Temperature testing the Radium Fuel Surge Tank

After countless CAD models, design revisions, rapid prototypes, a custom aluminum extrusion and working with our machinists, we have our first batch of Fuel Surge Tanks (FST). The FST is designed to augment a factory fuel system. It works by ensuring a constant and reliable supply of fuel to the engine under all conditions. Each fuel surge tank contains a high performance fuel pump that provides extra fueling capability.
Exploded view showing Fuel Surge Tank with internal fuel pump

Before releasing the system for sale, we thoroughly tested the device. A concern for the FST design was the potential heat that could transfer to the fuel from the internal fuel pump. Our testing was to see if the surge tank would act as a fuel heater.

The (raw aluminum) prototype, fully assembled and ready to test

Testing utilized two different fuel system configurations to evaluate and compare results. The first setup used the Radium FST with an internal Walbro 255lph pump. The second setup used an external Walbro 255lph pump without a surge tank. Both tests used white spirit as the working fluid. White spirit is a commonly used solvent found in fuel injector and fuel pump cleaning processes and has similar properties to gasoline. The minimal use of only 1.5 gallons of fluid would simulate a low fuel condition and make temperature changes more immediate.

Fuel Surge Tank plumbed for testing

We chose to operate our high pressure line during both tests at 4Bar (~58 psi) using a Radium Fuel Pressure Regulator. This pressure was selected to fully load the pump to create the worst case scenario where the pump is exerted to the maximum work load and heat levels peak.

High pressure line entering regulator (blue fitting), temperature probe plumbed into opposite side port

Ambient temperature was recorderd and was within 1 degree C during all tests. Fluid temperatures were monitored at the same locations in both setups and were measured using thermocouples in the reservoir(T1) and in the high pressure line(T2) via a port on the regulator.

Power was supplied to the pumps using a 12V battery with an attached variable rate charger. This allowed constant voltage with varying electrical loads. The tests ran at a steady 12.3V and temperatures were recorded every 5 minutes for 90 minutes.


The first test used the Radium Fuel Surge Tank setup (shown below). In this test, the high pressure line that normally feeds the fuel rail and injectors is sent directly to the fuel pressure regulator and returned to the FST.

Test Setup 1. Utilizing Radium Fuel Surge Tank (Blue)


The second test consisted of the same basic set-up. This time the reservoir's pump fed an external (in-line) Walbro 255lph pump (shown below) rather than the Radium FST. This eliminated any heating effects from the external surface of the pump.

Test Setup 2. Utilizing a Walbro external pump

The results were quite surprising. We speculated that the FST internal fuel pump would transfer more heat to the fluid due to its submersion. The results strongly proved otherwise...

The chart above shows the fluid temperatures (average of T1 and T2) over time. It is clear that having the pump internal to the Fuel Surge Tank (blue line) does not excessively heat the fuel. In fact, it appears that the FST might provide some extra cooling that does not occur with the external pump (red line).
The yellow line represents a single pump in the reservoir using the same fuel pressure regulator, which simulates the factory fuel system.The green line shows the ambient temperature.

These results show that over 90 minutes the fluid temperature increases 20-30 degrees celcius. This will not have any noticeable effect on engine performance. Fuel density only decreases by roughly 2%. When considering the air/fuel ratio, there is typically 12 times more air than fuel in the cylinder which would make any effects even more inconsequential.

Based on the test results, we are confident about releasing our Fuel Surge Tanks for sale. We will be releasing FST kits for specific vehicles and applications. We will also have FST that utilize other popular fuel pumps including the Bosch 040 and Bosch 044.

We will be publishing a more detailed informative blog entry on the FST very soon.
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How It's Made: Radium Cast Downpipe Elbow

Constructing a turbo kit for a specific vehicle involves carefully selecting the right combination of custom and off-the-shelf components and combining them together in a way that balances performance, cost, and packaging. One-off turbocharger conversions are relatively easy, however designing a turbocharger kit that must be consistently replicated many times over in an economic fashion, is much more challenging. Luckily, that is what Radium Engineering excels at.

