RE: Chris Harris video: BMW i8
Discussion
Me three.
For me, top speed is only a by-product of the things I really care about. With internal combustion, a car that can cruise quietly and comfortably with fair economy at 100, without wearing itself out, and punch its way up to that speed quickly, will have a top speed way in excess of 100. But I have no real interest in travelling at more than 100 mph on the public roads of any country.
For me, top speed is only a by-product of the things I really care about. With internal combustion, a car that can cruise quietly and comfortably with fair economy at 100, without wearing itself out, and punch its way up to that speed quickly, will have a top speed way in excess of 100. But I have no real interest in travelling at more than 100 mph on the public roads of any country.
Rich_W said:
I am talking about mid/rear engine sports cars not everyday stuff. i8 could be a Halo car for BMW in the same way SLS is for Merc and R8 is for Audi
So are we. I still fail to see the relevance of top speed on a car which will be used pretty much entirely on the public road. Loved the footage of it slinking along the coastal road in the afternoon sun; really did look like the future had arrived. Modern classic, future classic... such an awesome vehicle, I'm sure most of those shortcomings can be forgiven, considering the context. However I would imagine they would look ridiculously incongruous on some roads!
Lowtimer said:
Its also why they have never really made it in aviation in the 100-350 hp horsepower range - their inherent inefficiency absolutely crucifies them, even in comparison with the basically 60 year old piston engine designs we are still using. With the single exception of helicopters where the very low powerplant weight gives them an advantage, although that advantage comes at a very high purchase price and fuel burn.
Gas turbines, whether turboprop, turbofan or turbojet, are great once you get to the high power ranges, 1000 hp plus, and for applications which are going to cruise above 10,000 feet. Reasonably lightweight piston engines start to become too complicated to be practicable for service at more than about 4,000 hp, so today's big airliners could never use piston engines. And in the case of turbojets and turbofans, eve at low level they have the advantage at very high speeds where propellers become inefficient.
But for low level, low speed, low power aeroplane applications, the ones most similar to car applications, gas turbines just don't make economic sense.
Again I don't think we can hold up civil aviation as a model of efficiency when most aero piston engines still use carburettors - the icing of which has killed untold thousands of pilots in the years since fuel injection could and should have been applied - and those engines are huge and heavy for their meagre power outputs. I have contacts in the world of radio controlled aircraft, using real jet engines - there's one guy round here has a simply huge model Avro Vulcan with four real jet engines. The fuel consumption on that for the thrust capacity was quite impressive. Gas turbines, whether turboprop, turbofan or turbojet, are great once you get to the high power ranges, 1000 hp plus, and for applications which are going to cruise above 10,000 feet. Reasonably lightweight piston engines start to become too complicated to be practicable for service at more than about 4,000 hp, so today's big airliners could never use piston engines. And in the case of turbojets and turbofans, eve at low level they have the advantage at very high speeds where propellers become inefficient.
But for low level, low speed, low power aeroplane applications, the ones most similar to car applications, gas turbines just don't make economic sense.
I honestly don't think JLR did CX-75 and bought into Bladon just for column inches. That's one bloody expensive bit of advertising.
Energy regen - isn't this said to completely wreck brake feel? I'd rather go for a flywheel hybrid like that Porsche GT3 racer, and which I think Volvo are looking into. Makes bulky heavy batteries look wasteful.
Still, some interesting points made here, I'm not here to engage in a silly "no, you're wrong" flame-war!
RoverP6B said:
Energy regen - isn't this said to completely wreck brake feel? I'd rather go for a flywheel hybrid like that Porsche GT3 racer, and which I think Volvo are looking into. Makes bulky heavy batteries look wasteful.
Problem with flywheels is that they are generally empty when you start driving a car regardless what you did on your previous journey, unlike those 'wasteful batteries'RobDickinson said:
1485kg? Wow. Carbon and aluminum and still 150 kg heavier than an rx8 and 5 times the price.
The tech is interesting but it's far from unique, just dresses it up in a fancy body.
Remind me on the performance and economy stats for an RX8 again......... ;-)The tech is interesting but it's far from unique, just dresses it up in a fancy body.
(Like i said, with these new electrified powertrains, being a bit "heavy" is NOT the end of the world (the performance / economy numbers of the i8 back that up too!)
RoverP6B said:
Again I don't think we can hold up civil aviation as a model of efficiency when most aero piston engines still use carburettors - the icing of which has killed untold thousands of pilots in the years since fuel injection could and should have been applied - and those engines are huge and heavy for their meagre power outputs.
