Air tank and bypass valve

The air tank on the bike serves multiple purposes. Beyond just acting as a storage tank for air, it buffets the air pulses coming out of the motor. Because the compressor pulses on an off, the air stream exiting is more sinusoidal.  Also, the intake  on the motor only opens for part of every other stroke, so the inlet creates pressure waves as well. To prevent this, typically a motor will use an intake plenum to buffet these intake pulses. Packaging constraints on the motor prevent the use of an intake plenum here, however, with proper sizing and placement, the air tank can satisfy these needs. Further, the use of an intercooler offers an opportunity to remove heat from the intake stream, offering higher thermodynamic efficiencies and as a result, more power and improved fuel efficiency.

Figure IC1: Intercooler placement

Figure IC1 shows the intercooler, a standard part from a Mazda Millenia sedan, in place on the frame under the seat. The positioning is a bit of a trade off. It places the air tank in close proximity to the motor intake, so it is usable as an intake plenum, however, air flow across the heat exchanger is reduced. Eventually, ducting will be added to deal with this air flow concern. This particular intercooler was used due to its small size. To act as an intake plenum, an ideal internal volume of 3 times the cylinder displacement is needed. The Millenia intercooler is a bit larger than this value, but not significantly. It is also the smallest non custom intercooler available at a reasonable cost.

The compressor system on this motorcycle creates pressure any time the motor is running. Because of this, there will be times when the throttle plate is closed and the motor is not consuming air, where this constant air build up would eventually cause problems. To avoid this situation, a blow off valve was installed on the charge pipe between the intercooler and the intake. This valve operates based off a vacuum signal from the motor intake. When the throttle plate closes, vacuum is applied to a diaphragm on the top of the blow off valve. This causes the valve to open and vent out from the pipe.

Figure BV1: Blow off valve in place

Figure BV1 shows the final placement of the blow off valve. This placement is the only place inside the frame perimeter the valve could fit. Also, putting the valve near the intake allows for a constant velocity flow during gear changes. At this time, the throttle plate is shut with the motor still spinning at high rpm. Without the blow off valve, air flow velocity would come to a stop. With the blow off valve, the only change in air velocity flow occurs in the short section of pipe between the blow off valve and the intake.


Leave a comment

Fuel system outline

Combustion in the motor requires both fuel and air. The fuel system of the bike required a complete overhaul for this project. In its factory configuration, the GS500 uses a pair of carburetors to regulate fuel flow for the motor. This antiquated system lacks the control needed for any sort of precision tuning and is vacuum actuated, so it will not work under the positive pressure provided by the compressor. As such, the motorcycle was switched over to fuel injection. This provides high degrees of tune-ability and is not affected by the positive air pressure in the intake stream. The same system handling fueling controls is also used to control ignition timing. This will be covered in a later section.

To convert the fuel system to injection, the gas tank was replaced to accommodate an intake fuel pump. The carburetors were replaced with a single throttle body. Major fabrication was required to create a new gas tank for the motorcycle as there is not a commercially available fuel tank for the GS500 that accepts a fuel pump.

Leave a comment

Composite gas tank fabrication

The factory gas tank for the GS500 uses a small vacuum operated petcock to provide fuel to the carburetors. There is nowhere on the gas tank that a fuel pump could easily be adapted and welding in a flange to accept a fuel pump is extremely unsafe. An empty used gas tank, even with thorough effort towards cleaning, contains fuel vapors that are easily ignited during welding. Brand new gas tanks are prohibitively expensive to purchase.  Fabricating a new gas tank offered a unique opportunity to shed significant weight from the motorcycle. This weight loss, especially in a position significantly higher than the center of gravity, leads to increased performance, efficiency, and handling. To bring this weight down, the same path was taken as the charge pipes. Carbon fiber was used to fabricate a new tank with the means to accept a fuel pump. This tank was based off of the factory tank with major work done to rework the bottom surfaces.

Figure GT1: Fiberglass mold of the bottom of the factory tank

Figure GT1 shows the beginning of the molding process from the factory tank. Several layers of fiberglass were used to replicate the bottom of the tank.

Figure GT2: Bottom gas tank mold

The fiberglass mold was removed, as seen in figure GT2.

Figure GT3: Half top gas tank mold

Due to required draft angles for mold removal, the top surface of the tank was molded in two pieces, bisecting laterally.

Figure GT4: Top fiberglass tank molds

Once removed from the tank, the top two molds connect together, making a shell of the outside surface of the gas tank. With the bottom mold from above put in place, the inside cavity of these molds is an exact replica of the space occupied by the stock gas tank and all its exterior surfaces.

Figure GT5: Foam gas tank plug

The exterior molds from the tank were assembled and the cavity left filled with a two part expanding polyurethane foam. This foam expands to fill the molds, making a foam replica of the stock gas tank. From here, the surfaces along the bottom of the tank are easily reworked to address the needs of mounting a fuel pump.

Figure GT6: Reworked bottom tank surface

Figure GT6 shows a comparison between the mold of the bottom of the stock tank and the large flat surfaces created to allow for the mounting of a fuel pump. The shape of the tank was also changed along the bottom of the tank to create a flat interface surface for later bonding of the top and bottom tank pieces.

