cars with variable power output
Discussion
McSam said:
The engine management isn't just a fixed thing, it's a huge and very complex map of settings. The car considers its operating condition and your demand, and goes for the most efficient solution. No modern car, whatever its power output, is "set up" for peak power when you're cruising around at 1/8th throttle. The injection strategy, valve timing and ignition points all move around to achieve as efficient a delivery as they can, there's no need to "change maps" to do this, all these different areas are included in the one map the car has already.
In terms of engine related maps, I'd agree with this. Fuelling maps are typically based on load (throttle opening) and engine speed. Cruising and pottering round are sat in different portions of the map to driving like a nutter. So having 2 maps is a bit redundant.
However, with cars with drive by wire throttles, you can control load by altering the pedal map. So that in normal mode full pedal travel = full throttle, but on economy mode full pedal travel < 100% throttle.
It can also be done mechanically; sometimes find manual cars that are oriented to economy, with pedal travel similar to an auto, i.e. 'full' throttle then full + bit similar to a kickdown switch.
98elise said:
I'll probably get flamed for this, but thats one of the advantages of EV's. An electric motor doesn't anything like the same same losses when you have a high opeak powervs a low peak power motor. Thats why the Tesla Model S can have a 400+ bhp motor, yet also have decent economy.
Hybridisation does seem to give us a chance to have our cake and eat it. Economy when not pushing on with extra power when needed.
Renovation said:
I think having an electronic power restrictor is a good idea, it means you could lend your wife / kids / mum a 400bhp car but restrict it to say 150bhp.
I can understand restricting power for your kids, especially if they are young drivers. But restricting power for your mum or wife....why??DJFish said:
Don't Ford offer the Focus with a 'kids key' that limits power, stereo volume & top speed?
So your offspring can borrow the car with less chance of pranging it.
Also didn't TVR do the Cerbera with a high & low octane switch on the dash to toggle different fuel maps?
Ford MyKey or something equally stupid. Got a new Mustang in America which was limited to 85mph and stereo volume to middle-ish.....85mph feels particularly slow when the satnav is saying next exit 150-odd miles down the interstate! So your offspring can borrow the car with less chance of pranging it.
Also didn't TVR do the Cerbera with a high & low octane switch on the dash to toggle different fuel maps?
Calza said:
Taking the M5 as an example, I get that on light throttle it will be nowhere near either peak figure but wouldn't it achieve a better MPG cruising on the 400bhp setting instead of 500bhp?
I think I covered this above, but nonetheless I'm interested in your logic. Why should it?We had jet ski come in part ex a while ago that had about 280hp. And that came with 2 keys.one 'learner' key that restricted it to about 40mph. Then another 'full cat's key that let you get the full 73mph. And after having a go in both modes, the lower power key made sense. But I think it was more limiting the revs that the power.So don't know it the equivalent on a car would be nice to drive in low mode.
TwigtheWonderkid said:
If I restricted the power on my car when my wife drove, she would soon be my ex too.
In all seriousness, one of the many reasons mine is an ex is that she more than once used more power than she was capable of handling & I dared to complain that the car came back with more dents than it went out with.Monty Python said:
The Dodge Challenger Hellcat has variable power output - the joke was that you wouldn't give the car to a valet with 700bhp so you "restrict" it to 500.
If you watch the 'Jay Lenos Garage' video on the Hellcat the marketing guy says he doesn't know why they bothered really, and it could be a lawyer thing. I think it's a novelty and a 'just because it's easy and we can' thing. A valet mode is included on the new Corvette and it disables the stereo, locks the 'glove' box, etc. It also doesn't allow any safety systems to be disabled and restricts the top speed. It even records dash cam like video and most data on how the car was driven. You can then show their manager if you need to do so. 
I'm sure all the valets in the USA are now going to drive the new Corvette like a new hearse.
I don't really think limited power/torque outputs are needed unless you want/need a valet mode on your car. Or if it spins the tyres because of the power/torque in a straight line. Otherwise just have a variable throttle response.
McSam said:
Calza said:
Taking the M5 as an example, I get that on light throttle it will be nowhere near either peak figure but wouldn't it achieve a better MPG cruising on the 400bhp setting instead of 500bhp?
I think I covered this above, but nonetheless I'm interested in your logic. Why should it?If we assume that rev for rev the 500bhp map has more power than the 400bhp map, then at any given speed engine speed the available power will be higher in p500? So at partial throttle, it will be relative to the maximum number?
Could be absolute waffle of course!
Calza said:
I'm not saying I'm right by any means, I was always curious. My thoughts were along the lines of:
If we assume that rev for rev the 500bhp map has more power than the 400bhp map, then at any given speed engine speed the available power will be higher in p500? So at partial throttle, it will be relative to the maximum number?
Could be absolute waffle of course!
That's reasonable enough logic If we assume that rev for rev the 500bhp map has more power than the 400bhp map, then at any given speed engine speed the available power will be higher in p500? So at partial throttle, it will be relative to the maximum number?
Could be absolute waffle of course!
certainly for full throttle that's a fair assumption, though I would expect that most of these switchable maps would not differ at all until you got past 75% throttle, or at least half, to make it more driveable at normal speeds.For the sake of argument, let's assume that the map is different all the way through the pedal travel, and the 500bhp map is always giving you 25% more power than the 400bhp one. Even if this is the case, you don't drive faster
the driver innately adjusts themselves to the pedal response very quickly, and simply uses less travel, achieving the same acceleration and therefore the same fuel consumption as they would have done in the other map.If you were using the exact same pedal positions all the time, then yes, it would make a difference. To how many speeding tickets you got, as well as your fuel consumption! It still takes the same amount of power to drive the car in the same manner, no matter what inputs you have to do to get it.
Calza said:
Taking the M5 as an example, I get that on light throttle it will be nowhere near either peak figure but wouldn't it achieve a better MPG cruising on the 400bhp setting instead of 500bhp?
No, the 400bhp mode doesn't shut down any cylinders or anything. The only time I ever use P400 is parking in a tight space. P500/P500S are a little bit jerky when trying to park.Gassing Station | General Gassing | Top of Page | What's New | My Stuff