Hi guys, sorry if this has already been answered but I had a look and couldn't find what I was after.

So my question is, if I am out on the freeway, and not in a rush or anything and I was seeking the best fuel economy, what speed should I travel at?

I have an '02 TJ VR-X if that makes a difference at all?

I heard that often that cars are designed for ideal economy at around 80kmh, because the drag coefficient is much higher when traveling at 100 or 110? Is that true? Or is traveling at 100kmh more efficient?

I tried testing it a little with the inst-fuel display, but I hear that it isnt too acurate?
Also I couldnt get a decent comparison due to also small things like wind and road gradient.

Thanks for all your help and advice :D

I think i remember hearing that 90 was the ideal speed for economy...

100km/h is pretty sweet if your not in a rush, maybe there is no perfect speed??? Remember, the faster you go the higher your wind-resistance.


Make sure your air filter is clean or replaced often, and always check your tyre pressures, dont leave them un checked for more then 2 weeks, these are easy tips that offer real world results.

never really read into it, i know when i was on my red P's and sticking to 90 my fuel econ was slightly better to now being on my greens sticking to 100, but nothing i would justify any extra time to each trip with

as for idea speeds that would depend on the loaded weight of your car at the time, any body kits or wings fitted, tyre size and pressure, current wind speed and direction outside the car, if your using the ac ( compresser drag) and a few other things

not worth the hassle over a very minor saving in fuel

According to my fluid dynamics textbooks, depending on the car it is about 90 - 100 kph, after this, fuel economy decreases sharply, which is why I always wondered whenever the subject of open speed limits on freeways would come up, why none of the detractors would point this one of few valid points out, instead sticking to the BS the government likes to pedal.

Thanks for the thoughts guys. Generally i stick to around 95 on the freeway as i don't like driving slowly at 80 for a couple extra Ks out of the tank. :P
And like Pretzil said, I heard the Veyron's economy is so high when driving at higher speeds that it would empty a full tank in something like 12 minutes.

On the topic of air filters however, swapping the stock filter and snorkel for a pod filter increases performance (and is legal for red P's) correct?
But does it effect economy at all? Either for the better or worse??

Thanks

12mins to empty a tank sounds like bs to me.

not sure on the legality side of things but in nsw the sheet of paper they give you when you get your red and green p's states that no engine modifations are legal for p platers.

and imho your better of switching the stock panel filter for a high flow filter ( lukey / k&n) than installing a pod

Best fuel economy is 0 KPH with the engine off. The fuel in the tank lasts forever.

A bit impractical, really. lol

Not much difference between a steady 90 KPH and 100 KPH, what makes a big difference is the stop/start nature of urban traffic. Really chews the fuel.

12mins to empty a tank sounds like bs to me.

Not bullshit,James May said it when he was doing a top speed run.

Best fuel economy is 0 KPH with the engine off. The fuel in the tank lasts forever.

A bit impractical, really. lol

Not much difference between a steady 90 KPH and 100 KPH, what makes a big difference is the stop/start nature of urban traffic. Really chews the fuel.

This.

Any time you need to use your brakes you're wasting all the energy the car has made getting itself going.

Thanks for the advice 95ts, I'll look into it :)
I'm still a novice when it comes to car upgrades so please forgive me.


Best fuel economy is 0 KPH with the engine off. The fuel in the tank lasts forever.
Excellent, although it would take a while to get to the local shops unfortunately :(


Any time you need to use your brakes you're wasting all the energy the car has made getting itself going.
Yeah the brakes convert the kinetic energy into heat. Too bad the reverse isn't possible, then you could run your car off the heat from your steering wheel in summer xD

Not bullshit,James May said it when he was doing a top speed run.

He also said the tyres are good for 50 minutes at top speed. lol But not to worry, as at top speed a tank of fuel only lasts 12 minutes. Can someone lend me one to test this out? lol

Not much difference between a steady 90 KPH and 100 KPH, what makes a big difference is the stop/start nature of urban traffic. Really chews the fuel.

