[MightyMo]

Mo data on MPH & Octane vs. MPG

With various questions about the Mo's highway MPG and also how octane affects it burning in our minds, I hit the road last night at midnight to do a little testing. First off we found the "test track", nothing more than a relatively flat and nicely repeatable 6.5 mile long section of Hwy 85 here in Silicon Valley, stretching south from Steven's Creek to Winchester for those in the know. While there are some minor elevation changes in the road, it's nothing that makes the Mo's RPMs shift at all on cruise, and we GPS verified that the start and end points of our test track are at the same relative altitude (within 20 feet).

Starting out with 91 octane fuel at 70MPH in the cool 60 degree night air, and then filled up the tank with 87 and ran it again at 70MPH. 23.2 vs 22.3MPG. With the resulting %4 difference, and assuming a $.20 spread from 87 to 91, 87 would have to be *$4.96* a gallon before 91 octane is cheap enough (percentage wise, 91 octane gets cheaper compared to 87 the higher prices go) to warrant buying 91 for the increase in performance. That's not to say that you shouldn't use it anyway in hot weather or when towing, or ocationally to get the detergents in premium fuel to clean out your fuel system, but never get it for improved MPG.

I then also did runs at 50, 60 and 80 MPH to fill in the graph, and then 30, 40, and 50 on surface streets to flesh out the bottom of the graph. Surprisingly the MPG drops off fairly linearly, I expected a much more steep curve because increased RPMs and wind drag should combine to hit hard. Also interesting to see that the tipping point for max MPG is at roughly 40MPH, which basically translates to the maximum speed at minimum RPM.

Here's all the data and graph, enjoy folks:
http://www.zfilms.org/Stories/Murano/2004/6-14/MoMPG.jpg

 

[SugarRushMurano]

This post is incredible...

i can not believe you (and your gf) actually do this experiment...
Thumbs up. Hope this will mute all the rants on murano mpg in the future

 

[Kris]

MightyMO,

great post. A admire you for the test....................


I drove 10 months ago from Atlanta, GA to Owensboro, KY. Some 360 miles. Outside temps - approximately 80F. Cruise control on 73 mph (mostly). At the end computer showed 24.5 mpg.......so I trust your results.

 

[bob1]

Thanks for the work, you get the Murano Extra Effort award.
This is a such a hot topic with soaring prices. It's nice to know the board members are looking out for each other.
Bob1

 

[Eric L.]

Very interesting results! I too doubted the folks who said use super for the mileage increase, since a 10% increase in fuel economy would have been amazing in the MO if it were due to fuel alone!

 

[hfelknor]

I don't use super for the MPG increase.
In point of fact I would have bought a 4 cyl Highlander if I wanted MPG.
Of course I have no argument with people who are trying to stretch a buck with these high gas prices. More power to you guys.
I just thought I would present an alternate view.


One of the reasons that I specifically bought the Murano was because it came with the 350Z motor in it.

I use the super for the power increase.
It's not a big difference, but it does make the engine respond in a crisp manner.
In point of fact it is probably the 4% increase that is seen in MPG.
That would make it about a 10 HP difference and that is significant and difficult to achieve from available performance parts.

Homer

 

[Gonzo]

Most impressive data.... but what was most impressive was that your girlfriend went through this with you. Wow! She is a keeper.

However I have some questions and comments. Please don't take this the wrong way what you did was great. However a 6.5 mile leg really isn't long enough for accurate data, its a bit short. Furthermore with this short trip and small refilling it doesn't really test the octane sufficiently. I would think that you would really have to go through one complete tank of the next octance prior to testing. With such a short trip you never really got "100%" of pure octane for testing.

If you where using the MO's computer for MPG calcs I would throw that away and just use gallons divided by gallons at the pump. Again the short trip and refill technique may introduce errors.

Am I reading your graph correctly... 40 MPG at 40 MPH? That could not be right could it?

