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Turbo Exciter Kart:

225cc four stroke turbocharged go kart


The gas turbine engine can't be beat when it comes to outright performance. And my Formula Turbokart proves that a gas turbine can be used effectively to power a racing kart. However, there are times when Formula Turbokart is too intense for me, and I need something a little more user friendly. So, a while back, I picked myself up an Exciter Kart, which is referred to as a "TaG Spec Shifter Kart. TaG is short for touch and go, which basically means it has an electric start. Unlike an out and out 2 stroke shifter kart, which can be almost as much a handful as my turbine kart, an Exciter Kart is a more user friendly version of a shifter, with a docile and reliable air cooled 4 stroke Yamaha engine of 225cc displacement, which produces around 23 horsepower. The best part about it is the electric start and onboard battery and alternator, so you can just gas and go. Just roll it off the trailer, hit the start switch, shift into gear, and you're off.

However, lately I've been feeling like it could use a little more horsepower. Not a whole lot, maybe 10 more horsepower or so. I chose to accomplish this by adding a turbocharger.


Turbosupercharged Engines:

This website is primarily focused on gas turbine engines. However, lately I have become interested in another type of gas turbine; the turbocharger, or exhaust gas turbine driven supercharger. Turbochargers combine with conventional piston engines to provide extreme levels of performance while still maintaining the drivability and ease of use of a typical piston engine.The turbocharger is essentially a centrifugal supercharger, which is design to pressurize the intake manifold of a conventional piston engine, allowing it to burn greater quantities of fuel per unit time to make greater levels of horsepower from a given engine displacement. The neat thing about a turbocharger, and the thing that separates it from a mechanical supercharger, is that the centrifugal compressor is driven by a turbine, which extracts energy from the engine's exhaust gas; which normally would be wasted as heat to the atmosphere. The turbine, usually a radial inflow turbine, is driven at very high speeds by the expanding exhaust gas, and that turns a shaft which drives the compressor, similar to the way the turbine drives the compressor in a gas turbine engine.

Turbocharging is a great way to make extremely high levels of power from relatively small displacements. Turbocharged diesel engines have specific outputs similar to naturally aspirated gasoline engines, and turbocharged gasoline engines can have power to weight ratios as good as or better than gas turbine engines, at a cost of reliability at really high levels of boost pressure. Plus, adding the word "Turbo" to anything automatically makes it 150% cooler.

To learn more about turbocharged piston engines, check out this page.



Anyway, this simple project would be to add a turbocharger to the engine on my Exciter Kart, to increase the level of performance. But before we could do that, we first wanted to do some acceleration tests on the Exciter Kart, to set a baseline performance and determine how much we would have improved by.


Update 5/21/06

The first step was to set up a performance baseline. We temporarily installed a GTECH-Pro SS peformance meter to record our runs. We recorded a total of five runs and recorded the performance of our runs. We took the best value of each run.

0-60 acceleration: 4.2 seconds

1/4 mile acceleration: 15.5 seconds @ 75 mph (1/4 mile performance would have been better but the stock gearing offered a terminal velocity of 75 mph which slowed us down.)

Estimated Horsepower: 22 horsepower

Decent performance, but we wanted more! Into the "shop" then...


Now, it was time to turbocharge the engine.

First, we had to figure out what we were going to do with fuel delivery. Ideally, electronic fuel injection is the way to go when turbocharging a gasoline engine. It allows you to maximize performance as well as drivability, and with electronic boost controls can make an engine even more flexible and powerful. For a true, super high performance turbocharged engine, electronic fuel injection should be used.

