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Fuel Consumption and Fuel Octane

cheekychimp

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Not another thread so much on how much you get from a tank but more upon how octane ratings and maybe timing would affect fuel consumption.

I have been running Shell V-Power for a while now as it is the highest octane rated fuel I can get over here without adding "octane boosters". Car ran great with it but I'd been seeing lowere mileages recently. I had been putting my foot in it a lot as usual, plus quite a few short trips taking Nathan to school, so I really thought nothing of it.

Recently money has been a bit tight with the new house, end of year tax bill so I figured I'd cut back and use regular. To be honest I couldn't detect any noticeable difference in performance. That doesn't mean anything, I'm not a dyno after all but the first tank of regular I use and I get 404 kilometres and I figure I've still got 40 km in the tank. I've owned this car for over three years now and I have never got over 400 km out of a tank. Admittedly I did some longer highway based journeys recently going to the airport to pick up friends etc but that also meant much more weight in the car than usual (full grown guys plus luggage).

I thought higher octane fuel and more timing led to better efficiency more power and better fuel economy? Have I got this wrong? Any chance the engine is cutting timing due to lower octane fuel, I am seeing less power and I'm getting better economy from not being able to push so hard?
 

prove_it

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What car?

Generally, only way to improve fuel mileage is to lean out the fuel trims. Higher octane with more timing does aid increasing the efficiency, but the same amount of fuel is being delivered unless adjusted with a tune.
 

gvr4ever

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Unless you've changed the compression or tune of a car, then going beyond what the car needed from the factory is likely a waste. A car tuned to 87pump can't really take advantage of 93pump. I know, US standards...
Now cars that require premium and get less will turn into a gas guzzler. Rental services are really bad about this. They will put cheap gas in nice cars. The injectors spray more fuel to prevent knock. Cars that require premium fuel will get the best fuel economy with premium fuel.

Not sure what car you're talking about, but the answer is, it depends. In the US, winter fuel generally has more additives, so overall less energy is in the fuel. We get worse fuel economy in the winter.
 

prove_it

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Warming up your car for 5-10 mins will waste more fuel too.
 

89Patches

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I get better fuel mileage using Shell 94 vs any other 94 stuff. Like another 50km more too a tank. That's just all hwy though. In the winter months I don't even keep track I get probably half the mileage compared to summer.
 

FlyingEagle

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THE Ottawa
I suggest that if you have fuel with less ethnanol, you might get better mileage.

I've always thought that MTBE or Ethanol or whatever they add for emissions, was the main reason there was less punch in the gasoline.

Wonder what mandates are in place for gasoline imported/produced/distributed in the Hong Kong region.

Good read on wiki about tetraethyllead and other chemicals in fuel, including levels in the blood and phase outs for chemicals additives.

http://en.wikipedia.org/wiki/Tetraethyllead

 
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slugsgomoo

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Ethanol has 30% less energy per gallon than gasoline. E10 therefore has 3% less energy than straight gasoline. If your driving habits, traffic patterns, and whatnot are so consistent that you can clearly call out that 3% variation, congratulations you must be an EPA mileage test center!

Running 87 instead of 92 (or 94 vs 98 or whatever pisswater you poor bastards who only get RON have to deal with), will likely get better economy in a car that's tuned for it, with obvious negative ramifications if the car requires premium and gets regular.

the focus is set up to run on 87 or 92, and just be more aggressive with tune on 92. So far no one has documented an economy difference, however I know they've dynoed around 30WHP difference between the two fuels.
 

cheekychimp

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The car is the VR4. It's the only car I have now, I sold the Type R to pay for the new kitchen /ubbthreads/images/graemlins/smile.gif

It isn't a stock ECU, it has a chip that was burned locally, but I have absolutely no idea what the exact tune on it is. We paired it with the correct MAF and injectors and it has always run like a champ so I never touched anything else. From what has been said above, I'm presuming it was set up for regular and I was probably seeing no benefit from using the V-Power stuff. But I thought Jeff (keydiver) used to run an octane reset code feature on his chips which stopped the car pulling timing for long periods after getting a tank of low octane fuel. Surely that suggests the car pulls timing when lower octane fuel is present? Are you guys saying that peak timing was set from the factory and that if a higher octane fuel is used the timing maps will still need to be adjusted (i.e. increased) to take advantage?
 
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prove_it

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The 1g maps are ridiculously over advanced in the timing areas. They are aggressive even for ethanol. I'm talking up to 24* at redline. Most of the time the ecu is pulling timing and running in between the high octane and low octane map. You will see a loss of power on a 1g with low octane fuel. That would also hurt fuel mileage as the ecu will take the already rich as hell mixture and richen it even more as the octane counts go down.

Hard to say what your ECU is doing, or if the high-low maps are stock or changed. If you have a logger that will display octane count and the timing retard data, that will tell you if the ecu is pulling timing and adding fuel with lower octane fuel.

