Rocketeer MXV6 Development Insight No.2 - Dual Carbon Fibre Inlet Plenums

March 5, 2017

 

 

We have been extremely busy making progress on the development of our production ready V6 conversion kit for the Mk1 & Mk2 Mazda MX-5. The interest we have had so far has been astonishing, we are thrilled to engage with such an enthusiastic community who appreciate what it is we do. As such, we thought we would share some of our development insights with you, we hope you will find this interesting, whilst serving to keep you updated on our progress.

 

We continue this series by taking a closer look at the the Rocketeer dual carbon fibre inlet plenums, designed for the Jaguar AJ V6, used in the Rocketeer MXV6 engine conversion kit. The latest design is shown in the rendering below, but we are going to take you through the evolution from our prototype running on throttle bodies, to the below proposed design. 

 

Since its inception, the Rocketeer MXV6 prototype has used Jenvey throttle bodies. The original Jaguar intake was too large to fit under the standard body of the car, and we wanted to preserve the original aesthetics of the MX5.

 

 

By using the Jenvey throttle body kit, and by designing and manufacturing our own lower plenum for the Jenveys, we managed to reduce the overall height of the trumpets, meaning the engine could breathe underneath the original bonnet. The rendering below shows the Rocketeer lower plenum for the Jenvey throttle bodies,

 

 

This worked perfectly for experimental purposes, the engine made good torque, and reasonable power figures on the dyno (234bhp), however, as expected with the throttle bodies now operating in a tight space, maximum power was down on the quoted 240bhp from Jaguar. Contributing to this, the early design was compromised in because of the severe transition between round, and oval ports, as demonstrated on the below image:

 

 

In addition to packaging constraints, the Jenveys do not have idle control, or vacuum so whilst they served their purpose for development purposes, we knew this wasn't going to be the solution for production MXV6 kits. Further still, the cost is fairly prohibitive, the Jenveys alone would account for more than 25% of the entire cost of our kit. We knew we could do something better, whilst reducing the total cost. 

 

We toyed with the idea of developing our own throttle bodies, but eventually settled on twin carbon fibre inlet plenums. The beauty of this type of design was that it allowed us to retain the original bonnet, feed a long intake run with relatively cold air, and using two MX5 1.8 throttle bodies, we gain idle control . Our initial design is shown in the rendering below. 

 

This design was partly inspired by the inlet manifolds from Aston Martin V12, some of the port dimensions and fittings for the AJV6 are actually the same (halved for a 6 obviously), We performed CFD analysis on this design, to help ensure that  the cylinders were filling equally. Whilst the flow in the manifold was not bad, this design didn't allow the cylinders to fill evenly. 

 

As a result we developed a more symmetrical design with tapered runners, which eliminated this adverse characteristic seen in the previous design.

 

 

The rendering below shows the CFD performed on the latest design (filling of one cylinder shown), which we will be prototyping over the coming weeks.

 

In addition to this, we do have a plan for a throttle body conversion which is much improved over the system fitted to our prototype car, we realise this could appeal for other applications as well as the MXV6 conversion. For more information on the Rocketeer MXV6 conversion kit, or any of the individual components shown, please feel free to contact us. 

 

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