Originally Posted by WDCreech
Dynomometer or weight/e.t. calculator!
A crankshaft dyno will tell you power off the shaft in the configuration the engine is tested with in the dyno room.
The disappointment begins with chassis dynos and et calculators as the power you thought you built goes away pretty fast with the installation. The dyno guys like to use a pretty conservative formula to compute back to crankshaft power. But this formula only takes into account averaged driveline and tire losses. It does not take into account the differences between accessory power consumption dyno to installed nor losses of exhaust and induction which can become considerable with nothing more than pipe length changes or additional bends. These little things add up fast.
Ages ago when I worked in Ford's dyno room we found it was pretty easy to loose nearly half an engine's crankshaft power measured in the engine dyno room to what got delivered where the rubber meets the chassis dyno roller. These were Y-Blocks and early FEs and MELs and the losses of installtions, drivelines, and bias tires of the age were undoubtedly higher than those of today. But I think this makes a reasonable benchmark when playing with numbers for average installtions.
While ET doesn't lie, there's a lot of variables involved, even more than a chassis dyno as now you have the environment, driver reactions, and chassis dynamics involved.
The nice thing about knowing engine room dyno numbers versus chassis dyno, and ET is these things identify the areas that need to be worked to reduce the difference between the the engine dyno numbers and the installation and operational numbers. This also part of tuning, goes back to speed costs money, how fast can you afford to go.
The pros get this data and grind to to grist all the time, makes it hard to run against the big money.