Developing the Sprogley Motorsport Enclosed Airbox...
The SM Enclosed Airbox started out as a little project for myself to build a 1-off intake for the Peugeot 106 Project. A few months down the line and after successful dyno testing, we started production on units to add to our ever-growing list of products.
We initially tested the prototype of the SM Airbox in Feb, 2020. In this test we compared its performance to the stock Airbox of a VW Lupo ith the 1.4 16v 75hp engine. The primary purpose test being a bit of fun and an opportunity to make a video, but none the less comparing the differences, if any! We were very surprised to see, despite some discrepancies in the conditions that may have played in the favour of the SM airbox, there was a huge difference.
The SM airbox made 10bhp and 10lbft more than the factory unit, which is huge for a low capacity NA engine. As you can imagine, we were over the moon with the results and subsequently put the SM Airbox into production.
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We decided however, after months of sales and happy customers, as well as the introduction of the Pro version of the airbox, that we needed to step the game up. We would conduct a second, much more thorough test comparing the SM Airbox against the competition.
We took Claytons very well sorted VW Lupo Gti to the dyno, along with 5 intakes. These were the SM Airbox, the SM Pro Airbox, a BMC CDA, a generic eBay Airbox and an open Ramair cone as found in the SM Airbox.
The criteria for the testing was as follows:
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The whole test was performed on the same day within the space of a few hours. It was conducted in an open dyno cell where the cell temperature was the same as it was outside. This meant that the AITs wouldn't have varied by more than a degree or two. This also meant that the intake temperatures were accurate to real world conditions, not controlled ones.
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Car was warm prior to any run
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3 back to back runs were recorded for each intake
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Car was left for a good 15/20 minutes to cool between each intake change
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The bonnet was closed for every run
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The fan was on for every run
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The cold air feed from the front of the car was the same and attached to each intake for every run. For the open cone, it was still left on and directed at the air filter to give it the best chance.
The Results...
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SM Airbox with SM Pro tub fitted - 169.9bhp / 151lbft
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SM Airbox - 169.7bhp / 159lbft
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SM Pro Airbox - 169.1bhp / 151lbft
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BMC CDA Airbox - 165.8bhp / 154.7lbft
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Generic eBay Airbox - 165.2bhp / 154.2lbft
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Ramair open cone filter - 163.2bhp / 146.31lbft (This dropped down to 158.3bhp over the 3 runs due to heat soak)
There are some important things to note from these results.
Firstly, the outstanding performance of the SM Airbox. We were completely confident in our Airbox performing as well as the competition, and with a starting price of around £70 less, to us its a no-brainer when it comes to bolt on performance for your car. But what we didn't bargain for was just how much better the SM Airbox actually performed. its peak performance exceeded the next best thing by around 4bhp, a very impressive figure when it comes to naturally aspirated performance. We put this down to the the filter element in our own Airbox being larger, with greater surface area than any of the others. On a personal level, I'm very proud to say that we have managed to develop one of, if not the best performing universal enclosed air filters on the market.
Secondly, the performance of the SM Pro Airbox. The performance of this didn't come as a complete surprise. The Proram air filter which until this point was used in the Airbox, was larger in size than the foam filter. We believe this actually caused a slight restriction due to the lack of room around the air filter, subsequently resulting in a lower result. The main feature of the Pro, its heat resistant tub could not be showcased on this particular test and therefore made very little difference to the results.
Therefore, from this test onwards, we altered the spec of the SM Pro airbox to use the regular foam filter, and subsequently altered the price to reflect this. We have no doubt that for a track / race car, or someone that wants the absolute best performing parts for their vehicle, the Pro is certainly the one to have. The number 1 performer on our test is effectively now the 'new' SM Pro Airbox.
Thirdly, the perfect demonstration of heat soak. We can say straight off the bat, that the difference between the SM Airbox and the open Ramair cone filter has nothing to do with the quality or performance of the filter its self, as they are identical.
It just goes to show that simply sticking a cone filter on your car really isn't going to boost the performance, it may even effect it negatively! Just by adding our enclosure and air feed to a perfectly designed air filter, you are seeing a 7 - 12bhp gain in performance! Peak figures aside, we should also note the drop in performance when using the open cone over the 3 runs. With little time for the engine bay to get really hot, the cone dropped in performance by 5bhp. If you put the same setup in a more extreme situation like a race track, the drop in performance could be even greater.
Its important to bare in mind here that this is on a naturally aspirated car. We believe the result may be different again with a turbo vehicle, so we will be going back to the dyno once again very soon to test this theory.
If you are interested to know more about the day testing the airbox, seeing first hand the gains made and hearing the amazing intake noise that it produces, we covered it on our YouTube channel, go check it out!
Since then, we have continued to develop and grow the range of Airboxes into what is now its own brand, SprogTech. We are very proud to have designed, manufactured and sold 100s of our airboxes around the world on a huge variety of vehicles.