bhp question..

[Matt82]

An example: 200lbft at 2000 rpm, or 100lbft at 6000rpm, which produces the most accelleration?

The second one while making half the force, is making that force three times as often, so the total work done is higher. Higher value of work done means more energy has been used and that energy is being put into accellerating the car...

what do you make of that statement? im too tired to get my head around it completely

 

[Matt82]

pretty obvious isn't it?

so obvious i had to post up and ask

the torque is the force behind the acceleration felt, so less torque, less acceleration

 

[Matt82]

the figures in the example are the same engine

but will it accelerate faster at 2krpm (with 200lbft) or at 6krpm with 100lbft, in the same gear

 

[Matt82]

It's right and its why we should laugh at the bloke down the pub who reckons his diesel crapbox is 'well fast' because it 'has loads of torque'

its not a diesel/petrol thing

peak torque wasnt mentioned at all, its the same engine, same gear, but does it accelerate harder at 2k or 6k rpm

 

[Matt82]

Without gearing, at 2000 RPM. However, if you are travelling at 20 MPH at 2000 RPM, increasing to 6000 RPM will take you to 60 MPH. But, if instead you change gear at 20 MPH so that you are at 6000 RPM, the resultant torque changes from 200 lb-ft to 100 lb-ft * (6000/2000) = 300 lb-ft.

and in that lower gear, if you were at 2krpm, that would = 600lbft. non?

 

[Matt82]

i give up... more torque at more rpm = better

vtek diesel for the win

 

[Matt82]

If we we're doing it properly we would take the integral of the portion of each cars power curve in the rpm range used during the acceleration. But its so much easier to quote peaks.

its the same car, same engine, same gear but is it more accelerative at 2krpm or 6krpm

 

[Matt82]

and how does "more work being done" translate to "pushing the car down the road harder"?

 

[Matt82]

...at the instant at which the engine is producing 200lbft, isn't it producing more acceleration than the instant at which it's producing 100lbft???

thats what i thought. 200lbft twist is a stronger twist than 100lbft

 

[Matt82]

Yes but you are getting either 2K strong twists or 6K weaker twists.

1 Strong push per second moves you 2 foot across the floor, 3 weak pushes per second move you 3 foot across the floor. The 3 weaker pushes accelerate you faster and provide more power.

its not an impact gun, it turns in one continuous motion

with low torque, high rpm (high bhp) you can make a quick car (imagine a little honda vtec) because the lower gearing.

higher revs allow for lower gear, getting more torque to the road. the honda is quick because the gearing is lower not because its doing 9000 small pushes....

 

[Matt82]

when i get home ill be able to dig out some of the plots we had when we had put gtech on our cars. that can plot torque vs G force

 

[Matt82]

keates

rate of acceleration is measured metres per second per second.

if using the same car, 2nd gear and accelerating from 2krpm (200lbft) and then accelerating from 6krpm (100lbft), which will have the higher rate of acceleration? OTBE

 

[Matt82]

thanks, it was logical then, as i expected haha

 

[Matt82]

i think youre just adding unnecessary confusion, it doesnt need to be that difficult at all.

gearing it mentioned, its the same car so the gearing is the same, for the sake of arguement make it first gear

so far, for the "bhp=acceleration" arguement, the only reason is that at higher revs its doing the torque more often (which makes no sense to me because the engine isnt an impact gun, it rotates smoothly consistently)

i want to find my gtech plots to show how torque corelates to G