The funny thing about this fact, is that on a freeway drive, hybrids like the prius often use more fuel than big v8s etc, the tiny prius engine loses any advantage it had from the electric motor in stop start driving when the brakes aren't being used.

Before anyone attacks that statement, Yes the engine is economical, but has to work way to hard to maintain speed over small variations in elevation on the freeway compared to the torque of the bigger engine

There is another factor to be taken into account: by driving under the speed limit you are slowing down most other traffic and creating a hazard.
How did you feel last time you were behind some bloke doing 80 in a 100 zone with double lines for the next 5km?

There is another factor to be taken into account: by driving under the speed limit you are slowing down most other traffic and creating a hazard.
How did you feel last time you were behind some bloke doing 80 in a 100 zone with double lines for the next 5km?

Legally, there is nothing wrong with it unless its stupidly slow. You drive to the conditions and YOUR own abilities, and not someone elses. Its a speed LIMIT, not a speed to be done at all times.

Regarding the most efficient speed, the UK government argue that this is 56mph or 90 kph. All trucks in the UK over a certain length are limited to this speed to maximise fuel efficiency on trips and also to reduce danger to other road users. Each car is different but normal passenger cars are not efficient at 100kph, it would be more like 80-90.

Many years ago, during the first world energy crisis, they dropped the speed limits in the USA to 55 mph (about 90 km/h). I am not sure if those limits still apply, but my friend who hasa just returned from there said that in LA, they were all driving at 100 MPH!!! Maybe not that high, but they certainly do drive fast over there on freeways with 5 or more lanes each way.

Personally, I have done checks on speed vs economy and have found that I could not detect any sustainable economy difference between 90 and 1i0 km/h. Even at 130 km/h (outback Qld - flat roads), the consumption increased only about 10%. These figures are for my wife's Magna. For my Pajero, consumption increases when you get over 100 km/h, but that has the aerodynamics of a brick. I cannot detect any sustainable differences between 80 and 100 km/h. Sometimes I get better economy, other times, no difference. Wind direction and intensity, vehicle loading and traffic have more effect on consumption.

For my 380 I'd say about 90km/h. Back in the day on my red P's I filled up here in Sydney (Liverpool) jumped onto the Hume HWY and drove at 90km/h on cruise to Just before Albury before tuning around am doing the same thing back again. Doing so saw me get 560k's from probably a mm below the half line on the fuel gauge, got home went to work with the fuel light on drove home then thought I better get some fuel, it was on the way to the servo where I literally ran out of fuel after doing 1002k's of a single tank of 67 liters with the only mod at the time was that it was lowered, no other mods whatsoever. It's been doubted here many times that I did that many k's on a tank but to all the doubters i say screw you lol

The 380 tank was 71 liters I thought?

If you had used your right foot instead of cruise control, you probably could have done anywhere from 10%-30% better on fuel depending on the undulation of the road.

How did you feel last time you were behind some bloke doing 80 in a 100 zone with double lines for the next 5km?

I took a deep breath, relaxed and thought of the fuel I was saving - and waited for a safe overtaking opportunity. lol

The only "hazard" is caused by impatient people like yourself who believe the speed limit is what you need to drive at, and try to pass when it is not safe to do so. lol

The 380 tank was 71 liters I thought?

If you had used your right foot instead of cruise control, you probably could have done anywhere from 10%-30% better on fuel depending on the undulation of the road.
I'm sure in the owners manual in the capacity section it says 67litres.

And yea I'll be doing another test soon I think after a service but this time it's got the Berklee muffler Galant intake (don't believe in K&N filters) so that's still stock, brick subs in the boot will come out and I'll have to throw on the standard 17's and leave cruise control off and the road is a bit hilly for the first 200 or so k's then it starts to level out after Goulburn.

