Octane Rating

[jimmy3530]

Hey everyone:

Just a quick survey....I'm wondering if everyone is filling their tank with 93+ octane gas all the time as is recommended. I know that it will self adjust to a lower rating but I wanted to know if there is a significant (measurable) drop in performance, mileage, or possibly something else. I use my 2000 C4 as a (almost) daily driver and my gas mileage is absolutely terrible to start with and so I seem to be at the pump every couple days.

Thanks

[function12]

I use 93 and mine is a daily driver. I usually get 17MPG city driving. I do hit triples at least once a week.

Edited May 7, 2010 by function12

[Orient Express]

91 Premium is the only pump grade available here in California, but we do have pumps that sell 100 Octane race gas. So what I do is on every fill-up I mix 4 gallons of 91 with 1 gallon of 100 gas. This gives me a 93-95 octane gas. I also get about 19-24 mpg out of each tank.

[number9ine]

Hey everyone:

Just a quick survey....I'm wondering if everyone is filling their tank with 93+ octane gas all the time as is recommended. I know that it will self adjust to a lower rating but I wanted to know if there is a significant (measurable) drop in performance, mileage, or possibly something else. I use my 2000 C4 as a (almost) daily driver and my gas mileage is absolutely terrible to start with and so I seem to be at the pump every couple days.

Thanks

93 here in NY. 91 RON+MON/2 (AKI) is the minimum octane listed in my owner's manual, and 87/89/93 is what's available at the pump. When I lived in CA, I did 91.

I understand that the car will adjust to a lower octane by detecting higher instances of detonation with the engine sensors and adjusting the timing to compensate. While it might help reduce knocking that would hurt the engine, I imagine that over time it causes increased wear and tear on something. I'll take the manufacturer's word for it.

If you want better mileage I'd suggest a lighter foot, and less weight in the car. If you get on it like I do you're gonna be visiting the pump more often. :) I'm stunned by my car, driving like I stole it will get me 19-21 MPG on the computer. My friend has an '04 C4S and his gets 17-18 MPG or so on a hot foot. Are you getting less? If so you may want to let a mechanic have a look. Simple things like oil, air filter, tire pressure, plugs, etc. can have a big effect.

Mark

[perryinva]

I use 93 in Virginia all the time. Try to always stick to a Top Tier station as the '02s and newer have no fuel filter. Get 22 mpg avg with a normal foot on my '02 C2 6speed.

[cyclocross]

I always use 91 AKI in my daily driver ('02, C2, 6-speed) here in California, either Chevron or Shell.

Sometimes I add two gallons to xylene to 12 gallons of 91 to have 95 AKI. There is a noticeable boost in mid-range. I have not tried a top-end run. Adding the xylene brings the aromatics content up to around pre-RFG levels. Problem is the stuff runs about $20/gallon.

My commute runs 21-22 MPG. Highway driving yields 27-29 MPG.

[geoff]

91 octane is as good as it gets in southern California. I usually fill up with Chevron, since my mileage was consistently slightly better than when I tried Mobil, Shell, 76 or Costco and it came with Techron already added. I don't add anything else to the tank other than the gas out of the pump. I've noticed over the past 6 months or so my mileage is worse in all my cars, by up to 10%, and friends have told me the same. Some of it is due to the driver, but something has changed in the gasoline formulation recently, more than the usual seasonal chemical changes from prior years.

Anything less than premium gas will be less expensive to fill up your tank, but you will probably end up spending more on gas than what you are saving by burning the cheaper grade. You can run a few tanks of each to convince yourself and do the math.

[jcan]

I fill up with 94 in Canada. I've also heard that these engines use Nikasol and that a lower octane rating gasoline can cause the nikasol parts to fail (cylinders) .... Has anyone else heard this?

[hopeforcash]

I'm using 94 in Canada as well. Though I'm thinking whether or not 91 is adequate. Since only driving occasionally, I guess the 94 additional cost is minimal.

[rrspikemarty]

91 in CA. mpg in line with everyone else with fairly 'light' foot.

:lol:

[Greenhorn]

I use 91 here (Ontario, Canada). I could'nt notice the difference between running 94 & 91. I use shell 91 which contains no ethanol, most of the 94 sold up here (Sunoco/PetroCan) does.

[hopeforcash]

Is ethanol bad?

[Jonas007]

No, there's no reason why ethanol would be bad for your engine. The 94 Octane stations in Canada typically use about 10% ethanol in the blend, and from previous race experience on a highly boosted car, I could notice the difference from the 92 octane fuel (Esso) up to the 94 octane (Sunoco), where I would have almost 0 knock on the 94, but would see 8-10 "knock units" on 92 or 91 on my logs. This was running 24psi on the car though (non Porsche car), so fuel impurities were evident quite quickly under the boost.

