One bit you missed out was that carbs and ignition timing would also be tweaked on the test bed for best BHP. And likely the engine very carefully selected too - or even blueprinted.
However, torque is important. No one is suggesting you change up at peak torque. But torque, not BHP, is what makes the engine and therefore car accelerate. Of course the two are related.
The use of variable valve timing allows a good peak BHP figure *and* a decent rev range with good torque.
It is the twisting action - ie the torque - which determines the rate of change of speed. The more the torque at any one point, the faster the rate of change. Ie acceleration.
I'd suggest you find out the relationship between torque and BHP.
The SI unit for power is the watt, though in automotive environment it might be bhp or similar. Again you really ought to know this. It's GCSE O level
No its not.
A simple question.
Lets assume a car produces max torque at 2,000 rpm, and at 4,000 rpm torque has dropped off by 20%.
Are you saying the car will accelerate in 4th gear at 2,000 rpm more than in second at 4,000 rpm? Because that is what you're saying.
I can assure you that in second it will be accelerating 1.6 times as much as yours in 4th gear assuming the energy associated with rotating mass is negligible.
I doubt you would understand why either.
Power (watts) = Torque x W
Where W = is 'omega' and is specified in radians/sec
Do you know what a radian is?
Torque would be measured in N-m
Do you know what a Newton is?
1 bhp is generally taken as 746 watts. If German you might use PS which is 735.5 watts.
Peak torque will define the peak acceleration available in one fixed gear. But maximum acceleration at a speed is always at the maximum power. Advice to people starting out on race circuits, change down and then change down again.
The torque between the engine and wheel change dramatically when passed though the gearbox. That's what it does, low gear increases torque by the gear ratio, Overdrive reduce torque by the ratio. Then it gets bumped up again by the final drive ratio.
What actually drives the car is traction force. Definition of Wheel Torque is Traction Force x tyre contact radius. Traction Force = Torque / tyre contact radius. Bigger wheels, lower traction force.
The gearbox and final drive, any shafts and CV joints all have windage and efficiency losses. These turn a bit of power in to heat. But a large amount of the power/torque makes it though to the wheels.
But Newton Force = Mass x Acceleration. Acceleration = Force / Mass Acceleration = (Traction Force - drag force) / Mass
Acceleration = ((efficiency x Gear ratio x Final drive ratio x engine Torque / tyre contact radius) - drag force) / Mass -(1)
Phew!
Power = work done / unit time Work done = force x distance Power = force x speed, Force = power / speed. Multiply the top and bottom of the equation (1) by speed.
Acceleration = ((efficiency x engine power) - drag power) / (Mass x speed)
Now isn't power a lot simpler than torque? All of those nasty gear ratios and tyre size variables get lost in substitution of Power = Torque x engine speed (at road speed).
OK you still need someone to tell you the rpm/mph in each gear so you can look up the engine power at your road speed on the dyno chart. Or you just go drive it and see what rpm/mph is in each gear.
Need a dyno chart? Rototest Research Institute.
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They measure power at the hubs so don't need to guess efficiency. It seems 27 of the 530i's ponies have jumped out of the coral before getting to the hubs.
Oh. but I do. And it's a red herring as regards acceleration. Unless you think a lighter car with the same torque doesn't accelerate faster than a heavier one.
Good. You've looked it up. Now try and understand what it is.
Ok then. You've yet again not got the point.
Sigh. You don't know the main purpose of a gearbox is to multiply the torque? Did wonder when you try starting to compare apples with pears.
Not when you bring in different gearing, no. It's the twisting force at the driven wheels which counts.
Perhaps you don't realise horsepower is an imperial unit. So far easier to calculate using imperial units. Which just shows your lack of understanding of it.
That contradicts your last statment. Unless peak torque and peak BHP coincide. Which isn't really possible.
Talking about gears is a total red herring. A low gear will obviously increase the torque at the driven wheels. But assuming no friction etc losses makes no difference to the BHP measured at those wheels.
All this depends on the car, capacity of engine its maximum power torque , weight of the vehicle , its not a linear process , with modern vehicles electronically controlled its not unusual to have the outputs restricted
The Jag doesn't. The BMW has. BMW VANOS arrived in the early '90s. I had the first 24 valve engine before VANOS arrived. Extremely 'peaky' and felt very fast when you thrashed it. The later VANOS version had a much smoother torque curve and didn't 'feel' so fast. But figures showed it to be better.
I entirely agree. It depends on so many things, some of which have been discussed. But if I can indulge, at an instant in time, the instantaneous acceleration is due to power (transmitted to the wheels).
There is no contradiction. Read Peter's post until you have understood and agree there is no contradiction.
Gears are no more a red herring than torque. It is power that accelerates, and is a quantity independent of torque and gears and hence far more meaningful than torque (or gears).
Given you believe that torque determines acceleration and that gearing confuses you, it's not me who's confused.
Do you understand that for a car to attain a speed it must attain kinetic energy?
Do you understand the rate of change of kinetic energy is motive power?
When you understand these two simple concepts we can move forward. The more you try and shift incompetence onto others, the more stupid you look.
Please explain. A horsepower is merely an old antiquated measure of doing work. The English version of the horsepower is the ability to raise 550 lbs 1 ft per second, or even 33,000 ft·lbf/min. The German definition of PS is raising 75kg at 1m/sec.
But you don't seem to understand this and will claim it is me who doesn't understand simple GCSE physics.
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