TCFI Twin Cam Fuel Injection

Why is the TCFI auto-tuning capability superior to competitive products?

Competitive systems claim to have auto-tuning capability. Prospective customers should ask whether a given system meets two important criteria:

1. Is auto-tuning real-time and continuous? Real-time means that the system makes immediate air/fuel ratio corrections based on oxygen sensor feedback. Continuous means that the system makes corrections whenever it is running.

2. Can the user monitor, control, and override the auto-tuning corrections? Any “feedback” system using a sensor to make corrections is subject to operating regions where instabilities or errors exist.

Only the TCFI system meets both criteria. 30 seconds after engine start, when the oxygen sensors have warmed up, the TCFI system continually updates independent front and rear cylinder air/fuel correction tables, referred to as the block learn multiplier (BLM) tables. The BLM tables have the same cells (RPM rows and throttle position columns) as the air/fuel ratio command table. Correction values are in percent units. A value less than 100% means that fuel is being taken out to correct a rich condition. A value greater than 100% mean that fuel is being added to correct a lean condition. An actual BLM table is shown below. Most of the values are between 90% to 110%, showing that the system is now well tuned and just making small corrections. The user can download the setup file from the TCFI at any time and monitor the BLM tables.

Part of the second criteria listed above is the ability to control and override the auto-tuning corrections. Only the TCFI system offers this capability on a cell-by-cell basis. You will notice cells highlighted in blue with values 0 and 1. Closed loop feedback is disabled in any BLM cells with value 0. This is useful in operating areas where exhaust reversion effects may cause incorrect sensor readings. The table has the value 0 in cells corresponding to decel (RPM above idle and closed throttle) where reversion effects are most pronounced. BLM update, but not closed loop feedback, is disabled in any BLM cells with value 1. This means that the system always starts with 100% fuel in these cells. In this table, the value 1 is used in the range of 750 to 1,500 RPM and 0% to 5% throttle position (TPS) to compensate for the unstable cold start characteristics of a particular engine combination that includes an aftermarket throttle body. Please refer to the TCFI Idle Tuning Tech Note for more information on this subject. 


What is the difference between the Gen 4 and previous Gen 3 TCFI versions?

The TCFI Gen 4 is identical to the previous Gen 3 (TCFI III) version with the exception of the housing and wire harness hookup. The Gen 4 version has a lower profile housing that allows installation on Sportster® applications. For Twin-Cam applications, the WEGO IIID wide-band exhaust gas oxygen sensor interface now conveniently mounts on top of the TCFI module. The WEGO IIID wire harness has been simplified to allow easy plug-in connections for power and ground using the existing Harley-Davidson four terminal diagnostic connector.

The same setup files and software can be used interchangeably with Gen 3 and Gen 4 product versions.

Typical TCFI Gen 4 Installation on Twin-Cam Model


What special considerations apply to 2006 and later models?

2006 and later models use a new throttle body with smaller injectors (rated 3.91 gm/sec versus 4.22 gm/sec for 2001-2005 models). The smaller injectors limit maximum power to about 90 HP. Fortunately, Screamin Eagle® offers a high performance throttle body that comes complete with larger 4.89 gm/sec injectors for under $400.  

2006 Dyna® and all 2007 and later models are factory equipped with front and rear oxygen sensors. The Delphi® controller operates in closed loop under part throttle conditions. This system uses 2-wire narrow band oxygen sensors that maintain the air/fuel ratio (AFR) near 14.5. If you attempt to install an “add-on” device such as Power Commander® that changes the injector pulse width, the Delphi® system will compensate within a few miles and return to the factory programmed  AFR values. The only solution is to completely replace the factory system with a unit such as our TCFI. And you won’t have to weld in oxygen sensor mounting bosses, as H-D® has already done that for you.  


Does the TCFI system fully support the new 96 CID engines introduced in 2007?

Yes. Installation is very easy since the exhaust already has provision for oxygen sensors. The ECM controls the 6th gear light. The new engine requires less spark advance. We have new firmware and setup files for 2007 and later models. The TCFI does not support the active intake and exhaust used on some international models, as these are usually removed for performance applications. 


Can the TCFI system be used on 2008 and later touring models with electronic throttle control?

