Eh?
till you hit 10k posts is the reference here I think.
bhp question..
- Thread starter Matt82
- Start date
till you hit 10k posts is the reference here I think.
The first, 2000 RPM.
All I'm saying is that it's not the maximum potential rate of acceleration at that velocity if you are able to choose a different gear
Soldato
- Joined
- 10 Mar 2006
- Posts
- 3,975
10k posts
It's all about time really isn't it. I was thinking about this the other day and even though it doesn't really make sense to my feeble mind to include time in the equation, it's definitely needed.
It's all about time really isn't it. I was thinking about this the other day and even though it doesn't really make sense to my feeble mind to include time in the equation, it's definitely needed.
Opps!
I'm curious, will I feel any different on 10k or 10,001 compared to my current 9,997?
Or a slightly different approach to the same chart. This time, RPM is the constant gradient.
This chart lets you choose the gear for maximum acceleration (resultant torque). When the torque lines cross, in this case at 30 MPH, you should change. The next gear offers more.
This chart lets you choose the gear for maximum acceleration (resultant torque). When the torque lines cross, in this case at 30 MPH, you should change. The next gear offers more.
Caporegime
- Joined
- 18 Oct 2002
- Posts
- 37,804
- Location
- block 16, cell 12
thing is, the car with 200lb torque at 2000 rpm can be faster than a car with 100lb at 6000rpm, because you havent said that the 200lb at 2000rpm is the 'peak' output...nor do we know its redline, it could peak 200lb at 2k rpm and maintain that all the way to 9000rpm...(unlikely but possible)
my car has the impossibly low 130lb torque @ 7000rpm. will i outdo most 2.0 tdi's in a rolling drag? yes but also maybe and for various reasons;
firstly they rev limit to 4k - 4.5k or whatever it is, i can go to 8400rpm havign quite a long 1st and 2nd gear (1st goes to 45mph, 2nd goes to 64 mph) most common cheap TDI wont do that and may require 3rd for 60...costing them time and effort allowing me to jump ahead.
however, if we were both at 40mph and i was in 3rd gear and he was also in 3rd gear - he would ream me because i would be out of my power band but he would be closer to his...
so to answer the questions, it depends on what RPM you start and how steep the power curve is to decide which is quicker but given the question of 2x identical weighing cars that happened to both have the exact same speed (one at 2k and the other at 6k) and they both floored it at the same time, then presuming that the peak torque has already been reached its the engine that can flow better and should usuallly be the 6k car that accelerates the fastest...
my car has the impossibly low 130lb torque @ 7000rpm. will i outdo most 2.0 tdi's in a rolling drag? yes but also maybe and for various reasons;
firstly they rev limit to 4k - 4.5k or whatever it is, i can go to 8400rpm havign quite a long 1st and 2nd gear (1st goes to 45mph, 2nd goes to 64 mph) most common cheap TDI wont do that and may require 3rd for 60...costing them time and effort allowing me to jump ahead.
however, if we were both at 40mph and i was in 3rd gear and he was also in 3rd gear - he would ream me because i would be out of my power band but he would be closer to his...
so to answer the questions, it depends on what RPM you start and how steep the power curve is to decide which is quicker but given the question of 2x identical weighing cars that happened to both have the exact same speed (one at 2k and the other at 6k) and they both floored it at the same time, then presuming that the peak torque has already been reached its the engine that can flow better and should usuallly be the 6k car that accelerates the fastest...
You are just adding unnecessary confusion; the original question was very specific, two torque figures and two RPMs and the instantaneous acceleration in either case. Providing the gearing is optimal for each engine, the one producing the most power will be accelerating hardest at that point.
Caporegime
- Joined
- 18 Oct 2002
- Posts
- 37,804
- Location
- block 16, cell 12
he doesnt say if the torque increases or is that IS peak torque, not does he mention the gearing these are important to get a greater understanding than a dumbed down x=y and therefore 100lb wins!
true if you want to protect his mind and ensure that he does not think outside the box, you could just re-quote back to him torque x rpm but that doesnt really help with practical implementation, nor would it help him superimpose the same criteria to differet cars/outputs/reality without understanding more of the dynamics involved.
true if you want to protect his mind and ensure that he does not think outside the box, you could just re-quote back to him torque x rpm but that doesnt really help with practical implementation, nor would it help him superimpose the same criteria to differet cars/outputs/reality without understanding more of the dynamics involved.
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
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
What you are missing is it is producing that twist 2000 x per minute, the other engine is producing half the twist but at 6000 x per minute.
Then there is the curve, we are talking acceleration, so how does the torque drop off above 2000rpm? as soon as you accelerate, the engine is no longer doing 2000 rpm, its is now doing 2100 rpm, so what is the torque now? (this is the main issue with diesels if you want to think of it in that context).