However, since our engine was carbureted, and it would be too difficult and beyond the scope of the project to try to adapt or develop a fuel injection system for this little engine, we decided to go with the stock carburetor. There are two ways to approach turbocharging a carbureted engine. The first is a "blow through" system, and the second is a "draw through" system. A blow through system, where the carb is mounted after the turbo can theoretically provide higher levels of power, primarily because it allows the use of an intercooler, and the blow through system also allows for improved engine response, better starting and idling characteristics, and overall better operation. However, in a blow through system the carburetor must be extensively modified so that it can operate under higher than atmospheric pressure. A draw through system, where the carb is mounted before the turbo, is much more simple because the carburetor can go pretty much unmodified. It is just flowing larger quantities of air and fuel than it would normally. There are certain drawbacks to a draw through system, but for the purposes of keeping it simple, I decided to go with a draw through system.


Next, I had to find a turbocharger. This was harder than I thought, because there are no turbo engines in production of such a small displacement, and I basically had to find the smallest turbo with the smallest A/R ratio that I could find. My search was over when I found this little gem on Ebay. According to the data plate, it is a Lombardini TD025M-03C turbocharger with an integral wastegate. It's really hard to appreciate from the pictures just how small this little turbo is, but trust me, it's tiny. Even with the size of the turbo, due to the small displacement of the engine, I don't expect it to spool up too quickly, so it won't add a whole lot of low end torque to the engine, but instead, more top end horsepower. This is just as well, because I will not be lowering compression ratio, and this Yamaha engine has plenty of low end torque as it is. Where it really needs help is in the top end, and the turbo should do nicely here.


Next, we'll have to figure out boost limits, boost controls, and also how we are going to lube the little turbo. Stay tuned...


Update 6/05/06-

We've removed the engine from the eXciter Kart and brought it into the shop. The first thing we will do is locate where the turbocharger turbine will mate up to the exhaust outlet pipe. Then we will remove the exhaust, weld a flange onto it, and bolt up the turbocharger. Then we will be able to focus on the intake plumbing, including mounting the carburetor to the compressor inlet, and run a compressor discharge pipe directly into the engine intake port.

The stock wastegate actuator is set to crack at around 17 psi, indicating that it was probably used in a Diesel application. Since we will be doing very little in the way of modifications to the engine, 17 psi is way too high and will likely destroy the engine. Instead of modifying the existing wastegate actuator, I located a wastegate actuator that will open at 8 psi. We will have to fabricate a bracket to mount the new wastegate onto the turbo, since the size and layout of the actuator is different.

Lubricating the turbo should prove to be fairly simple. I have located a pressure outlet on the engine that will serve as an adequate feed to the turbo. I will have to run a gravity drain line back into the oil sump as well.

Stay tuned for more!


Update 6/22/06-

As you can see from the pictures below, we have preliminarily mounted the turbo assembly onto the engine. I cut off a section of the exhaust outlet pipe, made up a homemade flange to mate up with the exhaust housing, welded it to the exhaust pipe, and then bolted up the turbocharger to the exhaust pipe. I had to clock the turbine to get the compressor oriented the way I needed it.

The next step is to fabricate a mounting bracket to support the turbo. Then we will have to make a special mounting bracket for the wastegate actuator. After that I will hook up the pluming on the intake side, where we will relocate the carb.


Update 8/13/06-

We have now relocated the carburetor to the compressor inlet using a short section of silicone hose and some clamps. We have also mounted the new wategate actuator with a bracket fabricated out of steel plate. I will cut holes in the steel plate to lighten it and then put a coat of paint onto it to finish it off. I need to make another supporting bracket which will go from the wastegate actuator plate to the engine. The next step is to run the oil lines from the motor to the turbo and then back. Then we will connect the compressor discharge to the inlet port of the engine.

In the pictures you will notice the exhaust downpipe. I decided to use as large a diameter downpipe as possible to minimize backpressure and heat. The downpipe was made out of standard mild steel exhaust piping.