No. Due to the integration of additional functions such as ABS brakes and cruise control along with links to the infotainment systems, replacement of the original equipment ECM would involve a level of complexity (including setup and tuning) beyond the capability of most aftermarket installers. For these models we suggest using our Twin Tuner in combination with the Twin Scan Complete kit.  


Are there any special considerations that apply to the new 2007 and later models with CVO 110 CID engine?

No, the new TCFI Gen 4 fully supports the ACR system.


What is the advantage of replacing a 2007 and later ECM with your TCFI system?

All 2007 and later models use narrow-band oxygen sensors and closed loop control to maintain the AFR at 14.6 during idle and cruise. Our TCFI system with wide-band sensors allows closed loop control under all conditions including wide open throttle. You can set the AFR to any desired value from 10.5-15.0 in every RPM and throttle position cell. Other add-on systems such as the Power Commander® must either entirely disable closed loop control or restrict fuel modifications to wide open throttle cells.


What is the difference between wide-band and conventional oxygen sensors?

Conventional (narrow-band) exhaust gas oxygen sensors have been widely used in automotive applications since 1981. Conventional sensors have one to four wires and can only sense air/fuel ratio over a relatively narrow 14.5 to 15.0 range. The primary application is maintaining AFR near the 14.6-14.7 range required by catalytic converters during idle and cruise. The range of narrow-band sensors is inadequate for performance tuning. While originally developed for lab and specialized automotive applications, wide-band sensors are ideal for tuning. The 5-wire Bosch LSU 4.2 sensor used with the WEGO operates over a range of 10.3 to infinite air/fuel ratio and can be used for closed loop operation under all conditions.

For more information about wide-band oxygen sensors including the Bosch LSU 4.2, we suggest that you visit the Tech FAQ on the Daytona Sensors website at


How long does it take to install and tune the TCFI for a typical application?

The TCFI is a simple plug-in that will take about 15 minutes to install. On 2001-2006 models, you can expect to spend about 2-3 hours installing the WEGO sensors as this requires exhaust removal and welding of mounting nuts for the oxygen sensor. Starting with the 2007 models, the WEGO sensors fit in place of the stock narrow-band sensors. Initial tuning of the TCFI will probably take about 1-2 hours, with another hour spent doing final checks after the customer has logged some time on the system. If you are doing your first installation, you will need some time to familiarize yourself with the system. If you encounter problems with an aftermarket throttle body or wiring issues on a custom bike, additional time may be required to complete the installation.  


What skills and resources do I need to successfully install and tune this system?

You need to make a realistic assessment of your skill level. We have encountered issues with customers that simply lacked the requisite PC literacy and resources to be successful with the TCFI. If you have never worked with H-D® EFI systems, the TCFI is not the place to start. Tuning the TCFI requires competency in PC operation, using Microsoft Windows based programs, and basic engine tuning and fuel injection mapping concepts. The TCFI installer is assumed to be familiar with the Delphi® fuel injection system and to have access to basic test equipment and factory service manuals. We suggest that you download the TCFI Installation & Tuning Manual, study it, and make sure you feel comfortable with it before purchasing the TCFI system.

If you have experience with the Screamin Eagle® Race Tuner (SERT), you should have no difficulty transitioning to the TCFI. From a software standpoint, the SERT Tuning Mode corresponds to our PC Link TCFI and the SERT Data Mode corresponds to our TCFI Log.    

Our tech support is limited to TCFI and engine tuning issues. We cannot provide tech support for PC or Windows related issues. You need broadband Internet access to download software and firmware updates and an email account to send us files for tech support purposes. You will also require a program such as PKZIP or WinZIP to archive files prior to attaching to an email.

One often overlooked resource is time. When you are first starting with the TCFI, you will probably require 1-2 hours to read the instructions and practice with the software. 


Can the TCFI be made to work with every possible combination of engine parts?

Mixing engine parts from several different vendors involves some risk. Sometimes you get very lucky and come up with a combination that wins the dyno shootout, most of the time the system can be tuned to give good performance and drivability, but on a few rare occasions it just can’t be made to work. At this point in time, the industry doesn’t have enough of a knowledge base to accurately predict what parts will or will not work together. The problem has been around for years, but was masked by the forgiving nature of carburetors. Sloppy engine building techniques such as not bothering to CC heads and calculate the compression ratio or selecting parts for cosmetic appeal compounds the risk. 


