Twin Cam swap your FXR!

Having trouble with your Evo? Want to start making some more reliable power? We'll show you how to get it done using our Ramjet Racing Twin Cam conversion kit and share some key points from our vast experience. While there are some other ways to complete the conversion, we find this kit to yield the most benefits. Buckle up and grab a notepad cause we are going to cover a ton of info. We'll start off from the first and biggest part of the project, the drivetrain choice.

Twin cam engines and generations

The Twin Cam engine was produced from 1999 to 2017. While the Two generations remained roughly the same, there are some key changes to take note of. Keep in mind we'll be taking about the Twin Cam A engine (Dyna & Touring). The B engines (Softail) cannot be used for this swap.

First generation (1999-2005 & 2006 FL). The "early" generation is a little smaller in displacement at 88" however some would say they are built better from the factory. Especially the '99-'02 as they came from the factory with the Timken left side crankcase bearing. This is a common upgrade done in the '03-'17 engines over the factory roller bearing when starting to make some serious power.

These engines do have one downside in comparison to the 06+ generation, spring loaded cam chain tensioners. These tensioners are notorious of failing around the 30,000 mile mark. Some engines have had them break much sooner as the plastic tensioner becomes brittle with age. Luckily our friends at Feuling Parts have a cost effective oiling system upgrade to convert to the late style hydraulic tensioners. This will also increase oil volume and pressure to help the engine run cooler and quieter. This would be a great time to replace the camshafts while in there, but hey you we're going to do that anyways.

Side note, if you plan on installing a big bore kit and/or big camshafts right away, the '05-'06 engine would be in your favor. The '05-'06 have the late model style beehive valve springs that allow up to 0.585" lift. The '99-'04 models have dual sprung valve springs that only allow up to 0.535" lift.  

This generation is a more popular choice as they typically are a little cheaper and easier as more of the FXR generation parts fit. We'll get more into that in the drivetrain section.

Second generation (2006-2017). Also know as "late model", these larger 96"/103" engines also have some pros and cons.

One big benefit besides being larger displacement, is being equipped with reliable hydraulic tensioners from the factory. If the mileage on the engine is fairly low (20,000 miles or less), this could save you the expense of having to open up the engine and replace parts as mentioned on the early generation engines. Granted it is always a good idea to open up a used engine prior to use.

One downside to using the late model engine is the entire drivetrain must be late model Twin Cam parts as well. This can be quite spendy, however may be worth the cost if your looking for a factory six speed transmission and updated primary components. This does make sourcing parts easier on or off the road as shops are more likely to stock them. We'll cover more in the driveline section.

Driveline AKA Transmission and Primary combo

Keep in mind during this section, the transmission case and primary cases must be FL Touring parts. Dyna and Softail cases will not work! Most of the internals and other odd end parts from Dyna, Softail and Touring models will all work. 

First generation drivetrain (1999-2006).  If you choice to use an early Twin Cam engine, you must match watch out for the two different transmission and primary generations. 99-00 and 01-06.

'99-'00 Transmission case will allow you to use your existing 1989-93 FXR primary cases, drive components, starter, etc. Easiest and most cost effective option however finding some OEM 2 year only transmission cases can be difficult. Luckily we carry Twin Cam FL transmission cases and complete 6 speed transmissions!

'01-'06 transmission case will require '01-'06 FL primaries, mid shift conversion, a '94-'06 Starter/Jackshaft and either a '94-'06 Clutch assembly or a replacement 102T clutch basket ring gear. This is due to a inner primary to transmission mounting hole location change, FL models having forward controls, a change in starter jackshaft bushing sizes and a change in the starter pinion gear tooth count (10T). The mid shift conversion consists of drilling 2 holes in the inner primary. One for the shifter tube and one blind threaded hole for the shift tube retainer tab bolt. This can be a little in depth for the at home mechanic so an experienced shop such as Ramjet Racing or a machinist would be advised.

Another thing to note on the transmission case changes is the pivot shaft diameter. All FXR's use a 5/8" swingarm pivot shaft that goes through the transmission case. 99-01 FL transmission cases use the same 5/8" FXR shaft. 02-06 FL cases will use a larger 3/4" shaft. To use a FXR swingarm and pivot shaft on the 02-06 case, you will need a pivot shaft reducing sleeve. This is preferred as it will retain your stock wheel, spacing and caliper. You can use the '00-'06 swingarm if you are looking to use a more modern style caliper however your wheel spacing, bearing size, and axle will be changed. For an easy bolt modern caliper solution, check out our Brembo rear caliper conversion kit. Either swingarm option will use '86+ FXR/FL rubber pivot block isolators.

Second generation drivetrain ('07-'16). If you choice to use a late model Twin Cam engine, there are no major year changes to the transmission or primary cases, however there is one thing to note on the transmission side cover. '07-'13 used a cable clutch and '14-'16 used a hydraulic clutch. Worst case switching between the two is as simple as changing the side cover and clutch pushrod components. 

The tough part is going to be the mid shift conversion in the primaries. While there are some bolt on external mid control applications, a mid shift conversion give is a much cleaner, factory appearance. This will require an experienced shop such as Ramjet Racing or a machinist as a shift tube will need to be welded into the inner primary.

When it comes to the swingarm and pivot shaft, there are two options. Use a 02-08 FL factory swing arm and pivot shaft or use you stock FXR swing arm and pivot shaft. The 02-08 FL swingarm will directly bolt up as the pivot shaft size is the same (5/8") however, the axle size, wheel spacing, and caliper will change as well as a ~1" lower shock mount. To use the FXR swingarm and pivot shaft, simply press a pivot shaft reducing sleeve (3/4" to 5/8") into the transmission pivot shaft hole. Factory wheel spacing, axle size and shock location is retained. 

