Flachbau

I agree. The only true test of an engine is on a bench dyno - as the factory does. It is common knowledge too that the factory will dyno some 25 random engines and average their results to come up with the final 'disclosed' hp figure.

Again I agree. It is the only way to measure apples to apples and to get real apples to apples you need to be using the same type of dyno (engine, load bearing or inertial).

HP reads off the the dyno aside, unless you are willing to drive it like you stole it (which I hope the majority of this forum is willing to do - even without access to a local autobahn), who cares what the dyno says

Flachbau

I'm not sure that I know what you mean 'wheel' hp v. 'ground' hp? Do you mean wheels on the dyno's rollers v. wheels on the ground? If so this is in effect the difference between a inertial dyno (perhaps what you are refering to) and a load bearing dyno. One (the inertial dyno) measures the acceleration of the rollers and estimates hp by the velocity of the turning drum and from that extrapolates torque, the other (the load bearing dyno) measures the force to turn a resistance object (typically a brake) or 'load' and measures actual torque and from that extrapolates hp.

Maybe this is what you mean?

Flachbau

This is from an article from German Motorcars website which I think reinforces some of the points being made in this thread:

'A Dynamometer can only measure actual power at the output location. Actual power produced AND delivered by an engine will be highest if measured at the crankshaft, lower at the transmission output shaft and even lower, but more meaningful, still, at the rear wheels. The power that you use is the power at the rear wheels. Some Dynamometer companies add to measured rear wheel power readings a factor that is based on ESTIMATED rear wheel power losses (under what power conditions? 3.0 ltr.? 5.0 ltr.? Under coasting conditions? with a 185/70/15 radial tire? a 335/35/18 radial tire? New heavy radial tire vs. worn old, light, racing tire? Who knows?) In short, there is NO meaningful "average" tire to get a correct rear tire power transmission loss measurement for all cars - so obviously, unless they actually measure the power lost in the rear tires, under driven load conditions, NO dyno company should BE ADDING incorrect power figures into the measured power. It's simply wrong. The fact that they add varying amounts of power to the actual, "true" amount of power delivered and measured to the surface of the drive roller creates a situation that makes it an onerous task to compare power figures from different brands of dynamometer systems. '

JamesE

Here we go again....

My comment about under reading was tounge in cheek.

My understanding is that the dyno that 9m use, approx. fly wheel hp by coast down calculations, and hence will adjust for different set ups.

I also totally agree with Jean that turbo cars are more prone to heat-hp issues than NA cars and the 60-130 test is a good one. However dyno's have there place...

JBL930

I would love to do a 60mph-130mph run, anyone fancy lending me their AX22 for a day?

Turbo Jonny

I thought my post would generate some discussion! I am out of my depth to comment but its interesting watching things unfold.i was happy that my engine seems pretty healthy and have something to compare when i do a cat bypass or other mod.9m did say that this was the best way to use the figures.Out of interest we did another run after disconnectig the lambda sensor and hp went down by 5 , so probably didnt make any difference at this stage.

I have now had info from Ruf that an Eks electronic clutch was fitted ( now removed ) for a short while.They didnt have a record of any other mods but couldnt say for sure without seeing the car.

nathanUK '81 930 G50

I am going to get one of these when I get my 930 back together. If fitted to one of the front wheels (as it is RWD) it will give very accurate acceleration times. 0-60 or any other speed to speed.