What grade of gas/petrol ??

[wigan]

In these times of high prices, I was wondering what you folks put in your tank? I've always been on the cheap side and put in the lowest grade. My B seems to run fine on 87, wondering if it would be beneficial to put a higher grade in?

 

[Stewart]

If it runs fine on 87 keep using it. I've been running 91 in mine which I'm sure is way over kill but hey its a toy so it doesn't bug me much.

 

[SAustin]

I was using 91/94 in my stock '74 but mainly for the same reasons as Stewart and it performed better than 87.

If your's runs fine on 87, you're laughing. Our gas prices hover around $1.17/litre (about $3.50 usd/gallon).

 

[Steve_S]

The type of fuel a car requires is dependent on the state of tune and how the engine is built. Higher performance cars running high compression will require higher octane to prevent detonation. Lower compression and a mild tune will allow the use of low octane fuels. Experiment with different grades and go with what the car runs best on. If you don't feel a difference between 87 and 92 then stick with 87. Also try different brands. I've found that my cars hate Shell gas, for example. it takes a long time to really figure this all out unless you drive all day, every day. Varying weather and driving conditions can foul up your test results!

 

[jlaird]

Might even mix two grades to get something in between.

 

[Steve_S]

Actually, a chemical engineer once explained to me that mixing different octane gasolines will result in a higher octane than either one alone. When my father was driving his (now mine) MGB he used to mix 87 and 91, which was reported to give an octane rating of 92-93. This was in the leaded gas days, and later when I owned the car and the head had been converted and the engine rebuilt, I started using straight 91/92. It's run fine since.

 

[19_again]

Tony always says use 93!! So I will!

 

[Steve_S]

Using 93 on a car tuned for 87 will not hurt anything, but it's throwing money away and might cause a slight power loss. The fuel in the combustion chamber needs to ignite at a certain and specific time. high octane fuels will take longer to burn and can therefore throw off your timing. A modern car will adjust for this by automatically advancing or retarding the timing to a certain extent, but an MGB has no such capability.

 

[swift6]

There was a recent tech question on one of the big car mags (Road & Track I think) where a question was asked about mixing octanes. The answer was that the pumps already mix low grade and high grade in order to get the mid grade. From personal experience in my younger days, a gas station that I worked at did indeed only have two underground tanks. One for high grade and one for low grade (no diesel at that station). The pumps mixed the two for the midgrade. Not sure what percentages of each though. Simple math doesn't work it out exactly on a one to one basis.

 

[14dna]

Believe it or not,when the temperature gets lower, your octane level should reduce as well. Higher octane requires high temps to fire. As you raise the combustion ratio of an engine, you also raise the cyl. temp. The biggest advantage to high octane, is its natural cleaning power. All said and done, Most of our "B"s should run 91 to 93 octane until late fall or early spring, and then run 87.
Dave

 

[R6MGS]

Since I work for an oil company...I get a discount so I've always just put the highest octane in all our cars, never had any problems. But I've heard this debate many times, it all depends on the car.

 

[don62]

I was told that my 76b was made to run with lead fuel.
Should I ad any additive to it?
According to my manual it could ruine the engine if I run
with unleaded????

Thanks

Don

 

[Steve_S]

If your head has been converted to unleaded then no worries. If it has not, then I would consider an additive.

 

[tony barnhill]

 

[Daimlerdb18]

Actually, a chemical engineer once explained to me that mixing different octane gasolines will result in a higher octane than either one alone. When my father was driving his (now mine) MGB he used to mix 87 and 91, which was reported to give an octane rating of 92-93. This was in the leaded gas days, and later when I owned the car and the head had been converted and the engine rebuilt, I started using straight 91/92. It's run fine since.

It's true that blending high and low octane gasolines will oftentimes give a result higher than the volumetric average. I spent a couple of years as the blend chemist for a Gulf Coast refiner and figured out that our truck loading blend system was giving away significant octane using volume averaging. Modern gasolines with ethanol blended in are certainly a different proposition. The advice about simply trying a gasoline grade to see if it changes performance is valid, bearing in mind the harmful effects of severe knocking. I use 93 in my MGA only because the head was shaved by the previous owner and it pings when using 87. As far as a specific brand of gasoline being better or worse, the little secret of refiners is that most gasolines from different companies are mixed in the pipelines going to the consumer markets (it's called fungible product). The big difference then is in the additive packages which each brand offers and the cleanliness of the jobber and gas station in handling the products.

 

[PAUL161]

Of all the talk on Octane ratings, I haven't heard anyone mention altitude. From sea level to high in the Rockies has a strong influence on what Octane gas you use. If you live at altitude, say 5000 feet or above, low Octane should be plenty if your engine is set to factory settings. If you live at or close to sea level, a high Octane gas would be more advisable. Also, just because you have a pre hard seat head, doesn't mean that you have to rush out and dump a 1000 bucks for a new hard seat one. If the engine runs fine, leave it alone. If the head has to be reworked or replaced because of a problem, then go with the hard seats. I always abide by the old saying,"IF IT AINT BROKE, DON'T FIX IT". Contrary to some experts advise, using that old adage saved me a few bucks over the years.

 

[swift6]

Yep, the altitude thing is because of reduction in air density that effectively reduces your compression ratio. Thus, less octane needed. Along the 'Front Range' of Colorado (averaging 5,300 feet) our effective compression ratios are nearly a full point lower than they would be at sea level.

In regards to the 76 B though. What was the first year of catalytic converters for B's, '76 or '77? If it came with a catalytic converter then it would never use leaded fuel. The lead would coolect in the catalyst and render the converter useless forever.

 

[R6MGS]

Hate to take this back to the good old lead additive debate.....but I rarely use it, even in my wifes daily drivers MGA with stock heads, we put about 5000+ miles a year on it without any problems at all.