 

[EdMPT]

I wonder if there is any "true" horsepower gains from a higher octane, at least in a production vehicle. My knowledge on this is limited, but I thought higher octance was required for cars with high compression to prevent pre-detonation. Hence the reason race cars and such use the race specific higher octane (I think it's around 104 for stock drag cars).

So does that mean that in a vehicle that operates at lowers compression gets a more explosive detonation with 91 vs 87 octane? I would assume there is some difference, but is it measurable?

My thinking is probably not much at all, especially if a cold air induction system and free flow exhaust only give a few percent increase. But it would be interesting to know for certain if 4 octane could make that much of a difference. I have tried both and I think I can feel a difference, but really I am not sure. As for MPG difference hmm my driving is too variable to tell, however I also live in Silicon valley and managed 99.9 mpg for a stretch of about 4 miles coming down highway 17, I wonder if that's as high as the Mo calculates?

So..anyone have access to a dyno? Or care to take the Murano down a drag strip with different octanes? he he he

 

[MightyMo]

Gonzo, you're right, there are certainly ways to refine the test for more solid numbers, but given the time constraints we did the best we could.

I failed to note that we started out on fumes with 91 octane, so it was a full tank of 87 I put in before the second test. A gallon of 91 mixed in with 20 gallons of 87 isn't going to do much, and we did drive around for a bit to make sure we were feeding on the 87 before doing the second test (remember the Mo has a return-less fuel system, so you need to burn what's in the lines). Yes, you could argue the extra weight of the 20g of fuel could be a factor, but we weren't measuring the MPG during acceleration so it should be a minimal change. Also I felt that doing two runs back to back in the same weather conditions was more important for consistency than waiting a week to run another tank through before a second test.

Yes, we were using the Mo's computer for MPG data, no way with such a short trip could we refuel and do the math against miles traveled, and even with a longer trip if you don't come back and use the exact same pump you're going to have some variance.

Yes, 40MPG at 40MPH. However, that surface street we used for that data was flat but possibly a bit downhill. I used it more to see where the max MPG point was, don't use those numbers as absolute MPG (see how the 50MPH changes from freeway to surface? That's why we did 50MPH twice.)

Next time we drive out to Utah on a road trip we'll hit the Bonneville Salt Flats and really get some good data

Actually, next test I can think of is for tire pressures to resolve that debate. Run them at 45, 40, 35, 30, 25 and see how the MPG changes...maybe sometime this week if my GF's tolerance for my insanity has been fully replenished

Oh, I should also do a 91 octane vs. 100 octane at some point for giggles, see if the motor & ECU have any potential to use the better fuel (I doubt it).

 

[MightyMo]

EdMPT, ideally you'd want a 2004 2-wd SE with the synthetic 6-speed to dyno, but I've also got a G-Tech Pro Comp , so I can give it a try at some point on the road for fun. However, the fact that when cruising the ECU had to burn more fuel with 87 octane means power being delivered was lower than with 91 and it had to use a larger throttle setting to maintain speed. The reason for the lack of power would be retarded ignition timing because the 87 octane is more prone to pre-ignite (detonate), not because 91 has a "more explosive detonation" than 87 (it doesn't, same energy content, it's just a question of how easily it can pre-ignite).

99.9 is probably just as high as the display can show. It's almost certainly keeping track of fuel injection times from the ECU and comparing that against miles traveled, so if the result from that calculation is out of bounds it's going to show 0 or 99.9, but that doesn't mean it's inaccurate. As noted before in another thread the Mo like almost all vehicles these days shuts off fuel flow completely when coasting/decelerating, so if you were going down 17 it wouldn't be burning any fuel at all, hence the 99.9.

 

[Eric L.]

Most impressive data.... but what was most impressive was that your girlfriend went through this with you. Wow! She is a keeper.

However I have some questions and comments. Please don't take this the wrong way what you did was great. However a 6.5 mile leg really isn't long enough for accurate data, its a bit short. Furthermore with this short trip and small refilling it doesn't really test the octane sufficiently. I would think that you would really have to go through one complete tank of the next octance prior to testing. With such a short trip you never really got "100%" of pure octane for testing.

