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Today is the final day of the Roger Albert Clark rally in Yorkshire, UK. The weather has been very challenging, with 20+ cm snowfalls closing stages and even entire sections of the event. This is the worst weather in this area of Great Britain for late November/early December since 1993.

Normally, a 911 driver looks to the sky, sees the clouds forming and thinks ‘yes – today is a good day’. But here we are, four stages from the end of the rally and there is not one 911 in the top 20 runners. Fifteen of the top twenty are Ford Escorts! This is clearly unrepresentative of the relative strengths of the cars: further investigation is required.

Francis Tuthill, friend of TwinSpark Racing, is currently the leading 911 in 33rd position. Francis is running a Tuthill Challenge car, one of the ten 911s that will contest the Tuthill Porsche Rally Challenge in 2011. I’m sure we’ve written about the Challenge in the past – if not then Tuthill Porsche Rally Challenge 2011 details are here, from an article in Autosport magazine.

The Challenge cars run a carb-engined, 3-litre 911 SC engine making 230bhp. They are geared for torque, which keeps them crackling along. I drove one at the launch with Terry Kaby as my instructor and, while I made a complete mess of it, it was great fun. In the recent Morocco International Historic Rally, Michele Mouton, driving a Tuthill Challenge car  finished just four minutes behind winner Gregoire de Mevius in a full-spec 911. This is a great result, given the horsepower difference of 60 or more in favour of de Mevius.

So where are the 911s on this event? Sliding in the snow looking for grip is where. Sources local to the rally say that only two of the Porsche 911s competing have limited-slip differentials! Crazy.

A limited slip diff is critical in a fast road, race or rally 911.Without it, as soon as one wheel loses traction, the differential simply stops working. Hardly ideal.

TwinSpark have been working in partnership with a transmission firm currently off the enthusiast radar who have been developing a new limited-slip differential for the 915 gearbox. We’re about to try the first of a plate-type diff in one of our own cars – remember everything we sell is tested in our cars first. We hope to have the diff in the car in the next few weeks, and will report on our experience via the blog.

It may be that out first experience is a road trip to Tuthill snow camp in Norway, which will probably be a similar test to this year’s classic RAC Rally. I suspect we can probably get there with more reliable grip than some rallyists are managing at the minute.