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A plenum development story – Part 3

Updated: Nov 20, 2020


In parts 1 & 2 of this blog collection we have taken you through the process of development from the very start up to the final theoretical stage where we concluded there is a high probability that we can come up with a viable product. Now we need to make some real life parts and fit them to a car!

So far all of the testing has appeared to be completed in the virtual world but we left out some aspects to keep things simple. In reality we had to be very mindful that the part(s) we were designing and running CFD analysis on would actually fit the car. Before we even started designing the various versions to run on the CFD we spent a lot of time working out where the parts needed to go to ensure we had suitable clearance around various things in the engine bay from oil breather lines, gear shift cables, the gearbox and a whole host of other brackets and hoses. We did this with a combination of 3D scanning and some rough and ready 3D printed components that we could adjust and move around until the fit was exactly where we wanted it. Then once we had that worked out it was back onto CAD to create some of the 3D models you can see in the last blog post.

The overall shape of the final iteration is actually nice and simple and if we ignore some of the radiuses on the corners it is pretty much just round tubes so we decided to make the prototype out of aluminium tube. This is not quite as straightforward as it sounds as the sizes required are not readily available so it required some machining work to get the part to connect to the OEM inlet runners and the link tube being optimised for flow is not an “off the shelf” size so that was largely hand fabricated. The throttle body flange was simply a flat plate and there is a requirement for some vacuum connections so these were manually turned on a lathe. The resulting parts were then TIG welded by G19 Engineering, we do have a TIG set in house but G19 can do far far prettier welds, some of the best we’ve seen, so may as well make it look the best we can!! The below picture is “as welded”….

We then bolted up some of the other parts, fitted the MRN badge and installed it into the car!

The next issue was connecting the new 82mm GT3 throttle body to the MAF pipe, as it’s just a prototype we purchased some smooth bore wire reinforced silicone flexible tubing and we were ready to run. It’s not the prettiest piece of hose but its fit for this preliminary testing phase, a “proper” solution will be present on a production part (if all of this works).

After fitting and connecting it all up the moment of truth arrived and an attempt was made at starting the car….. It did nt go well! The car was struggling to idle and blipping the throttle was not particularly good at all, we also had a CEL (Check Engine Light) come on, this did not look good at all! After a little bit of thinking it was actually blindingly obvious what was going on, the car was applying say 2 degrees of throttle because that is what it was used to when idling with the smaller throttle body but that 2 degrees on the 82mm throttle is actually a lot more open area, we have no way of telling the car there is a larger throttle fitted so it was a little confused to say the least! The CEL was flagging an issue with the MAF (Mass Air Flow) sensor, again, the car was expecting to see XX flow rate for a given throttle opening angle but it was seeing quite a lot more air. After a little internet research it was intimated that the car would “re-learn” the new throttle over time, some numbers from 50miles of driving up to 500miles was suggested so we reset the CEL and set about driving the car. Well that actually worked just as suggested online, sure enough after around 50miles of driving the car was idling just fine and a blip on the throttle pedal resulted in an engine response as expected!

An acceleration baseline test was done with a VBox logger with the standard intake and we are waiting for a day with matching ambient temperatures before we test with the prototype intake, the UK has been rather hot these last few weeks and in the interest of a fair comparison we need to wait for comparable conditions…… results will be published in the next blog post along with what is required for making a serial production part and the first batch of production parts will be announced with one of those fitted to the test car, hopefully we will be able to round up these blogs with some Dyno numbers and sale price!!

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