Update 6/22/07-

Finally, a break in my busy schedule has allowed me to put some more time back into my projects. Since the last update, much has been done. First, we fabricated a charge pipe to deliver the compressed air/fuel mixture from the turbocharger to the inlet port of the engine. While doing this, I had somewhat of a revelation:

Any time you increase the airflow into the engine, you must also increase the fuel flow commensurately. A draw through carburetor set up should do this automatically. However, with a turbo engine, any time you add boost to the equation, you must enrich the mixture beyond what you have to do in a non turbo engine. The vaporization of the added fuel helps keep the charge cool which prevents detonation. Originally I was going to change the jets on the carburetor to make the mixture richer, but the major downside with doing this is that the mixture then becomes rich all the time, even when you are off boost and you don't need the extra fuel. Also, changing jets would have made tuning the fuel flow a little difficult since I don't have any kind of dyno to measure the engine under load, and measurement might be hard while driving the kart.

Engine with charge pipe fabricated and installed

Then I had an idea. I decided to leave the carburetor alone. The carb could provide all of the fuel the engine would need when running off boost, making the engine idle better and have better throttle response. Fuel enrichment under boost would come from a fairly simple electric fuel injection system that I came up with. The injection system would only provide the additional fuel flow required to make the mixture richer when running under turbo boost. The carb would still deliver the base fuel flow to the engine, but the injection system would provide a supplement.

New fuel system schematic

The system works as follows. An electric fuel pump from an automotive electronic fuel injection system takes fuel from the tank and puts it under pressure. The pump is capable of delivering up to 125 psi of fuel pressure. The pump feeds a rail with a BEGi rising rate fuel pressure regulator on the end of it. The pressure regulator maintains a base pressure of approximately 30 psi in the rail and bypasses the rest of the fuel back to the tank. Fuel is taken off the rail and split off at a tee. One leg of the tee goes to a low pressure returnless fuel pressure regulator, designed for carbureted fuel systems, which lowers the pressure down to 5 psi to deliver it to the carburetor bowl. This allows us to eliminate the stock fuel pump, which was a mechanical pump operated by manifold vacuum. The other leg of the tee goes to a shutoff solenoid, then to a manually adjustable needle valve, and then finally to a fuel nozzle with very small delivery jets. The fuel nozzle is mounted directly into the charge pipe, to deliver extra fuel directly to the engine's inlet port. It is important that the fuel nozzle has an extremely small orifice, since the amount of fuel that will come through the injector is very small. Remember, this fuel is in addition to the base fuel flow that will come out of the carburetor, to provide a richer mixture under boost. Overkill? Perhaps...But I like experimenting with new gadgets, and I believe that this system will allow me to run even higher levels of boost with this engine. It will be interesting to see just how much more power I can get out of this little Yamaha engine.

Electric fuel pump and filter

The rising rate of gain fuel pressure regulator increases fuel pressure at an exponential rate to turbo boost pressure, providing fuel enrichment for safe boosted operation. Click here to learn more about how it works.

Low pressure regulator for carburetor feed, and charge pipe mounted hobbs switch, which opens the fuel injection solenoid at 1 psi of boost. Hose barb sends compressor discharge signal to the rising rate regulator

Electric solenoid and needle valve for mixture adjustement

Fuel nozzle, taken from a starting fluid injector from a Diesel engine. An extremely small .012" orifice controls fuel flow and provides good atomization. The white chalk mark on the charge pipe indicates where the nozzle will be installed. The hose barb to the right is for the all important boost gauge

Got boost?

In operation, the system should work something like this: At idle and small throttle openings where no boost is being made, the carburetor delivers all of the fuel that the engine needs, because the fuel injector solenoid valve is closed. Since the carb is untouched, as well as the compression ratio of the engine, the engine should respond very well when running off boost. The electric fuel pump and low pressure regulator will keep the float bowl in the carb full at all times. Then, when you floor the throttle, the conditions will change. At first, the carburetor will still be providing all of the fuel. But as the turbo spools up and starts producing 1 psi of positive pressure, the pressure will trigger a hobbs switch, which will open the solenoid valve to the fuel injector. At first, 30 psi of fuel pressure will be delivered to the injector nozzle. Then, as boost pressure builds, the pressure will send a signal to the rising rate fuel pressure regulator, which will begin increasing fuel pressure at the fuel rail exponentially with boost pressure, making the mixture more rich as maximum boost pressure of 8 psi is reached. Once 8 psi is reached, the wastegate will open, bypassing some exhaust gas around turbine, maintaining 8 psi and a rich mixture all the way up to redline, or when I release the throttle. The manual needle valve will allow me to tune the fuel enrichment as I drive. I am fairly confident that this system will allow me to run higher levels of boost safely (with racing fuel), and I am very excited to test it.

