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MGB Gas Octane for MGB's

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billspohn said:
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.
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My C is built to be a street-friendly race car, sort of the thing M.G. originally built back in the pre-war days. Drive it to work during the week, race on weekends. I don't race the car, but the point is that every ounce of power that could be pulled from the engine, and still be comfortable to drive, has been. Therefore it won't run on anything but premium.

It also gets a whopping 12 MPG average, with an incredible 17 MPG on the open road at 80 MPH. I find its best economy is at sustained high speeds.
 
The Alfa is a 1750cc, 11mm cams (slightly advanced), Webers, 9.5:1 comp. Bit of a "transplant". From an earlier GTV.

We have 87, 89, 93 around here. It pings on 89, with noticably less performance.
 
91,95,98 seem to be the most common availible here we run 98 in our's. Bob
 
Well, this fool only puts 93 in his MG' & will continue to pour pennies down the drain - but then, I rarely, if ever, have problems with any of my MG's! The little '63 Midget that I'm restoring: the engine looked brand new when we tore it apart (I've owned it 6 or 7 years & have only put 93 in it also!)
 
Tony, the other guys have good reasons - they have higher compression than stock and they'd probably ping on 89. If you have stock compression on the MGB and Midget, you don't need it and you don't benefit from it. The fact that you have clean engines when you tear them down is irrelevant.

But hey, those big gas companies appreciate it, I'm sure.... /bcforum/images/%%GRAEMLIN_URL%%/grin.gif
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]The fact that you have clean engines when you tear them down is irrelevant.[/QUOTE]
How 'bout the fact that I never have to rebuild carbs, fiddle with valves, etc.?

I remember back when I bought my '92 Sonoma new, Amoco had a deal - sign the vehicle up & use their highest octane for 75% of your gas & if you ever had any gas system (fuel injection, valves, etc.) related problems, they'd pay to repair....still have that truck - 218,000 miles when the engine finally gave up the ghost - never had the heads off, never had any fuel related problems whatsoever, never messed with injection system or anything other than normal maintenance...when I finally threw a rod because the bottom end gave out (I pulled MG's all over the country with that 4.3 V6!!), the heads looked like they'd never been used!

Sorry, but I think good gas burns cleaner & doesn't leave deposits or choke the valves....
 
Good gas burns cleaner, but octane has nothing to do with how good the gas is. As I mentioned above, I refuse to put cheap fuel in my cars. But choosing too high an octane is like advancing the timing to get more power. It won't necessarily help and might actually hurt performance! Then again your car may run best on high octane regardless, and that's fine.
 
I know one thing - my 380SL won't run on anything under 93!
My big Dodge truck doesn't care what it gets; my '79 MGB pings on less than 93.

&, remember, older engines are different than the newer ones!
 
Anything pre 71-72 needs the higher Octane, unless you have put in hardened vavle seats. After 72 all manufactures put in hardened valve seats, therefore reducing the need for super high octane and also, reduced compression ratios. Those in the 9:1 ratio or more should have higher octane. Amoco, now BP used to involve more cleaners in their Gold Ultimate fuel for cleaner injectors etc. If your car does not ping use what is comfortable for you. If you are a spirited driver, use higher octane.
 
Steve_S said:
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.
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Steve,

Where do you get 92 oct gas here in SoCal?
 
Pardon me, I should say 91 octane. Traveling around, I see premium vary from 91 to 93 octane, so I tend to always say 92. I believe there are still a few places with 92 around but I don't remember where off hand. It isn't worth driving around hunting for it.
 
LarryK said:
Anything pre 71-72 needs the higher Octane, unless you have put in hardened vavle seats. After 72 all manufactures put in hardened valve seats, therefore reducing the need for super high octane and also...
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Eh? Please correct my ignorance, but I though hardened valve seats were to compensate for the loss of the lubricating / protecting qualities of the lead in the fuel, and didn't have much (if anything) to do with the octane of the fuel.

I run RON 98 in my '71 GT (18V series, HC engine) - anything less and she runs on - the same for my sister's 70 GT.
 
Sultanoswing is correct. EPA regs required cars to be able to run on unleaded fuel as of (if memory serves) January 1, 1972 manufacture. This is the reason for hardened seats/valves in most cars at that time. Also lower compression ratios, as the unleaded fuel of the day was slightly less octane; Tetraethyl (sp?) lead also served as an octane booster.

But, according to Lindsay Porter's book on the B series engine, British Leyland used a slightly different mixture in the material used to cast B series heads to comply with the no-lead rules. I don't have the book at hand to give an exact citation.

Also, there was unleaded Amoco available for years before this, we called it 'white gas'.

Colin
 
We do have 92 octane fuel available in western Washington State, at least at our Arco Stations. It probably is available all over the coast states, but I wouldn't bet on it.

I stopped using high octane when I found that it was a complete waste of money and all my vehicles ran very well on 87.

Guinn
 
Some semi-related info: the Alfa has been running primarily on whatever I find without ethanol mixed in, mostly from a convenience store (Citco) nearby. Ethanol makes it stumble and idle poorly. 93 is the "grade" in all cases, tho. A few days ago I was sniffin' "E" so put BP (Amoco) 93 in it. Mostly 'cause I was already there. Now I'm noticing it holds an idle BETTER than with the other blends I've been running. Seems to pull a bit smoother, too. Gonna stick with the "New White Gas" for a few tanks and then try another refinery's offering. Just fer S&G.
 
Doc, I've been using 93-octane "white gas" since I don't remember...& I'm finally happy to hear somebody else can see the benefits.

On a side note: My big Dodge truck has always gotten 87-octane (regular) gas...on our trip this last weekend, I put a tank of Amoco 93-octane in it & another this morning...more pep, faster from stop lights....now, I won't do it always like I do in the 380SL & my MG's but doing it occassionally appears to help!
 
You won't see any benefits unless the car is tuned for it! If your truck is tuned for 87 but runs better on 93, then something is wrong... or at least changed.
 
Steve_S said:
You won't see any benefits unless the car is tuned for it! If your truck is tuned for 87 but runs better on 93, then something is wrong... or at least changed.
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Or its cleaning things out!
 
You guys should just rejoice in the fact that you can still get gasoline without Ethanol. No choice about it in Colorado. It's all at least a 10% mix. Year round now. When we had MTBE it was only added in the winter months. Or if you want to have some real fun... we could start discussing octane and altitude. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif
 
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