What level of tech support does Daytona Twin Tec offer?

We have staff available to take tech support calls during normal business hours. If an initial telephone conversation cannot resolve the issue, we will ask you to email us the current setup file and a data logging file exhibiting the problem. We will try to get you a solution within 24 hours. 

Please do not ask us to read you the instruction manual, lead you through basic PC or Windows operations, or fax you pages from H-D® service manuals. We do offer an extensive Tech FAQ on engine tuning principles and we will gladly offer advice on specific tuning issues.    

Most tech support calls involve tuning issues that can easily be resolved. A small percentage of applications have underlying mechanical or parts compatibility issues that cannot be resolved by tuning alone. The most common issues encountered include inappropriate exhaust systems, mechanical/thermal problems with aftermarket or modified throttle bodies, and inadequate starting systems for high compression engines.   

We do not offer any installation, tuning or diagnostic services at our facility.  


Can you recommend some books that cover basic automotive electronics and engine control systems? 

We have listed a few suggested volumes that are available at Amazon (

Understanding Automotive Electronics (Sixth Edition) by W. B. Ribbens (highly recommended – covers control system theory)

Automotive Fuel and Emissions Control Systems by J. D. Halderman (used by many community colleges for ASE certification programs – much of the material is directly applicable to motorcycle EFI systems)

How to Tune and Modify Engine Management Systems by J. Hartman (automotive oriented – material in first 15 chapters is generally applicable to motorcycle EFI systems).

What is the difference between speed-density and alpha-N fuel injection control systems?  

The OE Delphi® system is a speed-density control system. It remains a speed-density control system even when devices such as the RevTech DFO, Dynojet® Power Commander®, or Screamin Eagle® Race Tuner are added. The TCFI is an alpha-N control system. 

Speed-density control calculates air flow (and consequently meters the correct amount of fuel to attain the desired air/fuel ratio) based on engine RPM (the speed term) and manifold pressure and temperature (the air density term). Once calibrated, speed-density systems can accurately meter fuel as long as the manifold pressure is well behaved. Speed-density system are somewhat forgiving  for minor vacuum leaks and inconsistent throttle body behavior. However, speed-density control cannot cope with the erratic manifold pressure characteristic of long duration, high overlap camshafts. 

Alpha-N systems are typically used in racing applications where the camshaft characteristics preclude speed-density control. Alpha-N control calculates airflow based on throttle angle (the alpha term) and engine RPM (the N term). In addition, most alpha-N systems make a correction based on air temperature. The accuracy of an alpha-N system is highly dependent on consistent throttle body behavior and is adversely affected by any vacuum leaks. Adding closed loop feedback from a wideband exhaust gas oxygen sensor greatly improves the accuracy of an alpha-N system. The major advantage is that  alpha-N control has no dependence on manifold pressure and is able to tolerate radical camshaft profiles. 

Speed-density versions of the TCFI are available for special applications where alpha-N control is not suitable, such as motorcycles with turbo or supercharger installations.


What is the difference between open loop and closed loop fuel control?  

Simplified block diagrams for engine control modules with open and closed loop fuel control are shown above. The open loop system has inputs for RPM, throttle position (TPS), and cold start related variables (such as engine temperature and elapsed time since engine start). Fuel lookup tables translate these inputs into a predetermined fuel injector pulse width. The fuel injectors then deliver fuel to the engine. The overall accuracy of the system is dependent on the lookup tables and the fuel injectors. If the lookup tables are not correct or the fuel injectors become clogged with deposits over time, engine operation will suffer. 

With a closed loop fuel control system, a feedback path is added to allow the system to make corrections. In the case of the TCFI system, wide-band oxygen sensors measure the actual engine air/fuel ratio (AFR). The system compares the AFR command from the fuel tables to the measured AFR from the sensors. The difference between the AFR command and the measured AFR is referred to as the AFR error. The system slowly makes corrections to the injector pulse width to drive this AFR error to zero. These corrections are stored in a block learn multiplier (BLM) table organized into RPM and TPS cells. The BLM table is continually updated. When engine operation shifts to a new cell (for example the RPM changes), the system can use the BLM value last saved in this cell as a starting point for further corrections. Over time, the system will learn the BLM value required for every cell in order to drive the AFR error to zero. This process is referred to as auto-tuning. With the use of wide-band sensors, closed loop control is possible throughout the range of 10.5-15.0 AFR.  

