Since last time a bit has happened around here. The original turbocharger was found to have bad oil seals when we brought the pressure up to operating specs. This caused oil to leak around the compressor and conversely was introduced into the combustion chamber. A quick test of the engine looked positive, but the smoke screen it created was very thick. A newly remanufactured turbo was purchased off of Ebay through a great seller and was shipped out quickly to us to get the engine back up and running.

The new turbo is a VT-50 model, and is basically and updated version of the ST-50 we were using previously. The VT-50 has compressor guide vanes and should be capable of flowing a bit more air in a more efficient manner.

Unfortunately for the build, there were complications. As stated previously in the build, the combustion chamber was built smaller than is normally acceptable. We were really pushing the limits of what we though could be done, and pushed a little too far. The plumbing used for the combustion chamber was simply not adequate to flow the amounts of air we needed to bring the engine up to full operating speeds. With less air flow, the engine will get hot very quickly and will go into surge. This is when the air backs up in the compressor and causes a stagnation of flow. The reduced output flow of the compressor then heats up quickly. These hot gasses can weaken the metals used in the construction of the turbine blades and are not something you typically want to see in a turbine engine.

There is good news, however. The engine did run. It was loud, mean, and generally nasty. Just the thing for a jet powered motorcycle. Since we were aware that there could be problems with the small combustor, we have been ready to build a second larger combustor all along. The second combustor is being built now, and there should be some results from testing in a few weeks. The new combustor should be more than capable of flowing the gasses, and we will use what we have learned from the testing of the first one to ensure that we have success.

Below are some pictures of the new turbo and complete engine mounted in the stand used for testing.

The side of the engine with the new turbo visible

As is clearly visible here, the new VT-50 turbo has a larger compressor housing when compared to the ST-50 models. The turbos are pretty much identical otherwise. You will notice that the length and mounting points are the same, and the combustor bolted on with no problems. This is especially handy in being able to choose from different turbos to adjust power output, and also makes replacements easier to find.

The same mounting will be used

The mounting plate fabricated to to mount the original ST into the frame fits the VT perfectly. You can also see the exhaust flange which was purchased locally at a local large truck parts supplier.

The new turbo inlet

Although the compressor inducer (the visible blades in the turbo compressor) is the same size as the ST-50 turbos, the total flared inlet is a bit smaller. You can see this in the mounting plate on the front of the turbo. The ST-50 turbo opening went all the way to the edges of the round opening of the mounting plate. The VT-50 turbo is about 1/4" shy of making it to the edge. This will not affect performance in any way, as the VT is supposed to flow more air.

The oil lines and flow valves

The oil lines that supply the turbo with its lubrication and cooling are visible here. The oil is pumped up from the tank underneath, through a valve and on to the turbo. This has since been changed from the braided lines to hard metal lines to avoid them melting in the high heat. The system also uses an oil bypass now to control the pressure to the turbo. The system above uses the valve to control pressure by closing the valve to reduce pressure to the turbo, and opening it to allow more pressure to the turbo. Reducing turbo pressure causes a back up pressure on the pump though. The new bypass system has a tee fitting in the line, with one side going to the turbo and the other going to the valve and then dumping back to the tank. To increase pressure to the turbo the valve is closed, and to reduce it the valve is opened. This system relieves the pressure on the pump by allowing the unused oil to flow directly back to the tank instead of building back pressure in the oil lines. As I said, the system above was wrong for many reasons and should never be attempted. Nor should anyone use flexible lines so close to the turbine. If a line was to blow off, the oil hitting the hot turbine would surely cause a fire.

The support equipment

Below the engine on the cart from left to right is the shurflo oil pump, the battery, the oil tank (silver can) and on the ground is the temperature sensor (yellow). This is a very sparse set up used to test the engine very quickly, and as stated previously has since been changed to hard metal oil lines. An electrical harness with switches was also added to the cart for easier control of the pump and ignition unit. The black hose leading to the right is the fuel supply from the propane tank.

The rear of the engine

Another view of the support equipment. The battery is behind the pump, and as you can see it is smaller than most builders use. It is a sealed gel cell battery as is used in burglar alarms, electric scooters, and computer back up power supplies. It is 12 volts and is rated for 12 amps. I have had no problems with it supplying power to the oil pump for an hour while using it to power the ignition system as well.

The exhaust turbines of the engine

You can see the temperature probe on the left hand side of the engine outlet. IT has been very useful in the testing of the engine to make sure that the exhaust temperatures do not exceed safe operating limits. The oil film visible on the metal parts here is the result of testing the engine with the previous ST-50 turbo. The small pipes from the combustor to the turbine inlet are what I believed caused the compressor surge. Hindsight is 20-20 isn't it?

The new combustion chamber should be ready for testing in a few weeks. Hopefully the lessons learned from this combustor will prove beneficial to making the next one a success. I have no doubts that I can build a successful combustor, the trick is getting a combustor small enough for the bike to be successful. Remember the space constraints that I have to work with.

With all of the other parts needed to run the engine in place and ready to go, progress should pick up somewhat. Special thanks goes out to our sponsors and friends who have worked with us to make the project get this far. We promise not to disappoint everyone. The sound of this engine running shook the very ground it sat on, and will only get better from here on out.

I would also like to thank www.hackaday.com for linking to our build from their website. Our traffic has increased a lot since then to say the least. Potential sponsors, now is a good time to get on board! Those interested in sponsorship should contact me directly via email at russwmoore@badbros.net. Until next time, thanks for following along.

Russ W. Moore
Bad Brothers Racing

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