90GT Greg Brown Engine Build
02-05-2016, 02:24 PM
#106
Rennlist Member
no, there is no way to fool the dyno unless you lessen the mass of the over 1 ton rollers substantially. i think many can do the blip of the clutch and Gas to get a little spike that changes the peak HP output printed number. (remember andersons 420rwhp dyno run, it was really about 415 on the nice arc, but the spike at the end added 5hp) things like that.
brake dynos.. much more factors to have change, tweek and be altered.
yes, no one really cares about flyweel HP, but actually they do. is a bigger number and all manufacturers quote this, so its important. everyone uses about 15% and thats probalby close enough. thats the bragging number.
to your comment about wheel torque.... you never get that number at the dyno so, how can you care about it? you get engine torque as measured at the rear wheels. so, the real number everyone should care about is the HP,..... because that is the number that indicates the rear wheels forces you have!
brake dynos.. much more factors to have change, tweek and be altered.
yes, no one really cares about flyweel HP, but actually they do. is a bigger number and all manufacturers quote this, so its important. everyone uses about 15% and thats probalby close enough. thats the bragging number.
to your comment about wheel torque.... you never get that number at the dyno so, how can you care about it? you get engine torque as measured at the rear wheels. so, the real number everyone should care about is the HP,..... because that is the number that indicates the rear wheels forces you have!
Raw torque numbers from like inertia dyno's should -always- be identical, yet for some reason they are not. It's a simple math problem for how fast a given car can accelerate the exact same drum mass, yet somehow certain dyno owners figure out a way to improve the results over what the next one reads. So users flock to that guy because he does a much better job representing what their dollars bought. Ahem.
Water-brake and to a lesser extent eddy-current dyno's allow some room for interpretation. For the brake dyno it's variables around pump efficiency and internal recirculation. Plus the density of the water changes with temperature, but amazingly that little feature corrects out a lot of the air-temp correction if you are only doing one pull and can keep the water close to ambient air temp. The eddy-current dyno's are much better but folks still try to out-guess the heat loss in the generator to make "better" numbers.
Then there will be operators who figure out how to come up with a high "flash" reading, something to brag about but nowhere near useful; the engine was pinging/detonating like mad! And not much chance the fuel will be that cold in real-world driving conditions. Stupid stuff.
And correcting fro driveline loss? Who cares, if the engine is going to be used in the car it's tested in? I'm not so interested in how fast the engine can spin up the smog pump or other accessory as I am in how much torque is available to accelerate the car. So wheel torque is the number I'm looking for.
Water-brake and to a lesser extent eddy-current dyno's allow some room for interpretation. For the brake dyno it's variables around pump efficiency and internal recirculation. Plus the density of the water changes with temperature, but amazingly that little feature corrects out a lot of the air-temp correction if you are only doing one pull and can keep the water close to ambient air temp. The eddy-current dyno's are much better but folks still try to out-guess the heat loss in the generator to make "better" numbers.
Then there will be operators who figure out how to come up with a high "flash" reading, something to brag about but nowhere near useful; the engine was pinging/detonating like mad! And not much chance the fuel will be that cold in real-world driving conditions. Stupid stuff.
And correcting fro driveline loss? Who cares, if the engine is going to be used in the car it's tested in? I'm not so interested in how fast the engine can spin up the smog pump or other accessory as I am in how much torque is available to accelerate the car. So wheel torque is the number I'm looking for.
02-06-2016, 02:36 AM
#109
Of course that makes sense. Unfortunately, It seems that is keeping darton from making mid (wet) sleeves for the 928.
05-02-2020, 09:22 PM
#112
Rennlist Member
Jim,
nice to hear directly from you since this is your car. I remember back when I was young and Rolls/Bentley used to refer to their engine power as “Adequate”
nice to hear directly from you since this is your car. I remember back when I was young and Rolls/Bentley used to refer to their engine power as “Adequate”