The 2007 and later Delphi® systems are similar, except that they use narrow-band oxygen sensors that limit closed loop fuel control to 14.6 AFR. H-D® uses the terminology “error integrator” in place of BLM.   


The block diagram above shows how closed loop fuel control is implemented in the TCFI. An initial estimate of horsepower and injector size (flow rate) is used to calculate a base injector pulse width. Base injector pulse width corresponds to the amount of fuel required to generate a stoichiometric mixture (14.7 AFR) at wide open throttle (WOT), 6,000 RPM and standard atmospheric conditions. Base injector pulse width then corrected for intake air temperature (IAT) and barometric pressure. At any given RPM and throttle position (TPS), the corrected base injector pulse width is multiplied by the values in the Alpha-N table (main fuel table), AFR table (the AFR command), front cylinder trim table (only for the front cylinder), and block learn multiplier (BLM) tables. The BLM tables store closed loop correction factors based on feedback from the WEGO system. Independent BLM tables are used for front and rear cylinders. The BLM tables are continually updated whenever the system is operating in closed loop (generally 30 seconds after engine start). The BLM tables are updated based on the AFR error (difference between AFR command and actual AFR read by the WEGO system). Additional cold start enrichment fuel is applied based on engine temperature and elapsed time since engine start. Priming fuel is injected when the run/stop switch is cycled on. A fixed pulse width injection is also used during cranking (RPM < 400). Two tables set the priming and cranking pulse widths based on engine temperature. Separate control loops are used for the front and rear cylinders. 


How does the block learn multiplier (BLM) value respond to AFR changes? 

The figure above shows how a closed loop fuel control system such as the TCFI responds to a disturbance. AFR is the air/fuel ratio measured by a wide-band oxygen sensor. The measured AFR value is initially equal to the AFR command (zero error) and the BLM value is 100% (no fuel correction). A disturbance reduces the measured AFR to about 12.5. The system responds by lowering the BLM value to remove excess fuel and thus reduce the AFR error. After several seconds, the error is again zero with measured AFR equal to the AFR command.     


How does the TCFI closed loop idle speed control work? 


The output of the idle RPM control loop is idle air control (IAC) stepper motor position ranging from 0-127. A higher IAC value allows more air flow and increases engine RPM. A table sets the idle RPM command as a function of engine temperature. This allows a higher idle RPM while the engine is cold. Closed loop idle RPM control is only enabled when vehicle speed is zero and TPS is less than the idle TPS value (usually 1%). Under open loop conditions (such as the motorcycle being driven while the engine is warming up), IAC position is continually adjusted based on engine temperature and elapsed time since engine start. When the engine is fully warmed up, the system assumes that the IAC position will be close to a nominal value (usually 30). Additional idle air (IAC > nominal IAC value) is considered the same as increasing TPS since the effect on airflow is identical. Under cold start conditions, when the IAC value is high, the system may be using the 2.5% or 5% TPS rows in the fuel tables even when the throttle is closed.


Do I need a load control dyno with exhaust sniffer? 

Regardless of what some people may claim, it is impossible to properly tune a fuel injection system on a modified engine without some means of covering the entire engine load range (from decel to wide open throttle) and exhaust gas analysis. If you use a system like the Dynojet® Power Commande®, you had better find a shop with the DynoJet® Model 250 load control dyno and optional air/fuel ratio monitor. 

You can accomplish the same result with the TCFI and  WEGO by simply riding the bike for several hours. As you run through different engine loads and RPM levels, the system auto-tunes the fuel tables.  


What applications has the TCFI been tested with?

We have tested and qualified the TCFI with engines up to 145 CID capable of producing 170 HP. With  a dual independent runner throttle body and 6.0 gm/sec injectors, the TCFI  can support engines up to about 195 HP. 


How do I set up and tune the TCFI for a particular application?

We provide setup files for common applications based on using the WEGO for auto-tuning fuel tables. We suggest that you download the TCFI Installation & Tuning Manual for more details.


Do I need to spend time on a dyno? 

