tbourner Posted February 15, 2006 Share Posted February 15, 2006 Obviously I'm not talking about the Supe!! What's the best way to drive if absolute high mpg are required? Is it best to floor it up to the speed limit as quick as possible then sit in a high gear? Or accelerate as slowly as possible? Or somewhere in the middle? Is it best to sit in as high a gear as possible even if the engine's struggling? Or do you want to pick the highest gear you can to lower the revs but not so low as it struggles? Coast down sliproads or engine brake? What's an optimum rev range for constant speed driving? Link to comment Share on other sites More sharing options...
jamesmark Posted February 15, 2006 Share Posted February 15, 2006 accelarateslowly but not slolw as some one woudl rear end you, sit in high gear but dont allow the engine to toil as you will need to drop down a gear to speed up and then use more fuel,and always engine brake, when you engine brake you use very little to no petrol Link to comment Share on other sites More sharing options...
jamesmark Posted February 15, 2006 Share Posted February 15, 2006 oh and short shift Link to comment Share on other sites More sharing options...
Marco Posted February 15, 2006 Share Posted February 15, 2006 Always leave the car in gear when you slow down (like engine breaking), then you don't use any petrol. When you're in neutral you do. Drive smoothly! Dont have any unneccassary weight on board Check your tire pressure Link to comment Share on other sites More sharing options...
Kip Posted February 16, 2006 Share Posted February 16, 2006 I have some experience with this in the Supe - I like a challenge!! I have learned, do not let the boost gauge needle move and you'll get excellent MPG - I hear you chuckling. Here is the other bit - note the way you are driving and pretty soon you will realise you can drive like this in normally aspirated cars and the same style of driving will get good results... Failing that go on an Advanced Driving Course and learn a whole new way of driving. Link to comment Share on other sites More sharing options...
Pete Posted February 16, 2006 Share Posted February 16, 2006 Failing that go on an Advanced Driving Course and learn a whole new way of driving. Like mine eh The main points are to leave lots of space between you and the car in front. They'll always be braking and speeding up. Slow and steady wins the economical race. Everycar has a speed which the engine runs most efficiently at. A steady 60 odd mph probably for most. Don't pop to the shops - walk! Those short journeys zap the fuel. Link to comment Share on other sites More sharing options...
Ian R Posted February 16, 2006 Share Posted February 16, 2006 keeping the car under 3k revs works for me Link to comment Share on other sites More sharing options...
mawby Posted February 16, 2006 Share Posted February 16, 2006 Always leave the car in gear when you slow down (like engine breaking), then you don't use any petrol. When you're in neutral you do.I've heard this mentioned before, the arguement being the engine is turning by the force of the car moving, whereas if it's in neutral then the engine has to idle revs by burning fuel. However, I experimented with this not so long ago and found it isn't true. The route between my house and my work has several long steep hills. So for one week I engine breaked all week long, then the next I coasted down all the hills. Coasting gave me an extra 4-5 mpg! This is with a diesel though, so I don't know if it's different for petrol engines, but as I understand it even if the eninge is being turned be the movement of the car it'll still be burning fuel. Surely the engine wont be turning over dry? Link to comment Share on other sites More sharing options...
Pixelfill Posted February 16, 2006 Share Posted February 16, 2006 I have some experience with this in the Supe - I like a challenge!! I have learned, do not let the boost gauge needle move and you'll get excellent MPG - I hear you chuckling. I don't see how this bit works, I don't let the boost gauge move from 1.2 bar, and my mpg is appalling !! Mike Link to comment Share on other sites More sharing options...
tbourner Posted February 16, 2006 Author Share Posted February 16, 2006 Well the fact that you can push start a car without needing to use the starter shows that engine braking is capable of reducing effort from the engine. Trying to keep the boost guage between 10 and 20 InHg seems to be best for economy. Use the same principle of throttle control in the NA seems a good idea. Link to comment Share on other sites More sharing options...
