Yesterday I attended a rolling road session, which was geared towards classic minis, although a handful of MINIS were in attendance too. Four or five minis strutted their stuff on the rig and then the first MINI rolled onto the blocks. It was wired up accordingly and began its 'run'. Fairly quickly I noticed that the RPM readout on the testing equipment seemed well out of kilter with what the car was doing (i.e. computer reading 2500, car doing more like 3500+). The 'run' continued and when the computer reached around 4000+ rpm (car sounded like it was redlining) the car lurched (slipped) on the rollers and the test guys immediately slowed and stopped. They checked the car, further secured it and re-tested.
The owner of the mini pointed out that the rpm showing on the rig and the rpm of the car was different but the guys kinda shrugged their shoulders and said they couldn't figure it out. They said it must be something to do with MINIS electronics and they didn't have a software patch for it. They ran the car again, this time without incident, but the figures the guy got on his printout were just daft (although I wouldn't mind owning a standard Cooper throwing out 208.5bhp).
I noticed when the guy’s car came off the rig that he had about 4 warning lights showing on his speedo. The only light that should have been showing on the rig would have been the handbrake light. He drove it round the block and on his return said that he'd had to switch the engine off and re-start it to make the lights go off. His car only had ABS, no ASC or DSC.
Needless to say the other MINI owners and I decided against putting our cars on the rig.
I wondered if any other MINI owners had run their cars on a rolling road and if they had experienced difficulties such as those mentioned above. Surely (as some of the guys tried to suggest) it's not a case of you can't put a MINI on a rolling road because of it's 'sophisticated' electronic management system. The rig used was at a Peugeot performance specialist and they must put cars on it that are more electronically sophisticated than the MINI.
The ignition pickup used at that dyno may have been calibrated for use with a different style of ignition. Some ignitions fire each cylinder separately while others fire cylinders in pairs, so even when there is no charge on a cylinder, the spark plug may still fire.
You can also extract RPM from the roller speed if you have a known good speed reading at a specific RPM. This information can be read with a diagnostic tool.
Thanks for the info Andy, much appreciated. I think I did hear someone mention a 'double firing effect' or something like that.
One thing I forgot to mention was that the car seemed to lurch on the rollers only when they had stopped accelerating, some of the guys thought the ABS might have kicked in but I didn't really understand the reasoning behind that
Oh, and it's been pointed out to me that it was actually 218.5 bhp on the readout, not 208 as I mentioned earlier
the problem with the bonnet being shut is that there wasn't a fan to cool the engine like you'd get at 70 odd mph... Having the bonnet open might have helped a little bit, but still couldn't have replicated it.
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