Switched from 93 to 87

[wasteoffilm]

After running 93 octane exclusively since mid-December, I cheaped out and filled with Mobil 87. I was headed in a certain direction, with one bar left on the gauge, toward a gasbuddy report of $3.85 premium. I get there, and it's $4.21, but only $3.65 for regular.

I've used Mobil 93 for 7 out of the last 9 tanks, and I honestly feel the difference. I'm 100 miles in, and lower end response is lacking a small bit. More noticeably, the intake noises sound sickened, kind of droning and sad. I can only assume the timing is compensating, as it should.

No mods, no tune. I really need to get the obd gauges going...

 

[RichieRocket]

wasteoffilm, I'm with you! For my limp-ankled driving style for everyday driving and commuting, 93 makes no sense cost wise. When it gets hot or when I'm towing I'll upgrade...maybe 89 (I'm also stock tune)

 

[wingman]

Understandable on the switch to 87 octane. My question is, have you noticed a difference in fuel economy?

 

[RichieRocket]

Understandable on the switch to 87 octane. My question is, have you noticed a difference in fuel economy?

Hey Wingman, I was hoping to get some data, but in the other mpg 87 vs. 93 thread, I realized my data was 'inconclusive'. The 4 tanks of 87 were run in Feburary when it was 30 degrees colder, and when I started using 93, we had a warm spell into the 70's! Plus, I was recording my average speeds, they varied from ~29 to ~36 mph. So all these variables make getting a real number very difficult.

If there is a benefit to 93, it looks like it does not justify the 40 cents higher per gallon price. A 1-2% mpg gain will not offset a 10% cost per gallon increase

What we need is Chevy to release the Brake Specific Fuel Consumption (BSFC) charts for the 1.4T on 87 and 93 in lab dyno conditions. Then we'd know for sure


Edit: One thing I forgot was ethanol content. The guy I spoke to at my state's Energy dept said the gasoline was 10% eth during the winter. I did not have the ethanol test kit back in Feburary, so I could not verify that. The last 93 tank I filled in late March tested 6-7% ethanol. (87 was roughly the same). So the tanks of 87 may have different levels of eth...All these factors are 1-2% stuff, but they can add up to change the numbers, especially since we are trying to measure a small amount...

I will add that last 93 tankful to the spreadsheet I have and post it.

 

[wasteoffilm]

Understandable on the switch to 87 octane. My question is, have you noticed a difference in fuel economy?

I personally haven't, but then I wouldn't. I have no typical usage for a tank of gas, mileage stays in the low 30's for my tiny 5 mile commute, and I can raise it up on my Sunday drives. I had this whole weekend off, and put over 100 miles on the car, blasting around the local twisty roads in third gear. DIC is currently at 34.2, but it reads anywhere from 1.3 to 4.8mpg high based on Fuelly.

 

[RichieRocket]

Here's my list with the last 93 fill-up:

As I said, it appears that 93 gets ~1.6 mpg better than 87 BUT there are too many variables to make anything solid out of these numbers.

Avg Spd: Driving cycles varied tank-to-tank
Ethanol: I have no measurements of ethanol content back in Feb, I was told it was 10% but did not verify
Outside Temps: Temps varied wildly over the last 2 months

As others have said, any mpg difference may show up more at hot temperatures when the engine computer is more likely to pull back timing?

I'm gonna run 87 from here out (I have stock tune), if I tow my trailer I'll bump up to 89.