Auto-tuning under actual riding conditions with the WEGO generally gives better results because the operating conditions are more realistic. Do the auto-tuning first. Then, if you want to get maximum horsepower at wide open throttle, do dyno runs to fine tune the ignition advance and air/fuel ratio.


What are the limitations of the stock throttle body?

The stock throttle body is inadequate for performance engines and will not flow sufficient air above 4500 RPM. Maximum power will be limited to about 105 HP (injector flow rating may impose an even lower limit). Our tests have shown that boring out the stock throttle body is ineffective. An aftermarket throttle body greater than 50mm is required for maximum power.  The stock air cleaner is grossly restrictive and must always be replaced for any performance application.

You can easily verify air flow restrictions with the TCFI Log data logging software. Examine manifold pressure (MAP) at wide open throttle. If MAP drops off as RPM increases, you know you have a problem.


What aftermarket  throttle bodies have been tested with the TCFI?

Aftermarket throttle bodies fall into two categories: single throttle body with siamesed runner (same configuration as the stock Delphi®) and dual independent runner.  We have tested the 53mm single throttle body system from Horsepower Inc. We have also tested the S&S Cycle VFI Tuned Induction  that is a dual independent runner configuration. There was no measurable difference in performance at high RPM and  wide open throttle between any of these systems on our 95 CID engine. However, part throttle operation between 1500 and 3000 RPM was smoother with the dual independent runner system.  

When a dual independent runner intake is combined with a dual independent exhaust (no crossover or 2-into-1 collector), the V-twin engine now operates as if it were two single cylinder engines. Problems with fuel distribution between cylinders, normally aggravated by the odd 315° and 405° firing intervals, are almost entirely eliminated. This greatly reduces the potential for tuning headaches.   


What issues have been encountered with aftermarket or modified throttle bodies?

You must budget some time to properly adjust the idle TPS setting and idle stop. Throttle blade, linkage or cable binding are often encountered with installation of an aftermarket throttle body. Our customers have also encountered thermal problems, where a mismatch in thermal expansion between the throttle blade and throttle body results in idle instability as the engine heat up. Improper installation or faulty throttle shaft seals can cause intermittent vacuum leaks that are difficult to diagnose. Note: please refer to the section on idle air control (IAC) actuator issues when changing throttle bodies on 2006 and later models. 


Will the exhaust system affect the TCFI?

Yes. The choice of exhaust system has a very significant effect. Unfortunately, many exhaust systems have been designed without any consideration of gas flow dynamics. This is true of both OE and aftermarket systems. The worst example is the OE exhaust used on “bagger” style motorcycles, where two pipes split off near the rear cylinder and then run to each side of the bike. At part throttle, air is actually sucked into the left tailpipe, wreaking havoc with oxygen sensor readings. The only solution is to install a true dual type performance exhaust.    

Our customers have reported that some aftermarket 2-into-1 systems, such as the Thunderheader can cause significant tuning headaches, whereas others such as the Supertrapp,  Vance & Hines Pro Pipe and White Brothers E-series seem trouble free. The problem with the Thunderheader appears to be over-scavenging around 2500 RPM with some camshaft combinations. Customers have reported that bending the ends of the so called “flow director” to increase backpressure at low RPM appears to help. 

WARNING: If you can insert a broomstick through the mufflers, you have the equivalent of open drag pipes and the WEGO sensors will not read accurate AFR values except at wide open throttle.

Please note that if you use drag pipes or other open pipes, auto-tuning may not be possible at idle or part throttle due to reversion effects. In this case, you have three options:

1.  Modify the exhaust to allow auto-tuning at idle and part throttle by adding a restriction such as the washers shown in the figure below or some other type of baffling. For race applications, you can remove the restriction after auto-tuning the idle and part throttle cells and then lock out closed loop operation by using the special value 0 in the BLM tables for these cells.

2.  Use a rubber hose to extend the exhaust length during auto-tuning at idle and part throttle. For more information, please contact our tech support.

