Using less than 93 octane? 13 50i

[bcredliner]

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.

Yes, moisture is the reason for fluctuation. It is difficult to assure you are getting the same amount of moisture each time air is used. Tire pressure is part of the handling setup. As an example, they will determine how much inflation they will start with, run some laps, see how it handles and bring it back in to make adjustments to improve handling. To best reach their goal some use nitrogen so the fluctuations due to heat are consistent as they may change the pressure in one or more tires to improve handling. That and a bunch more information will be saved for future reference. With nitrogen in tires the setup is easier to duplicate.


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

Just for grins, I tried nitrogen one time on my X. I couldn't tell any difference. Even if there had been a difference. It wasn't very long before I had to adjust the air pressure. It was not convenient because I didn't have a nitrogen tank. So the first time I adjusted the air in the tires it was with air.

[bcredliner]

Some engines will run fine on lower octane fuel without retarding timing to avoid spark knock. Some lower octane fuels might not have the cleaning additives though there are aftermarket cleaners that work fine. Generally, if an engine calls for 89 octane, using 91-93 is a waste of money. And, generally, if an engine calls for 91-93 octane the timing will be retarded if lower octane is used. Depending on how much timing is retarded the performance of the engine can be negatively impacted. The discussion of whether it matters should be apples to apples. If the question is about a 50i it is best to compare to another 50i. Comparisons are also somewhat faulty as they are not on the same road, same way of driving, same temp, same humidity etc. While impractical for most of us consecutive dyno runs with the considered octanes should be accurate.

[andrewwynn]

[mention]bcredliner [/mention]: my query is: if the engine calls for min. 89 (as 50i does), is there an improvement off using higher octane fuel; top tier where the 89 has the same detergent package (which may not mean much with direct injection; nothing to clean the intake valves at least).

I didn't notice any butt dyno problems at any speeds from 9-200kph. Kickdown broke the wheels loose going into fifth. (About 180 kph).

The car knew it was mid grade. It grades each refuel as mentioned above and I have no interest in trying lower than 89 although we can now get E15 88 and perhaps with the higher alcohol content and FI, could be a thing.

Maybe I test out a tank and see if it will be graded mid grade or I manage to get the first grade one out of 540 refuel.

I've also considered using octane boost.

My second car used premium and the price was always 20¢ more than basic. Scaling up that should make it 50-55¢ more but it's often 70-80¢ more per gallon which is got to be price gouging.

I know there is no benefit to put premium in a car that runs on 87 as long as the 87 has the detergents, so is there any benefit to run 93 in a car that requires 89 vs. 91? And does anybody have empirical data to back it up? I searched quite a bit and found nothing.

[bcredliner]

Originally Posted by andrewwynn

[mention]bcredliner [/mention]: my query is: if the engine calls for min. 89 (as 50i does), is there an improvement off using higher octane fuel; top tier where the 89 has the same detergent package (which may not mean much with direct injection; nothing to clean the intake valves at least).
IMO the answer is it might. If the engine advances the timing to adjust for the higher octane it might, as long as the 89 doesn't do so also. I think to maximize any potential benefits it would have to tune it on a dyno.


I didn't notice any butt dyno problems at any speeds from 9-200kph. Kickdown broke the wheels loose going into fifth. (About 180 kph).
You broke the wheels loose at 100 mph, in a 6000 lb X5 that has 4 wheel drive?

The car knew it was mid grade. It grades each refuel as mentioned above and I have no interest in trying lower than 89 although we can now get E15 88 and perhaps with the higher alcohol content and FI, could be a thing.

Maybe I test out a tank and see if it will be graded mid grade or I manage to get the first grade one out of 540 refuel.

I've also considered using octane boost.
[COLOR="blue"]Octane boosters do work but you won't know what the octane change is.[COLOR="blue"]
My second car used premium and the price was always 20¢ more than basic. Scaling up that should make it 50-55¢ more but it's often 70-80¢ more per gallon which is got to be price gouging.

I know there is no benefit to put premium in a car that runs on 87 as long as the 87 has the detergents, so is there any benefit to run 93 in a car that requires 89 vs. 91? And does anybody have empirical data to back it up? I searched quite a bit and found nothing.

No data but as above it might make a difference. I think the odds are worse.

[andrewwynn]

Officially: I plead the fifth.

Unofficially: I can confirm the ass whooping occured (that's a quote from Prince related to basketball and pancakes: YouTube the story it's amazing)

The road had a bit of mist on it and the rear tires are due for replacement. (3/32-4/32 tread).

I'm used to the rears breaking loose at full throttle shifts into 4th if the onramp is dusty. But was a surprise at 110.

FYI the only way I can tell the wheels break traction is the DSC complains and pushes up my foot with the gas pedal.

Lastly, 4wd yes but strong bias to the rear. (based on the tread disappearing twice as fast in the rear it's pretty obvious).

[andrewwynn]

since "air" is 80% N₂ that does make plenty of sense. I thought I saw a video where a guy weighed a tire before and after N₂ fill and it was a measurable difference.

A quick search of YouTube shows the real difference being the change in pressure caused by the amount of water vapor in a typical air fill.

I recently had TPMS complain on E70 just from ambient temperature drop.

I've noticed about 1psi drop per 10° F ambient. That's enough in itself to cause problems.

More research into O₂ filtering though the rubber: if that's the case simply refilling as pressure depleted will increase the N₂ ratio but I have a feeling the partial pressure from water vapor likey has more effect on the ambient temperature effect.

I definitely would lean on the zero point for consumers. Use filtered/dry air to achieve the same effect

Airplanes use N₂ so their tires are less of a fire risk combined with the magnesium rims.

[andrewwynn]

https://youtu.be/9WjdqJL70Js

Very sensible follow-up

[bcredliner]

Originally Posted by andrewwynn

https://youtu.be/9WjdqJL70Js

Very sensible follow-up

Great video!

[andrewwynn]

I think it's all about the water. One would hope that a concentrator would heat the air to dispel any moisture but I think we've come to an agreement there is no point to use N₂ in a street car. It would maybe be nice to use a scuba tank so you can use dried air.