Engine braking torque... good method to guesstimate?

[Mr Whippy]

This is in relation to a simulation for a racing sim.

http://forum.racesimcentral.com/showthread.php?t=2...

I've been playing with simulating cars for years and years now, and in this case I feel the author of the physics has got the engine braking torque a little low for the car.

Now, currently, the engine braking torque is ~ 110Nm at 7000rpm, linearly dropping to a 0Nm at 0rpm.

The Z06 engine develops about 500bhp at 6500rpm ~ 540Nm

So lets say we have an engine that puts out 500Nm at 7000rpm, but will brake at 100Nm off the throttle?


So...

Does that sound right to anyone? I feel it should be more like half the power output at those rpm's, about 270Nm.

Are there any good rules of thumb for engine braking torque and internal friction losses?

Thanks for any help

Dave

[ridds]

Very dependant on ring pack design, cylinder honing, bearing clearance, piston clearance, etc etc etc.

You're not a million miles away with 100 Nm

[GreenV8S]

If you have the car to play with, you can measure it easily enough.

If not, perhaps the rules of thumb described here will help.

[Mr Whippy]

Hmmmm, well I finally decided to have a look at 'Desktop Dyno 2003'

It gave me enough clues as to what expect for certain engines, and some interesting trends

I think I'd have to collate some info and try work out a good rule of thumb, though the Puma Racing site (forgot about that) is pretty good.

I intend to measure the data for my road car (simulating that too, just for fun), however I don't have access to a Z06 to test with

My logic is to do coastdown from 4000rpm to about 1000rpm in various gears with the clutch up and down, then match these times/accelerations in-sim.
Ultimately, the difference between two runs (clutch up/down) will be the engine braking component, and that left will be the component of the drivetrain, aero and tyre drag, and then by using several different gears I can determine how that changes (hopefully )

Sounds a bit geeky, but for me it's interesting

Dave