CorkSport Mazda Performance Blog

Mazdaspeed 3 Auxiliary Fuel Tank

The time has come to reveal our Mazdaspeed 3 Auxiliary Fuel Tank design!

Years ago there was an option to run Port Injection or Methanol Injection without the requirement of a smelly and messy tank in your cabin.  Sadly that option disappeared and left the community with a need for another purpose-built and designed option for high power Mazdaspeed 3s.

That’s right! There is soon to be another fender mounting fuel cell for the 2007-2013 Mazdaspeed 3 and it’s packed with more capacity, durability, and functionality.  

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We approached this project with a clean slate and set a goal to maximize capacity, work with both GEN1 & GEN2 Mazdaspeed 3s, and provide the functionality needed for both methanol and E85 port injection auxiliary fueling.  

This was no easy task; we encountered many challenges that forced us to look to different methods and innovations to succeed.  However, through those challenges we developed a tank like no other available for the Mazdaspeed community.  

The greatest challenge we faced was the manufacturing method.  We originally approached the design with the intent to use cut, formed and welded sheet metal as the material, but this quickly proved to create many unwanted issues.  Cost, design flexibility, capacity, durability are just a few of the issue we faced with sheet metal.  With that we looked to other processes…what about a gas can?  Those are plastic and have very irregular shapes…

From there we identified that rotomolding was the ideal path to pursue.  It helped us maximize capacity, incorporate the features needed, reduced cost, and increased durability/reliability of the tank. 

Speaking of durability first…

Yup…we parked a truck on the tank and it took it like a champ.  As you can see there is a small amount of deformation, but that’s it!  After that we wacked the tank with a 3 pound sledge hammer on the front face (much like if you hit an object on the road) and again it took it like a champ!

Upon closer inspection we did not find any cracks forming due to the truck test or the impacts of the sledge hammer.  After letting the tank sit for a bit we found that the tank actually formed back to its original shape before the testing.  

So what makes the CorkSport Auxiliary Fuel Tank strong and durable?  Two things:

1. The material used is Cross-Link HDPE (High Density Polyethylene) which is a very durable and resilient material by itself.  Add in the cross-link reinforcement in a 0.190” wall thickness and you now have a material that can handle a large amount of impact force and yielding (bending) without failing.  
2. The manufacturing process is the other key aspect here.  Unlike welding, there are no seams or welded joints that can fail.  In the rotomolding process, the HDPE is poured into a mold that is heated to the plastic molten temperature.  This powder melts and creates one continuous structure with an average wall thickness of 0.190”.  Even the brass threaded inserts are embedded into the plastic with no seam or seal to leak.  

Speaking of those threaded inserts, those are really neat.   When the mold is assembled, there brass threaded inserts are fixture inside the mold in set locations.  These give us the flexibility to have integrated mounting points for the brackets that mount to the vehicle AND for both methanol pumps and the standard 044 style fuel pump bracket.  

Now let’s look at a cutaway of the Computer Aided Drafting Model of the tank so we can see a couple other key design features.  BTW these would not have been possible (or atleast not cost effective) with sheet metal. 

Probably the most critical and useful features of the fuel cell is the integrated sump for the pump feed.  This is the little area under the blue line.  This “low” zone is called the sump and the point is to create a lower spot for the pump to be fed fuel.  This reduces the chance of fuel starvation during braking and cornering as well as allows you to get the full capacity of the tank to your pump. 

Next you can see a “chamber” on the left side.  This actually sits under the frame rail a bit which allowed us to increase the capacity to ~2.6 gallons but it also serves another purpose.  If you are running a port injection auxiliary fuel kit then you most likely have a fuel return from the regulator; this is where that return line connects.   The low ceiling in this chamber helps reduce aeration of the fuel due to the return line flow.  This green line also sits just below the low level sensor so you’ll know when you are getting close to this threshold.  

Alright let’s wrap this up.  Designed specifically for the 2007-2013 Mazdaspeed 3, you can utilize the tank for methanol or ethanol fuels and you can switch from either or if you change your setup.  Durable and chemical resistant material used can take beating and once installed the tank and black filler cap basically disappears from view.  

We are stoked to bring a new and innovative option to the Mazdapseed Community very soon.  

• Barett @ CorkSport

P.S. – that stainless bracket in the last image is my splitter mounting system for my 2009 Mazdaspeed 3.  Check out @halfmilespeed3 for more details!

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