WHAT GAS??

I have heard the arguments from all gas is the same (formulated by region) and cross delivered by many of the same companes, to particular gas brands. In particular, Chevron which was rated by a "BMW" valve wear index (!?).

This comes on the heels of one vehicle in my fleet (outboard) that sits up a lot and has been gtting gummed up carbs. I was told by the young mechanic (who I respect) to use good gas from a station that pumps a lot (ie fresh) and good oil plus an additive (marine stabil) to keep the carbs clean.

I tend to use the cheapest brand of gas available. We have a company in town called QT that has a good reputation an always thelowest prices.

SO, IS there a difference in brands of gas, and do you know of any good scientific data on the subject? Cheep (Chip)

I went to a lecture a few years ago where technicians from Shell where discussing the technical aspect of their fuels and oils, given the recent arrival, at the time, of their new Optimax product, and the phasing out of leaded fuels.

The single point from that whole lecture that stood out in my mind was shelf-life of modern unleaded fuels. The advice given was that we should make every effort to ensure that the fuel in our tanks was no older than two weeks! Anything older, and it was, at best, likely to cause performance loss, and at worst, at risk of causing gumming.

I assume, to some degree, that they were being pedantic, and were allowing for the maximum length of time that an average pump station is likely to store the fuel, but it raised a concern for us people with hobby cars that could quite conceivably see them sit in the garage for anything up to a month at a time.

I have no answers other than draining the old fuel and buying form fuel stations that have a good turnover.

Chip, there are differences in the adatives the various companies use and this does make a difference. It is true that all base gas comes from a very limited number of suppliers though. It is also very good to buy from a station that does a brisk business. But, with all of the attention to underground tanks in recent years we are getting better gas in addition to saving the environment. For the most part I buy gas only from Amoco and Shell. Chevron (Exxon) is good gas, but I can't buy gas at Exxon as a matter of conscience. The biggest mistake most people make is in thinking that high octane will make their cars run better. You only need and want high octane if the compression ratio of your engine is 9.5:1 or better. Using too high an octane in an engine won't hurt it, but it will run like crap or, at least, get bad gas mileage. On the other hand, running to low of an octane in a high compression engine will hurt it because it will diesel and the fuel will start burning to early in the cycle causing detonation (ping).

Lynn, HEAR HEAR!!!!!!!!!!!!!!!!!I haven't bought Exxon since Prince William Sound. Good for you!!!!

Many new cars have knock sensors and will pull timing out if pinging is detected. Therefore, using relatively high octane will insure maximum performance on these cars but 92-93 (R +M / 2) is enough for these motors, even some that are 10.0-11.0:1. My VW is 10:1 and I can tell a difference with 89 octane gas, although it is slight.

Putting anything higher than premium into stock cars is a waste. If you have turboed or supercharged the motor, or made other modifications, most notably raised the compression, then you certainly may need it.

Lynn and I had a good laugh about this at a recent race where two boys fueled up their stock daily driving Ford Probe 24V car with 102 octane. I'm sure it made a huge difference!

R

I agree re: Exxon. Have not been to one since the Valdeze incident. Outwardly cheer when I see one of their stations closed!

Ron: What do you think about gas brands? cb

I think you're going to be hard-pressed to find a "good" oil company. There are much worse examples than the drunken captain of the Exxon Valdez - that was human error, as I understand it, while some of the other oil companies are engaged in extreme human rights violations, purposeful harming of the environment, ...

Look into the actions of Shell, Chevron, Unocal, British Petroleum, and others and I don't think you'll be inclined to be so hard on Exxon for screwing up.

Some links:
http://www.moles.org/ProjectUnderground/drillbits/5_08/4.html
http://www.ibiblio.org/freeburma/boycott/oil/oiladrs.html
http://www.mtholyoke.edu/org/action/catalyst/orgoni.html

Me, I generally use the cheapest available gas in my Bronco. That's usually Sinclair or Phillips around here, and I'm sure someone can dig up some dirt on these oil companies...

As for the use of race gas in a street car, I believe there are reasons other than the higher octane rating to do so. One would be consistency - a lot of pump gas these days is pretty crappy, especially the winter formulation used in California (and Utah, for that matter).http://www.starbanner.com/articles/news/1386.shtml

Check this out:
http://www.e-bski.org/special%20pages/oilcompanies.htm


Looks like I'm being good without even trying.

