posted in: GTT Blog & News


Quite a bold title, however this is something we have been aware of for many years, seen before, and is now happening in the Mini ‘tuning’ world. Let’s start by saying a rolling road (or Dyno) is a great useful tool, and most operators will do their best to give genuine accurate power figures, and offer the best possible tuning they can. However even then, the tuning MUST still be tested and final adjustments completed a on a REAL road afterwards. Using onboard Air/ Fuel Ratio meter (Wideband) ,and a way of measuring /hearing engine knock/pinking this is a must. The R53 Cooper S gives quite different fuelling data on the real road compared to a rolling road as it happens. So you could end up gaining power on the RR but losing power compared to before once it’s back on the real road! Imagine having your car set up to produce maximum power on planet Mars, then ship the car back to Earth. You shouldn’t be surprised to find the Power/Fuelling/Timing is longer at its best! Ok a bit of an extreme example but it explains the problem well. The main reason for this article however is something  more serious than this, but before we get into that, we shall highlight a couple of  statements we often hear:-

  1. ‘My power is measured at the wheels, so is more accurate and cannot be ‘fiddled’.
  2. ‘ It must be genuine, as I only use the RR to get a baseline figure, then see how much increase over and above the baseline figure my tuning has given me’

Ok so both of these assumptions are actually not correct. I will name a number of ways the ‘wheels’ power figure could be over or under inflated. Also statement ‘2’ leaves much scope for the unscrupulous tuner to put down another tuners work if he wanted to. Simply by under inflating the initial power output readings, then applying his ‘magic’ at a cost of say £500 to you, then over inflating the power readout on the final run. Job Done!  You’re happy because you believe he has gained you a ‘proven’ 28bhp (He hasn’t really though), and he’s happy because he has fleeced you out of £500 and maybe turned you against the original tuner that did your work. Now we are not saying this happens every time, certainly not, but give someone enough motive, (e.g. money and gaining customers, or just plain jealousy and spite) then it could, and does happen. Normally it would be very well hidden and offered with a smile no doubt. At GTT we don’t even have a RR here, and to be honest we don’t want one due to any one of 30 reasons. However the power figures for the various GTT conversions throughout the last 12 years have all been proven in the past on a TOTALLY  INDEPENDANT Rolling Road with printouts available, whether it be the GTT210, GTT220, GTT260 or the GTT350T. Having said that, even results we have obtained in this way we don’t take too seriously. In a nutshell don’t get too ‘hung up’ on RR printout power figures, for any car, not ever. If you really do want a RR printout, then take your car to one or two completely independent (i.e. not Mini specialists) RR’s. Even then figures can be miles adrift for many different genuine reasons.  I will list some accidental and some deliberate ways of achieving too high or too low power printouts with notes explaining how it’s done added.


As said earlier a WHP (wheel Horse Power) figure only is not as great as it sounds. Here are 4 things that would lose WHP but not engine horse power.

  1. Tracking Miles Out…… With toe set at 5 degrees in (or out) each front wheel is pushing or pulling against the other. You are genuinely wasting much WHP, and this will show on your WHP readings, but is not because the engine is lacking power!
  2. The Brakes on the Front Axle are Binding… ..Ditto you’re losing WHP but the engine is not the culprit.
  3. Partially Flat Front Tyre ….ditto.
  4. Car Very Lowered….Ditto. Your drive shafts are not straight, but angling up at the outer ends. This loses WHP but the engine as above is still producing the power.

OK now let’s list a few ways your RR operator could deliberately achieve a LOWER figure than it should be. Some of these could happen by accident as well BTW.

  1. Rolling Road Operator applying the footbrake very slightly throughout the entire run! ……..Bet you hadn’t thought of that one? Yet this is the oldest one in the book!
  2. Tell the software it is a nice cool 10 degrees C in the workshop, but is really a power sapping 25 degrees C outside! …….The software will take off some of the measured power, (when in truth it should be adding a little on) to bring it back to DIN nominal ambient temperature figures. Same applies to humidity settings.
  3. Juggle the Roller speed (In effect this is the road speed and usually in MPH) to engine RPM calibration…… Also works by doing the run in different gear sometimes. Or by calibrating speed to rpm on one car then using same settings on another car with different gear ratios , for example an R53 Cooper S ‘Pre- Facelift’ followed by the ‘Facelift’ version. Also occurs with cars having different diameter wheel & tyre combos as this changes the final gear ratio to. This type of thing happens on RR shootouts all the time, but one can understand this when time is of the essence at these events. RPM can be manually entered to the software at a given roller speed or taken as a pulse from one of the HT leads, or direct through OBD2. RR’s are not all the same in this area.
  4. Not put his foot completely to the floor on the gas pedal during the power run ….I bet you didn’t think of that one either!
  5. Run car on RR too long and/or with insufficient cooling fans ….Causes over high charge air temperatures.
  6. Car running awful quality 95 Octane fuel. E.g. Murco/Jet/ Total/Asda etc…. Why is anyone still using this?
  7. It should be running Shell V Power or Tesco 99 Momentum always.

Next how to make the power figure impressively HIGHER or ‘over inflated’ (Maybe the RR operator has just applied his tuning and parts and wants to show you how ‘Sooo much better’ it appears now after the previously ‘fudged the other way’ power run.

  1. Fiddle the Roller Speed to Engine RPM as above, but the other way.
  2. Fiddle the Ambient temp and/or humidity as above, but the other way.
  3. Pop some very high octane ‘oxygen releasing’ race fuel in the tank just prior to the run.
  4. Just fiddle the graph, and be done with it.

NOTE. Not all the above apply to all types of RR or their software.  There are reasons your engine could genuinely be down on power. These are covered elsewhere but if you still want 5 faults that we see all the time here goes: Broken bypass valve, air leak, FPR pipe come off, belt slip and finally cylinders down on compression. As stated already most RR operators are very genuine…but not all of them, and not all the time!

It is quite an eye opener this article, and not intended to upset anyone (except unscrupulous competitor tuners maybe.) But it is something we should all understand and we aware of. There are those few who after reading this will still want to keep the blinkers on, and totally dismiss this article as they want to remain  in the belief that the RR printout they hold can still be unfolded down the pub every night or uploaded on their favourite forum with the comment  ‘It’s Hundred Per Cent Proven Mate’ …. So be it!

One final topic… ‘Increasing Max Rev Limit’. Does this give more peak power? Yes it can do slightly, and this is one way your tuner could genuinely be giving you slightly more  ‘PEAK power’ with his re-map. BUT there are downsides and other things to consider. As a SUPERCHARGED car remember you would not be gaining any power all the way up to the previous 7000rpm rev limit whatsoever by doing this. Then ask yourself ‘How often do I actually hit the rev limiter during an overtaking manoeuvre?’ Chances are you probably change gear at or before 6000rpm anyway. There are other issues we hear of that are possibly the result of running the car with increased rev limit. e.g. (1) Cars can drop more belts (2) Cars can drop a valve in the head (3) In combination with a -17% pulley change the supercharger is now being spun well beyond its recommended max speed rating, massively increasing the charge air temp as it exits the SC. (4) Stretching of the Big End bolts resulting in complete con-rod and engine failure. So on balance we feel the standard rev limit is usually best left alone on supercharged Mini’s. I suppose at least that is 5bhp power increase you could gain genuinely to show others down the pub if that if that were your primary goal, but for most of us it is of little use combined with unnecessary risks.