They still manage to comprehensively defeat gas turbines as commercial propositions though! It was my own point that these piston engines are pretty old tech, but still do a better job that gas turbines can at the speeds and altitudes and power outputs most similar to automotive applications. I am also familiar with model gas turbines and they are highly amusing, but their fuel-efficiency is abject compared to petrol engines which fly similar sized models.Incidentally while they are large displacement for their power, that is because they are mostly direct-drive, and therefore need to deliver peak power at around 2500 rpm. They are not at all heavy for their power, as you will find if you compare the installed weight of a Lycoming O-320 against the greater installed weight of the converted modern Mercedes car diesel tried by a few people last decade.
Equally, compare the power from your typical Lycoming 4-banger to a GM LS V8 (which has found favour in the US at least as an aero engine)... the LS is slimmer, lighter and makes three times the power as a baseline!
We really have come a long way from plugin hybrids...
Oh, and are THOSE really such a good idea when we've got a worldwide electricity generation crisis and phased blackouts could become a daily reality for us within a few years? At least we'll still have transport as long as we have something that can go bang next to a piston...
We really have come a long way from plugin hybrids...
Oh, and are THOSE really such a good idea when we've got a worldwide electricity generation crisis and phased blackouts could become a daily reality for us within a few years? At least we'll still have transport as long as we have something that can go bang next to a piston...
RoverP6B said:
Equally, compare the power from your typical Lycoming 4-banger to a GM LS V8 (which has found favour in the US at least as an aero engine)... the LS is slimmer, lighter and makes three times the power as a baseline!
We really have come a long way from plugin hybrids...
Oh, and are THOSE really such a good idea when we've got a worldwide electricity generation crisis and phased blackouts could become a daily reality for us within a few years? At least we'll still have transport as long as we have something that can go bang next to a piston...
The LS7 makes "3x the power" because it runs 3x as fast, but as mentioned, this means you need a step down gearbox to drive your prop...........We really have come a long way from plugin hybrids...
Oh, and are THOSE really such a good idea when we've got a worldwide electricity generation crisis and phased blackouts could become a daily reality for us within a few years? At least we'll still have transport as long as we have something that can go bang next to a piston...
It's also true to say, that if everyone drove plug in hybrids, the Electricity generation business would be well pleased, as suddenly they have access to an enormous (and free to them) "load leveling" system!
Correct. Make an LS that will run peak power at 2500 rpm and see what power to weight ratio you get then... alternatively include the weight of a gearbox into your comparison.
Incidentally an 0-360 (taking a closer comparison of capacity) weighs 290 lb dry, including carb, mags., ignition harness, engine baffles, spark plugs, tach. drive, starter and generator or alternator.
An LS7 weighs about 387 lb without clutch of flywheel. And of course that's dry. It needs not only oil but also a heavy liquid cooling system and radiator which the 0-360 doesn't.
Incidentally an 0-360 (taking a closer comparison of capacity) weighs 290 lb dry, including carb, mags., ignition harness, engine baffles, spark plugs, tach. drive, starter and generator or alternator.
An LS7 weighs about 387 lb without clutch of flywheel. And of course that's dry. It needs not only oil but also a heavy liquid cooling system and radiator which the 0-360 doesn't.
Edited by Lowtimer on Tuesday 6th May 15:57
Max_Torque said:
The LS7 makes "3x the power" because it runs 3x as fast, but as mentioned, this means you need a step down gearbox to drive your prop...........
It's also true to say, that if everyone drove plug in hybrids, the Electricity generation business would be well pleased, as suddenly they have access to an enormous (and free to them) "load leveling" system!
I didn't say LS7. There are some LS7 conversions but many other variants have been used: see http://www.seabee.info/seabee_engine_conversions.h...It's also true to say, that if everyone drove plug in hybrids, the Electricity generation business would be well pleased, as suddenly they have access to an enormous (and free to them) "load leveling" system!
Load levelling - the hybrids would consume more energy at the same time buildings do. It could only exacerbate an already challenging situation.
RoverP6B said:
Load levelling - the hybrids would consume more energy at the same time buildings do. It could only exacerbate an already challenging situation.
I'm not sure what you do at 3.00am in the morning, i am generally asleep and my house is not using any significant power, so instead we can use that to charge my car!In the UK, we have a number of studies underway where everyone in a single street has been given an EV, and how they use and charge them, and the "smart" systems required to optimise that process is being considered in some detail!
I seem to remember reading somewhere than on any given day, less than 1% cars in the UK will travel more than 50 miles. Given that of those that do, many will travel very large distances regularly and hence be completely unsuitable for electric propulsion, I don't think any feasible number of cars going electric is going to hurt the national grid significantly. If one of our cars was electric, it would would never get charged during the day; if both were, it might get some day-time charging a couple of times a year.
Gassing Station | General Gassing | Top of Page | What's New | My Stuff