I took a deep breath, relaxed and thought of the fuel I was saving - and waited for a safe overtaking opportunity. lol

The only "hazard" is caused by impatient people like yourself who believe the speed limit is what you need to drive at, and try to pass when it is not safe to do so. lol

I agree to a point. I just think if you're the guy going slower, and you know you're going slower than the posted limit, and have no intension of going the posted limit, and someone behind you looks like they want to go the posted limit, then pull over and let the person pass. I do it all the time. I have no right to hold traffic up because I want to drive slower than the posted limit, so I let people past without incident. No problem.

I'm sure in the owners manual in the capacity section it says 67litres.

And yea I'll be doing another test soon I think after a service but this time it's got the Berklee muffler Galant intake (don't believe in K&N filters) so that's still stock, brick subs in the boot will come out and I'll have to throw on the standard 17's and leave cruise control off and the road is a bit hilly for the first 200 or so k's then it starts to level out after Goulburn.

The trick with driving on a hilly road is to use some very light acceleration prior to the hill, then maintain steady throttle till you've almost reached the summit, then come off the accelerator completely and let inertia do its thing on the way down.

For my 380 I'd say about 90km/h. Back in the day on my red P's I filled up here in Sydney (Liverpool) jumped onto the Hume HWY and drove at 90km/h on cruise to Just before Albury before tuning around am doing the same thing back again. Doing so saw me get 560k's from probably a mm below the half line on the fuel gauge, got home went to work with the fuel light on drove home then thought I better get some fuel, it was on the way to the servo where I literally ran out of fuel after doing 1002k's of a single tank of 67 liters with the only mod at the time was that it was lowered, no other mods whatsoever. It's been doubted here many times that I did that many k's on a tank but to all the doubters i say screw you lol

As crazy as it might seem, I actually believe that kind of mileage would be possible from a tank. I drove down to Phillip Island last week, and for a good 100ks of the journey I was able to stay at 95kmh, and for that distance, the trip computer said I was averaging slightly over 8L/100. So if you were able to squeeze 71L in there, and you could average 8L/100 then you would be able to get 888km from the tank.
If conditions were ideal too, like a slight tail-wind for you, and the average road gradient between the two destinations was negative so you have the help from gravity, I don't see why it wouldn't be possible?
Just my thoughts.

I took a deep breath, relaxed and thought of the fuel I was saving - and waited for a safe overtaking opportunity. lol

The only "hazard" is caused by impatient people like yourself who believe the speed limit is what you need to drive at, and try to pass when it is not safe to do so. lol

Geez MadMax, give me a break! - where did I say I was impatient or that I believe the speed limit is what I need to drive at and then pass when not safe? I've had a licence for 52 years and have been booked once during those 52 years for being 13kph over the speed limit - other than that my record is as pure as the driven snow.
Please read the post again before you make unjust assumptions.:think:

Just on air filters, what is the difference between a K&N and anything else? I got a Ryco for around 40 bucks and the K&N was 110, why so dear?

Just on air filters, what is the difference between a K&N and anything else? I got a Ryco for around 40 bucks and the K&N was 110, why so dear?

Ryco is paper and k&n is cotton gauze and designed to last the life of the engine as long as it is kept oiled. Stick to the ryco, they flow the same

Ryco is paper and k&n is cotton gauze and designed to last the life of the engine as long as it is kept oiled. Stick to the ryco, they flow the same

I gained 2kw with a paper filter over a CLEAN AND OILED K&N, heh

2kw difference on a RR is nothing. That is simply test variance

60kph: it's just clicked into top gear. Remember, the power required to move your car thru the air increases with the cube of your speed.

60kph: it's just clicked into top gear. Remember, the power required to move your car thru the air increases with the cube of your speed.

Yup and engine efficiency isnt at its best at 60kph i can guarantee that.

