20-06-2012, 04:02 PM
Calibrated to what though...
If they read your RPM wrong, or your tacho is wrong... You can completely skew the results...
Say a car made 250lb.ft at 3230rpm - that's 153.7HP, say they read that as 3130rpm - that makes 148.9HP... And they NEVER read it accurately, they just run it up to 3k to guess the gearing... Not to mention if your tacho reads out too.... Unless they laser tacho it, it's fruitless...
Hence why most RR days are totally pointless, unless they know exactly what the RPM is, they can NEVER give an accurate HP figure, the only figure that might be CLOSE to correct is the Wheel Torque figure... And unless you go to the same dyno, on the same day, using the same engine RPM reading, at the same temperature - you can NEVER get an accurate figure, they'll say that they can correct the temperature and barometric pressure, but they just can't - they don't take into account if you have an intercooler, which is badly affected by ambient temperature...
And don't even get me started on handing out flywheel figures, look at my dyno graph, I ended up having to correct it by hand for a remotely close ATF figure, they based it on a 5% tranny loss, I went for 15%, and it's probably more than that, a 180k mile gearbox on old engine oil probably saps more than 15%, especially when you've got 300lb.ft+ going through it!!!
If they read your RPM wrong, or your tacho is wrong... You can completely skew the results...
Say a car made 250lb.ft at 3230rpm - that's 153.7HP, say they read that as 3130rpm - that makes 148.9HP... And they NEVER read it accurately, they just run it up to 3k to guess the gearing... Not to mention if your tacho reads out too.... Unless they laser tacho it, it's fruitless...
Hence why most RR days are totally pointless, unless they know exactly what the RPM is, they can NEVER give an accurate HP figure, the only figure that might be CLOSE to correct is the Wheel Torque figure... And unless you go to the same dyno, on the same day, using the same engine RPM reading, at the same temperature - you can NEVER get an accurate figure, they'll say that they can correct the temperature and barometric pressure, but they just can't - they don't take into account if you have an intercooler, which is badly affected by ambient temperature...
And don't even get me started on handing out flywheel figures, look at my dyno graph, I ended up having to correct it by hand for a remotely close ATF figure, they based it on a 5% tranny loss, I went for 15%, and it's probably more than that, a 180k mile gearbox on old engine oil probably saps more than 15%, especially when you've got 300lb.ft+ going through it!!!