Long story, yes, on a 1g ecu that functions like stock, you will see a loss of fuel mileage and power with lower octane fuel.
 

cheekychimp

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Strange then. I'm seeing the complete opposite at present. Then again to be able to say that with any certainty I'd have to do the exact same journeys back to back with different fuel and obviously with daily driving that isn't happening. I'll have to watch this over a longer period and switch back to V-Power for a few tanks to get a second opinion.

But anyway prove-it, what you are saying is that the timing ceiling on the stock 1G ECU is more than sufficient to take advantage of 98 RON (assuming that is a genuine octane rating)?
 

prove_it

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Oh yea, the stock timing maps of the 1G ecu are crazy aggressive. It was set-up with the factory 7.8:1 compression in mind. Almost no one runs those maps as they are very aggressive for even some race cars. You can't over-do octane at all. More is always better. You do stand to gain way more power with a light tune of some sort that leans out the fuel mixture. I've seen stock cars run 9.5:1 fuel ratio at WOT. Aggressive timing, over rich mixtures, and low compression all work well together, but it's not the best way to make good power.

Like I said, a simple logger will help tell you more details on where the ecu is at for running timing, fuel and octane count.
 

cheekychimp

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Quoting prove_it:
Generally, only way to improve fuel mileage is to lean out the fuel trims. Higher octane with more timing does aid increasing the efficiency, but the same amount of fuel is being delivered unless adjusted with a tune.



So how about this scenario? Assume the car was set up for 7.8:1 as stock and was rebuilt with 8.5:1 pistons. Assuming it runs without knocking does that constitute leaning out the fuel mixture enough to see any additional fuel economy or would that require an injector change and complete remap and it is likely the ECU is just pulling a lot of timing. I haven't noticed any drop in performance, so I am just assuming timing isn't being pulled but I doubt my butt can detect timing adjustments.
 

EHmotorsports

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compression,cams,intake,exhaust, anything changed after a car is tuned will directly change your AFR's.
 

dandanger

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If you can tune more torque to lower rpm's, you can use higher gears in city traffic, thus lowering fuel consumption. Though the rpm's under fifth gear are still so high in these cars that freeway drive-consumption does not improve.
 

cheekychimp

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Quoting EHmotorsports:
compression,cams,intake,exhaust, anything changed after a car is tuned will directly change your AFR's.



/ubbthreads/images/graemlins/rofl.gif LOL, I'm either incredibly lucky or completely screwed then, AMG intake, 2.5" exhaust, EVO pistons, the cams are stock I think. I'm surprised it runs as well as it does!!!
 
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turdb0

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I thought cars don't go over 60kmph anyways in HK. Haha... Every time I go up and down from Central to the hills of Causeway, it took the driver forever on those twisty roads.
 

cheekychimp

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Oh tell me about it! When it's quiet those roads are FUN but in rush hour, nose to tail, all stop and go ... AND on those steep inclines ... no fun at all. Do you still come over here? You should look me up if you do, I'm always up for meeting other members if the opportunity presents itself.
 

EHmotorsports

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Quoting cheekychimp:
Quoting EHmotorsports:
compression,cams,intake,exhaust, anything changed after a car is tuned will directly change your AFR's.



/ubbthreads/images/graemlins/rofl.gif LOL, I'm either incredibly lucky or completely screwed then, AMG intake, 2.5" exhaust, EVO pistons, the cams are stock I think. I'm surprised it runs as well as it does!!!




haha no possibly not screwed just skewed AFR's. it may not be enough to hurt the engine but performance and economy may suffer.
 

cheekychimp

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You know it's funny that you mention this now because even before I started using the regular gas I had been thinking of trying to tune the daily. My project car has been sitting for so long with an ECU problem that I still have the DSMLink v.2.5 that I bought for it sitting in a box under the stairs. I've never pulled the ECU on this car but Ken my mechanic said he thinks it must already be socketed because it supposedly has a custom chip written for the modifications the previous owner made (injectors and higher compression pistons as far as I know).

My laptop recently took a crap, but I think it's time I got it fixed and pulled that ECU to check. If it is socketed, I think I should just throw DSMLink in this car and see if it runs. If it does (and I can get the nitrous controls to run the cyclone correctly) it would confirm that the system works fine on JDM ECUs. That alone might give me the inclination to get stuck back into the project car and see what is wrong there in the ECU department. More importantly perhaps, I'd also probably be persuaded to upgrade to ECMLink. I know everyone will say that's a no brainer, but I've never been able to confirm that DSMLink runs properly on a JDM car so I've always been hesitant to fork out the extra $170 for the upgrade. Chances are, if everything works and I can tune the car properly I'll end up leaving DSMLink or ECMLink on the daily and finding another solution for the project car.
 
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