I don't know why 7500 rpm is important. It's the torque delivered at the wheels that's the important thing, so if you are in a lower gear your engine goes faster.
The Civic 2.2 diesel I drove was just like a turbo petrol. If I'd put a sticker over the rev counter that went 0-8000 instead of 0-5000 and put the stereo on full you would never have known.
I don't know why 7500 rpm is important
It's not. But with the right engine it sounds niiiiice. 🙂
The Civic 2.2 diesel I drove was just like a turbo petrol. If I'd put a sticker over the rev counter that went 0-8000 instead of 0-5000 and put the stereo on full you would never have known
This. I went from a turbo petrol (Subaru) to a turbo diesel (BMW 530d) They really aren't that different, the Scooby pulled hard from 3000-6000rpm, the BMW pulls hard from 1800-4000rpm, so either one could double it’s speed in one big pull without changing gear, the only difference is that the Scooby would be a gear lower to do that at most speeds.
Oh dear!
They got it. its currently in a 1990 discovery that weighs about 2 tonne - and its destined for my 1987 ninety. Nice and torquey Unlike modern revvy petrol engines that bog down once you load em up 🙂 bhp figure isnt everything.
Its not for road use 😉
cruise not economical..
think of a generator or a piece of plant machinery thats used to create electricity or hydraulic pressure they are wherever possible run at a constant load / torque output, the load applied and the torque produced are set to the most fuel efficient operating condition.
On a diesel the amount of fuel burnt = torque produced, as the gradient (hills) or wind changes so the load changes, if you then try and maintain a fixed road speed the amount of torque required to maintain the same speed also changes IE you force the engine into more inefficient operating areas of its cycle..
Drive with the accel pedal and half an eye on the tacho and an ear on the engine note (and avoid loading it) change gear to maintain a moderat engine speed matched to a low loading and you will burn the least amount of fuel on your journey.
Cruise is great for maintaining a set speed but rubbish at economy (esp if on a manual and incapable of making gear shifts automatically as you regulary end up in high load conditions).
same logic with petrol but delivered torque not directly proportional to torque..
hybrids before getting carried away, start looking into the effcy of conversion (ie how much fuel you have to burn to charge a battery to get back in electric use) its not a good equation, unless you drive it like you stole it in non electric form to gain lots of regen braking charge, but who would by a hybrid and then deliberatley drive aggresively to improve economy, most likley buyer will drive conservatively and hence get little regen and burn loads of fuel charging a batt which then gives back less energy than that burned to create it :roll:.
Full plug in better, but you shift the carbon burn somewhere else.
Stop-Start systems, a sales pitch to claim improved MPG when your not actually moving anywhere ?? maybe use the bus / bike on journeys where a stop-start car is worth having as the fact your not moving implies the car is not a good choice in the 1st place.
thisisnotaspoon - Member
My tuppence after having to endure 600miles in a diesel this weekend.
Petrol - floor it and revs x torque = power; simples! If you try and set off from 20mph in 5th of course nothing happens, knock it into 3rd though and shit leaves the shovel.
Diesel, floor it, and the engine thinks about it, makes a whirring sound, anddddddddddddddddddd nothing. Then you drop a few gears, floor it again, it thinks about it, makes a whirring sound and then sets off like an overweight Labrador, then you run into the rev limiter at 4000 and have to repeat the process again.
The saving grace of diesel is it seems to do the same mpg whether you thrash it or cruise. This is a product of slightly more efficient combustion and the above mentioned turbo lag means that airflow is only vaguely correlated to what your right foot is doing, if you built in throttle response that slow into a petrol ECU it'd probably be efficient too.
1) try using the gearstick..
2) diesels run massively lean at all times, their not throttled in the 1st place, turbo lag is a function of lower engine speed / gas velocity. A twin sequential CRD can be made to deliver torque across as wider range as a petrol and more of it (for a given capacity) just takes more cost than somewhat archaic hence cheap petrol engines.
The last diesel I had with glowplugs I replaced them myself, was a doddle. Mind you that was about 12 years ago now as not had any since with glowplugs.
All diesels have glowplugs to allow them to start in extremely cold temperatures (ie well below zero) - but they are still used to improve emissions from a cold start.
You are more likely noticing the fact that the durability is better nowadays as they are better controlled, and the fact that a direct injection diesel can start without glowplugs (but will be a bit more smoky) and therefore haven't had to replace any
Makes sense Paul I was under the impression they had none but could be they're need in really cold days, must have to be bloody cold as we had temps of -15c and less a few years ago here and still the VAG started first time every time without waiting. I have noticed when you unlock the car and open the door you can hear it priming so maybe that's how they do it. Never had to wait on the little orange light coming on and going out like on my old 306.
Learnt something there.
As said by a few others "I like the way diesel's drive".
Just out of interest, what apps are people using to record fuel economy??
I use Fuelly.
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hybrids before getting carried away
You don't quite understand how hybrids work.
When braking, about 25% of the energy you put in to accelerating the car is stored in the battery as usable charge. It's a fairly low percentage, but it's better than dumping it all as heat, isn't it? My car shows a graph of energy regenerated over time. On a typical country road, driving economically but not especially slowly, I'll get mabye 200-400Wh of energy back in a half hour period. That's very roughly enough to light a house for an evening. That's energy that would've been completely wasted in a non-hybrid.
However, most of the regenration comes when cruising. A normal petrol car closes the throttle to keep your speed constant - that is inefficient - pumping losses. The hybrid, when it wants to recharge the battery, opens the throttle a bit more which reduces losses and diverts some of the energy to the battery.
And as for getting carried away - this is not a theoretical system, they are on the roads and they work.
Diesel, floor it, and the engine thinks about it, makes a whirring sound, anddddddddddddddddddd nothing. Then you drop a few gears, floor it again, it thinks about it, makes a whirring sound and then sets off like an overweight Labrador, then you run into the rev limiter at 4000 and have to repeat the process again.
how old was that diesel?
sporty diesels have loads of torque at low revs, that is where they are impressive. thing I don't like is how they don't slow down as quick as a petrol - don't feel as tightly connected to the accel. pedal. Plus the don't sound quite as good when revved, although the alfa ones sound pretty fair.
