308 Gas Mileage Hi-test vs reg. unleaded

There have been some controlled tests that show cars get better mileage with regular (assuming that is what they were designed for). Regular actually has more stored energy per gallon, so this makes sense. However, the differences are always tiny.

DAve

 

I've often wondered about this myself (the effects of using a lower grade gas). But now with gas prices in the stratosphere, you can save a few bucks on a fillup with "regular". Keep us posted on your results.

 

If your car runs on a lower octane then use it. The definition of octane is a resistance to burn. Hirer octane fuels do not burn as easily and prevent pre-detonation. If you don't have to use it, it is a waste of money.

 

If your gas prices are in the stratosphere, that must put our European $7/gallon somewhere between Mars and Pluto ?!

 

Hi Clyde, thanks very much for posting this data... Always interesting to see.

Unfortunately, as a guy with a "stats" background, I don't believe that your sample size--i.e. the number of gallons of gas you've burned--is really big enough to conclude for sure that one is better than the other, with such a small difference. In other words, 1/2gal better (about 3%) could (I think, need to do the math to know for sure) be due strictly to "chance" or "sampling error" instead of an actual underlying improvement in mileage. As the difference goes up, or the number of gallons you burn goes up, this is less likely.

I'm grateful that you've posted, because I myself am interested in fuel consumption. Check out this thread:

My 328 Fuel Log After One Year of Ownership
http://www.ferrarichat.com/forum/showthread.php?t=60115&highlight=328+fuel+log


...BUT, I don't think we can really conclude anything from the data you have so far on mileage vs. octane... Would have to do the math to know for sure.


--Mike

 

As an engineer that's done lots of fuel economy testing, on-road and in the lab, it'd be hard to argue that it's scientifically valid, but interesting info. We'll skip all the combustion theory for now...

P.S.-just an interesting side note, knock sensor cars are REQUIRED by law to get within 3% of the same fuel economy with regular vs. premium.

 

Additionally, with the mpg ClydeM has listed, its essentially even money whichever he chooses.

 

I'm not a stats guy (one course in college and I have forgotten 95% of it). While we can say that the two decimal points of precision are probably not accurate, I think his comparison reasonably concludes that there isn't much difference between the two--certainly not enough to choose one or the other based on fuel economy.

I put regular 87 octane in my 308 and Mondial. Have never noticed a difference in economy or performance versus 89 octane. I have never bothered to even try 93 octane.

I really feel for you guys in Europe with fuel prices. I was watching Top Gear a week or so ago and they mentioned that the price of a gallon of gasoline in England was about $8 right now. Holy crap! We should quit our complaining! It takes dedication to drive a car that gets 15 MPG at $8 a gallon!

Birdman

 

It's not quite that bad. Its around 93p a litre for Shell Optimax (98 RON) which converts to around $5.90 per US Gallon (at an exchange rate of $1.75:£1).

 

I have always used the higher octane fuel in my 308 ONLY for preignition damage insurance. That's all. I don't know if it does, will, or has ever pinged back there ( I have a Tubi - it's too loud to tell) but I live in Alabama. We have hot summers. My QV runs hot, I use the air conditioner, and I live on top of a big hill with traffic. I would rather waste my money on expensive gas then an engine rebuild. Besides, if my major concern was saving $3.50 at the pump per fill-up, I wouldn't be driving this car. I would have a Toyota.

 

I have got to go make another long run and recheck my mileage per gallon (85 QV - GTB). I swear I was over 20...I must have messed up. It was a full tank run on a rally with the local FCA and included top speeds and put put driving from traffic light to traffic light. Just about every post I see says I should see 16-18 mpg at best. I am not running lean (but pass emmissions without any tweaking).

 

I've always used 87 octane regular unleaded in my '78 308 and have never had any pinging, etc. Believe me, if I heard the slightest ping the next nozzle in the tank would be the fancy one. I'm also of the belief that regular burns hotter and quicker and would keep my engine more free of gunk than Premium.