3.  Manually tune the fuel tables for idle and part throttle cells. This involves trial and error and is not recommended. Closed loop operation in idle and part throttle cells must be locked out by using the special value 0 in the BLM tables for the affected cells. Use washers with an OD that is 2/3 to 3/4 the ID of the pipe (for example, 1-1/2” OD washers are suitable for pipes with an ID of 2” to 2.25”). Weld ¼-20 socket head cap screws to the washers as shown. Drill holes at the bottom of the pipes about 2” from the end and use decorative acorn nuts to secure the washer assemblies. We suggest that you use stainless steel hardware.  

The washers will reflect positive pressure waves that will cancel out the negative pressure waves reflecting from the end of the pipes. You can turn the washers just like throttle blades to provide more or less restriction. Dyno tests will show a significant increase in midrange torque and a small drop in top end horsepower as the restriction is increased.


What is the effect of an open exhaust on torque and horsepower?

Harley-Davidson® engine tuners have known for years that while open drag pipes may make the most power at high RPM, some exhaust back pressure is required for maximum torque in the low to mid RPM range. Some years back, we ran dyno tests on a 2003 Fat Boy with a 95 CID engine and our TCFI system. The exhaust system consisted of stock headers and Cycle Shack slip-on mufflers without a crossover. Two dyno runs are shown in the figure below. Dyno run 10 (red) is with the Cycle Shack muffler inserts removed, resulting in the equivalent of open drag pipes. Dyno run 9 (blue) is with 1-1/2″ washers installed near the end of the pipes as described in the preceding section. At 3,500 RPM the engine gained more than 10 ft-lbs torque with the washers installed to provide some back pressure. At 5,800 RPM the engine gained almost 7 HP with the open pipes. On the street, the bike felt much faster with the 12% additional torque available when the washers were installed.


Should the WEGO be left hooked up?

Yes! Due to the inherent limitations of sensing airflow by measuring throttle angle, Alpha-N fuel injection systems cannot precisely control air/fuel ratio without feedback from a wide-band sensor system. The TCFI is not intended to be used without the WEGO. 


Can the TCFI solve starting problems with high compression engines?

Probably not. We have also encountered cases where the customer failed to CC the cylinder heads and calculate the actual compression ratio – only to later discover that it is much higher than expected. The stock starting system is inadequate for high displacement, high compression engines. For these applications, you must install compression releases and upgrade the starter, ring gear/pinion, and battery. Based on customer feedback, the best available starting system is the combination of a Tech Cycle 2.0 KW Tornado starter, Rivera Engineering 84 tooth ring gear/pinion set, and Yuasa YuMicron CX battery. 


How do you select the proper size fuel injectors?

Single throttle body siamesed runner systems usually require some tuning effort to balance fuel delivery between the front and rear cylinder at part throttle. Fuel imbalance problems become worse with more camshaft overlap/duration and with low exhaust back pressure. Fuel injector duty cycle limitations must also be considered. The industry is just starting to recognize the extent of this issue. If fuel cannot be delivered to the correct cylinder, the trimming process will not be successful.   

Accepted engineering practice is to use the smallest possible injectors (in terms of flow) for best control at idle and part throttle. When fuel injector duty cycle exceeds 50% in a system with siamesed runners, fuel will be inducted into the wrong cylinder. For example, at high duty cycle, the front injector will be spraying fuel while the rear intake valve is still open.  The TCFI cannot correct this problem. 

Dual independent runner systems do not suffer from this type of fuel imbalance problem and the fuel injectors may be run upwards of 80% duty cycle. At high duty cycles, fuel may puddle up in front of the intake valve but will ultimately be inducted into the correct cylinder. Stock Delphi® injectors are rated at 3.91 or 4.22 gm/sec flow depending on model year. Larger injectors are available from Marren Fuel Injection ( and RC Engineering ( The following table lists conservative rear wheel horsepower limits based on injector size and type of throttle body. 

Injector Size

Siamesed Runners

Dual Independent Runners

3.91 gm/sec (stock 2006-2010 P/N 27709-06A)

90 HP

Not available

4.22 gm/sec (stock 2001-2005)

100 HP

135 HP

4.89 gm/sec (2006 Screamin Eagle® P/N 27654-06)

110 HP

Not available

6.0 gm/sec

130 HP

195 HP

If you significantly exceed these recommendations, it may not be possible to balance fuel between front and rear cylinders. The result may be a lean cylinder and possible engine damage at high RPM wide open throttle. 

