by "cuts_off_prius" (cutsoffprius)
Published 03/18/2017 at 00:25
by "cuts_off_prius" (cutsoffprius)
Published 03/18/2017 at 00:25
No Tags
STARS: 3
Well this impressed me, for being a gas guzzler. I filled up a new tank, reset, got on a local congested road (avg mpg was in the teens around here), then merged onto the freeway to drive almost 30 miles just to see what I would get for highway alone. Traveling at 75 mph most of the time and sometimes a medium distance behind cars. I get pretty much the same readout on my mpg (vacuum) gauge at 55 mph and 75 mph, provided it’s not too windy out. Peak torque is at 2750 rpm, which is about 75 mph. I read on the forums that 70-75 mph is a sweet spot for these cars in terms of efficiency and speed. Range was showing 447 miles LOL. Can’t wait to go on a road trip in this. City (more urban) is terrible though, I average around 16-17 mpg then, sometimes down to 15 during winter. Car is an ‘09 328i xDrive (3.0l straight-6 230 hp w/AWD)
Speaking strictly on fuel economy, I wouldn’t recommend the typical SUVs or vans due to their larger surface area, resulting in more air resistance when going with the flow of traffic on the freeway (~70-80 mph). MPGs tank in SUVs at higher speeds, as I’ve witnessed before in our CRV. But if comfort and/or utility is your thing, go for it.
"AM3R, lost another burner" (am3r17)
03/18/2017 at 00:31, STARS: 1
Yeah my 335i is pretty similar. I’m averaging about 14.9-16.5 in the city right now but it jumps to 30+ mpg as soon as I do a decent highway drive. Winter is killing my average!
"MyJeepGetsStuckInTheSnow" (myjeepgetsstuckinthesnow)
03/18/2017 at 00:32, STARS: 0
That’s a lot lower than I got in the city. Hilly or hard on the gas/aggressive?
"hike" (hike15)
03/18/2017 at 00:38, STARS: 1
Bigger engines just Loafing along on the highway are great. I got better highway mpg with a hemi and 8speed than with a pentastar and 9speed.
"Axial" (axial)
03/18/2017 at 00:39, STARS: 2
V8 in a light weight car gets that, too. :x
"cuts_off_prius" (cutsoffprius)
03/18/2017 at 00:40, STARS: 0
I’m starting to believe this as well. 4 cylinders are awesome for city/suburban style of driving. But when you travel at 75 mph or faster, they start to suck a lot more fuel (and the CVTs start to settle at higher cruising rpms to keep up). Our family CRV AWD, which is rated at 32 highway, drops to about 25 mpg when cruising at 80-85 mph on rural Interstates.
"Dr. Zoidberg - RIP Oppo" (thetomselleck)
03/18/2017 at 00:42, STARS: 1
What the hell is that warning light
"cuts_off_prius" (cutsoffprius)
03/18/2017 at 00:44, STARS: 0
That 4x4 light is due to low battery voltage (system shuts off nonessential equipment like cruise control, AWD). I get that after about 15-20 minutes of continuous driving, so I need to change the battery soon. AWD disables itself at highway speeds anyway, so I doubt that affected my results much.
"cuts_off_prius" (cutsoffprius)
03/18/2017 at 00:52, STARS: 0
In these cars, stopping and accelerating at lower speeds really kills mileage more than one would expect, so I avoid using the brakes and coast more. Steady state driving is decent on the other hand. Best advice is to drive the route with the least signal lights or stop signs. Wish we had more roundabouts!
"Wrong Wheel Drive (41%)" (rduncan5678)
03/18/2017 at 01:32, STARS: 1
You had mentioned it but air resistance really is the killer. That’s why aero design is so important on any newer economy car. When calculating air resistance, the formula uses velocity squared so more speed is exponentially more air resistance.
"Wrong Wheel Drive (41%)" (rduncan5678)
03/18/2017 at 01:37, STARS: 1
I have one roundabout on the way home from work (depending on the route I take). Normally there is too much traffic for the idiots to handle using it efficiently. Plus it’s one of those stupid ones with random yield signs (instead of those entering yield to those inside of it already). But when I can hit it at just the right time it’s so much fun to just maintain speed with a proper racing line and fly through it like a race track.
