Blipping The Throttle

[PumaRacing 1]

You own a car with an engine that produces 150 bhp at 6k rpm. It certainly feels nippy out on the road and after taking it for a thrash one day you're sitting on the drive blipping the throttle. For what purpose is unclear. Maybe just to annoy the neighbours.

 

You find that you can actually use full throttle but only for a second or so because the engine hits the redline very fast. However, you mash the pedal to the floor with the engine at tickover and hold it there until the revs just hit 6k and then release it fast before the engine overspeeds.

 

When the engine hits 6k with the car stationary and no load of any sort being applied is the engine producing any power? If so how much? Where is the power going? How hard is the engine working at 6k when the car is stationary compared to doing 6k at full throttle and a steady speed up a steep hill?

[Martin@PRD 0]

Good one that David, you should start a pub quiz down at your local,

 

I was always lead to believe torque is the turning force and power was the ability to create it, so torque has something to do with it in this riddle, but how I’m not sure though wouldn’t the most of power be lost through heat?

 

I guess no power as there isn’t any instruments to measure it (A tree falls in a empty wood but does it make a sound if there isn’t anyone there to hear it?)

Edited March 10, 2006 by Martin@PRD

[boombang 2]

and if you drive past a tree at 120MPH and then it falls, does it make a sound if no-one else is around to hear it?

 

 

btw this has started a good debate in the office and no-one has an actual answer!

Edited March 10, 2006 by boombang

[Rippthrough 98]

If there was no power being produced then no fuel would be burnt and the engine would be at 0rpm.

Edited March 10, 2006 by Rippthrough

[Martin@PRD 0]

If there was no power being produced then no fuel would be burtn and the engine would be at 0rpm.

 

Heat (friction) and power to turn mass (engine componments)

[efy2bjg 0]

The engine is producing full power. The revs build very fast due to the small amount of power required to spin up the flywheel. As the drive line is disengaged, all of the engine energy/power is going straight into kinetic energy now stored in the flywheel. Cylinder pressures therefore load are low as the piston is easily pushed down during the power stroke due to the lack of resistance.

 

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Ben

Edited March 10, 2006 by efy2bjg

[Rippthrough 98]

Heat (friction) and power to turn mass (engine componments)

 

+ heat in exhaust + energy to accelerate components + energy to accelerate airflow + energy absorbed by ancillaries......

[boombang 2]

Wikipedia states:

 

"Brake Horsepower (bhp) - The measure of horsepower at maximum engine output, minus power lost from heat, friction, expansion of the engine, etc."

 

so by their definition the above doesn't matter.

 

Realistically surely only torque can be measured and BHP is derived from torque with a constant.

 

What I can't get straight in my head is if the engine is producing full power or because of lack of resisitance on it the torque is lower and bhp lower too - but is torque lower as there is less resistance?

[Ahl 4]

I don't think horsepower/torque is really the issue in this.

Ignoring the engine heat and friction losses, the engine is only producing as much power as is required to overcome the friction of the gearbox oil and shafts.

 

Kinda like what efy2bjg said, but it won't be putting out anywhere near full power, and it'll be using little fuel etc.

 

The engine would work much harder and produce much more power at full throttle, going up a steep hill.

[Martin@PRD 0]

Isn’t torque only evident when subjected to forces?

 

So if some power is lost through heat sound and vibration is the rest stored in the ‘’charged’’ components?

 

-------------------------------------------------------------------------------------------------

 

Dave stop pissing your self with laughter, it not fair playing god with us puny earthlings!!!

Edited March 10, 2006 by Martin@PRD

[mfield 20]

Probably completely wrong but,

 

Yes it still producing power

still 150bhp

The power is still going the same place as before

And really have not got a clue about load up a hill but would that be the same aswell ?

[Rippthrough 98]

Wikipedia states:

 

"Brake Horsepower (bhp) - The measure of horsepower at maximum engine output, minus power lost from heat, friction, expansion of the engine, etc."

 

so by their definition the above doesn't matter.

 

Realistically surely only torque can be measured and BHP is derived from torque with a constant.

 

What I can't get straight in my head is if the engine is producing full power or because of lack of resisitance on it the torque is lower and bhp lower too - but is torque lower as there is less resistance?

 

 

He asked about power at the end not bhp - so it's definately producing power. It will be producing power - the energy produced (which isn't being lost) is being stored in the components.

[sekim 0]

I think it will be producing full power.

 

If the throttle is wide open then it will be drawing in as much fuel and air as possible. The power it's producing will go into accelerating the engine internals, flywheel etc.

 

I don't think engine "load" is relevant... does an engine produce less power in 1st gear at 6krpm and full throttle than in 5th? I can't see that it should....

