Keith Calver......
MiniSpares Blog » Engine – 998 Tuning, Bolt-ons Keith Calver 24/08/2004
The single biggest restriction on any standard Mini is the ‘breathing apparatus’ – anything that is connected to the induction and exhaust systems. The standard exhaust being the biggest culprit – it is desperately restrictive in the name of noise suppression and cheapness of manufacture. Oddly enough it also increases fuel consumption when tested over a better designed, free-flowing unit, so this is the place to start – NOT I stress the intake which is where many start in the belief that’s the way to go. It is not. It is definitely the EASIEST place to start, and possible the cheapest – but will
net less gain for your money. Your best budget-verses-gain improvements should therefore be done in ‘reverse’ order – starting at the end of the exhaust then working your way back to the air filter.Exhaust System.
The key here is not to use something that is too big, as this will actually loose power. Unfortunately it is a pitfall far too many fall into in the belief that ‘biggest is best’, and the recent crop of dirt-cheap, 2.0″ systems. They are made 2.0″ for two reasons – Mini owners seem to be impressed by the ‘2.0″ exhaust’ term, and the manufacturers believe they are making a more efficient system as it slides over the tail-end of most commonly used LCBs. For further reasons ‘why’, see ‘Exhausts – sizing and styles’.It is entirely possible to fit an efficient system on it’s own to the standard manifold as Mini Spares/Mania can supply an adaptor for just such an application. This replaces the flared front down-pipe section from the cast iron manifold down to under the car to mate up with the RC40. They used to do just a short adaptor sleeve to fit the standard down-pipe but almost all folk found the flared end of their standard one had broken off once they’d got around to doing the job – so the adaptor was dropped as a pointless exercise. 1.625″ internal bore is as big as you need to go on an SBU to get the very last drop of power out – even on a full-race engine. My recommendation here is the twin box RC40 – simply because in all the years it has been around – nobody has managed to better it’s performance. And I’ve tried just about every last one that’s come on the market. The only one that gets very close is the latest Millennium system from MSC/MM. The benefit of the Millennium exhausts for those who are aesthetically selective is the choice of ‘exit’ pipes and styles. The RC40 is available in single box form for those wanting a ‘sportier’ exhaust note, but is slightly less efficient than the full twin box – loosing a couple of BHP and shortens/lowers the torque curve.Exhaust Manifold.
Progressing back along our route to power, the exhaust manifold is next. The standard iron one isn’t too bad for an entirely standard engine, but is less efficient than the standard iron inlet manifold. The fact they are cast as one causes power losses on it’s own by creating a severe, power robbing ‘hot spot’ in the inlet tract. Since separating them is only possible by destroying one or the other, loose the exhaust manifold.Generally I use and highly recommend the Maniflow ‘Cooper Freeflow ‘ exhaust manifold on SBUs. Originally developed by Maniflow owner Dave Dorrington when he was at Downton Engineering for the 970 S, it definitely has sufficient flow to cope with just about anything a 998 will could throw at it, and is easier to fit/seal than an LCB. Its design also suits the SBUs torque/power curve better than the commonly used LCB. And that’s another common pitfall – fitting an LCB to the SBU. Some vendors sell what has become commonly termed the ‘standard bore’ LCB to fit everything – for exactly the same reasons they sell the 2.0″ exhaust systems – it’s what the misinformed Mini owners ask for, and there is a very cheaply made ‘budget’ example available that costs less than a Cooper Freeflow. This ‘standard bore’ LCB is in fact a ‘medium bore’ LCB developed for the BBU so is simply too big for the road-going SBU. In back to back tests I’ve done with this budget LCB and the Cooper Freeflow, I’ve always found the Freeflow gives better results. Not to mention the fact they last a hell of a lot longer through quality manufacture too!
I also use an LCB on SBU for the road, but this is the pukka small-bore LCB developed by Maniflow specifically for the SBU. The primary and secondary pipes are smaller, as is the tail-piece (fish-tail, ‘Y’-piece). It does produce slightly better torque/power curves than the Freeflow but is marginally more expensive and less easy to seal off properly. Inlet Manifold.
Although the standard iron inlet manifold is reasonably good, a well-designed and proportioned one will better it. The iron one’s main problem is it’s internal sizing – it’s too big for the SBU. The MSC/MM aluminum manifold out-performs the standard one by quite a margin in all areas, maximizing airflow and gas-speed within the very prohibitive space. The parameters for the manifold were to set to allow the use on the standard air filter case should this be required, and this has been met.