With some of our cars running older engines, how do you all deal with the lack of leaded fuel? We have LRP (lead replacement fuel) and we all avoid it like the preverbial plague. It has a bad reputation for causing harm if used a lot in older engines.

We also get unleaded in two shapes and forms. Regular and Super unleaded. But from one of the posts above our octane ratings are higher than yours by some margin. Regular is 95 and super is 97 as standard. Normally a lead additive is added if people want to lead up their fuels. This can come with octane booster as well if required.

So are the octane ratings a universal standard or differing from US to UK/Europe?

When we go to the Isle of Man, there is only one fuel pump on the whole island that does super, but right next to it is another pump that does a 101 octane fuel which if I remember rightly is Av Gas! No planes or runways in sight!

Interesting to hear that fuel has a shelf life. Now that the season is over, my car will stand in the garage for some months awaiting next year's fun to begin. From the above I should be draining down the fuel and putting it in the lawnmower or leaf blower to use it up and start fresh next year.

How far can you take it? At Brighton this year I saw Paul and Roy refueling their car from a huge drum with green petrol issuing forth! They had been buying blue printed race pump fuel! They came first and second respectively within the club!

Malcolm

[ October 07, 2002: Message edited by: Malcolm M ]

The octane numbers are different between the US and the UK - there are two measures:

Research Octane Number (RON) - tested at 600rpm
Motor Octane Number (MON) - tested at 900rpm

In the UK we only use RON, whereas in the US they take an average of the two values (called Anti-Knock Index or AKI).

I think in general 89/93/94 octane in the US equates roughly to 95/99/100 octane in the UK (MON tends to be 8-10 points lower than RON).

I know all this because we had extended discussion on the topic on the M5 message board - and yes our engines are high compression (11.0:1)

ciao

Ian

I remember reading an interesting article in EVO magazine. They tested SHELL Optimax in a range of performance cars, both for increases in performance, and the petrol's ability to "clean an engine".

The test lasted about a month, I think. Anyway, Optimax proved to worth the extra few pence per litre. It increased performance by a few 10ths in some cars. It also did a good job of cleaning some fouled valves.

I belive it has an Octane rating of 97.

I've used it in my M coupe ever since.

J.P

Hi all,
The Optimax that is being spoken about is listed as 98 Octane whereas most 'super-unleaded' in the UK is 97 with regular being 95. Dave Parker & I both use Optimax in our Cosworths. (2.0 Turbo 16v) The fuel definately makes a difference with these cars, especially when the boost is up around 27psi or more! We both have low boost settings that we can use if we have to fill up with a 'lesser fuel'.

The Avgas that Malcolm speaks of is probably LL100 which is a 100 Octane Low Lead fuel used primarily for aircraft.

regards

Paul T

100LL aviation fuel in the US has a distinct blue tint to it. The higher octane (120?) aviation gas that I have not seen in quite a while was purple.

As to older engines, is it that much of an issue to put valves and valve seats in the heads that will allow the use of unleaded?? The issue is the lubrication qualities lead gives, primarily, to the valve/head mating surfaces. We made similar modifications to engines (agricultural) that used LP gas (it just so happened that the two we had were chrysler hemi industrial engines: one on an irrigation pump and the other in a grove sprayer.)

Paul hit on a very good point that we didn't mention: super/turbo-charging. Of course this is the other engine type that requires higher octane fuels besides high compression engines. Indeed with high boost conditions, especially without intercooling, you can't buy high enough octane gas to prevent detonation. The usual solution is to dump massive amounts of fuel in order to cool the intake charge. (The type of car and its ability to keep the induction components cool has a very big part to play in this.) This works to the point that the amount of fuel starts washing down the upper cylinders and pistons start burning. It is at this point that water injection is often employed to keep the intake charge temp down. Depending on the car and boost being run, you will see things like this being done even with intercooling. TwinTurbo 3000GT/Stealths suffered greatly with this problem once the HP passed 6-700 because of the lack of airflow in the engine compartment.

VP Racing Fuels has really expanded their product line recently. If you are in search for consistancy, and leaded fuels (they also have a series of un-leaded), perhaps you can track down your nearest dealer. Anytime I've ever called them, they were always very helpful and willing to give advice. Also, here is their site:
http://www.vpracingfuels.com/vp_01_fuels.html?mgiToken=D031D8023F0FD27C3#leaded

If you must store fuel, keep it in a sealed metal container and keep it off the concrete floor. Racing leaded fuels react to sunlight (probably UV) almost immediately, so if a plastic container is used for momentary storage, keep it in the shade.

Andy