How many rolling roads measure from the flywheel anyway - what the sodding difference does it make if it is auto - just more transmission losses but if you are actually saying that the 215 is at the fly and already corrected then little of the original statement makes sense and the fact that it is auto has no bearing on the price of potatoes..
I think the point about auto/manual is that you can get a reasonably accurate measurement of flywheel power from a rolling road from a
manual car if the following are true:
1) The dynamometer is calibrated and in good condition in the first place.
2) The operator is honest and knows what he's doing
3) The environmental conditions are measured and compensated for.
4) The car is strapped down evenly and consistently.
5) The power run is made with a consistent gear selected and, when the engine has peaked, the driver declutches and allows the rolling road to record the losses during the coastdown.
6) The power run and coastdown losses are combined to estimate the power at the flywheel.
7) A couple of runs are made to ensure the setup is recording a consistent result.
Rarely will you find a rolling road ticking all the above boxes, though, especially if they have tuned the car and it looks good for them to send you away with an impressive "pub figure".
I have caught operators putting in silly environmental corrections, riding the brake / clutch during the coastdown to increase the apparent losses (or just hurry up the session so the next car can get in) or even just terminating the coastdown early because they can't be bothered to do it properly.
Put an auto box into the equation, on the other hand, and even the best operator can struggle to load the car so that it stays in the required gear and the best you can do for a coastdown is to slip it into neutral. This doesn't account for the considerable losses in the torque converter and most of the gearbox losses.
Before you conclude that "at the wheels" figures are therefore more trustworthy, though, bear in mind that the losses on a rolling road are very different to the situation on a real road. Tyre pressure, performance and size, how hard the car is strapped down, the weight of the car, the speed of acceleration on the rollers, which gear the car is in, diff ratio.. All these factors can radically change the "at the wheels" figures such as to make them meaningless unless compensated by a proper coastdown (even more so when 25% is added
).
Rolling roads are a good tool for tuning a car as they can allow you to operate the engine in parts of its' performance envelope that are difficult / not legal to attain on the
road test track, especially with a lap top on your knees.
They are also Ok for "before and after" comparisons of the same car on the same day to show the relative change in power.
I personally don't take much notice of figures from rolling roads unless I have seen them recorded. Ask yourself how the car drives instead.
Sorry - I seem to have ended up on my rolling road soapbox.
I was refraining from saying that 215 at the wheels from a 2.6 was some pub-talk b*%^%%s for risk of offending but basically without forced induction or undrivable cams that probably don't exist on the ready market this sort of figure would be unachievable.
Agreed.
Kevin
Author
Topic: 3.2 cams in 2.6???? (Read 3788 times)