"NojustNo" (front24200)
03/18/2017 at 01:55, STARS: 0
man I wish. my G35 gets 19 miles to the gallon City or Highway. Doesn’t matter if my foot is on or off the throttle
"duurtlang" (duurtlang)
03/18/2017 at 04:59, STARS: 0
Does anyone here have any real expertise about efficient gearing? My engine makes peak torque at 4100 rpm, which is about the rpm it needs for 85 mph (non-Autobahn highway speed limit is 81 mph here). I believe my engine revs too high, especially at the German Autobahn, and was thinking about swapping in the gearbox (or the final gear) of a diesel. It will impact noise, but will it impact fuel economy in a positive way?
"BvdV - The Dutch Engineer" (dutchengineer)
03/18/2017 at 06:29, STARS: 0
The short answer is probably. My Twingo with it’s long 5th gear does about 1-2 km more to the liter than a Twingo with the same engine and the shorter 5th gear. It obviously does impact the acceleration in 5th gear, as I often need to downshift if I need to do 100 to 120 quickly.
Honestly, it all depends on the match between the gearbox and the engine, I could imagine it working if it is only a small difference in total ratio, but if the difference in total ratio will be big it might just have the inverse effect on efficiency. Since the car needs to have the same power at the wheels, the engine will have to produce more torque at the lower engine speed(P=omega*Tau), depending on the torque/speed map with constant fuel consumption lines of the engine this might give a better operating point or a worse operating point, thus leading to a higher or a lower efficiency.
Basically what you want to do is move your operating point (Intersection of torque and engine speed line) to a lower constant fuel consumption level in a map such as the one above. For sake of example say your current operation point is at 4100 rpm (429 rad/s) and 80 Nm, seen as the black circle in the map, and you want to achieve an engine speed 3000 rpm (314 rad/s) while maintaining the same engine power (so basically the same speed and torque at the wheels), that would mean a you need a torque of about 109 Nm to keep this equal (let’s assume drivetrain losses constant for the moment for simplicity’s sake). For this engine map that would mean you end up in the black star, which indeed places you in a lower constant fuel consumption level, thus increasing efficiency. So basically what you need to know is the gear ratios, and the torque speed map of your engine, preferably including constant fuel consumption levels, if you have those it is possible to find out if it would work. I hope I haven’t lost you by this point ;-P.
"Twingo Tamer - About to descend into project car hell." (oppisitelock)
03/18/2017 at 06:42, STARS: 0
I get the same motorway mpg as that with my 1.2 twingo... 4000 rpm at 80mph isnt good for economy.
"E90M3" (e90m3)
03/18/2017 at 09:04, STARS: 0
I’m wondering how my recently acquired 328i will be on fuel, I’ve got a 33 mile one way commute to my new job and I’m hoping it gets decent fuel economy. It can’t be worse than the M3. Also I’ve noticed that the economy meter in my M3 is off by a couple MPG.
"duurtlang" (duurtlang)
03/18/2017 at 10:43, STARS: 0
I sort of understand what you’re saying, somewhat. I am a bit of a Beta, but this kind of stuff ended with Atheneum (2001) for me. What I did get out of your post is that you’d need more data. Autoweek.nl provides me with some data (I filtered out the irrelevant data):
The first car is mine. The 406 diesel has an engine from the same family as my engine, but I’m not confident the transmission is the same (in fitment). I could find out. The 407 2.0 has the same engine I’ve got, but slighty tweaked due to it being a few years newer. You can see the rations for the first 4 gears are identical. The 407 2.2 has a higher displacement version of that same engine, and a 6-speed. I’d go for that 6-speed (if it fits).
And thanks for the help!
edit: I forgot this:
My car does have a computer to monitor engine consumption real time, but it doesn’t work and never has since I owned it. Probably due to the LPG conversion.
"cuts_off_prius" (cutsoffprius)
03/18/2017 at 13:04, STARS: 0
Yeah, it’s odd. I’ve read on the forums about the terrible mileage that G35/G37s get when I researched them to compare, for both city and highway. Maybe you’ll be saving more on maintenance still compared to a BMW.
