MGB Gas Octane for MGB's

[tony barnhill]

I've always put only 93-octane in my MGB's...there's been more discussions on the internet than I can think of about whether one needs premium gas or can go with a lesser octane fuel.

Today I received an original copy of the M.G. Car Company Limited at Abingdon-on-Thames <u>Special Tuning Guide for MGB</u> that I bought off eBay.....here's a sentence I found in it:

"The 'MGB' as delivered from the Factory in its standard form is tuned to give maximum performance with 100-octane gasoline consistent with complete reliability and reasonable freedom from pinging."

 

[rick_ingram]

I always run the highest octane rating that I can find in any of my MGs.

That is usually 92 or 93 octane.

I miss the days of Sunoco 260.

And the price at which I could buy same.

/bcforum/images/%%GRAEMLIN_URL%%/smile.gif

 

[Steve_S]

100-octane fuel in 1960's England was nothing like the fuels of today. They were, and still are based on a completely different rating system. In the UK, the RON system is used. In the US, it is an average of RON and MON ratings. This equals a difference of about 4-5 octane by the numbers for the exact same fuel. Therefore 100-octane today in the UK would equal something like 94-95 octane here in the US.

Regardless of what the car was originally designed to run on, you should use the appropriate fuel for your car's state of tune. Putting 93-octane in a low compression car is a waste of money and can lower performance. Octane does not equal power! It merely dictates at what temperature the fuel will burn, to put it simply. Putting the wrong fuel in your car will, in a manner of speaking, throw the timing off.

 

[tony barnhill]

True, Steve...I remember the service manager of the dealership where I bought my car new telling me to always use the highest octane possible.....I've always done that & my '79 (which is completely original with all its emissions equipment intact & working) has only had the Zenith Stromberg rebuilt once & that was after it sat for 3 years while I was out of the country....& the engine has never been opened for anything - at 120,000+ miles right now!!

That's all the experience/proof I need!

 

[PAUL161]

I use 93 in the "B" and it runs absolutely perfect. But, on the new cars and trucks, I use whatever the manufacturer specifies. My Chevy pickup has a unique feature, if I use to low of an octane and the engine starts to ping, it automatically adjusts it's ignition to temporarily compensate for it. Naturally, with a slight loss of power.

 

[Stewart]

The 75 I use 91 but I'm pretty sure its over kill. The 73 I'm going to run the lowest octane that it runs well on or what ever I can find that isn't contaminated with ethanol.

 

[DJThom]

Steve is right. Anyone with a handy Parry's Chemical Engineering handbook can find tha page that shows peak power as a function of octane with several contour lines representing compression rations. The low compression lines are nearly flat indicating the engines can't take advantage of the energy stored in the fuels.

Fuels are nothing like they used to be. The long life of engines is probably better attributed to various friction additives used over the years rather than the component of gas (measured by octane) that is actually meant to explode.

I'm in the middle of a move with all my books offsite, but one day I'll scan and post...

 

[Steve_S]

Long engine life has nothing to do with octane ratings. Quality of fuel, as DJThom hints at, is definitely a factor of engine health. On older engines, such as XPAGs, I can tell the difference in fuel quality between each fill-up. The car hates Shell but loves Chevron and Unocal. I refuse to go near Valero or any small name brands. There is no way to know where the fuel comes from between stations because they only lease the name and use whatever cheap fuel they want.

 

[tony barnhill]

Further reading I found this section about HC & LC engines:

"When fitted with H.C. engine (compression ratio 8.8:1)

The octane number of a mtor fuel is an indication given by the fuel technicians of its knock efficiency. High-octane fuels have been produced to improve the efficiency of engines by allowing them to operate on high compression ratio, resulting in better fuel economy and greater power. Owing to the high compression ratio of the 'MGB' engines, fuels with an octane rating below 98 are not suitable; should it be necessary to use a fuel with a lower octane number, the car must be used very carefully until the correct fuel can be obtained.

It is necessary to use Super grade fuels in the 100-octane range unless Premium fuels of minimum 98-octane are available.

When fitted with L.C. engines (compression ratio 8.0:1)

Premium fuels of minimum 93-octane Research up to 97-octane are required, with preference to 93/97.

Super fuels in the 100-octane range can be used if preferred."

Wonder what their 100-octane fuel relates to today? Same with their 98-octane?

 

[vagt6]

Tony, don't you have an exhaust gas analyzer? Would that help determine how efficiently your engine is using the fuel? I thought you said you had an analyzer or had used one.

Just a thought . . .