[rpm996]

Hey everyone:

Just a quick survey....I'm wondering if everyone is filling their tank with 93+ octane gas all the time as is recommended. I know that it will self adjust to a lower rating but I wanted to know if there is a significant (measurable) drop in performance, mileage, or possibly something else. I use my 2000 C4 as a (almost) daily driver and my gas mileage is absolutely terrible to start with and so I seem to be at the pump every couple days.

Thanks

What do you consider to be 'absolutely terrible?'

This is a high performance machine designed to go fast. Mileage, even for cars built just a few years ago, was a secondary consideration at best. Just look at the gearing, 6th is barely higher than 5th. It is no highway cruising/gas saving gear. Commuting around town with anything less than a feather foot is going to give you less than 19-20 mpg. Even a light foot won't gain you that much.

I do wish the tank were larger. My old 968 held nearly 20 gallons.

[jimmy3530]

Hi everyone and thanks for all the responses. RPM996, judging by the OBC, I'm getting approx 14 mpg during my commutes to work. That's what I'm saying is terrible only because i understand that's its supposed to be 19-20. And yes, agreed, the tank is small.

The car is approaching 50K so maybe I'll swap out the plugs to see if that helps. Tires are good, air cleaner is new. What else can I try?

[rpm996]

14 is low - unless you are really enjoying your commute

Might also clean the MAF (Mass Airflow Sensor).

Edited June 1, 2010 by rpm996

[jimmy3530]

How do you clean the MAF? It seems somewhat delicate. Wouldn't want to damage it.

[tonybony123]

hi i live in england uk. i fill up with 95 octane super unleaded i get fairly good milage but i bought this car to enjoy not to watch the guage so i dont give a hoot about the milage the pleasure i get from driving my porsche is worth every penny, you only live once so enjoy.

[jimmy3530]

Agreed with tonybony123! However, if something is wrong I'd like to fix it. I'll try cleaning the MAF. I should also note that when I said "city driving" its really stop and go traffic in gridlocked DC

[carrera3.2]

Here in Colorado, we can normally get only as high as 91 octane at the pump. That's OK at +5000 ft altitude because the higher the altitude (for a NA engine), the lower the octane rating has to be to prevent serious knocking. We have only about 80% of the oxygen content of ambient air as exists at sea level. The take-home lesson is that the closer you live and drive to sea level, the more critical it is to use higher octane fuel in your high-performance engine.

[kgoertz]

I thought I'd update an old thread.

FYI

Here in Ontario the two best choices for gas used to be either Sunoco (94 octane but 10% ethanol) or Shell (91 octane with no ethanol). I have been running mostly Shell for the past 2 years. I was using Sunoco before that but was concerned with the Ethanol and wasn't able to tell a difference between the two.

I filled up yesterday at Petro-Canada with the 'new' 94 octane. The pump did not indicate whether or not it included 10% ethanol but there are rumours that Petro-Canada is now selling a 94 octane non-ethanol blend.

I commented several times the next day that the car felt faster before I realized the reason. There is a clear difference in both "seat-of-the-pants" acceleration and engine noise. I am unable to dyno the difference, but even my wife noticed the difference in sound. It sounds a bit more like a banshee :-)

If anyone else has compared the two I would appreciate the feedback.

[tac27]

91 Premium is the only pump grade available here in California, but we do have pumps that sell 100 Octane race gas. So what I do is on every fill-up I mix 4 gallons of 91 with 1 gallon of 100 gas. This gives me a 93-95 octane gas. I also get about 19-24 mpg out of each tank.

Same product availability in Vegas. I do the similiar octane mix as OE with similiar results in fuel economy.

Tim

[1904carrera4]

Wow i must be one light footed driver, I run my 996 c4 cab as a daily driver on 95 octane super unleaded and see between 24 and 29 to the gal regularely. Before you ask, nope I don't make contributions to green peace or have a save the planet sticker on the rear screen I do use the cars potential when I feel the need and wouldn't go back to a Japanese cat if I was paid. I do think the extra Ron makes a difference in performance and economy

[dmfconsult]

Ethanol is usually only an issue in much older engines, as the old rubber hoses were not formulated to operate with it and the ethanol will dry them out and cause cracking. Anyone with a 996 will not have to worry about it. In Vancouver, both 94 Octane at Chevron and 91 Octane at Shell have no ethanol. I always run 94 Octane in my 996 as well as the classic american iron I have tucked away!

Edited August 15, 2011 by dmfconsult