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A plenum development story - Part 1

Updated: Nov 20, 2020

Here at MRN we try to keep our ears to the ground to see what customers like and dislike about other available products in the marketplace and also for any products/solutions that are simply not available. We have long been curious about the offerings on the market for inlet plenums for all Porsche models and their viability, function, cost and gains/losses when fitted so we decided to research into what is available and see if we could offer a part that is an improvement in some or all of the aspects mentioned above. We were under no illusion that this would be a long drawn out process and we have come up with what we feel is a very nice alternative to the other offerings available in the marketplace, in this first part of the plenum development blog we will try to explain the process used to develop the soon to be released (at time of writing) MRN Race plenum for the 987.1 platform. We are going to be a little enigmatic with this initial blog because until the product is due for release we want to protect our design, we hope you understand but all will become clear in subsequent blog posts. I’m going to skip past a lot of the viability/demand/costing parts of the process and get straight to the design/development stage……

Step #1 Reverse engineering

Most important for any performance/replacement part is “can the original part be improved upon?”. This is a broad question as performance can be a whole host of things such as weight, power, noise, efficiency, comfort etc. The initial phase was to use simulation tools to analyse the OEM component(s), using simulation tools is typically the fastest and most cost effective way to check viability prior to physically making prototype parts and also to optimise designs to a point where more often than not the prototype parts require little or no modification before moving to a production phase. First step was to purchase and CAD model the OEM inlet assembly, an internet auction site came up trumps with a full set of parts and after a good clean these were reverse engineered into CAD with a combination of 3D scanning and good old fashioned measuring. The below pictures show 3 stages of the CAD modelling process as screen shots and the last picture is a rendering. If you are familiar with CAD, there are over 100 features in that CAD model alone. The eagle eyed amongst you will spot the Porsche logo has been replaced with the MRN logo.

Step #2 OEM part analysis

We have many years of CFD (Computational Fluid Dynamics) experience at MRN so we used the tool to analyse the flow characteristics of the OEM plenum, setting up for CFD is a long drawn out process and has to be meticulous in the data input side because the old saying of “rubbish in = rubbish out” is particularly relevant with CFD. Luckily there is no requirement for thermal inputs into this study and after doing a couple of preliminary calculations it was clear that gravity had no effect on this study so that was turned off in the analysis as well (Gravity is primarily used where natural convection would be present in the study) which saved some calculation time. Below is a rendering of the OEM inlet assembly and also a video of the CFD result, the colour of the arrows indicates flow velocity where blue=slow, red=fast and the density of the arrows corresponds to the quantity of flow so a low number of arrows would indicate a lower pressure area.

As you can see, the OEM manifold layout does not distribute particularly evenly to each cylinder inlet so based on that we can assume there is some cylinder imbalance across the 6 cylinders – so room for improvement maybe?..... Subscribe to keep updated on the second stage of this blog either on the MRN website or our FaceBook page.

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