Here at Radium Engineering, our Lotus Elise/Exige turbocharger kit has been in development for over 1 year. Why so long? We have had our protoype turbocharger kit up and running since July 2010, however, moving parts into production takes a long time. This article outlines an example of the development that went into a single component of the turbocharger kit, the downpipe elbow. Now multiply that procedure many times over for all different custom designed components in the turbocharger kit and you can see the amount of time adds up quickly.

The downpipe elbow attaches to the exhaust outlet of the turbine side of the turbocharger. It is the piece that channels exhaust gasses exiting the turbocharger into the exhaust/muffler system. This part sees extremely high temperatures and must be designed to withstand them without warping, cracking, or degrading in any way.
We decided very early on that this piece would best be cast out of stainless steel due to its anticipated complex shape.
However, tooling required to produce a casting is very expensive and we were not going to make that investment without positive testing to back up the concept. Additionally, if we were going to make this large investment, we wanted this part to work on several different turbochargers without modification.

This is a behind the scenes look into what went into designing and producing the Radium Engineering downpipe elbow:

The first step in the process is to hand fabricate a pipe from stainless steel tube using off the shelf flanges and mandrel bends. This part is used to verify the performance and serve as a jig for measuring fitment of the elbow. The part shown here is ceramic coated. Notice how it transitions from bell mouth to 3" round.

Once the performance is verified, the hand fabricated part is measured with our FARO arm. This device accurately measures the part to within 0.005 inches in 3D space and creates exact data in Solidworks which serves as the foundation for the CAD model.

Based on the 3D data from the FARO arm, a 3D CAD model is created with Solidworks. With investment casting chosen as the maunfacturing process, much freedom in the shape of the part was allowed. Investment casting does not require draft or a parting line like other less expensive casting methods such as sand casting. The CAD model is fine tuned and all detail is added to ensure the best fitment possible.

After the CAD model is approved, we have a 3D print made. While there are many technologies for producing rapid prototypes, we choose FDM (fused deposition modeling) because of it's low cost and high level of accuracy. We simply export a CAD file and a few hours later, we have a plastic prototype in our hands.

The plastic prototype is used to test fit components and ensure all geometry is correct.

The plastic prototype is also bolted in place and everything is checked. We pay close attention to fitment as well as clearance from adjacent components and tool access to fasteners for servicing.

Most of the time, we find details to change on the prototype, so we go back to the CAD model and make adjustments and have another rapid prototype made. This iterative process can cycle many times until we have achieved the best design possible.
Once the design is locked down, manufacturing drawings are created. These drawings must clearly communicate to the vendor exactly what we want. The 3D CAD model and 2D prints are then sent to our casting company. Over the years of working in the industry we have been fortunate to find some of the very best in the business to work with.
We often request feedback from our vendors on new designs. This is useful for finding ways to reduce cost without sacrificing the form or function of the part. Once the design and drawings are locked, the PO is sent. Then we wait....

Months and months later, we finally receive the first article sample parts we have been anticipating.

The cast downpipe elbow is investment cast out of 347 stainless steel.

The first thing to do is to check the final part and make sure it matches the CAD model within the tolerances specified. This is done with the FARO arm.

Using a process like this, while tedious and time consuming up front, pays dividends when the final part is test fit. Perfect fitment is achieved on the first part revision. If there were any fitment or design issues, changes to casting tools can be very expensive and they add weeks and/or months to the project.

The downpipe elbow is an integral part in the turbocharger/manifold system.

These components are all standard in our Lotus Elise/Exige turbo kit.

Here the progression from prototype to production piece is clearly shown.

WIth the recent arrival of our cast downpipe elbows, we are now in the final phases of releasing our Lotus Elise/Exige turbocharger kit for sale. Please check back for pricing updates.

How does a Radium Fuel Surge Tank work?

After being asked many times how a fuel surge tank works, we decided it would be a good idea to produce a video explaining this. We teamed up with SullyLife and made a this short video that illustrates how a surge tank works and why it is needed on a performance vehicle. Enjoy!


Our complete line of Fuel Surge Tanks can be found here.