Using less than 93 octane? 13 50i

[Boston01X5]

Friend of mine is trying to run lower octane to save money at the pump… I guess technically 50i can run on 89. I haven’t dealt with turbocharged engines in a while but when I did always ran highest octane I could buy at the pump (93+)

What do you guys run with similar vehicle? (E70 X5 50i)? Is it worth saving $20 every fill up with a lower octane? Or will it do damage over time?

[andrewwynn]

I have done an experiment on wife's 50i this week.

When the tank was at ¹/₄ tank I filled to ¹/₂ with 89 then I drove that down to fumes and put in about ¹/₂ a tank of 89.

The scanner shows the engine knows it was "grade 2" fuel (3 being optimal). I noticed no significant change in acceleration in typical on ramp or 60-90 passing maneuvers.

We can get 93 for the price of 89 if we go to Sam's club but I can get 89 in town.

The forever history of the car showed 0 fills of 1, 40 of 2, and 499 of 3 quality.

The smooth running values were all nearly identical.

I couldn't find the knock sensor to see what they are reading, but plan to tomorrow for a baseline before I go back to 93 fill up Thursday.

My rational based on the filler door literally saying 89 min. where my e53 says 91 minimum.

When my e53 ran out of gas (stuck fuel float grrrrr), my sis n law brought me 87; the car went into limp on the initial acceleration, and once more in the 7 mile drive to the gas station.

The fact that the engine computer graded the 89 in the middle not the lower grade does give me satisfaction that it's likely perfectly ok and on long trips we would prob use 89 but stick with 93 for normal use since we def want the max performance and do take advantage of it regularly.

It amounts to about $30/mo or $360/yr savings in gas.

The first test the car averaged 21.7 mph going 80 avg for 130+ miles so with n=1 no detrimental hit on mpg.

I searched to find any tests of n63 and 89 and didn't have any luck.

A couple on xo have mentioned noticing a distinct difference in power from their 35i when using less than 93. I'm also specifically interested in n63 examples.

I will maybe do a couple 0-60 pulls tomorrow while I still have 89 so I can compare to 93 when I refill with premium thu.

[Attacking Mid]

I've used regular (85 here at altitude - equivalent to 87 at sea level) in all of my BMW gassers ever since a client who drove BMW's told me he'd switched to regular with no discernable effects. The N52 in my wife's E83 has the highest compression ratio at 10.7:1 of the engines we've had, and I've observed no negative effects from running regular. The M54 is barely a high compression engine at 10.2:1. Your N63 is in between at 10.5:1.

If you drive hard, it might be a different story, but we tend to drive pretty conservatively. As always,... YMMV.

AM.

[andrewwynn]

Yeah I can't run reg in my m54. The car coughed and sputtered on the first use of throttle. Very interesting about high altitude difference in octane.

I will be interested to see if I can measure any difference since the car does objectively know the difference, what does it know with that information?

[ard]

Id rather discuss what oil to use or if Nitrogen in tires is a scam.

[Boston01X5]

Originally Posted by ard

Id rather discuss what oil to use or if Nitrogen in tires is a scam.

I’d rather discuss what contraceptive your mother should’ve used, and how your comment is helpful at all…

[andrewwynn]

Originally Posted by ard

Id rather discuss what oil to use or if Nitrogen in tires is a scam.

N₂ Scam for road cars for sure. F1 cars I'll bet it's a measurable difference. I think it's a few pounds less unsprung weight per corner.

Oil; I'll bite: my m54 just turned 200 and I'm switching to 5-40. Wife's N63 is 85,000 and sticking with 5-30.

[bcredliner]

Originally Posted by andrewwynn

N₂ Scam for road cars for sure. F1 cars I'll bet it's a measurable difference. I think it's a few pounds less unsprung weight per corner.

Oil; I'll bite: my m54 just turned 200 and I'm switching to 5-40. Wife's N63 is 85,000 and sticking with 5-30.

There is very little difference in the weight of Nitrogen and air. It's not enough to use it to reduce unsprung weight. The racers that use nitrogen in their tires use it because the pressure does not fluctuate as much. It doesn't take much change in tire pressure to change the handling.

[ard]

Originally Posted by bcredliner

There is very little difference in the weight of Nitrogen and air. It's not enough to use it to reduce unsprung weight. The racers that use nitrogen in their tires use it because the pressure does not fluctuate as much. It doesn't take much change in tire pressure to change the handling.

Agree it isnt a weight thing



The pressure change stuff is false. All gasses follow the same laws. Nitrogen and oxygen will act the same/



It is because you cannot buy high pressure bottles of *air*; that nitrogen is nice and cheap and inert; that you can buy it 'technical pure' and totally moisture free.


This last part is THE key: moisture. THAT is what caused the pressure changes w temp.


And the nitrogen they sell in shops is NOT the same that race cars and airplanes use.

[andrewwynn]

Originally Posted by ard

Agree it isnt a weight thing



The pressure change stuff is false. All gasses follow the same laws. Nitrogen and oxygen will act the same/



It is because you cannot buy high pressure bottles of *air*; that nitrogen is nice and cheap and inert; that you can buy it 'technical pure' and totally moisture free.


This last part is THE key: moisture. THAT is what caused the pressure changes w temp.


And the nitrogen they sell in shops is NOT the same that race cars and airplanes use.

N₂ is N₂ I doubt much difference. I have a pilot friend with a little bottle he uses for filling up the suspension. I'm pretty sure the bottles will all be labeled nitrogen.

Race cars may insist on some unimportant purity like 99.99 vs. just 99.