how does the jerk function and engine braking vary?

[NSX_GTR_LM]

does engine braking vary as the torque curve just like accelleration? Is the jerk function based more on the engine speed? How do both of these vary on a car? Thanx in advance.

[Griffin]

Originally posted by NSX_GTR_LM
does engine braking vary as the torque curve just like accelleration? Is the jerk function based more on the engine speed? How do both of these vary on a car? Thanx in advance.

Not sure what ya mean about jerk function.

As for engine breaking yeah it varies, the amount of braking you have is directly proportional to engine speed. Higher speed. more breaking. Lower RPM, less breaking.

Griffin

[NSX_GTR_LM]

by jerk function i mean the third derivative of the position function, or the derivative of accelleration. The actual change in accelleration over time. It seems like it also varies with engine speed.

[GTS LAID]

heres an equation i came up with for Engine jerk function vs. a couple of things.


J=[Po/(m*x)] * a^(-x)

J= Jerk function
Po= Max power output
m= Mass
a= (-) slope function of Power vs. time
x= displacement

[t2000gts]

doesn't jerk = g force?

and i would venture to say the 'strength' of the engine braking does vary with the torque curve...only because it varies depending on the gear's torque multiplication as well, so torque matters. would you notice it? not likely.

[NSX_GTR_LM]

g force = accelleration, and therefore it shouldn't be equal to jerk

[Chui]

You should NOT be using your engine for braking, however...

[gts24]

Originally posted by Chui
You should NOT be using your engine for braking, however...

Chui,
could you please give me a list of VERY specific reasons why not to engine brake.

I am having a little argument with someone about this. I don't think you should do it ever with a small car like this.

[NSX_GTR_LM]

part of the reason i was interested in the relationship is more because people like to say they feel more kick in the ass when gassing it at high RPM as opposed to low, and are trying to use this as an explanation of why accelleration does not vary directly with torque, and i believe they were just feeling a larger change in accelleration when punching it at high rpm because they were overcoming engine braking as well.

[CloNeGTS]

Originally posted by gts24


Chui,
could you please give me a list of VERY specific reasons why not to engine brake.

I am having a little argument with someone about this. I don't think you should do it ever with a small car like this.

I wanna hear these reasons. What's wrong with a small car and engine braking??? Never heard of such a thing.

[Chui]

YOU'LL PREMATURELY WEAR OUT YOUR TRANSMISSION. It's not to be done with any car. Learn to properly heel and toe and use the more than adequate brakes on the vehicle. The torque reversals aren't good for the synchros the way everything is "optimized" for weight and costs these days. :rolleyes:

One thing I do do is to rev the engine in, say third gear and sometimes let the driveline resistance slow the car. If you mean doing this you're fine - except for the possibility of piston ring flutter which will result in oil consumption but ONLY under those conditions.

But if you mean driving hard, downshifting while braking and not properly rev matching, you're asking for [eventual] problems.

Also, you'll feel more jerk [acceleration] at lower engine speeds - specifically at or around the torque peak.

[CloNeGTS]

no no no......

Power braking is a compression brake, as in let the engine slow the car down while in gear. That should have nothing to do with shifting.

[t2000gts]

if you just leave the car in gear and get off the gas, that won't do much.

i limit engine braking to 4-3 shifts (6-5 for 6-speed guys) when coming to a complete stop with the AC on (with the auto, and the AC on, and a crazy throttle cable, the car doesn't want to stop).