Figure GT7: Surfacing work on the tank

Efforts were also taken to smooth and perfect the top surface of the tank. The original tank that molds were made from suffered from large dents and less than ideal surface finish. After the dents were filled, the foam tank was primered and brought to high gloss surface finish to prepare for final mold making.

Figure GT8: Bottom surface masked off for mold making

Figure GT9: Bottom covered in gel coat

The bottom surface of the mold, after primer and surfacing, was masked off, then covered in an epoxy gel coat. This provides a better surface finish than directly applying fiberglass. Several layers of fiberglass were then added to make a strong final mold.

Figure GT10: First half of top molds

The same process was followed for the top surface of the tank, again in two pieces.

Figure GT11: The final tank molds next to the tank plug

Figure GT12: Final mold surface finish

The surface finish of the final molds directly corresponds to the surface finish of the carbon parts as they leave the mold. The better the finish now, the less finishing needed to finalize the parts. With the molds finalized, the tank can be made, starting in 2 pieces.

Figure GT13: Materials needed to vacuum bag tank bottom

Figure GT14: Tank bottom mold under vacuum

Figure GT15: Tank top under vacuum

When fabricating parts out of carbon fiber, steps are taken to minimize excess resin in the layup and evacuate all air bubbles. This is especially important in cases of structural components or something that must not leak or seep. To achieve this, the tank components are vacuum bagged. The carbon fiber is saturated in resin, then applied to the mold surface. This whole assembly is then placed in an air tight bag, sealed, and held under vacuum during curing. Air pressure outside the bag compresses the layers of carbon fiber together, squeezing out excess resin and any trapped air.

In addition to concerns about leaking, there are safety issues with using a purely carbon fiber tank. Carbon fiber, while incredibly strong, tends to shatter when catastrophically damaged. In the event of a collision of significant impact, this would cause the gas tank to leak fuel onto the road. To prevent this, kevlar is added to the lay up. Kevlar, while less strong that carbon fiber, will soften when catastrophically damaged, but will not shatter. This behavior is very similar to safety glass used in automotive windshields.

For the tank, 4 layers of 2×2 twill 5.7 oz carbon fiber is used along with 2 layers of kevlar along the inside of the tank as seen in figure GT16.

Figure GT16: Kevlar tank lining

When removed from the mold, the tank has a high gloss surface finish and is extremeley strong.

Figure GT17: Top half fresh out of the mold

At this point, the tank is two separate pieces; a top and bottom; and does not have any cut outs for the fuel pump, mounts, or filler cap. Also, some minor surface finishing is needed where the mold seams fell.

Figure GT18: Gas cap bonded in place

Figure GT19: Gas cap close up

After drilling a hole, the gas cap assembly is bonded into place. The fuel pump is mounted to the bottom of the tank in a similar fashion, although with further carbon fiber reinforcement.

Figure GT20: Fuel pump with carbon fiber mounting ring

The fuel pump being used here is a stock piece from a 2003 Suzuki GSXR600 motorcycle. It has an internal pressure regulator, limiting fuel pressure to 43.5 psi.

It is mounted to the bottom of the tank with the mounting ring show above. Bolts squeeze the tank bottom between the fuel pump and the mounting ring, with the same resin used for fabricating the tank used, thickened with glass microballoons.

Figure GT21: Fuel pump in place, tank sealant applied

The epoxy resin used to make the tank is listed by the manufacture to be non reactive with gasoline. To be safe, however, the tank is coated in several layers of POR15 tank sealant. This provides extra insurance against any leaking. This is painted on with the tank halves separated, then applied again through the gas filler hole after the tank halves are bonded together.

Figure GT22: Top tank sealant

With the two halves sealed and prepped, they are bonded together, mounts are added, and a final gas tank is ready for use on the bike. Final weight for the gas tank, with the fuel pump in place, is 4.4 lbs. Nearly 25% of the stock tank’s 16 lbs weight and an approximately 5% reduction of the overall vehicle weight.

Figure GT23: Finished gas tank

Figure GT24: Finished tank on bike


Throttle body

The other half of the fuel system starts into the control systems on the bike. Key to a fuel injection system is the fuel injector, allowing computer control of a pressurized fuel stream into the motor. This fuel injector and the throttle body that houses it replaces the original carburetor. It also offers host to a variety of sensors needed for the computer control system.

The throttle body being used here is from a 2003 Suzuki SV650. This includes a 19 lb/hour fuel injector and an appropriately sized opening for the air flow needed. Unfortunately, this throttle body set up is set up for running dual throttle plates, a feature I do not need, and has the valves and sensors needed spread across two throttle bodies. The SV650 is a V twin motor, so it utilizes two connected throttle bodies.

Figure TB1: Stock SV650 throttle bodies

The SV650 throttle bodies were separate with all connecting linkages removed. The secondary throttle plates were removed. On the SV650, one throttle body houses the throttle position sensor(TPS) and the other houses the idle air control valve(IACV). Both of these assemblies are needed on the bike, so IACV was removed from the unused throttle body and adapted to work on the used throttle body.