 

That's my best, un-educated guess anyway

[Rippthrough 98]

Slightly less than full power.

 

The airbox isn't getting fed cool air from the front of the car any more, it's having to pull it through

[Martin@PRD 0]

My final answer,

 

If the foot is off the pedal at 6k then

 

When the engine hits 6k with the car stationary and no load of any sort being applied is the engine producing any power? ----- None?

 

If so how much? ------ Minus

 

Where is the power going? ----- Losing with compression, vacuum, hydraulic pressure, heat, frication and mass of components?

 

How hard is the engine working at 6k when the car is stationary compared to doing 6k at full throttle and a steady speed up a steep hill? --- about the % of efficacy lost by other forces?

 

If not right can I phone a friend?

Edited March 10, 2006 by Martin@PRD

[boombang 2]

He asked about power at the end not bhp - so it's definately producing power. It will be producing power - the energy produced (which isn't being lost) is being stored in the components.

but how do you measure that power and compare to the 150bhp if you don't use BHP?

 

 

however if you re-arrange the order of sentences in the first post:

 

"When the engine hits 6k with the car stationary and no load of any sort being applied is the engine producing any power?"

 

yes because:

 

"You own a car with an engine that produces 150 bhp at 6k rpm" doesn't say owt about load there does it

[Rippthrough 98]

but how do you measure that power and compare to the 150bhp if you don't use BHP?

however if you re-arrange the order of sentences in the first post:

 

"When the engine hits 6k with the car stationary and no load of any sort being applied is the engine producing any power?"

 

yes because:

 

"You own a car with an engine that produces 150 bhp at 6k rpm" doesn't say owt about load there does it

 

Whether you measure it or not it's still bloody there. You can measure the fuel and air being consumed if you like instead.

 

Do people dissapear when you can't see them?

[Rob_the_Sparky 9]

You own a car with an engine that produces 150 bhp at 6k rpm. It certainly feels nippy out on the road and after taking it for a thrash one day you're sitting on the drive blipping the throttle. For what purpose is unclear. Maybe just to annoy the neighbours.

 

You find that you can actually use full throttle but only for a second or so because the engine hits the redline very fast. However, you mash the pedal to the floor with the engine at tickover and hold it there until the revs just hit 6k and then release it fast before the engine overspeeds.

 

When the engine hits 6k with the car stationary and no load of any sort being applied is the engine producing any power? If so how much? Where is the power going? How hard is the engine working at 6k when the car is stationary compared to doing 6k at full throttle and a steady speed up a steep hill?

 

Engine is producing the normal power you would expect at the throttle/rev combination. Power is going into a combination of increasing Kinetic energy in the rotating masses of the engine, friction losses and pumping losses (if that is the right word for it). Since none of these are particularly large the revs raise rapidly and throttle must be released to prevent the engine either grenading or hitting a limiter.

 

At steady speed up a hill the engine is producing the same power (assuming you are still using full throttle to maintain a steady speed) but the power is transferred to an increase in potantial energy in the car as well as all the engine/drivetrain losses.

 

Rob

[cybernck 400 1 Cars]

what's also interesting is when someone first fits a boost gauge to his turbo car,

tries revving it and gets no boost registered, although the dump valve is obviously

releasing the compressed air out .

[Rippthrough 98]

what's also interesting is when someone first fits a boost gauge to his turbo car,

tries revving it and gets no boost registered, although the dump valve is obviously

releasing the compressed air out .

 

Turbo lag + instrument lag.

[cybernck 400 1 Cars]

i don't recall saying "in the first second of revving"... as it doesn't happen at all.

[Rippthrough 98]

i don't recall saying "in the first second of revving"... as it doesn't happen at all.

 

 

Hold it on the red line at full throttle and it will.

 

Wouldn't want to though.

Edited March 10, 2006 by Rippthrough

[Martin@PRD 0]

Come on Professor chuckle buttie, give us a clue

[RichF 1 2 Cars]

ok I'll bite...

 

I've always considered power (in whatever units e.g. BHP) to be the energy required to cause a positive change in kinetic energy or to maintain kinetic energy against forces that are acting to reduce it e.g. friction.

 

Obviously in Dave's scenario kinetic energy is only changing whilst the revs are rising and the rate of change (in other words the time taken to get the engine from 1000rpm to 6000rpm) is much faster when there's minimal load on the engine.

 

So I reckon the power is still 150BHP (at the point where the revs just hit 6000rpm) and all of it (save for the noise, heat etc. losses) is directed at getting the engine components up to speed.

Edited March 10, 2006 by RichF

[Daxed 7]

Having mulled over this one for quite a while whilst the dinner is cooking, I feel safe in saying it probably depends on how many 'springs' you have in your engine at the time.