's (Zippper's Thundermax, Daytona Twin-Tec) - These are aftermarket replacements for the factory ECM and have full programmability.

My personal opinion is that #2 is the way to go. I've just found that they do a much better job than piggy backs. The tools they provide to develop the tune are worth their weight in gold. Yes, they cost a little more than piggy backs. But it just works much, much better to actually teach the ECM what's going on than try to fool it.

The stock Delphi ECM is very full featured and reliable, and with the capability of teaching it properly, I haven't found any advantage at all to replacing it with an aftermarket piece (number 3 above). That's the most expensive route, and in some ways, it's actually going backwards. I'll spare you the details, but if you're curious, google "Speed-density vs. Alpha-N".

Among flash tuners, again my personal opinion is that the Powervision stands head and shoulders above the others. It greatly, greatly simplifies the process of tuning, boiling it down to just a few taps of the touchscreen. Plus it has about a thousand other really cool features. You almost have to write a novel to explain all the cool things it can do, but bottom line, you can take full control of your EFI and monitor virtually anything going on. It also provides wideband tuning support via an add-on product, and even closed-loop wideband support via another add-on product.

The FP3 is not a bad product, but it has two drawbacks that make me shy away from it. Number one, all editing of the tune has to be done on your smartphone, and there's no way to receive tunes except from V&H. There's no way to for example pull the tune into a PC to examine and modify it or share it or have someone else (other than V&H) send you a tune. That's a pretty big limitation, you're basically forced to operate in V&H's little world and hope that what they provide works ok for what you're doing. Any kind of extensive changes are cumbersome at best as you punch numbers into a smartphone. Number two, it has no facility for supporting wideband sensors, and no add-on product to support them. So all tuning must be done with the factory narrow band sensors, which have limitations especially in high load, high rpm situations. So there's really no way to develop a high quality tune with an FP3. You can create an acceptable tune however.

So anyway, at the end of the day, my recommendation is a Powervision. It's really a remarkable device. It's not the cheapest tuner on the market, but hey, it's something you buy once. Do it right the first time and have no regrets, that's my advice. Good luck whatever you decide.

 

Number three.... limited vin(bike ecm) usage... one bike.. can't use if you upgrade/total/sell or otherwise move to a new bike (like lifestarts@40 mention he was thinking about above... he'll need to buy another tuner if he gets a dyna)... $300+ gone must stay with bike forever ... not cool.


this is why i'm saying ask in the tuner sub-forum. most of the people here that say.. "oh it's great " don't really understand why we are saying back off the fp3 for now and do your research. they might have been fine with a micro tuner for much less. you don' know what you don't know. sure you could buy it and be happy but, understand the pros and con's before doing so. if you come back to it, thats fine.

it's not negativity, it's a heads up.

 

Talking FP3, you can use your smartphone to review and change any and all tables in your tune. V&H will even help you if you tell them what exactly is happening they will tell you which tables to go into and which numbers to change and what to change them to.

I put Bassani Slip ons and a 4 inch round air cleaner and I used the tune V&H recommended. I was till getting lean surging at low RPM cruise speeds and they told me to go into the Air Fuel mixture table and told me exactly which numbers to change and what to change them to.

V&H will also build a custom tune for you specifically for your bike and modifications you have done.

Since the FP3 does use a smart phone for tuning, you can contact V&H on your phone while blue toothed to your tuner and they can actually connect to your tuner thru your phone and review your tune and makes changes for you.

If you are just going to go minor upgrades the V&H FP3 at $319 is hard to beat.

 

Oh trust me, I'm aware of how it works. And I absolutely agree with you, if all you're ever going to do is stage 1 stuff, it's a compelling solution. Probably the best option in that case.

But if you're going to make internal engine changes that in turn require extensive changes to large tables, and V&H doesn't have them available, then the Powervision is a much better tool. Much, much easier to get there. Likewise if you want to get everything out of your build like us obsessive types, wide band tuning is essential. It's a more advanced tool for more advanced needs, no question.

So it really comes down to a person's needs.