Description:

For those unaware of what a twin-screw supercharger is, I posted many years ago a photograph of what I believe is the earliest twin screw supercharger conversion carried out on a Jaguar V8 by Dennis Priddle of AJ6 Engineering - Opcon Twinscrew Jaguar V8 - Jaguar Forums - Jaguar Enthusiasts Forum

The AJ6 Engineering website itself is a wealth of information on this topic and talks in depth about the benefits of twin screw superchargers over the roots style, as originally fitted on the supercharged versions of the Jaguar AJV8. In a summary, a twin screw supercharger is a true compressor and is more efficient than a roots supercharger, generating more power whilst creating less heat. Many of us who have tried to spin the Eaton M112 faster will know about this and why it has earned the nickname, “Heaton”!

Following years of experimenting with twin screw superchargers on my own STR, I am now able to re-make a refined version of the 2.1 KB kit which our well known supercharging expert avos used to offer. I was able to take a careful look at a 2.1 KB kit made by avos and take all relevant measurements in order to reproduce a slightly improved version, with a better finish than the hand-made versions avos made many years ago.

For background, I initially bought a 1.7 Opcon Autorotor from avos around 8 years ago, which I understand made around 380rwhp on his 4.0 XKR (up from a stock 320rwhp). On my 4.2 STR, it made just over 400rwhp with a 2.5" upper pulley. After switching to a 2.16" upper pulley, I was able to achieve around 430rwhp. This was on an essentially otherwise stock car and the power delivery was transformed, even though the way that the 1.7 was adapted was very poor and blocked a lot of airflow. I ran this 1.7 supercharger for many thousands of miles without issue, and as far as I know it remains happily in use in New Zealand with another forum member.

As has been proven by a number of enthusiasts, the 2.1KB is better again than the 1.7 and can comfortably make 450rwhp on our engines. I have mounted the 2.1 KB further forward in my revised version of the kit and was therefore able to optimise the inlet further, achieving virtually unrestricted airflow into the supercharger. I have put mileage on my kit and tested it under various driving conditions without any issues, and it has performed even better than the 1.7KB (with which I previously achieved 430rwhp). I estimate with a smaller pulley that 500rwhp will be achievable with the 2.1 KB, and this reportedly already has been achieved on a STR using a ported TB, larger aftermarket MAF and tune.

I am able to make these kits for the STR/XJR, which I understand would also fit the XF SV8 (although I do think the kit would make much more power here and on the X358 XJR). I am currently now working on the X308 XJR and X100 XKR kits, which should be completed shortly. If anyone is interested in a kit, please feel free to PM me. The way I have designed the kit means that it is entirely bolt on and reversible, so it can be installed by any DIY mechanic at home.

If desired, I could in theory make the kit with a 2.6H (or even 2.8 or 3.0 KB) and relocated TB like avos innovatively designed, however in my opinion the 2.1 KB is the best compromise for cost and ease of installation. It also sounds incredible and is louder than the larger units! 

NB - this is not a business, but purely a hobby from a Jaguar enthusiast who has come to know the excellent effect of  twin screw superchargers on our engines. Hopefully, it will allow those who wanted kits after they were discontinued to now be able to obtain them, and also lead to more aftermarket development for this platform.