Since I downgraded to 87 octane...

[nixter]

I've had my 911 for about a year now and I had always put the high octane gas in the tank figuring the higher the octane the better right? Well after reading a whole whack of different opinions for and against on this forum I decided to try out the 87 octane variety. That was about 6 tanks ago.

One my first tank I was a little dismayed by what I thought was slightly less hp and an almost diesel-truck sounding engine note when the engine was working hard to get out of low rpms.

The second and 3rd tank proved similar but I thought I keep with it a while as I figured there may be some strange "breaking in" stage or some nonesense.

Sticking with it seemed to have payed off as by the 4th and 5th tank I started to notice some major differences! First thing I noticed was that I had more power in cold weather (could be in my head).

2nd thing I noticed is that I am getting better milage! That one seems strange to me but I'll take it. My fuel gauge is a little dodgy so I normaly refuel around the 145 mile mark. Around 150-160, my warning light comes on. I seem to be getting an extra 5 or so, not much but still something.

The major difference I've noticed is the overall consistancy of the engine through the rmp range. Before I was always leary of running the rmps up high as the enigne had this very whiny, high pitched sound that just didn't sit well with me. It always gave me this feeling like something was about to give in a bad way. Now the enigne has a nice confident growl as the needle approaches and passes 5 and 6.

I'm on the 6th tank now and I'm a believer! This engine was apparently designed for this gas and I guess those guys knew what they were doing.!

Oh yeah, the other major thing I've noticed is more cash in my wallet

Btw, regarding my warning light coming on around 155 miles, does seem right to you guys? What kind of milage do you folks get from a full tank?

Thanks,

Nik

[vesnyder]

Nik - interesting results. I've tried lower octane and could not tell teh difference- but not as scientific as you. My light usually come on closer to 200 - normally close to 20 MPG - but I will have to pay closer attention. Bad time of year to be looking since the car rarely leaves the garage until April!

[fred cook]

Interesting results! However, according to my owners manual my 1980 SC coupe is supposed to be fed 91 octane fuel. You may find that in hot weather (coming soon) that the 87 octane might be prone to causing "knock" in your engine. However, if you can run 87 octane for 6 months out of the year, that is a savings.

The low fuel light on my '80 SC comes on at about 300 miles. I get approx. 17-18 mpg in town and a fill up when the light is on takes about 17 gallons. Just in case you are wondering, I don't particularly baby this car and use the throttle liberally.

[IROC]

Originally posted by nixter
Btw, regarding my warning light coming on around 155 miles, does seem right to you guys? What kind of milage do you folks get from a full tank?

Thanks,

Nik

Heck, my light comes on around 550km or so (340 miles). I usually get around 600km (375 miles) out of a tank before I fill it up with around 18 gallons.

This is with my 3.2, though. The old 2.7 would get easily go 400+ miles between fill-ups. I once got about 540 miles out of one tank with the 2.7.

Mike

[69911e]

I don't have an SC, but in my other cars(BMW's and Porsche) I found the cost per mile the same running 93 octane or 87 octane. There is less than a 10% difference in price plus the extra ignition advance you can run with the 93 increases the MPG about 10% (plus there is more HP).

[Superman]

Well if you guys get 20 mpg, and have 22 gallon tanks, then I'm not sure why your fuel light would be coming on at 200 miles. That's less than a half-tank.

[jbrinkley]

I found it odd that a couple weeks ago I got 21.5 mpg with Steve's chip. I didn't stop for gas (93) till some where past 410 miles.
This was a four hour trip to houston with some higher speed stuff when I was feeling lucky. I was impressed. Later I found out my O2 sensor was unplugged also. Go figure

[masraum]

Originally posted by nixter
I've had my 911 for about a year now and I had always put the high octane gas in the tank figuring the higher the octane the better right? Well after reading a whole whack of different opinions for and against on this forum I decided to try out the 87 octane variety. That was about 6 tanks ago.

One my first tank I was a little dismayed by what I thought was slightly less hp and an almost diesel-truck sounding engine note when the engine was working hard to get out of low rpms.

The second and 3rd tank proved similar but I thought I keep with it a while as I figured there may be some strange "breaking in" stage or some nonesense.

only if you are using a brand of gas that has better cleaners in it

Sticking with it seemed to have payed off as by the 4th and 5th tank I started to notice some major differences! First thing I noticed was that I had more power in cold weather (could be in my head).

cold weather will always give more power regardless of the gas you use because you are getting more O2 to the engine since the air is more dense. Also lower octane gas burns faster, so you will likely get more power with it, until detonation blows holes in your pistons when you hit hot weather.

2nd thing I noticed is that I am getting better milage! That one seems strange to me but I'll take it. My fuel gauge is a little dodgy so I normaly refuel around the 145 mile mark. Around 150-160, my warning light comes on. I seem to be getting an extra 5 or so, not much but still something.

The major difference I've noticed is the overall consistancy of the engine through the rmp range. Before I was always leary of running the rmps up high as the enigne had this very whiny, high pitched sound that just didn't sit well with me. It always gave me this feeling like something was about to give in a bad way. Now the enigne has a nice confident growl as the needle approaches and passes 5 and 6.

Not sure about that, but lower octane should be fine during the colder winter months

I'm on the 6th tank now and I'm a believer! This engine was apparently designed for this gas and I guess those guys knew what they were doing.!