"cuts_off_prius" (cutsoffprius)
03/18/2017 at 13:14, STARS: 0
328i get pretty much the same fuel economy as 335i (which has direct injection), to give you an idea. It also depends on the drivetrain and weight. RWD manual E92s get the best mileage, probably followed by RWD auto.
"E90M3" (e90m3)
03/18/2017 at 13:51, STARS: 0
I got 28-30 on the highway in my 128i, I’m hoping this is a slight improvement
"BvdV - The Dutch Engineer" (dutchengineer)
03/18/2017 at 17:00, STARS: 0
I’ve done some analysis on the basis of the numbers you gave and an engine map I had laying around from some project, I don’t know what it’s from, but the torque and speed range comes close enough to use it as an estimate. It does cause the fuel consumption figures to go a bit crooked, since I did some scaling, but the general trends should follow from the pictures below. The clearest is this one, showing an acceleration from 100 to 130 km/h in 30 seconds while in fifth (and sixth for the 6 speed).
From this I draw a few conclusions:
The 5th gear of the 6 speed is almost equal to your 5th gear
The diesel gearbox is focused on low down torque, I think it won’t be very useful in your car
Both the 5 speed 407 gearbox and the 6 speed 407 gearbox do a nice job of shifting the operation points along the rpm axis, while staying useful.
The next figure is for a range of cruising speeds (80, 100, 120, 150 kmh) in 5th (and 6th gear). With the dots representing the operating points.
And the corresponding fuel consumption:
I need to tweak the model I had laying around a bit to get better values fuel consumption values, but I can draw a rough conclusion already:
The improvement will be about 2 km/l for the diesel gearbox, but that one doesn’t seem to aid drivability, as shown above.
The 407 6 speed will give you an improvement of around 1 km/l in fuel consumption.
The 407 5 speed will only give you a small improvement, between 0.25 and 0.5 km/l.
I hope this makes it a bit more clear, and helps you to find out if it is worth it to change the gearbox.
Disclaimer: a lot of these conclusions are based on assumption and estimations, due to a lot of data on the engine and gearbox being impossible to find for this specific car(like the consumption map, and gearbox efficiency). And, yes, I had too much time on my hands today.
"duurtlang" (duurtlang)
03/20/2017 at 14:17, STARS: 0
Dank je voor de info! Daar heeft vast veel werk in gezeten, zelfs als je er al een model voor had liggen.
Ik ga de bak niet zo maar vervangen maar mocht de bijna 3 ton oude koppeling aan de beurt komen en de boel er dus toch al onderuit moeten dan ga ik eens heel goed naar die 6-bak kijken. Het gaat me niet alleen om brandstofverbruik (LPG...) maar ook om die toeren (lawaai, mogelijk slijtage) naar beneden te krijgen. Ik rij veel in Duitsland.
Misschien als ik een diesel 6-bak kan vinden met een eindoverbrenging vergelijkbaar met de diesel 5-bak uit het voorbeeld is dat ook het overwegen waard. Als de 5 van de diesel 6-bak redelijk overeen komt met de 6 van de 2.2 bak dan kan ik de 6 van de dieselbak als een soort overdrive benutten en blijft de auto vlot.
"BvdV - The Dutch Engineer" (dutchengineer)
03/21/2017 at 03:45, STARS: 0
Graag gedaan! Mocht je ooit nog een doorrekening van die andere bak willen, laat maar weten.
"duurtlang" (duurtlang)
03/21/2017 at 07:11, STARS: 0
Mocht je je ooit vervelen heb ik nog wel wat voor je; mijn motorombouw die momenteel gaande is. Ik heb de eerste auto (205 CTi), de bak van de 2e (GTi 1.9) en 3e (turbodiesel) en de 2.0 turbo motor van de 806. De bak die in de auto komt is de 1.9 GTi bak, maar dan met de 5e versnelling uit de turbodiesel bak.
Toerental bij 120 zal zo’n 3050 zijn lijkt mij. Maar valt er wat te zeggen over performance als je deze getallen ziet?
Helaas is de auto niet voor komend weekend klaar. Anders had ik hem zeker meegenomen.