Figure TB2: Isolated throttle body

When the secondary throttle plates are removed, holes are left in the throttle body. These holes must be plugged to allow for positive air pressure to be achieved. Additionally, the throttle body has castings that can be used to mount the IACV, however, spacers need to be fabricated to properly position it relative to the throttle.

Figure TB3: Throttle body plugs and spacers

Plugs and spacers were machined for the throttle body from aluminum stock on the lathe. This was done manually, unlike the valve housings which were done with CNC capabilities.

Figure TB4: Throttle body plug in place, mounts for the spacers circled

Figure TB5: Spacers in place, IACV linkage circled

The IACV is an idle control valve. It does this by slightly opening the throttle as the bike warms up to raise the idle. An actuator attached to the throttle plate is pressed by the IACV, limiting how far the throttle can close. In figure TB5, the fabricated linkage is circled. This linkage is normally found mounted to the unused throttle body.

Figure TB6: Throttle body with IACV mounted

In figure TB6, the throttle body is shown with IACV spaced and mounted. Also seen is the orange fuel injector. At this point, the throttle body is ready for use on the motorcycle.




Click Older Posts below or follow the index on the right at the top of the page to continue

Leave a comment

Control unit and other electronics

A key part of the successful completion of this motorcycle is the integration of the electronic controls. Fuel injection requires a computer control system to operate. In addition to the computer control system, a handful of sensors were added, along with a complete reworking of the electrical system.

To handle the computer controls for this motorcycle, the Megasquirt II ecu system was purchased. This is a do it yourself ecu that shows up as a blank PCB board. This ecu system was chosen because of its low cost and its highly adjustable nature.

Figure ECU1: Megasquirt system ready for assembly

Figure ECU2: Assembled Megasquirt and relay board

The Megasquirt ecu must be configured in hardware for certain conditions; type of injectors, type of IACV, ignition system, etc. This system handles all of the fuel control needs, ignition control needs, and communicates with an external PC for tuning purposes. Along with the ecu, a relay board was assembled. This contains the needed fuses for the electronically controlled components of the bike, allows for a hub for all of the wiring, and provides relays to supply power to the key systems. For the operation of this system, four key sensors are added. A throttle position sensor, located on the throttle body, measures percentage of throttle opening. A manifold absolute pressure sensor, located at the ecu, fed from a vacuum port after the throttle plate, measures load on the motor and positive pressure provided by the compressor. This same vacuum port provides a vacuum signal to the blow off valve. An intake air temperature sensor in the intake pipe shortly upstream of the throttle body reads the temperature of the compressed intake air. This allows for fuel corrections based on different air densities. Finally, a wideband oxygen sensor with a separate control unit measures the oxygen content of the exhaust gases. Exhaust gas analysis is used in real time tuning of the fuel maps. This tuning is key to the vehicle operating in a reliable, efficient manner. An incorrect fuel map will lose power, increase fuel consumption, increase emissions, and can catastrophically damage the motor.

Figure ECU3: Completed electronics; TechEdge wideband controller, Megasquirt ecu, relay board

Because space is such a concern and the components in the ecu are heat sensitive, the electronics are mounted under what was the passenger seat of the motorcycle.

Figure ECU4: Tail mounting of electronics

Figure ECU5: Carbon fiber mounting plate

Figure ECU6: Carbon fiber seat cowl

A carbon fiber plate was fabricated to run under the seat for the electronics to mount on. The passenger area of the seat was hollowed out to provide ample space for the components with a carbon fiber shell added to further protect the components.

The addition of all of the piping under the seat filled the space normally taken up by the stock battery. The stock battery is a 12v lead acid battery that is extremely heavy, prone to draining in a short period of time, and occupies a lot of space. For this project, a new battery was needed. A 4 cell LiFePO4 battery was fabricated from 3.3 V cells. This provides sufficient amperage for starting and running the bike, is much safer than a lead acid battery, significantly reduces weight, and is far easier to fit on the bike. The battery tucks up nicely between the end tanks on the intercooler.

Figure ECU7: LiFePO4 battery pack

Final weight for the battery is around 1.1 lbs, about 10% of the stock battery.

Leave a comment

Finalized mechanical system

The fabrication up to this point completes the mechanical system for the internally supercharged motorcycle. The following photos show the motorcycle with the mechanical systems needed for the engine to operate in place, short of a few hose connectors and bolts.

Leave a comment


With the mechanical systems in place, work moves to the computer for tuning of the system. Tuning in this case is done using the Megatune software package that is provided with the Megasquirt ecu system. This software allows for direct connection between a personal computer and the computer on the motorcycle. Once connected, real time information about the motor, including measurements from all of the sensors are available. While tuning, key programming can be changed immediately.

Figure T1: Megatune screen shot

With the engine running, the computer will datalog values in real time for making adjustment to the programmed maps.

Figure T2: Datalogging with Megasquirt

Figure T3: Megatune fuel map

To start the vehicle, however, the program must be configured to some specifics about the engine. Cylinder count, displacement, fuel injector specifications, and more are used to generate a base map for starting the tuning.

Leave a comment