Compare with a Bike engine that makes lower torque, but revs to 12000 rpm, so ultimately, produces more BHP than a 1200 car engine of the same or much higher torque. In a 500kg car, which will accelerate faster? the 1200 Car engine or the 1200 bike engine? (I already know the answer to this as my 1200 bike engine kitcar made 0-60 in 3 seconds).
Torque is only one part of the equation, you need to look at the HP as well, which is calculated Horsepower = Torque x rpm / 5252
therefore the 2 examples...
200x2000/5252 = 76.16 hp
100x6000/5252 = 114.24 hp
Now, for a given car weight, which do you think will accelerate faster?
EDIT: Bah got beaten to it xD
Then there is the curve, we are talking acceleration, so how does the torque drop off above 2000rpm? as soon as you accelerate, the engine is no longer doing 2000 rpm, its is now doing 2100 rpm, so what is the torque now? (this is the main issue with diesels if you want to think of it in that context).
Compare with a Bike engine that makes lower torque, but revs to 12000 rpm, so ultimately, produces more BHP than a 1200 car engine of the same or much higher torque. In a 500kg car, which will accelerate faster? the 1200 Car engine or the 1200 bike engine? (I already know the answer to this as my 1200 bike engine kitcar made 0-60 in 3 seconds).
Torque is only one part of the equation, you need to look at the HP as well, which is calculated Horsepower = Torque x rpm / 5252
therefore the 2 examples...
200x2000/5252 = 76.16 hp
100x6000/5252 = 114.24 hp
Now, for a given car weight, which do you think will accelerate faster?
EDIT: Bah got beaten to it xD
If you work on this basis, so that the drive wheel is already rotating, and being driven by each engine. Allow the wheels to suddenly come into contact with the road, which will then accelerate the fastest?
Or you dump the clutch in 1st gear on the car 200@2000 or 100@6000? which will accelerate faster?
This is where torque supplies the initial motive force, however, you cannot ignore the fact that 200 torx is being provided 2000x per minute and 100 torx is being provided 6000 x a minute, smaller pulse, but way faster. Ultimately the smaller force will win out through sheer number of deliveries.
This is the work rate of the engine. Torque is the forces abilty to provide rotation, rpm is the number of times per minute it can provide that force.
One last thought, pretty much any human can provide 200 torx to a bolt, actually quite a bit more with the right tool, but unlikely to be able to do it at more than 1rpm.
Which can accelerate faster? the man 200 torx at 1 rpm, or the engine providing 100 torx at 6000 rpm?
All should now be clear
Caporegime
- Joined
- 18 Oct 2002
- Posts
- 37,804
- Location
- block 16, cell 12
thing is, if you regard the gearing as being identical... one car at 2000rpm will be doing say...10mph...and the other ar 6000rpm will be doing 30mph...so one car would already be going much faster than the other at a set point. hence you need to understand about how the gearing would work, and therefore about higher/lower rev limits and about peak torque numbers to contextualise what is happening. Otherwise, things like drag, weight and umpteen other things become a relational factor?
if you want to keep it dumb - can you not just accept the answer from page 1 that torque x revs = power and leave it at that?
If the gearing is the same then the lower power engine wins I'm afraid, this is why I stated gearing must be optimal for each engine. The point is that engine torque is pretty irrelevant, it's the torque at the wheels that gives you acceleration.
For the sake of argument assume the overall gearing in first gear is 13:1 (which you'd get from a first gear ratio of 3.7:1 and a final drive of 3.5:1, not uncommon values). Ignoring losses, the 200lbft engined car will be producing 2600lbft at the wheels. The 100lbft engine is producing half that. The instantaneous acceleration will therefore be around half for the more powerful engine.
Now if the gearing is adjusted for the more powerful engine to acheive the same wheel speed as the less powerful one, you end up with a gear ratio of 39:1, giving a wheel torque of 3900lbft, nearly twice that of the less powerful engine at the same road speed.
As you can see, the gearing of a car has to be matched to the engines characteristics to make the best use of them.
No because thats wrong, torque and power graphs should always cross at 5252 rpm, so you need to add in the /5252 in as well
I'm very confused, I thought it was really simple, isn't the measured Torque value a 'mean' over the entire revolution of the engine? and not 'peak' Torque of each detonation?
If so, then the 200lbft@2K would accelerate quicker?
Here's some info (if valid)
http://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htm
The key line being
If so, then the 200lbft@2K would accelerate quicker?
Here's some info (if valid)
http://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htm
The key line being
So think of it as..:
If first car is at 2 rpm and second car is at 6 rpm then, each car is producing x torque / y length of time it's being produced for.
So car 1 produces 200 / (1/2) = 400 acceleration (1 second / 2 rpm) while car 2 produces 100 / (1/6) = 600 acceleration
On a side note, am I right in thinking that the most fuel-efficient acceleration is throughout the 'high-torque' band?