Forum » EFI Tuning Fundamentals » horsepower target in injector sizing tutorial

# horsepower target in injector sizing tutorial

### EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals

Page 1

Hi Andre,

The example for the sizing formula in the video states 600hp. I'm guessing that's crank horsepower?

Correct, that was flywheel power.

Hi Andre

Whats the relationship between HP at the flywheel and HP at the wheels?

Is there a formula to calculate WHP using the flywheel HP?

Do you have a link to the video that talks about injector sizing?

Andy

@DPC, the link between power at the wheels and flywheel power is tenuous at best. It's an argument that's raged for as long as we've had chassis dynos and the answer sadly is complex. It's very dependent for example on the specific dyno - Our 350Z registered around 187 kw atw on our old Dynapack but it makes around 145 kw atw on our Mainline. On a rolling road the power will also vary depending on the tyre you're using and the pressure in the tyre. It will also vary depending on how hard you've strapped the car down.

A general 'guide' that should be always considered an approximation at best is on a hub dyno you might want to add around 10-15% to the hub power number, where as with a roller you're likely to be closer to 20-25%. Of course then the next consideration you need to think about is wheteher the drivetrain loss remains constant as you increase engine power? For example if you have a 200 kw atw car and you modify the engine to make 400 kw atw, has the drive train loss doubled? Has it remained at a fixed value? Or has it done something in between.

@Whittlebeast, you can find the module here: https://www.hpacademy.com/dashboard/courses/efi-tuning-fundamentals/injector-sizing/

Please note that there is an error in this module that we're aware of and we are actually re-recording this module this week along with a couple of other minor touch ups.