Ron - how would you calculate from a chassi dyno number to flywheel hp on a 4-speed car ? take 75% of the number you believe to be actual ? ie... (guess) 556 x 75% = 417rwhp ? That is how I arrived at the numbers... I remember it was 416.8hp and 442tq... at the wheels...
That's probably pretty close....a 25% drop from the crank to the rear wheels is reasonable. The problem being is that Chassis dyno numbers can be all over the map. Some read high while others are very conservative. An engine dyno can also be inaccurate as well....depends on the calibration/operator and correction factors.
Regardless of what the readings are/were....that is a pretty stout combo and i'm sure your customer is happy. Again, very good job !
Ron
Why do most people say you loose about 25% between engine and rear wheels?
Certainly the transmission, driveshaft and rearaxle rob power.
Just an example:
You run a car on a dyno with a 100hp engine you might get 75hp at the rear wheels. That´s a loss of 25%.
All the parts between engine and rear wheels take 25hp.
Take the same car and only change the engine with 500hp.
Now take away the 25%. You should have 350hp at the rear wheels. The same transmission, drive shaft and rearaxle now robs 150hp
compared to the 25hp on the 100hp engine?
This is why I don´t believe in that % stuff.
If it takes 25hp to move all the parts, it always takes 25hp no matter what engine.
Correct me if I´m wrong.
Mario
Efficiency is a ratio of ouput over input and will always be a percentage. Consider the input that is put into the car coming from the flywheel and the output is what you get at the rear wheels. A percentage is lost throughout the drivetrain, not a fixed amount. If the drivetrain is 75% efficient, then a 25% loss occurs. I do know that efficiencies do change at different loads, rated efficiencies are usually full loads. 75% is just a good estimate.
