top of page
  • adminmrnracetech

A plenum development story - Part 4

Updated: Nov 20, 2020


Following on from the previous blog posts we are now in a position to give up the rest of the information on this product! Apologies to all of the subscribers about the time taken to reach this stage but we wanted to get all of the information collated and wrap everything up in this blog post. Having said that, we have diverted a little from the original plans due to some issues that are out of our hands like the weather! In Blog post Part 3 we mentioned we used a VBox logger to set a baseline and were waiting on comparable conditions to retest…. Well that is yet to happen but in the mean time we have been to the dyno so we figured that results from that would suffice.


So as you will know we had a fabricated aluminium prototype part fitted to our test car, well the plan was never to produce the production item in aluminium. Even though the shape of it lends itself quite well to a fabricated part we chose a different method. For several reasons such as repeatability, weight, and aesthetics we decided a carbon fibre part with CNC machined aluminium connections would be the best route to fulfill all of the requirements. And the below picture is the first part to be assembled.

The carbon fibre (CF) parts are woven carbon all the way through, not GRP with a Carbon skin over the top like some low cost CF parts that you find, the tooling that we have invested in for this is a CNC machined aluminium item to ensure the best surface finish and dimensional consistency. The throttle body attachment and connections for vacuum and AOS (Air/Oil Separator) are CNC machined from aluminium and anodised black. The MRN badge is 3D printed. All of these parts are then bonded together with some very special glue using a 3D printed bonding jig to ensure correct alignment. There is an O-ring groove in the face where the 82mm GT3 throttle body attaches to ensure a perfect seal. As the final finishing touch we add some heat reflective tape to the underside of the carbon, this is not to protect the CF but to prevent the heating of the inlet air inside the plenum, we don’t know what the net effect of adding the tape is but we think it is better than not having it at all.

In the previous blog post we used a universal wire wound silicone pipe to connect the MAF tube to the throttle body, this worked well but it’s by no means a “production item” so we invested in some tooling and have had bespoke silicone hoses made as shown below.

The eagle eyed among you may have spotted there is only one AOS connection on the MRN plenum, to make sure we supply a complete conversion kit we will be including a CNC machined and anodised blacking plug, we also provide a pair of blanking caps for the vacuum solenoids that sit under the inlet manifolds and are no longer needed.


In order to test the part as thoroughly and accurately as possible with the equipment available to us, we did the following:

Baseline testing – We removed the fabricated aluminium prototype and refitted the OEM parts, the car was then driven for roughly 150 miles to ensure all of the calibration was back suited to the OEM throttle body. The fuel tank was filled with Shell Optimax to make sure we had enough to last the full testing procedure. We also fitted an Exhaust Gas Temperature (EGT) sensor to each branch of the headers taking care to ensure the sensors were fitted the same distance away from the engine. The sensors were calibrated at 2 temperature points prior to use and were all of a suitable variation (+/- <2C). We wanted to see if the EGTs would show up any air flow distribution issues between the cylinders. Tyre pressures were done and the car was then driven to the dyno and tested to get a starting point of 286.1BHP at the flywheel. Our test car is completely standard apart from a Carnewal exhaust mod and our desnorkel plate.

The MRN CF Race plenum was installed straight after the baseline dyno testing was complete, we then had to run the car as much as possible to allow the car to re-calibrate to the new 82mm throttle body, this was undertaken via the journey back from the dyno then a couple of trips in the evening followed by the trip back to the dyno the next day, we totaled a little over 100 miles and two cold starts by doing this and the car was running well on arrival to the dyno.

Modification testing – We wanted to do two tests to cover off the possible uses for the plenum so the first thing to do was put the car straight on the dyno with no mapping and see where we were at. The ambient temperature on this day was a couple of degrees warmer than the previous day but the dyno should compensate for that. The result was a peak of 294.5BHP, an increase of 8.4BHP over stock at the flywheel.

Remapping – The car was then remapped which involved removing and stripping the ECU to read the files, after the ECU was refitted it could be written to as many times as needed via the OBDII port. After a lot of work on both the fueling and ignition tables the end result was 310.5BHP. Now we fully understand that in the world of comparative testing we should have had the car mapped as standard to cover all bases but there is a cost involved in doing that and we figured the method above follows suit to what our customers will likely be doing so chose that route. With that in mind we are unable to categorically say that our inlet singularly attributed to the full 24.4BHP gain. During the remapping process we asked for some bespoke modifications to the throttle linearity tables and some adjustments to closed throttle behavior to get the car to feel like it’s in Sport mode when it is not, all of these modifications have made a vast improvement to the way the car drives and I for one could not be happier with the end result.

Dyno below shows OEM run in Green then the MRN Race plenum (no mapping) in Blue.

Dyno below shows OEM run in Red then the MRN Race plenum after mapping in Blue.

EGTs – This was not as conclusive as we had hoped. Below are two screen shots of the car as OEM and after fitting the new plenum (pre-mapping). Both shots are of a WOT (Wide open throttle) pull in the same gear from the same starting RPM. The main point of note is the disparity between the hottest and coolest where the OEM has a temperature difference of 95C and the MRN plenum gave 73C. The other point of note is that the average temperatures are lower across the board with the MRN plenum but as this was done pre-mapping that is likely down to the AFR (Air/Fuel Ratio) being a little out. The large variation in temperatures with the OEM inlet correlates to the CFD analysis and verify that the new plenum does do a better job of feeding each cylinder equally.

OEM result:

MRN Plenum (pre-mapping) result:


In the for sale section you can find the plenum kit for sale, this will be a complete kit which will include everything you need to carry out the conversion including a Genuine Bosch 82mm throttle body and all fixings, fasteners, seals etc. LINK

Due to the nature of this product we are able to offer a bespoke option for the oval badge! For a small fee we can 3D print whatever you want instead of the MRN badge. The most cost effective way to undertake this option is to design your own badge where we will provide a 3D CAD file for the mating face and you can then send us the completed 3D file to print of if you have your own 3D printer you can print your own for us to fit or fit it yourself! (we can advise on material types etc). Alternatively we can do the CAD work, print and fit your ideas (subject to approval). Just send us a message if you want to explore the customisation option.

821 views0 comments

Recent Posts

See All


Commenting has been turned off.
bottom of page