If you where using the MO's computer for MPG calcs I would throw that away and just use gallons divided by gallons at the pump. Again the short trip and refill technique may introduce errors.

Am I reading your graph correctly... 40 MPG at 40 MPH? That could not be right could it?

It read 40mpg at 40mph because that is the steady state cruising requirement. However, accelerating up to 40mph from a stop is enough to make the overall mileage much much less.

As an example you can try yourself. Drive on the highway for a bit and note the mileage after resetting the mpg display. Then accelerate hard, and note how quickly the mpg decreases. You can cruise for 30 minutes and have teh display read 25mpg. Then accelerate from 60 to 80 and drive at 80 for one minute, the overall mpg will fall to a much lower number. Whenever I see this, it makes me feel like I wasted my 30 minutes of conservative driving.

 

[Gonzo]

Yea I know what you mean... I've been trying to drive with a light foot but whenever I get on the highway at rush hour you have to accel quickly here or you get run over.... I loose any gains.

 

[EdMPT]

Wow, that g-tech is a pretty neat toy. It would be interesting what kind of results it would show. Especially with the tire pressures.

Just out of curiousity, where do ya get 100 octane gas?? Boy you could use that for all kinds of things...fuel additives, air filters, ect. Question is how much time do you have on your hands...


Good stuff already though...thanks!

 

[Halo]

Union 76 sells 104 at some stations, usually out of one pump. It's just a bit over $4 per gallon near me. I have used it in the S2000 a few times because I was worried about detonation after I got the S/C.

 

[sincityswany]

MightyMo,

Thanks for the info on the tests and 87 vs 91 gas.
It helped to put me at ease a bit about the less than stellar mpg that I've gotten to date.

Since my MO only has 1260 miles on it, maybe its just taking awhile to "break-in".

Until this last week, I was only getting 15 mpg at best....and that is with about 50/50 highway and surface street driving. It's just now starting to climb up to the 16.5 and above range.

I have yet to take it out for a good long road trip to see what kind of numbers I get for strictly highway travel.

 

[MightyMo]

I've found driving style really makes a BIG impact on things, and the CVT does take a while to learn.

For instance, when accelerating, it's natural to gradually keep pressing on the throttle more and more to keep the RPMs rising to provide the 'normal' audio feedback of acceleration. No no no, press it enough to accelerate but keep the engine under 2K RPM. Especially once the torque converter locks up at 18MPH you can ride the motor at 1.5K RPM up to freeway speeds.

 

[HwnMurano]

Thanks for all your research MightyMo! Very interesting and informative.

I'm looking forward to your study on the impact of variables in tire pressure on MPG.

Many Thanks!

 

[Gonzo]

I agree MightyMo. That is exactly how I typically drive.... just under 2k to my desired speed. I find that I am happy its "daily" acceleration with light throttle input.

 

[MightyMo]

Considering all the recent posts about pinging with low octane fuel I thought I would wake this old thread up and give an update:

With our pathetic 91 octane CA fuel I very very occationally get brief pinging when juuuust at the right speed, like minimum rpm at 20MPH as the torque converter locks up and the ECU ends up asking more from the throttle than it should and lugs & pings the motor. It stops almost instantly and is very hard to reproduce. My assumption is that this is a weak spot in the ECU fuel/throttle maps and since it's so infrequent (once a month maybe) I don't worry about it.

However, with 87 octane, I get this transient pinging far more often, usually a couple times a week it'll bite me. For this reason I have totally stopped using 87 octane and gone back to 91.

 

[bob1]

Since the gas price went nuts many months ago, I switched to 89 octane (mid-grade). I had only used 93 before and have listened for pings but not found any. The only report is a loss of 1-MPG.
When high test gets back to 1.80 a gallon I'll switch but for now 89 octane seams to work OK over here in Georgia without any pings.
Bob1