Comparing other's MPG by octane rating? - Fuelly Forums

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Old 01-14-2018, 12:56 PM   #1
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Comparing other's MPG by octane rating?

Hi all,

New user here.

Loving the features so far, but wondered if there's any way to compare MPG of the same models by their octane type?

So far I've been running my vehicle exclusively on Shell V-Power 99 (UK) on the basis that the manufacturer recommends higher octane fuel and Shell allude to potentially better MPG by using V-Power.. Comparing my average MPG to others on Fuelly, I can see mine's dead centre of the bell curve. I guess it's fairly unlikely others with the same model are using exactly the same fuel as myself.

On the basis that V-Power is a considerably more expensive fuel than standard Unleaded 95RON (ignoring Shell's other claimed benefits of engine cleaning properties and just focusing on the cost-per-mile) I'm curious to discover if it's really worth the extra cost!

Thanks in advance
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Old 01-14-2018, 01:08 PM   #2
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Welcome. I gave V-Power a try, and felt that performance was a little better (smoother), but there was no appreciable improvement in mpg to make the exorbitant price per litre worth while. I went back to using Morrison's 95 octane.
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Old 01-14-2018, 01:46 PM   #3
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Hi and welcome. I always use premium, 97 is the best I can get here. Not too fussed about the cost increase as it makes little difference unless you're doing silly miles! You really would need someone in exactly the same car, doing exactly the same journey in the same conditions using the same driving style to make any fair comparisons. There are far too many factors that affect fuel economy, it's near impossible to arrive at any conclusion unless you experiment yourself in your own car.
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Old 01-14-2018, 02:29 PM   #4
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Most cars had knock sensors in 2002. I'm sure the M series had higher compression and probably called for premium, but it would not hurt to try a lower grade to see if the timing would be retarded enough to prevent preignition (knocking). It looks like your mpg is among the better for that type so I would assume you are driving conservatively.

I would approach it with caution, starting with a few gallons of mixed fuel, maybe 50/50 and see how it works for you. Then if you get destructive engine knock you could add premium and most likely be OK.

My wife has driven cars for tens of thousands of miles that recommended premium, on regular gas (her choice) but any car with that recommendation will have instructions for operating on lower octane fuel in the owners manual for places that do not offer the highest octane.
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Old 01-14-2018, 04:56 PM   #5
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I would add that if your car has never had the cylinder head off and carbon deposits removed it could be much more susceptible to knock. If that is the case then I find Chevron techron fuel injection cleaner to be excellent at cleaning injectors and carbon deposits without removing anything
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Old 01-15-2018, 05:28 AM   #6
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Regular gas is like fast burning gunpowder, compared to premium that takes just a little bit more time to reach the peak pressure. These days you can think of it like this, if I limit my load maximum to 80% with a compression of 10 to 1, then my effective compression is 8 to 1, i am only "inhaling" 80% of the available atmosphere.

If my compression is 12 to 1 then with everything else being the same at 80% load it's 9.6 to 1. (12X80%)

Most important is much better ignition control and quality makes preignition practically impossible as long as the fuel is atomized by the injectors properly. The knock sensor allows the engine to find it's own max advance by retardation when the knock is produced until it is eliminated. Modern systems "learn" and continuously adjust the parameters until they can actually anticipate your actions.

That pretty much eliminates the possibility of knocking by backing the timing off until it quits knocking. It's a 6 hour job on a 96 300zx, I think they pull the engine but slightly after my time.

If your car can't control its knocking, give it a shot of techron in the tank. I have had that action alone shut off a CEL, not even necessary to reset. Lots of folks spend a lot of money and finally they figure out the spray pattern on the injectors is crappy something the system can not really compensate for. By that time they have removed the injectors and opened up the potential for vacuum leaks.

The better approach is the one that requires the least effort with the greatest potential reward, this is where techron MIGHT save your arse. Not every time but close to most of the time, sometimes it is not the whole cure but starting out with an engine capable of running on all cylinders is step one.

Bottom line, if everything is kosher it should run fine on regular (lower) grade fuels as long as you don't use 100% throttle regularly. If it knocks then try the techron. If that doesn't get you there they you have to live with what you have.

You will almost certainly notice lower power, which is the systems response to what would be spark knock in older cars without feed back systems for engine knock.
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Old 01-15-2018, 10:36 AM   #7
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The Beemer has a compression ratio of 10.2:1. If you use it to its full potential then use the V-Power. Otherwise, give the 95 a try. Just as R.I.D.E. says.
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Old 01-15-2018, 12:19 PM   #8
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Mine is 9.2:1 is that good?
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Old 01-15-2018, 01:29 PM   #9
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Higher compression usually means higher performance. Mind you, the Jazz is 10.8:1, so that rather knocks that on the head. And Honda recommend 95 RON.
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Old 01-15-2018, 01:37 PM   #10
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I just read that turbocharged cars generally have lower ratios as the turbo already compresses the air. Interesting.
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