BMB came straight out of the traps at the start of the year, winning at their first attempt, the Winter Cup at Lonato. This new company is a collaboration between Birel and Carlo Boscolo. Boscolo is one of the famous dynasty of engine men that count Baroni, Corrona, Villa and Bossaglia among his rivals. Famous for his successful period with Ital Sistem, Boscolo has now turned his attention to the modern generation of TaG engines that now dominate the karting scene across the world.
Among the models on offer from BMB is the 125 HAT, which has many common features as found on the KF range of engines, but in a simplifi ed form. The engine is very neat and small, sitting very low on the chassis. Its compact design is thanks to careful positioning of the balance shaft below the crank. The engine has no exhaust valve but despite this is still expected to produce a solid 30 horsepower with a fl at and torquey power curve. Induction is through a vertical reed assembly into the front of the crankcase, which is fed by a Tryton HB27 two jet carburettor. At fi rst glance the engine looks like the last of the Formula A units which have all but disappeared now. The exhaust is a kissing cousin of the KF2 unit and produces a very similar noise and a bit, as this engine is prepared to rev to 16,500. The rev limiter actually comes in progressively from 15,500 so there is no point in chasing RPM for power, this unit is designed to deliver power across the range.
The clutch is unusual in that there is substantial initial slip, followed by a fairly sudden engagement. The design of the clutch is different to many in that it has leading shoes, which are apparently arranged in this way to enhance reliability. The internals of the engine are no great secret, a monobloc cylinder head with carefully controlled water fl ow is married to a beautifully fi nished cylinder of classic three port design, with a cast iron liner. Also reminiscent of classic 100cc design is the oval exhaust port with its two adjacent boosters.The bore and stroke is slightly over square at 54.28mm x 54.00mm. Another reason for the compact nature of the engine is that it employs an external water pump, with the radiator on the left side of the kart. It is a feature of modern chassis that there is plenty of room for this large radiator and still get some air to the brake. The senior KF classes are not so concerned about this issue as they have the benefi t of front brakes which take a lot of the load and heat off the rear.
And now for the track test. Andy Cox had arranged to meet at PFI and fortunately the rain stayed away. Andy has formed a new company to promote the class with Vega importer Paul Deavin. Paul has had a very long relationship with Vega as well as many years experience at the top of 100cc racing. Two karts with new engines were available, one of which needed to be run in, Michael Simpson was also on hand and generously offered to do the fi rst running in session, I used to run in 100cc engines in three laps before boredom took over. Having mentioned this weakness to Andy, I was jocked off the job…perfect! Michael delivered me a run-in machine with carb jets set ready for action. The fi rst impression was of the excellent level of grip from the Vega XH tyres, this is the current generation of product and will deliver good levels of grip for at least 150 laps. The drop off in time against a new set proved to be less than 3 tenths. The wet tyre will be the current Vega W5 as used in international events. The kart handling was very neutral with these tyres and, although the butterfl y carburettor lends itself to being snapped open, and the pedal travel is very short, I believe it is actually better to feed the throttle in, which gives better drive off the corners. With this level of grip it is easy, and essential,
to brake late and hard into the corners, wait for the kart to settle before driving straight off the bend. Sliding the kart is a defi nite no. As the engines loosened up after running in it was possible to tighten the jets, just a little, with an instant improvement to the performance. As with most modern reed engines these were very sensitive to the slow speed setting. Within just 10 minutes on the slow jet, the engine went from gurgling rich to gasping for fuel. Because this is a relatively low revving, low compression engine, I imagine that it will be less seize sensitive than its 100cc forebears. However, good care must always be taken to keep the carburettor in good condition. Service intervals on the engine are expected to be at least 5 hours for the top end with a new piston assembly and 10 hours for the bottom end. The engine is no slouch in standard form and limited tuning will be allowed. I believe that a minimum exhaust duration of 180 degrees will be the principal restriction with a minimum head volume as well. All components must be of original manufacture including exhaust, carburettor, airbox and all other ancilliaries. The engines are to be delivered complete excluding water kit.
Where to race
The BMB 125 HAT is being introduced internationally and may be known as Kart Grand Prix, although this is awaiting ratification from the FIA. Whatever the name may finally be, this is a quality product that may well appeal to KF refugees that can no longer stand the cost. It is bound to take a little while for the category to gain serious support but it will be racing here in the UK and across Europe in the coming months. At present there are plans to run a grid of Pro and Master drivers at the last round of the MSA Super 1 Series this year at PFI.
The engine comes complete as described above for £1650.00 + VAT and will fit any modern international chassis. Most karts these days have radiator and pump mounting brackets, if not there are proprietory clamps on the market to take care of the problem.
• The official website for the new class is www.kartgrandprix.co.uk
• Graham Smith made a video from a Kart Grand Prix test day which you can see at youtu.be/QZiw5_o9d9g
• I would like to thank Andy Cox, Paul Deavin, Michael Simpson and the team for a very enjoyable day.