911hillclimber wrote:I am sure many would like to discuss the Dyno BHP v the Rolling road bhp. Can you tune (say) a set of PMO's on a dyno as well as (I hope) you can on a set of conventional rollers?
Hi Graham, the main point here is that the engine dyno as opposed to a rolling road is by far the more reliable and accurate way of setting up an engine.
The problem with the rolling road is that it can only approximate the environment the engine is running in, whereas the engine dyno in it's cell is a totally
controlled atmosphere, which can be replicated exactly time and time again.
Air intake temperature is very critical in the setup of your PMO's for instance and rolling roads have little or no control over ambient intake temperature, in fact
that's one of their biggest drawbacks. If you image your car strapped down on a rolling road screaming at 7000 rpm, the air temperature around the engine
would bear no relation to the car on the road at the equivalent speed with large volumes of cold air being forced into it. The engine dyno air intake on the
other hand is thermostatically controlled and can be set to replicate any conditions, both in temperature and pressure.
This is only one example of the way sensors are used all over the engine to read what's going on, from the air intake as above, to individual head temperature
sensors, exhaust gas analysers, fuel flow meters, knock sensors, breather pressures and so on, you really know exactly what's going on inside your engine!
As well as all that for the engine builder the most important aspect of the engine dyno is that there are no variables at all in the testing. You take away the
gearbox drag and drive train variables, the halfshaft and wheel bearing factors, all of which effect your true readings. (You also save on the wear of those parts as well)
So each time the engine runs you get the true reading every time.
Going back to your PMO's Graham to sum up, if you had them tested on a rolling road one day and went back a couple of weeks later, you would get a different
reading due to weather, humidity, ambient temperature etc; therefore it would be pointless going on the rolling road say in March if your hillclimbs are in the summer.
The engine dyno would set them up for your optimum conditions using whatever averages you liked, and as for air pressure, now in a hill climb it will be different at the
start as to the top so.......................
HTH
cheers, Mike.
previously..
1994 968 Club Sport Riviera Blue
1994 993 C2 Carrera Riviera Blue
1972 911S to Martini RSR Prototype Spec
1973 911E to RS Lightweight Specification
1981 924 Carrera GT ex Mexborough car
3.2 Carrera Sport x2