Technical Articles

ThunderMax EFI Controller

ROB SKENNAR started as an apprentice at Rollies Speed Shop and has been working there for as long as we remember. He has done training course after training course including the S&S EFI course so what better person to ask to help us install the ThunderMax EFI Controller.

Rob explained that these days the skill base of a mechanic is changing. “Screwdrivers and spanners are giving way to computers. If you want to tune a Harley these days, you need to sit down with your laptop to understand what’s happening. It’s no longer a matter of taking off the float bowl and changing a couple of jets. Those days are over.”

Rob explained that the ThunderMax EFI Controller is a complete stand-alone Engine Control Module (ECM). “There are other systems which utilise the original Harley EMC,’ he said. “The ThunderMax is different. It’s a complete replacement unit. You remove the original ECM; the ThunderMax ECM bolts straight in its place and all the original plugs snap back in; no wire cutting or splicing is required.”

The kit also comes with new wideband sensors. “If you have a late model Harley, the original Harley narrowband O2 sensors are replaced with the ThunderMax wideband sensors. Earlier models will need to have sensor bungs welded to the exhaust

Rob has fitted the ThunderMax EFI Controller and O2 sensors to a number of bikes before so he got the job done in short time. It was now time to focus on the software. “You load the software from the supplied disc to a PC and choose a base map that’s closest to your bike’s set-up,” he said. “This is actually quite easy if you have basic PC skills; otherwise get your dealer to do it.”

ThunderMax efi

The software comes with a large library of base maps and there’s a list of key elements to help you choose the right one: throttle body/injector size, engine displacement, type of exhaust system. Also, your engine’s cranking compression and cams make a significant influence on the ignition timing.

Having decided on a base map, Rob downloaded it to the ThunderMax EFI Controller on our Harley; a simple two-minute task.

Okay, it’s time to start the bike and test the ThunderMax EFI Controller on the road. If you’ve chosen your base map well, the bike should run pretty hard straight off even though it hasn’t yet tuned itself. “I reckon you need to do 1000 km to reach your target; clock a few miles up,” said Rob. “It needs to learn, it needs to be ridden in every rev range. If you never ride your bike over 3500 revs, it will never tune itself over 3500 revs.”

The ThunderMax EFI Controller utilises a very fast, powerful processor that looks up the base map, checks the O2 sensors, and makes adjustments to the air/fuel ratios in real time as necessary. It writes these changes to a secondary map called ‘off-sets’ so it doesn’t have to reinvent the wheel every time you go for a ride.

How much will it adjust? Quite a lot, actually. Up to 50 percent from the installed base map; although it’s still advisable to install the closest base map to minimise the system’s learning time.

The Idle Air Control and its stops are also automatically adjusted, always learning.

Our test bike had a flat under acceleration between 2500 and 3000 rpm initially so we purposely rode in that range until it retuned itself. Every time we went there, it went a little better until the flat spot had disappeared. In fact, the more we rode the bike during the next couple of weeks, the better it went.

ThunderMax Ron

Most owners will be happy with the way their bike runs with the ThunderMax kit fitted. However, if you love to fiddle, with your PC connected to the ThunderMax EFI Controller, you are in total control of every element of your bike’s tuning—air/fuel ratio, ignition timing, rev limit, idle speed, speedo calibration, accelerator pump, etc—are simple click-and-enter affairs. You also have access to numerous monitors to help you perform ‘live’ (engine running) tuning and to keep a watchful eye on vital engine data while amending maps: battery voltage, spark advance, engine speed, throttle position, injector duty cycle, barometric pressure, air temperature, engine head temperature, etc.

The ThunderMax EFI Controller uses the default of 13:1 air/fuel ratio as its target. “This is a good balance between power and economy,” said Rob. You can easily change this if you wish to target air/fuel ratios at specific rpm ranges and throttle positions: eg. you can concentrate on fuel economy for cruising or richen up full throttle maps for best power.

Every Harley mechanic in the world will tell you the new EFI Harleys need to idle around 1000 rpm. Nevertheless, we took the opportunity to drop ours to 912 rpm. The bike seemed to like it okay; and it was certainly pleasant to knock the edge off the high idle.

