YACT: Loss of energy during shifting

[Goosemaster]

I've been watching speed channel sparingly for a while(few weeks) and have notcied something [that is possibly quite] interesting.


I notice a GREAT DEAL of wasted energy during shifting in both Drag strip and in autocross(?term?) ..as in the car sort of "jumps." I have read a little bit about how the porshe 911 "hops" at the drag strip, which is what caused me to notice this.


Is it atrributable to bad drivers or just powerful clutches? If due to the powerful clutches, isn't that a waste of energy, as it seems to slow the cars down?

Couldn't someone develop a system that times the engine rotation with the clutch rotation, sort of a like an automatic manual transmission, using a cyllonoid(sp?) controled mini-motor to rev-match?


It seems like this would
a) reduce clutch slippage
b) reduce the engine compression which reduces revs/s and engine efficiency of a high--reving engine, as the slower revolving engine slows the clutch and therfore the overall car


Excuse any errors

 

[AgaBoogaBoo]

Originally posted by: Goosemaster
Excuse any errors

excused 😛

 

[Evadman]

The "hop" is the kenetic energy of the flywheel and engine internals being transfered all at once downstream. It is possible to release this energy in a more controled manor, but then you are releasing stored energy, not generating more, which = slower. It is really only detremental if the drive tires break loose because of the momentary surge.

<edit>
wait a minute, are you talking about how the front of the car rises upon shifts? (not neccewssary off the ground, but the front end comes up.)

When under acceleration, the front of your vehicle risies due to torque. All wheel driven vehicles do this to some extent. This is actually a good thing, because it transfers weight to the rear of the vehicle (where the drive wheels are) and helps the rear wheels get more traction. Also, you will notice that in most instances the passenger side raises higher due to the rotational energy of the engine. Most drag racers will have different spring rates between the driver and passenger sides in the rear due to this. it would be bad if the passenger side rear tire came off the ground, or if the weight was reduced too far.

Granted, this is wasted energy to some extent for 2 reasons. The first is why spend energy raising the front of your vehicle from the ground? you want it to go down track. Hence: wheelie bars. The second is that a vehicle is not very aerodynamic when the front wheels are 10' from the ground, as Don Garlits has proved. Standing a top fuel dragster on its rear wing takes skill 😛

 

[Goosemaster]

Evadman, I was reffering to when cars sometimes I see drag races where it seems as if they are using the engine-braking-technique. The car seems to lower, such as when you engine brake and the car surges foward and down. They seem to noticably lower in velocity.


Maybe they were isolated instances.


I do understand your edit...I was reffering to something else, which you sort of addressed in the beginning of your post. Still good info.

Thanks anyways

 

[Evadman]

Originally posted by: Goosemaster
Evadman, I was reffering to when cars sometimes I see drag races where it seems as if they are using the engine-braking-technique. The car seems to lower, such as when you engine brake and the car surges foward and down. They seem to noticably lower in velocity.

You may be watching a ET limited race. Some classes state that you can run no quicker than say, 8.8 seconds. If you cross under 8.8, you loose. This is called "breaking out". In most cases, you will have a vehicle that will easily do faster than the breakout limit, and need to apply a breaking method at the far end of the track. What you want to do is get as close to the breakout time as possible without crossing below, but still beating your opponent. This may require slowing down (and usualy does)

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