Not really, the owners manual says otherwise.

Oh yeah, the other major thing I've noticed is more cash in my wallet

Btw, regarding my warning light coming on around 155 miles, does seem right to you guys? What kind of milage do you folks get from a full tank?

Thanks,

Nik

In my '88 I used to get 15-17 mpg on my daily commute in the winter and 17-19 on the same commute in the summer and got about 22-24 on long trips without trying to get good mileage.

Maybe since you live in Canada your summer months are cool enough that you can run the lower octane year round. If so more power to you.

[jtratza]

jbrinkley you were lucky if you were doing some high speed stuff on the stretch of I-10 into Houston. If its not construction holding up traffic its all the police on patrolling it.

Guys something has got to be "different" if you're only getting 150 miles per tank or you're only filling it to the half way mark. I haven't checked recently but I was getting mid 20's on trips with the usually 80 to 90 cruising speeds we have on most Texas roads. A couple of weeks ago I got to south Texas (340 miles one way) and still had some gas in the tank. This weekend the wife and I went to Austin. I filled up in Austin for the return and made it home with better than half a tank after driving back at the usually 80 to 90 on highway 290 and with the top off (targa not wife) all the way. I cannot imagine running 87 especially with summer temps around here.

[mede8er]

Seems to me this would only be relevant to low compression 3.0 CIS cars.......

[hpmad]

hello,

I have a 80 SC, 3.0L completly stock.

I get 21mpg in town and 28/29 on the freeway at 90mph...

my light comes up at 200miles in town. but the needle is dodgy bellow 1/2 tank...

in theory, you can put 87 octane in your car (using the standard US rh+something/é method. I usually put mid grade, but I think that I will try using lower grade to see what I get. I might however still use chevron gaz....


cyrille

[jmohn]

OK, One more time.

The same gallon of gasoline can have 3 different octane ratings "Motor Octane Number" (MON), "Research Octane Number" (RON) and "Pump Octane Number" (PON). The MON octane test gives the lowest octane number, the RON method (used in Europe) gives the highest. American fuel is rated by the PON method which is an average of the MON and RON methods. Which means a European car (like my SC) which requires 91 RON (European) gas would use 87 PON (American) gas. Using a higher octane fuel than the engine was designed for will NOT give more horsepower or better milage nor make it run cooler or "better" (it may, however, reduce "pinging" in an engine that has carbon deposits). Using a lower octane than the engine was designed for WILL cause problems (detonation, reduced power, damage to pistons and valves). While slightly advancing the ignition timing and using a higher octane fuel will produce, marginally, more power, you, almost certainly, will not notice any difference from the drivers seat. Please continue to buy whichever grade of fuel you prefer, as long as it meets the minimum engine requirements, buying a higher octane fuel than is required will not hurt the engine in any way it's just not necessary.

Jerry M
'78 SC

[wholberg]

I have had the same experience as Nixter. When I bought my 87 carrera I ran premium. After reading several posts about premium vs. regular gas on this forum, I switched to unleaded regular. Almost immediately, I noticed that the car had better low-end torque and ran more smoothly. I haven't checked the mileage yet, but anything more will just be bonus!

[RickM]

....and some of have to take into consideration the fact that our fuel is "oxegenated" from October through April. I will not put this stuff into my 911.

[kevjandon]

Like said above,

My 83 SC owners manual says 91 RON octane. US gas is not measured in RON.

91 RON means 87 at the US pumps.

My SC runs much better on 87.

[TerryH]

My European SC's fuel door asks for 98 RON. This is more than most gas pumps in CA can provide.

So, I run only premium fuel which is apparently heading for $3 a gal. soon.

[sammyg2]

Where are you going to find non-oxygenated gasoline?
Since the ban of MTBE, all refiners that I am aware of are using ethanol as a blending stock. The percentages vary a great deal with region and time of year, but I am not personally aware of any US refiners who are not using at least a little alcohol in their gasoline.
Maybe I'm too isolated in California, do they still make gas without alcohol in NJ and I'm just not aware of it.

[sammyg2]

98 RON is roughly equivalent to around 91 or 92 octane as is labeled on the pumps in California. There is not a straight coversion factor, it varies with the gasoline blend. Premium should be fine in your car.
If you run 91 octane premium and still experience pinging, all you would have to do is back off the total advance a couple of degrees, or clean the carbon out of the combustion chambers.

RON is measured by lab tests that measure the percentages of the sample through distillation, then a number is assigned based on the make up. Purely theoretical, but consistant.

Mechanical octane is measured with a knock engine. They use a carefully calibrated and certified internal combustion engine with a variable compression ratio. They get it running on the sample and gradually increase the compression ratio until the sensors pick up pre-detonation. That level tells them the mechanical octane rating which is almost always significantly lower than the RON.
If you take both those numbers from a sample, add then together and divide by two, you get the number that is on the pumps in the US.

[RickM]

Sam,

They offer non-oxegenated fuel after April 30th. They revert back Oct 1st. I don't believe there is alcohol in the fuel during this "off" period but I'll ask a friend who works for Mobil/Exxon.

[anthony]

I get 21mpg in town and 28/29 on the freeway at 90mph...

That would be a dream. I usually get 16-17mpg and maybe 21mpg if I soft foot it and keep the revs down while on a long freeway trip.