Once the fuel nozzle is installed, I will mount the engine back into the kart frame, and begin to hook up all of the plumbing and wiring to make the system work. Update coming soon.


Update 7/22/07-

I have been busy this past month working on getting the Turbo Exciter Kart ready for its first test drive.

First, I mounted the engine into the kart chassis, and reconnected all of the existing wiring and linkages.


After that I installed the complete turbo system and reinstalled the seat to check for clearances when installing all of the hardware for the new fuel system and turbo system.


I started by installing the boost pressure gauge. I fabricated a pair of mounting brackets and mounted it on top of the front fairing. I will run the vacuum hose and the wiring later on.


Next, I found a good spot under the front fairing for the electric fuel pump and drilled four holes in the floor pan to mount it. I mounted the fuel filter under the steering column. It's a tight fit under there, but it is out of the way.


Next, I fabricated another bracket to mount the fuel enrichment solenoid right on top of the engine. The solenoid will be energized by the hobbs switch, and will initiate fuel enrichment when running under boost.


The pictures below show the location that I selected to mount the rising rate of gain fuel pressure regulator, which will use a boost pressure signal to meter the level of fuel enrichment. I drilled four small holes in the frame, and then installed the mounting bracket after trimming it and putting a coat of black paint on it to finish it off. What is not shown is the location of the low pressure fuel regulator, which will send 5 psi fuel to the carburetor bowl. I mounted the low pressure regulator where the old mechanical fuel pump used to be, on the engine.


Below is the fuel I will be using. Since I am running a high compression ratio and turbo boost, I am going to need very high octane. This leaded racing gasoline has an octane rating of 116. Don't try this in your car, although at around $18/gallon, who would want to?


All that's left now is to run all of the plumbing for the fuel and turbo systems, and then do a small amount of wiring. Once we put the finishing touches on, then we will be ready for our first test run. Stay tuned!


Update 8/1/07-

The next step on the Turbo eXciter Kart project was to finish up the fuel plumbing and the wiring to operate the new fuel system, and then put the finishing touches on the kart in preparation for the first tests. Here are a few pics of the kart I snapped during this process:


I fabricated a small switch panel in front of the HP regulator to mount the fuel pump switch and a switch that I could use to manually trigger the enrichment solenoid, like, for example, to aid in cold starting. I adjusted the rising rate regulator to a baseline setting, all the while observing how the fuel spray pattern out of the fuel injection nozzle changed with varying pressures. I also simulated positive manifold pressure to adjust the fuel pressure curve under boost, and experimented with needle valve settings.

After that, I buttoned up all the wiring and hoses, and put the remaining pieces of bodywork on. The build was now finished, as shown in the pictures below:

With the kart completely built, it was time to fire up the engine for the first time in its new configuration. I flipped on the fuel pump switch, set the choke, and hit the starter. The engine sprung to life almost immediately, which was a pleasant surprise. I filmed a quick video of the first start and idling. The video can be seen here.

Some observations of the first engine run:

With the choke on, the engine started the first time, and every time, immediately. It also settled into a nice idle fairly quickly. I noticed that the engine ran a lot smoother with a little bit of choke on. When I took off the choke completely, the engine started to run really rough and even knocked when I goosed the throttle, despite the high octane fuel. With a little bit of choke, throttle response was immediate and smooth, and the engine settled into a stable idle. I'm assuming that the turbine in the exhaust path is creating enough back pressure and heat even at idle, that the mixture needs to be richenend a little to smooth it out. I am glad I added a supplemental fuel injection system to really make the mixture richer when running the boost.