On a final note, the S&S Cycle VFI Tuned Induction is supplied with appropriately sized fuel injectors that will support engines up to 150 HP. 


Why is limiting the injector duty cycle so important?

At low duty cycle, fuel is injected while the intake valve is open and air flow carries the fuel into the correct cylinder.
At high duty cycle, both injectors are spraying simultaneously and there no control over where the fuel goes.


How are injector requirements calculated?

The math is relatively simple. 

Injector flow = (HP x BSFC) / (Number of Injectors x Duty Cycle)


Injector flow is in units of lbs/hour

HP is maximum engine horsepower

BSFC is brake specific fuel consumption (assumed to be 0.45 to 0.50 lbs/HP-hour)

Number of Injectors is always 2 for a V twin type engine

Duty Cycle is 0.8 (80%) – the accepted industry standard (injector flow does not increase appreciably above 80-85% duty cycle)

For example, a 135 HP engine with 0.45 BSFC, two injectors, and 80% maximum duty cycle will require injectors flowing:

(135 x 0.45) / (2 x 0.8) =  38 lbs/hour

Injectors are commonly rated for flow at 43.5 psi (about 3 bar). The injector flow rating must be corrected based on the actual operating pressure. The Delphi® system runs at approximately 58 psi. Flow varies as the square root of the pressure:

Rated Flow = Required Flow x (Rated Pressure / Actual Pressure) 

For our example, the injectors should have a nominal rating of:

38 x (43.5 / 58) = 32.9 lbs/hour (at 43.5 psi)

Some companies rate injectors in lbs/hour, Delphi uses a metric rating of gm/sec. The appropriate conversion constant is 1 gm/sec = 7.93 lb/hour. 

Back to our example, we would require injectors with a metric rating of:

32.9 / 7.93 = 4.14 gm/sec

The 2001-2005 model year stock injectors rated at approximately 4.2 gm/sec would be adequate for this application.

You can use our fuel injector calculator to estimate your injector requirements. Use a BSFC of 0.45 for normally aspirated engines and 0.60 for turbocharged or supercharged engines. You can use a maximum duty cycle of 80% for most applications, but remember that fuel imbalance can occur in siamesed runner intakes when the duty cycle exceeds 50%. Use the default value of 43.5 psi for injector rated pressure. Unless you have changed the fuel pressure regulator, use the value of 58 psi for the actual system pressure. The calculator below will show the required injector flow rating in the three most common units. Note that the calculation is based on engine horsepower. Increase expected rear wheel horsepower figures (as would be measured on a chassis dyno) by 10-15% to arrive at engine horsepower. TCFI and Screamin Eagle® Race Tuner (SERT) systems require input of injector flow rate in gm/sec at the system operating pressure. If you have an injector rated in a different unit or at some other pressure, you can use the conversion calculator below. 


Are there known issues with the injectors on 2006 H-D® models?

H-D® has issued Service Bulletin M-1185. Most 2006 models have narrow 8° spray pattern injectors (P/N 27625-06) that cause poor cold start, idle, and cruise. The replacement injectors (P/N 27709-06A) have a 25° spray pattern. You must verify that the injectors have been replaced. The TCFI will not operate correctly with the original injectors. 


What injectors and throttle bodies are available for 2006 and later models?

The injectors and throttle body changed in 2006. P/N 27709-06A stock injectors are rated at 3.9 gm/sec – less than the 4.2 gm/sec parts used in 2001-2005. Screamin Eagle® P/N 27654-06 injectors rated at 4.9 gm/sec are recommended for performance applications. For applications over 100 HP, the 50mm Screamin Eagle® throttle body (P/N 27623-05) is an unbeatable deal. 


Can the new Screamin Eagle® 50mm throttle body be used on earlier models?

The 50mm Screamin Eagle® throttle body (P/N 27623-05) has slightly larger port diameters and is intended to be used with matching Screamin Eagle® heads or modified heads. Kuryakyn offers adapter flanges (P/N 457) that allow using the Screamin Eagle® throttle body on earlier heads. However, if you use the throttle body on 2001-2005 models, you must rewire the idle air control (IAC) connector (see details in following section).


Is there an issue with the idle air control (IAC) actuator when changing throttle bodies?

