My BMW had good enough tyres to allow a full bore takeoff from rest in a straight line even in the wet. The problem was pulling out from a side road etc on lock. Like all RWD cars, far more likely to have traction problems then.
or too little power :)
230 bhp. And a much better power to weight ratio than your Jag MkII which was so good at spinning its wheels. ;-)
The Jag was on narrow crossplies.
The power to weight ratio is almost identical on the two vehicles.
Not really. BHP in the days of the Jaguar were more ponies than horses. Even before Jaguar exaggerated the figures. MkII Jags may have been fast in their day - but pretty average in modern terms.
So, you meant to say that on anecdotal evidence the power to weight ratio was 'much better' for the BMW than the Jag.
Even though the figures available say otherwise, and place them as almost exactly the same.
No doubt Germans would only ever release accurate figures, and the British always inflate theirs.
For a forty year age gap between the two vehicles, I think the Jag was pretty incredible.
Born out by performance figures. Unlike maker's BHP claims, they don't lie if from a respected source.
Which MKII Jag and which BMW?
More a question of age. The way BHP is measure changed over the years.
I had two of them. Nice enough cars, but a bit over-hyped. Apart from the looks, of course.
What didn't I like? The dreadful steering. Low geared and still heavy. The pedestrian gear change.
530i e39 and mkII 3.4
OK, then, here we go:-
Engine size nominal BHP Weight (kg) 0-60 (seconds) MkII Jag 3.4 210 1499 11.5 BMW E39 3.0 231 1605 6.9
And as regards interior space and boot, a 3 Series is closer to a MKII than a 5 Series.
you stated 'much better ' power to weight ratio. using your figures above jag 140 per tonne bmw 144 per tonne
using car folio figures you get: jag: 210 and 1448 gives 145/tonne bmw : 228 and 1605 giving 142/tonne
Neither vehicle by either set of figures is 'much better', it is a tiny difference (about 2 percent or so either way) and could be negated by a tank of petrol, different octane fuel, or a fat driver or even where you get your car weight figure from
0 - 60 figures are irrelevant to your claim and would be vastly influenced by skinny old tyres on the jag and slicker gearboxes on the bmw.
I can't see how 0 - 60 figures are irrelevant when it comes to power. Twice the time suggests 1/2 the power.
I would say skinny / fat tyres are starting to become insignificant, as would an extra second in gear changes.
It you want to compromise as say 'power at the wheel' then we could all move forward, otherwise the numbers / times speak for themselves.
Not sure they do - a 5% increase in bhp/torque leads to a much quicker car - 8.5s in the case of the 3.8:
Yes. Backing up my theory that Jaguar weren't too accurate about the BHP output in the older days. But then no different from other makers.
If you remember Rolls Royce refused to quote a power output on their cars. Just referred to it as adequate. Whether because so many fiddled theirs or not, I dunno. But BHP isn't a true guide of on road performance anyway.
First you have know what sort of ponies you are taking about.
Wheel - where it counts. Flywheel (Net) - nearly useful but depends on transmission. (DIN power, current SAE) Gross - utterly useless (old SAE). This is what Jaguar quoted back in the 60's. They run the engine on dyno with no ancillaries. No oil pump. No coolant pump. No generator. No air con or power steering drive belts. No air filter, it's running in a nice clean dyno cell and they aren't bothered about it lasting 250k miles. No silencers, just a big drain pipe from the header going out a hole in the wall. Deduct at least 12% for 4 cyl, 16% for 6 cyl and 20% for V8. More for DOHC as it needs more oil to feed cam bearings.
Torque is useless. No one sets a 0-60mph time using peak torque, its run though peak power rpm, changing up at the redline every gear. If you drive at peak torque rpm then you are losing the race. If happy with the performance could have bought a car with 1/2 the power - except then have to rev it to the peak power rpm and that may be too much fun for some. I redline my 140bhp/ton (net including driver and fuel) every day in 2nd.
Tiff Needell said Hyundai V6 mkIII coupe is "adequate", 116bhp/tonne,
135mph, 0-60mph 7.3 secs. If we take the benchmark as being 7.5 secs. Jag MKII 3.8 inadequate, BMW 5 series 530i adequate.For power/weight ratios you also have to know what standard of weight was used. DIN/SAE/JIS, these all have different amounts of driver and fuel/oil/coolant and have changed with revisions to the standards over the last 50 years. Clearly in real life and for setting a 0-60mph time you need a driver (75kg), full oil/coolant (about 10Kg) and some fuel (10-40Kg). Installing a lighter weight fit woman (60kg) in the drivers seat will improve recorded 0-60mph performance figures.
Aston Martin claimed +15% for the DB4/5 inline 6.
Marek had, at John Wyer?s suggestion, researched horsepower claims on American engines and had found a mean discrepancy of 32 per cent ? John Wyer?s reaction was ?We can?t lie that much, we can only lie 15 per cent?.
Page 21 footnote Claimed 325bhp, DBS Vantage actual 272bhp. 19.5% lie.
[snip]
Excellent article, Peter.
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.
OMG
Energy has to be transferred to a car to get it to a certain speed which will attain a kinetic energy of 1/2 mv^2.
The faster it gets to that speed the more power required.
Torque x rpm is power, but it is the combination of both that determine the energy over time, ie power, transferred to the vehicle.
If you continue to believe that it is just torque that matters .................................... Oh dear.
If you have that feature it helps to maximise power between gear changes, I don't believe the Jag and BMW mentioned earlier have this?
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.
It seems 27 of the 530i's ponies have jumped out of the coral before getting to the hubs.
Correct. That was the only point I was making.
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.
Perfectly possible. Quite common on 2 strokes.
BMW 530d at 60 mph in 4th, 2315 rpm with 369 Nm (89 Kw) BMW 530d at 60 mph in 3rd, 3300 rpm with 350 Nm (131 Kw).
BMW 530i at 60 mph in 3rd, 3890 rpm with 295 Nm (120 Kw) BMW 530i at 60 mph in 2nd, 5900 rpm with 277 Nm (169 Kw).
Both cars are pedal to the metal on the flat. Which car is accelerating the quickest and which gear does it accelerate quickest in? The one with more power or the one with more torque?
Once yuo have hit maximum bhp would you accelerate any more as at that point you can't deliver any more energy , hence why every gear has its maximum deliverable speed
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