 

[Steve_S]

As noted above, 100-octane would be equivalent to 94-95 in the US. However there are other differences between the fuels in question such as leaded versus unleaded, Ethanol, MTBE, additives, etc. These all affect the amount of energy released when the fuel is burned.

 

[tony barnhill]

Tony, don't you have an exhaust gas analyzer? Would that help determine how efficiently your engine is using the fuel? I thought you said you had an analyzer or had used one.

Just a thought . . .

Oh, I'm not concerned with my usage/efficiency/economy...I've never checked fuel economy in an MG in all the year I've owned one...I'm just intereted in the difference in the 100-octane they talk about & the 93-octane I always ue.

 

[DrEntropy]

I'm with ya, Tony. I kinda-sorta pay attention to the mileage on mine, more as an indicator of the state of tune than for "economy's sake." The 'old' octane ratings (and the differences in the "standards" between UK & US methods) are misleading. The 93 we have available should be (in most cases) sufficient. I, too, miss Sunoco's "choices" tho. And ethanol is th' pits.

Last eve on the NBC news they ran a piece on the added burden ethanol has ACTUALLY put on CO2 levels. More of the 'greenies' need to see THAT info. I could find no reference to it on-line yesterday, here's the link now:

https://www.msnbc.msn.com/id/21134540/vp/23072972#23072972

 

[billspohn]

Steve is correct - anyone using more than 89 in an MG is pissing away money to no good end. The higher octane fuel burns more slowly and gives less power. It is needed in higher compression engines to prevent detonation.

Both MGB and MGC will run very nicely on 89, and using anything higher isn't 'babying' them or in fact doing them any good at all.

Most MGs will in fact run on 87, but because of the proclivity for carbon build up in that heart shape Weslake chamber, especially if it hasn't been smoothed before, you may get ping with that lowest rating.

93 octane will support 10:1

The gas companies love the fools that keep buying high test when they don't need to - it makes them untold millions of dollars.

 

[RickB]

When I lived in Alaska I found you could buy airplane gas at filling stations. I'd put in a combination of the highest octane regular gas and 5 gallons of airplane fuel.
My MGC ran very well on this.

I was surprised to find out that Alaska is very rare as a state that let you do this without a pilots license.
Individual aircraft ownership up there is very high in terms of aircraft per capita, so its a lot more common to be selling airplane fuel to the general public.

My beloved Washington state officials explained to me that they have a different taxing system for aircraft fuel and road fuel, thus I can not buy aircraft fuel for use in a car.

 

[Steve_S]

Actually Bill I do use 92-octane in most of the MGs. The MGC won't run on anything else but it is in a very high state of tune. I have experimented with other octanes in some of the cars and found 92 to perform the best in some of them, but not offering an advantage to all.

 

[billspohn]

My MGC is in a moderately high state of tune with tricarb, headers, cam, and flow owrk done, BUT - I intentionally left compression stock, with the result that it runs perfectly on 89.

Would I get a few more BHP with 10:1? You bet, but as it is a long distance touring car it didn't make sense to bother.

 

[billspohn]

PS - I use the following: (normally Chevron)

MGA coupe, MGC, both stock compression - 89

Jamaican - stock Camaro compression - 87

Jensen CV-8 and Interceptor 10:1 - 92

Fiero - 8.5, 13 psi boost - 92

Lamborghini 10.7 - 94

MGA race car 12:1 105

 

[DrEntropy]

This fool puts 93 in the Alfa and both Lotus cars, too. There's a noticeable decline in performance on anything less. I'd like nothing better than to stop wasting my dollars on 93 but when I hear a sound like gnomes in the crankcase with ball-pean hammers, it compels me to run the highest octane I can get.

The MG gets it as well, as there's a Crane cam and a DCOE Weber feeding the slightly higher than 9.5:1 compression, from piston and chamber changes. Anything lower produces less performance and detonation.

 

[billspohn]

This fool puts 93 in the Alfa and both Lotus cars, too. There's a noticeable decline in performance on anything less. I'd like nothing better than to stop wasting my dollars on 93 but when I hear a sound like gnomes in the crankcase with ball-pean hammers, it compels me to run the highest octane I can get.

The MG gets it as well, as there's a Crane cam and a DCOE Weber feeding the slightly higher than 9.5:1 compression, from piston and chamber changes. Anything lower produces less performance and detonation.

The Lotus at 9.5 would need high test. The Alfas at 9:1 usually run on 92 or so.

If your MG at 9.5 needs high test, it needs it. Try one grade down some time and see if it makes much difference. It should probably work on 91-92, depending on what is available in your area.

I see people putting premium in their 8:1 Jensens that run fine on 87, and they don't want to hear that they don't need to - sigh....