High gas prices..how about regular?

[c4racer]

OK - lets approach this from a slightly different angle.

Currently here in CA, gas is running around $4 a gallon. Typically the delta between 87 and 89 is 10-15cents and the delta between 89 and 91 is 10cents per gallon.

Typical fill up for an X5 is ~20 gallons, right? So you are paying on the order of $80 to fill it up. Extra 10 cents a gallon to go from 89 to 91 is $2. Extra 20 cents a gallon to go from 87 to 91 is $4. How often do you fill up? For me, probably twice a month or less. I think I can swing the extra $8. It's a drop in the bucket compared to what we are paying for the gas. They put the best additive packages in the premium grade fuel - it's worth the extra few dollars per tank just for that, plus these motors are ~11:1 compression and were designed to run on 91 octane fuel. So why skimp? Doesn't make sense to me to even consider it.

[Buzzcut]

Jordo,

Point of fact, ethanol, because it is an oxygenate, should be cleaner burning and NOT leave a residue. Of course, the ECU knows just how much oxygen there is in the cylinder, and will richen the mixture in response. Maybe that's why you get that residue.

You are absolutely right that ethanol is a "bang". Gasolines there days are precision mixtures of various hydrocarbons, all of which burn at slightly different temperatures and pressures, engineered to smooth out the "bang" as much as possible. Putting ethanol in there in such a high concentration kind of defeats that.

With that said, neither has been an issue for me so far. I had absolutely no issues in 15,000 miles of splash mixing E85 in my Saab. We will see if the X5 does well with it.

[JCL]

C4racer: I understand your point. Personally, I think that the smartest way to save money on gas is to drive less. Then, modify your own driving habits. Then, finally, worry about your own specific vehicle, and the resultant cost per fill up.

That said, the difference between grades is more than that here.

I paid $1.45 per litre yesterday (91 AKI). That is $6.60 per Imperial gallon, $5.50 per US gallon. The difference between 87 and 91 grade here is about $0.25 per litre, which is about $1 per US gallon.

If Californians were paying over $5 per gallon, and there was a $1 per gallon hit for 91, I could see the question coming up more often. It is getting closer to whatever the actual tipping point is for people to start to change their purchasing behaviour based on energy costs.

[Buzzcut]

Car and Driver did a big article about 10 years ago, using various cars, running them with different octanes on a dyno.

A Saab 9-5 turbo lost as much as 15% of its power on 87 octane. But that was a turbo, and boost was cut to prevent detonation.

On a non-turbo, at most the engine is going to cut timing. This will hurt power a bit, but not anything like 15%. I'm going to speculate and say 5%, if that.

Considering how much people pay for cold air intakes and such, which at best will give you maybe 5% more power, a few bucks for a tank of gas might be a small price to pay for more power for some people.

[JCL]

Originally Posted by TowX

With my current 4.4 I was forced to put 89 octane in it once last summer. Was pulling my race car to MidOhio and pushed the tank capacity a bit too far and had to get off at the next available exit and fill up. Took 22.7 gallons so I was on fumes. The problem is that this Mobil station was out of 93 and I had to put in 89. I didn't get maybe two miles up the road and every time I accelerated hard (4500 lb trailer in tow) it surged and was way down on power. I suspect the surging was the knock sensor constantly retarding the timing to deal with the crappy octane. And even on the flat Rte 30 driving at 70, even in 5th it struggled to pull hills. Normally I get 11-11.5 mpg pulling my trailer on long trips. I was down to almost 9 with the low octane. I got 100 miles on a half a tank of that junk, stipped and pulled one of the 100 octane jugs off my trailer and added 5 gal of the really good stuff ($7.50 a gal unfortunately). Within a couple of miles I got my lost power back!! I figure I had created an octane of about 92.5 or 93. So I won't ever put anything but 92 or 93 in it now.

Most pumps produce mid grade by blending 87 and 91. So, if they were out of the good stuff, the mid grade pump could have been pumping 87.

My cut off point was 89. Locally, I noticed a difference (in summer) on 87. I couldn't notice, or measure, a difference on 89. But since fuels vary so much regionally, the only way to tell is to test your local fuel. When I travel to areas where I don't know the suppliers, I tended to use 91 just so that I didn't have to think about it.

[JCL]

Originally Posted by Big "J"

I know this thread is focused on V8 engines. Are there any thoughts or recommendations for those of us with I6 engines using 87 or 89 regularly?

Situation is exactly the same for the I6 and the V8.

The recommendations only change when you get to a turbocharged engine like the 35i.

MD has an I6, my X5 was an I6 as well.

[HPIA4v2]

Originally Posted by Buzzcut

Jordo,

Point of fact, ethanol, because it is an oxygenate, should be cleaner burning and NOT leave a residue. Of course, the ECU knows just how much oxygen there is in the cylinder, and will richen the mixture in response. Maybe that's why you get that residue.

You are absolutely right that ethanol is a "bang". Gasolines there days are precision mixtures of various hydrocarbons, all of which burn at slightly different temperatures and pressures, engineered to smooth out the "bang" as much as possible. Putting ethanol in there in such a high concentration kind of defeats that.

With that said, neither has been an issue for me so far. I had absolutely no issues in 15,000 miles of splash mixing E85 in my Saab. We will see if the X5 does well with it.

IMHO,
Octane booster in premium gas doesn't come solely from ethanol, it's more likely Toluene or Xylene (very high BTU when burned), when I auto-cross with a bunch of friends most kids dump 2-3 gallons of Xylene before their heat run which can be had at Home-depot for around $10/gallon but the octane is like 116 on this puppy, it's alternative to race gas.

Ethanol packs less BTU than gasoline for the same mass/vol density. that's why E85 will cost less but poor mileage. OK, water probbaly has high number of octane(resistance to detonation at high temp and presure) but zero BTU

This is the same analogy betwen propane and natural gas, all backup home power generator will produce less wattage when switched from propane to natural-gas it's no way around it.

[JCL]

This was a fairly recent thread with a very similar question as the OP.

http://www.xoutpost.com/bmw-sav-foru...69876-gas.html

[JCL]

Originally Posted by Buzzcut

I'm going to throw a hand grenade into this conversation...

I started mixing E85 into my gas. ....

It is hard to say if there is a hit to mileage.

Here is a thread on another member who was experimenting with E85. I posted BMW's paper on warnings re E85 in that thread.

http://www.xoutpost.com/bmw-sav-foru...l-mixture.html

It shouldn't be hard to say if there is a hit to mileage. It may be hard to measure the mileage accurately given other changes like weather, driving habits, etc, but the hit to mileage should be pretty close to 22%, eliminating all the other variables. That is just due to the 26% lower energy content of pure ethanol, and the resultant 22% lower energy content of E85, on a volumetric basis.

[Jordo]

Originally Posted by c4racer

OK - lets approach this from a slightly different angle.

Currently here in CA, gas is running around $4 a gallon. Typically the delta between 87 and 89 is 10-15cents and the delta between 89 and 91 is 10cents per gallon.

Typical fill up for an X5 is ~20 gallons, right? So you are paying on the order of $80 to fill it up. Extra 10 cents a gallon to go from 89 to 91 is $2. Extra 20 cents a gallon to go from 87 to 91 is $4. How often do you fill up? For me, probably twice a month or less. I think I can swing the extra $8. It's a drop in the bucket compared to what we are paying for the gas. They put the best additive packages in the premium grade fuel - it's worth the extra few dollars per tank just for that, plus these motors are ~11:1 compression and were designed to run on 91 octane fuel. So why skimp? Doesn't make sense to me to even consider it.