The IAC actuator and wire harness connections changed on 2006 and later models. If you install an aftermarket throttle body on 2006 and later models and reuse the original equipment IAC actuator, you will not encounter any problems. If the aftermarket throttle body requires the earlier style actuator, you must swap the wires going to pins A and C. If you install the new 50mm Screamin’ Eagle® throttle body (P/N 27623-05) on a 2001-2005 model, you must swap the wires going to pins A and C on the IAC actuator. Incorrect IAC connections will cause idle speed control to fail. This will result in erratic engine operation and the ECM setting IAC related diagnostic codes.  


Can the TCFI be adapted to work on bikes with the older Marelli fuel injection system?

A conversion harness that allows TCFI installation on Twin-Cam 88® engines with the Marelli fuel injection is available from Thayer Sales (585-762-4705). Please contact Thayer Sales for details. The TCFI cannot be adapted to earlier Evolution® engines as these lack a crank trigger.  

 TCFI Conversion Harness for Marelli Fuel Injection


Will the TCFI work with the fuel injection used on new Buell® models? 

No, the TCFI is specifically intended for use with 2001 and later H-D® models with the Delphi® ECM. The Delphi® ECM has a 36 pin connector. Newer Buell® models use a small ECM with two 12 pin Deutsch connectors. Check out our Twin Tuner for Buell® models. 


Can I use the TCFI on a custom motorcycle?

If you start out with a fuel injected Twin-Cam engine, you should not encounter any problems. You must retain all the original equipment sensors and actuators. Two areas that are often overlooked are the instrument cluster and turn signals. Like the stock Delphi® ECM, the TCFI requires a vehicle speed sensor (VSS) signal. If you are using an aftermarket instrument cluster, you can connect the VSS sensor directly to the TCFI.  With the TCFI, you can eliminate the stock turn signal/security module (TSM/TSSM) and use any aftermarket turn signal controller. The Marelli conversion harness shown above can also be used as an engine wiring harness for TCFI installations on custom bikes. 


How can an aftermarket tachometer or shift light be connected to the TCFI?

The Delphi® ECM and TCFI both have a tach signal available on pin 3 of the 36 pin ECM connector. This is a one pulse per revolution (PPR) 12 volt square wave signal with 50% duty cycle that is compatible with all standard tachometers and other RPM activated accessories such as shift lights. 2004 and later models use the J1850 data bus for communication with original equipment tachometers, however the tach signal on pin 3 can still be used if you are installing an earlier style H-D® or aftermarket tach.


How can an aftermarket speedometer be installed on 2004 and later models?

2001-2003 models have the vehicle speed sensor (VSS) connected to the speedometer. A VSS signal is routed from the speedometer to pin 33 on the 36 pin ECM connector. The J1850 data bus is used to send distance data to the turn signal/security module (TSM/TSSM) for turn signal cancellation. On 2004 and later models, the VSS is connected direct to pin 33 on the ECM. Speed and distance data is sent on the J1850 data bus to the speedometer and TSM/TSSM.

For all model years, the ECM requires a valid VSS signal for idle RPM control and turn signal cancellation. If you plan to install an aftermarket speedometer, you must maintain the VSS signal to the ECM. For 2004 and later models, you can try connecting the VSS input on the aftermarket speedometer to the existing VSS signal on pin 33 (leave the existing VSS ground and power connections undisturbed). After completing the hookup, you should test drive the motorcycle, download data with TCFI Log software, check VSS data, and verify that the ECM is still receiving a valid VSS signal. If the speedometer does not function with this hookup, it is not compatible with a fuel injected application.


Are there issues with the crankshaft position sensor air gap?

The crankshaft position sensor used in H-D® applications is a variable reluctance magnetic pickup manufactured by Delphi®. The sensor output voltage is proportional to RPM and drops off sharply as the air gap increases. The air gap must be .040 ±.005″ for proper system operation. If the air gap is greater than .045″, the ECM may not trigger correctly at low cranking RPM. The nominal clearance is .845 ±.005″ measured between the sensor mounting surface on the engine crankcase and the top of the flywheel teeth. The nominal length of the sensor is .800″ from the sensor flange to the tip. We have encountered several aftermarket crankcases with excessive clearance. You can easily correct this situation by machining some material from the bottom of the sensor flange to restore the correct air gap.