The sound of the engine is incredible at idle. Without a muffler, it is very loud. A turbo usually provides a little bit of muffling, but not much, as my neighbors can attest. You can sort of hear the turbo spooling up and down when you rev it, but I can't wait to get into the seat and really run it hard to hear and feel the turbo power.

After a little bit of tweaking and tuning, expect a test run with a video and a full report, but so far, I am very encouraged with what I am seeing.

Stay tuned...


Update 8/29/07-

I put the finishing touches on the Turbo eXciter by tricking it out with some custom made "Turbo" decals which I applied to the bodywork. I also made a few adjustments to the jet needle on the carburetor to richen the mixture up slightly to allow the engine to run smoother.

Then I filled up the gas tank, inflated the tires, charged the battery, and got the kart ready for the first test run, which would take place at a secret location. Here are some pictures of my new turbocharged shifter kart next to its big brother, Formula Turbokart. The two of them look mean and ready for action. While the eXciter kart could never compete with JFS-100 powered Formula Turbokart in terms of outright performance, the nice thing about the eXciter is that it will be more user friendly, easier to drive, and ultimately probably more fun.

With the kart loaded up in the pickup truck, I left early sunday morning to test the kart. I unloaded it, and attempted to start it. Unfortunately, while I could get it to start, I couldn't get it to run smooth, maintain a steady idle, or keep it from stalling. I tried to jump on and take it for a ride straight away, but I knew something was wrong, and finally it stalled out on me and wouldn't start again. I aborted the test and headed back home.

Back in the garage, a little bit of investigation revealed that the rubber boot on the inlet port of the head, to which the compressor discharge pipe connects, had ripped, probably when I was tightening down the hose clamp. The ripped boot was allowing a massive vacuum leak, and I'm surprised that the engine even fired up at all. I fabricated a new piece out of metal and will get it replaced ASAP. Then I will make another attempt at a test run, and hopefully get some video of the kart running, probably in the next couple of weeks.

Keep watching this space!


Update 9/30/07-


I am pleased to announce that I have completed the first successful test of the Turbo eXciter Kart, and while the test was not perfect, and there is much room for improvement, the first test was very promising. Unfortunately, I was not able to shoot any video of the kart in operation, since I did not have anyone to help me. Hopefully I will be able to get some video footage on subsequent tests.

After unloading the kart, the engine started immediately, and I hopped on, shifted into first gear, and eased out the clutch. The kart rolled away smoothly and was very responsive to the throttle and I just tried to take it slow at first. After warming it up a little, I started getting into the throttle a little bit more aggressively. I noticed that the boost buildup was very linear to the throttle pedal, almost too much so. It is almost as if the turbo is too small for this engine, which is hard to believe. There was no lag to speak of, and the boost would immediately build to 7 psi where it would stay at higher throttle openings, meaning that the wastegate was doing its job, although it is questionable if the wastegate will be able to hold off the boost once I get the fuel tuning right.

Eventually I decided to go to full throttle. At full throttle, the engine seemed to pick up a stumble, as if it was getting too much fuel, even though I had my supplemental enrichment system turned off completely. If I backed off the throttle to around 70% opening, the engine would pick up hard acceleration again. The acceleration felt as strong, if not a little stronger, than the stock motor, although the potential for more performance is obviously there if I can figure out the fueling. It seems like if I get it to idle smoothly, it becomes too rich in the top end, but if I try to lean it out, it runs really rough at idle and stalls out. After some good running, the test was cut short by a bad oil leak and the sprocket slipping off the keyway on the rear axle. Both issues were easily fixed, and I have made some tweaks to the carburetor to try to get the engine ready for the next test, which should come in the next couple of weeks.




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