Marco Posted February 16, 2006 Share Posted February 16, 2006 However, I experimented with this not so long ago and found it isn't true... It is true. Look at it this way: when it's in neutral the engine runs by itself, put it in gear without giving any gas, and the engine will stall. My brothers corolla (MrDriver on the site) has a computer on board that calculates the fuel consumption real time. We tried engine braking and the computer always says 0! Link to comment Share on other sites More sharing options...
mawby Posted February 16, 2006 Share Posted February 16, 2006 It is true. Look at it this way: when it's in neutral the engine runs by itself, put it in gear without giving any gas, and the engine will stall.I can only got on what I found, and as I said it was a diesel so that might make a difference. I still find it surprising that the engine would run with zero fuel usage, or can we assume that 0 on your computer actually means less than 1? (ie very small) Come on, one of you techie people will know the correct answer. Ian C? Chris Wilson? Settle the argument for us. Link to comment Share on other sites More sharing options...
tbourner Posted February 16, 2006 Author Share Posted February 16, 2006 Well on overrun the injector duration is 1.5ms, and at idle it's approximately 2.0ms - so you should save about 25% fuel whilst going down sliproads. Link to comment Share on other sites More sharing options...
tbourner Posted February 16, 2006 Author Share Posted February 16, 2006 Here's an ECU readout from a 1.3 Micra; obviously there is a huge difference between WOT and lifting off for a split second: --Time--------RPM-----MAF-v----Thr-v----Inj------Duty 09:15:27-----6525-----4.69-----4.1------14.75-----80.2 09:15:27-----6550-----4.66-----4.1------14.75-----80.51 09:15:27-----6600-----4.69-----4.1------14.75-----81.12 09:15:27-----6625-----4.62-----4.1------14.13-----78.01 09:15:27-----6675-----4.73-----4.1------14.75-----82.05 09:15:27-----6725-----4.69-----4.1------14.57-----81.65 09:15:27-----6775-----4.76-----4.1------14.75-----83.28 09:15:28-----5462-----1.84-----0.42-----0.43------1.96 09:15:28-----5462-----1.86-----0.42-----0.43------1.96 09:15:28-----5650-----1.86-----0.42-----0.43------2.02 09:15:28-----5688-----1.90-----0.42-----0.43------2.04 09:15:28-----5800-----1.94-----0.42-----0.43------2.08 09:15:28-----5875-----1.92-----0.42-----1.43------7 09:15:28-----5975-----1.92-----0.42-----1.43------7.12 09:15:28-----6162-----1.96-----0.42-----1.51------7.75 09:15:28-----6200-----1.96-----0.42-----1.59------8.22 09:15:28-----6325-----2.03-----0.42-----1.65------8.7 09:15:28-----6412-----2.14-----0.42-----1.69------9.03 09:15:28-----6538-----2.44-----0.42-----2.69------14.66 09:15:28-----6700-----3.30-----0.66-----6.41------35.79 09:15:28-----6662-----4.37-----1.98-----12.75-----70.78 09:15:28-----6775-----4.65-----3.14-----13.81-----77.97 09:15:28-----6550-----4.66-----3.82-----13.77-----75.16 09:15:28-----6675-----4.72-----4.06-----14.75-----82.05 09:15:28-----6700-----4.66-----4.06-----14.63-----81.68 09:15:28-----6762-----4.70-----4.06-----14.71-----82.89 09:15:28-----6800-----4.74-----4.06-----14.53-----82.34 I'm still waiting for an idle plot to compare to. Link to comment Share on other sites More sharing options...
mawby Posted February 16, 2006 Share Posted February 16, 2006 Well on overrun the injector duration is 1.5ms, and at idle it's approximately 2.0ms - so you should save about 25% fuel whilst going down sliproads.OK, that makes sense. Still doesn't explain my results. Maybe there was another factor I wasn't aware of? Link to comment Share on other sites More sharing options...
Supragal Posted February 16, 2006 Share Posted February 16, 2006 it's basically a case of being in teh right gear at the right time, keeping it all moving, having good anticipation and reading the road a long way back and not flooring it. I am the master of budget driving Link to comment Share on other sites More sharing options...