While using late model parts is the more expensive option, it does allow you to use all the latest parts and is much easier to source parts on or off the road. You'll also have a factory 6 speed transmission and we find this style one piece starter not only much more reliable but also able to be replaced on the side of the road (primary cover does not need to be removed)

Ignition and fuel delivery

Another big decision to make. Stay carbureted or convert to EFI? Lets check out what it takes and what parts are compatible.

Carbureted option. Either engine generation will allow you to use your Evo carburetor and most air cleaners however both engines will require a new ignition system. This is definitely an easier and more cost effective option. Lets go over some details on both engine generations and how to get it done.

 As mentioned your Evo carburetor and most Evo air cleaner will work. The TC engine uses smaller 3/8" breather bolts. As long as your current air cleaner will accept these and you are able to source some that are correct length, it should bolt right on. One part you may need is a TC intake manifold depending on your ignition choice. Lets get into that.

There are a few options for ignition systems. Daytona Twintech, Dynatek, Thunder Heart, etc. All will require a little wiring however they are very straight forward.

The easiest option is a Thunder Heart ignition kit. This will include the ignition module, coil and some wiring. This kit is easy as the included coil will work in the factory Evo location and the wiring is very minimal. To sum the wiring up, connect ignition module wires to the provided coil, to your crank position sensor, Key on power and tachometer. To change maps or make adjustments, simply download their software and tune away! The only downside to this kit is it does not use a MAP sensor. This can be helpful when tuning performance engines as it measures engine load.

Another great option is using a Daytona Twin Tec or DynaTek ignition module. These are a popular option and can widen tuning capabilities. Both systems are quite similar so we'd recommend to research both to see which may have the features you're looking for. Keep in mind, this option will require TC spark plug wires, '99-'06 carbureted TC coil (custom mounted), a MAP sensor and a TC intake manifold as it has the MAP sensor hole. For wiring, you could use a factory touring harness however it can be difficult and laborsome to weed out all the unneeded wires. We'd recommend to use a Namz plug and play ignition harness (plus the ignition module of your choice) or a Daytona Twin Tec ignition kit. These harnesses will plug into all the engine sensors and ignition module. The only wiring required is a ground, key on voltage, run/kill switch (optional) and tachometer (optional). Tuning these is made easy with external knobs to adjust the spark curve, rev limited and more! A simple street tune by following the provide instructions is sufficient for most engine builds. If a custom curve is desired, you can link some of the ignition modules to a computer.

EFI option. Much more work and cost, yet a lot of reward. This involves a ton of wiring, fuel tank fabrication, custom ECM mounting and sourcing EFI parts. Both generation Twin Cams will accept an EFI system, so keep this in mind as we continue. There are however two different EFI system. Throttle by cable "TBC" ('02-'07 FL) and the later Throttle by wire "TBW" ('08-'16 FL). Lets dive into them.

Throttle by cable will accept you stock carb throttle cables as well as most Evo and TC air cleaners as the bolt pattern is the same between carbureted and TBC EFI. This system works great, has quite a bit less wiring, and does not use o2 sensors on the First/Early generation engines. This does limit tuning capabilities as the bike will need to be on a dyno or have a Thundermax ECM installed with o2 sensors.

Throttle by wire uses no throttle cables and will require a new air cleaner as the mounting bolt pattern has changed. This system is often more preferred as it can provide smoother runability and better tuning results. As mentioned this system will require some more wiring due to the o2 sensors, twist grip sensor in the handlebars and some additional wires going to the throttle body. The amount and size of the wire will also vary as there are two different electrical system year generations within TBW. '08-'13 (J1850 system) uses nearly double the wires and they are larger in diameter. This system is much easier to diagnose and modify wiring. 14'-'16 (CANBUS system) uses about half to wires and they are much thinner. This is due to each wire sending multiple signals using different voltages. The downside is modifying this harness is difficult and can throw engine codes easily. 

For either EFI systems, there are two options for wiring. Use a factory harness or a Namz EFI Ignition harness. Due to the amount of parts needed for EFI, it can be easier to purchase a wrecked or donor bike and attempt at modifying the factory harness first.

For EFI fuel delivery, you'll need a M8 Softail (CANBUS) or '07-'13 Sportster (J1850) fuel pump. A fuel pump mounting adapter plate (or cut up a factory EFI tank) will also need to be welded to your tank. There are a few companies out there that offer a precut threaded mounting plate to weld into your gas tank.

Exhaust choice and options

When it comes to exhaust choice, you typically have two options. FXR or Dyna. Most FXR exhaust will fit however you most likely will need to fabricate a new bracket. This all depends on if the header will clear the new mid controls. Another reason to mock up the drivetrain and exhaust prior to welding in the foot control mounts. Many of the Dyna exhausts will work as well. We find the early model Dyna exhaust ('99-'06) typically have the most clearance around the foot controls. If a new exhaust bracket is needed, this is a fairly easy job for an experienced fabricator. 

Final thoughts

We just covered a ton of info and hope this helps you dial in your game plan. These swaps may seem difficult how every with the info in the blog, you should be off to a much easier start! If you have any questions or information you'd like to see added, please reach out to us. We'll be happy to help get your build moving!

- Ramjet Racing in Phoenix, AZ