Anyone with a fuel injected Harley should be paying close attention: Quite simply, it is not only far better when EFI systems are controlled by actual feedback directly from the engine (via sensors) it is also easier.
Older, open loop EFI systems, while more efficient than carburetors, also involve a lot more effort to be any more effective. Or it did. With the advent of so-called closed loop EFI on 2006 Dynas, H-D has made a giant stride in precision engine management. Trouble is, all the Factory system manages, in fact the reason for the whole EFI thing, is emissions compliance. The deal boils down to something like this: Narrow band oxygen sensors and an ECM/ECU that lock into lean 14.7 air fuel ratios on cruise. In effect, all the tools but no intention to offer true performance.
Zipper's Performance ThunderMax system, on the other hand, builds on this firm foundation by providing the exact set-up required to turn closed loop EFI into the high-precision, high-performance system it should be! Swapping the stock ECM for the ThunderMax unit and switching to Zipper's wide-band O2 sensors is pretty much a plug and play operation on '07 and newer Harleys (as well as '06 Dynas) but the real beauty of it is that folks with older, open loop factory fuel injection can update and upgrade as well by adding oxygen sensors bungs to the exhaust. (See the sidebar for more information on doing that correctly, courtesy of Bob at R and R American Cycle).
Once you install the ThunderMax with Autotune EFI along with the O2 sensors, you not only get fuel injection that can be tuned close to a stoichiometrically erfect 13-13.5 to 1 air/fuel ratio for bestpower from any combination of hop-up arts, but does it all automatically! To betechnically accurate it's more of an auto adjusting capability than actual auto tuning, since certain other parameters must be base-lined and a decent preliminary map must be installed, but we'll get to that...right now
Taking On Oxygen
It's All About The Bung HolesOk, you can stop laughing now! I know the terms are a crackup, but the process is serious-adding the mandatory oxygen sensors for closed loop EFI. The fact is, it's no big deal for those of us with '07 and later models, since almost all exhaust systems made for those applications already have bung holes (that is the proper term, dang it-stop giggling)! But adding closed-loop so-called automatic tuning types of EFI upgrades to older Harleys means adding O2 sensors to exhaust pipes that were never designed with them in mind, so putting them in place-the correct place-means measuring twice or even three times before doing any cutting, drilling, or welding. It has mostly to do with getting the sensors somewhere close to the right distance from the exhaust valves and plain old clearance issues. For instance, try an install on a Heritage Springer. The space available between the tight curve of the cross over header, behind the barrel, over the tranny top, across the primary and in front of the oil bag leaves minimal room for a sensor, to be kind about it. But if you yank that header off, slam in a bung, pop the pipe back on and find out that the sensor won't screw in, or hits something in those tight confines, you will not be a happy Harley rider...plus, you'll get to do it all over again!
The point is, installing the bungholes in your existing exhaust is arguably the make-it-or-break-it part of the exercise for upgrading to autotune EFI. It'd be real nice to supply you with a foolproof technique for adding these necessary evils, but fact is, there ain't one! This is one arena of endeavor where there just is no good substitute for logic, experience and caution. All we can do (and will, courtesy of Bob Robinson at R and R American Cycle) is show the best starting point, some tips, and point to a good strategy and some useful tactics to help ensure a successful mission.
Now, let's watch how it's (supposed to be) done...