Sorry mate, just making sure where on the same page here, if the engine is at it's most efficient at peak torque and let's say a TBC petrol engine's peak torque is at 2300 RPM. Doesn't that throw the RPM X Torque thing out the window? If it was a N/A with liftcam like a Type R that would make sense.
No. Power = torque x rpm thing is fixed. They are directly related, and the relationship is mathematical one. Doesn't matter whether it is a turbo, diesel, petrol or whatever. In imperial terms Power
(in hp) = (Torque
(in lbf) * rpm
) / 5252
(this is why if you look at any legitimate imperial unit dyno graph the power and torque lines will cross at 5252rpm).
From that for your figures for the Focus ST, 270lbf torque at 1750rpm means the car manages 90hp at 1750rpm, while the 250hp at 5500rpm means it is managing to still produce 236lbf of torque at those revs. The BMW has peak torque at 2500, managing 232lbf. But from the 265hp at 6600rpm it has managed to still be producing 211lbf at 6600rpm.
Remember that as long as torque is not falling away too quickly power can still be going up. Hence for your example turbo petrol engine after 2300rpm acceleration is reducing even though peak power might not be until 5500rpm.
For fun, compare the figures above with this graph
for a somewhat played with 2 stroke 125cc bike. This is producing peak torque at 10000rpm, same revs as it produces peak power. This is producing a hell of a lot of torque for its engine capacity, with 13.13lbf (1/17th of the torque of the BMW 130 for an engine 1/24 of the capacity), but with such a peaky power delivery there is no way it would be described as torquey (great fun though).
But that would be ideal would it not? Especially in a performance orientated hot hatch style of car. If a competitor has a top speed of 130 and you create more torque balanced across the gearbox to achieve 150MPH, then said manufacturer wins top trumps.
To an extent. Produce X torque a Y rpm and you will have to use higher gearing than another car that produces the same X torque but at 2Y rpm. Hence at any particular speed despite having the same amount of torque the 2nd car has twice the thrust. Hence why you want torque over a wide rev range, with the torque hanging on for as many revs as possible. Same torque produced at higher rpm will result in a higher top speed. If you have an engine biased to torque at low rpm then you will lose out on top speed.
It isn't the gearbox giving you that torque. The higher the gearing the more thrust (which is the torque you feel) that you lose at the wheels.
There's a specific reason they turbocharge cars to produce more torque and HP than there naturally aspirated brethren or it wouldn't be worth doing.
Turbos give you a bit more power on the cheap, as far as fuel consumption, weight, etc, as they are taking advantage of wasted energy in the exhaust, hence why they are popular. But they are gaining more torque than they are losing rpm for that torque.
That said, personally I would prefer a normally aspirated engine which revs out, with peak torque at fairly high rpm (hence when you start to push it, it is like the engine is encouraging you saying 'thrash me, thrash me', while the one with torque at low rpm and dropping off is saying 'I am bored, change up and go to sleep'), and rather more instantaneous throttle response.
In sixth there's one MPH between them, although I can see what BMW have done..
The BMW is geared for about 175mph at peak power in top gear (not a hope it would manage that) while the Ford is geared for just under 150mph at peak power in top gear (which it should manage). Seems the BMW is geared for cruising (can always change down for decent umph) while the Ford is has a closer ratio box
Enjoying this Keith, I know text can come across as a little stabby so don't take anything I put down as undermining or aggressive
I have spent a fair bit of time playing around with power / torque figures and gearing, when trying to work out gearing that works for doing top speed runs on bikes. With some highly tuned bikes it is entirely possible to have enough power to hold a speed, while the rev range that useful torque is produced over is so small that you can't reach that speed. One example was a bike that had enough power to hit 265mph, but gear it to do that speed and between ~235mph and ~260mph in top it didn't have enough thrust to even maintain speed, let alone accelerate.
All the best