The ThunderMax also carries a three-year replacement warranty. A comprehensive tuning manual comes on the software disc, but it’s also available on-line at www.thunder-max.com if you want to check it out before you buy.

Okay, so if the new Harleys use O2 sensors, why change them? Because new Harleys use ‘narrowband’ O2 sensors which can only adjust the air/fuel ratio within the 14.7:1 range. “This is way too lean, especially when you change your air cleaner and/or exhaust, and the reason why new Harleys run so hot,” said Rob. Additionally, the Harley ECM only uses the feedback signal under light-load, steady-speed, part-throttle, conditions. In other words, the narrowband O2 sensors do not work in high performance applications.

The optimum air/fuel ratio for cruising is 13.4—13.6:1; and 12.8—13.2:1 for wide open throttle. When you install an aftermarket EFI module (regardless of manufacturer) you need to eliminate the original Harley O2 sensors to stop them trying to lean the mixture within the 14.7:1 range.

ThunderMax wideband sensors, on the other hand, can accurately measure air/fuel ratios from 9:1 to 16:1 and anything in-between. Mating the wideband sensors with the very fast processor in the ThunderMax EFI Controller means your Harley will be perfectly tuned—you’ll get maximum horsepower, torque, throttle response, fuel economy, and lower engine temperatures—every time you ride it. And you don’t need to put it on a dyno; it does it all automatically.

The future is here—self-tuning EFI Harleys have finally arrived.

The ThunderMax EFI Controller is available from Rollies Speed Shop: 07-3252-5381.

The cat is out of the bag: D&D Fat Cats

THIS ARTICLE was supposed to be about the new ThunderMax EFI Controller, but, as often happens, it turned into something bigger than Ben-Hur.

We’d heard a lot about D&D Fat Cats on various internet forums, and a recent article in an American bike magazine did an exhaust system shoot-out which was won by D&D Fat Cats. So when Rob Skennar, the Workshop Manager at Rollies, suggested we try a set, we jumped at the opportunity.

Most Harley riders reckon 2-into-2 exhaust systems look cooler than 2-into-1 pipes. However, if you want better low-end power and mid-range torque, a good 2-into-1 system is the way to go.

D&D’s Fat Cat 2-into-1 system combines a huge, four-inch, high-flow muffler and stepped headers. We could tell just by handling the pieces as we unpacked them that this set was all quality.

The set comes ready to install: both O2 sensor bungs fit stock sensors without modification, mounting flanges are pre-installed (no C-clips required), the heat shields are pre-installed, there’s a new mounting bracket which bolts to the transmission case, and new gaskets are included. It’s basically, take off the old set, unpack, and install.

Our huge four-inch muffler with louvered baffle was loud without being too loud. There are a couple of options: Quietest design, wrapped with sound control material, it allows earliest available torque with no loss of horsepower at the top end on stock and moderately modified engines; original baffle design, louvered and unwrapped to provide higher flow; high flow perforated, big bore, designed for the rider with extensive performance modifications who wants maximum high rpm output.

When we were doing research for the EFI story, it was interesting to see a note about D&D on the ThunderMax website: “During the development of our EFI systems, many hours were spent tuning engines for their best overall power curve. Many exhaust systems were used during testing, and their effect on an engine’s output was noted with great interest. The D&D systems were consistently at the top of the performance list, especially when tested on larger displacement performance engines. D&D’s philosophy is to trust their own R&D program, developing their product line to reflect what they learn during their countless hours of testing on the D&D dyno. But they didn’t stop after they made big power, they also built systems that are engineered to fit and look great!”

Inspect a D&D pipe and you’ll find true craftsmanship. The 2-into1 Fat Cat we fitted to our bike delivered a high and wide torque curve that was excellent for our style of riding.

Rollies Speed Shop are the Australian distributor, both wholesale and retail, for D&D Performance Exhausts. Call them for more info: 07-3252-5381.

Electra Glide Fat Cats

About D&D Performance Exhaust


IN 1972 David Rash could not find the exhaust pipe he needed for his race bike. He knew that the proper exhaust for his engine configuration would give him an edge over his competition so he fabricated one himself. Thirty years and 250,000 pipes later D&D Performance Exhaust systems are some of the leading performance motorcycle exhaust systems in the world.

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