Marco Posted February 16, 2006 Share Posted February 16, 2006 I can only got on what I found, and as I said it was a diesel so that might make a difference. I still find it surprising that the engine would run with zero fuel usage, or can we assume that 0 on your computer actually means less than 1? (ie very small) .... On the display it was actually 0 liter/100Km. Link to comment Share on other sites More sharing options...
toyotasuprauk Posted February 16, 2006 Share Posted February 16, 2006 This is interesting. I often coast down hills rather than leave it in gear as I thought it saved fuel. I thought when it was neutral the revs are say 1K idle doesn’t use much fuel but when your in gear going down a hill they might be 3k so therefore using more petrol. Link to comment Share on other sites More sharing options...
mawby Posted February 16, 2006 Share Posted February 16, 2006 Well on overrun the injector duration is 1.5ms, and at idle it's approximately 2.0ms - so you should save about 25% fuel whilst going down sliproads.Hang on. This is where I could make myself look very stupid but here goes, If the car is idling at 1000 revs, with 6 injectors each firing once per revolution, so that's 6000 injector fires. If the injectors are open for 2ms per fire then thats 12,000 ms that the injectors are open and allowing fuel through. If the car is going down hill (not coasting), at 3000 revs * 6 injectors = 18,000 fires, at 1.5ms per fire = 27,000 ms. Even at 2000 revs going down hill it would still be 18,000ms. So that would suggest coasting is more fuel efficient. Link to comment Share on other sites More sharing options...
tbourner Posted February 16, 2006 Author Share Posted February 16, 2006 hmm, interesting theory. What was Clarkson driving when he said modern cars use NO fuel AT ALL on overrun? Link to comment Share on other sites More sharing options...
Suprasteve Posted February 16, 2006 Share Posted February 16, 2006 Hang on. This is where I could make myself look very stupid but here goes, If the car is idling at 1000 revs, with 6 injectors each firing once per revolution, so that's 6000 injector fires. If the injectors are open for 2ms per fire then thats 12,000 ms that the injectors are open and allowing fuel through. If the car is going down hill (not coasting), at 3000 revs * 6 injectors = 18,000 fires, at 1.5ms per fire = 27,000 ms. Even at 2000 revs going down hill it would still be 18,000ms. So that would suggest coasting is more fuel efficient. i see your point but surely the injectors are not actually forcing fuel through them to maintain the revs. i.e if the car is heavier or going up hill with the same rpm it would still alter the amount of fuel going through the injectors ??? perhaps you got better fuel consumption when coasting rather than leaving in gear was the fact that the engine would slow the momentum down more and therefore coasting would take you further ??? but hey what do i know ? Link to comment Share on other sites More sharing options...
mawby Posted February 16, 2006 Share Posted February 16, 2006 i see your point but surely the injectors are not actually forcing fuel through them to maintain the revs. i.e if the car is heavier or going up hill with the same rpm it would still alter the amount of fuel going through the injectors ???If there was higher engine load (like going up hill) then surely the injectors just stay open longer rather than increasing the pressure of fuel going through them? (If this keeps up I'll have to move this thread into the technical section!) Link to comment Share on other sites More sharing options...
andrew7 Posted February 16, 2006 Share Posted February 16, 2006 Economy is about your right foot.... Anytime you are on either the gas pedal or the brake, it is costing you petrol. If you minimise the hard use of both of these, then you will get the best economy for your car..which was the question wasn't it?....... Link to comment Share on other sites More sharing options...
stevie_b Posted February 16, 2006 Share Posted February 16, 2006 I tend to keep the car between 2k and 3k revs (preferably towards 2k). A previous car manual (not a supra one though) said that the car was most efficient at 56mph in 5th gear: this worked out at about 2.5k rpm. Link to comment Share on other sites More sharing options...
MrDriver Posted February 16, 2006 Share Posted February 16, 2006 .... On the display it was actually 0 liter/100Km. Yes MfS is right. This is even mentioned on Top Gear, when Clarkson did this trip with a VW twinturbo diesel I think. He tried to drive as economical as possible and had to do every trick in the book to drive as far as he could get. Greets, Peter Link to comment Share on other sites More sharing options...
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