Caterham 7 with 440bhp supercharged Duratec 2.3 Cosworth

 

I designed and built this Rotrex Supercharged Caterham 7 long before Caterham did so. At the time, there was one supercharged Caterham that I was aware of but it was using a small (C30) supercharger and “only” pushing 300bhp or so. I wanted to go big and use the larger (C38) range of blower. This had a huge impact on the design of the compressor system because the Rotrex unit would not fit in the obvious / only location where there was any space. Ie. Under the intake manifold. This is where that existing car had mounted it and also where Caterham ended up mounting it on their 620R model some years later.

 

I was aiming for 400bhp+ so I needed the larger C38 blower and I also wanted to use the 2.3 Duratec rather than the 2.0. I purchased a steel crank, stronger rods, custom pistons, Cosworth head, custom ground cams, dry sump system, shorter bellhousing, paddle clutch etc etc. If you have ever looked in the engine bay of a Caterham, you will see that packaging is a real problem. I wanted a good intercooler that would flow from side to side in the top of the nose so I was aiming to mount the supercharger on the exhaust side somewhere. I found a good solution which would provide short intake runs but it required a custom exhaust manifold for clearance. I also wanted to run Jenvey individual throttle bodies and, at that time, no real intake plenums were readily available so I had my own made to suit.

 

Lots of chassis work took place, including adding a roll cage, multiple diff strengtheners, front chassis triangulation, custom engine mounts etc. I worked with Bruce at Arch Motors who make the Caterham chassis’. He was able to consult Jez Coates who was Caterham’s previous long standing Technical Director about chassis rigidity. This helped enormously in knowing where to add strength but also where it was not as critical. An example would be the transmission tunnel connecting chassis tube at the rear of the bellhousing. This was such a pain in the neck when installing and removing the engine and gearbox as they could not be installed as a single unit. It transpired that this connecting piece did almost nothing for chassis rigidity so we removed it.

 

This was a ground up build from a bare chassis to the best specification possible. The engine was mapped on an Omex ECU and made 435bhp on the engine dyno at Xtec Engineering. Bear in mind this was with very mild cams, relatively low boost and sub optimal intercooler set up. On the track, the car had so much torque yet it ran out of power higher up the rev range. Since then, I have fitted much more aggressive cams, improved the intercooler and will run a larger version of the C38 Rotrex. I would expect close to 500bhp. Watch this space.