105km/h, consistent throttle, cruise control off.

http://i419.photobucket.com/albums/pp271/db_newman/5288d309.jpg

Although, this is difference between 4sp auto, 5sp auto, and 5sp manual. Mine is 5sp manual. Distance measured over 200km at night.

Cool SRS light there.

12mins to empty a tank sounds like bs to me.
Try driving your car at 417km/h and see how far you get before you run out of fuel. lol


He also said the tyres are good for 50 minutes at top speed. lol But not to worry, as at top speed a tank of fuel only lasts 12 minutes. Can someone lend me one to test this out? lol
Tyres last 14mins, fuel lasts 12. Must be a safety feature ;)

I've never really tested it but I've always been told it generally sits somewhere between 80 and 90km/h. I like getting to destinations in a timely manner though, so I can't bring myself to test the theory thoroughly.

What is really need is a series of curves showing efficiency vs engine speed. From this, one could derive the best throttle/engine speed combination. Then you would have to superimpose the vehicle drag against the engine performance. Damn it - just drive like you always do...

Personally, I think that the best engine speed would be where maximum torque is - about 3000 R/min. In top gear, that would put you way over the speed limits anywhere in Australia except the NT. 2500 to 3000 R/min would be my pick - whatever gear you are using.

Dont some later magnas have instantaneous fuel use? (Or is it just distance to empty???) and could someone try different speeds (throttle off) to minimise fuel use?

Cool SRS light there.

LOL I think someone forgot to take out their battery when they did thier climate control conversion and disconnected their airbag switch!



On the topic of air filters however, swapping the stock filter and snorkel for a pod filter increases performance (and is legal for red P's) correct?
But does it effect economy at all? Either for the better or worse??

Thanks

The whole discussion about POD/Air intake filters and the like has been argued time and time again. Differing opinions and nothing really settled. Some drivers beleive its makes thier cars so much more "responsive" and feels like it has more power others argue that it does didly squat and if not properly designed can do more harm than good (e.g. ends up sucking in hot air from engine, putting it too low in bay = water issues in intake etc)

As a general rule - its not going to make a difference to actual power levels as the car is a bog stock n/a car. The difference that a pod filter would make would really only be noticeable in a inducted engine. They make the car sound nicer but will not do much else. In many cases they have caused extra problems. A better filter is not a bad thing for the engine in the long run but that $100+ for a K&N filter could be much better spent for buying quality parts & oils - e.g. semi/full synth oil, genuine filters etc which will actually make a quantifiable difference to the engine's wear and performance in the future.

Also FYI - you are on P plates in Victoria - you are NOT allowed to make any modifications that increase performance. Furthermore - irrespective of your driving conditions - exposed oiled POD filter is BANNED. Any oil filter is completely banned and only "Dry element" - i.e. Paper, filters are allowed but these must be in the original airbox.

See EPA rules (http://docs.google.com/viewer?a=v&q=cache:5O9RbNu2pQIJ:epanote2.epa.vic.gov.au/EPA/publications.nsf/2f1c2625731746aa4a256ce90001cbb5/c90ec843f3bbbe8fca256d9f00181c59/%24FILE/1031.pdf+intake+modifications+victora&hl=en&gl=au&pid=bl&srcid=ADGEESgL1Nhdw1APj_n2B5_vN0DdTtLW33iwNfCnjZN1 sqVy6xZl2WlEA6eZLrQAqEEcobAGFg0n3YTqKWK79_LssS3F3b pPmCSEPS2gwjmUfcMaTP1iKX_snQzCc8VyoH2LnizSXeUn&sig=AHIEtbRlDtg2GBzQmCYN4_S7amCxIAXOVA) for details.

Section 1: Replacement air cleaners are permitted provided that they have all connections and systems present on the original air cleaner and operate in an identical manner.


Section 1(b) :Dry element pod type air cleaners are permitted on EFI vehicles. Oiled, oil-soaked or fluid-treated elements are not permitted.