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Correct Octane for BJ8?

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SteveHall64Healey

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Gents, can anyone advise on the correct octane rating to be used in a BJ8? I'm in Canada, and have been starting with Sunoco 94 and then adding 3-4 points using an MMT-based octane boost.
thanks,
steve
 
The higher the better. I use Shell V-power, 99 octane. I recently read an independent study that tested about 12 octance boost products. Most claimed to add 2-3 octane but the test showed they average between 0.5 and 1.0. The best performing product was an Australian one, which added about 2.5. Maybe a member down under can supply the name. It was something like NF Nitro? I couldn't find it on Amazon.
 
SteveHall64Healey said:
Gents, can anyone advise on the correct octane rating to be used in a BJ8? I'm in Canada, and have been starting with Sunoco 94 and then adding 3-4 points using an MMT-based octane boost.
thanks,
steve
Click to expand...
I was told a long long time ago(early '70's), when this same question came up that the Healeys are okay with regular gas do to the various octane ratings of gas around the world and that was another reason for the timing adjustment on the side of the Dizzy.
 
In posting this question, I was hoping that someone might have possession of an original manual or sales brochure in which BMC recommends a specific octane level. Unfortunately, we all seem to be operating under the assumption that 'more is better', or safer at least. I suspect we may be overdoing it - not to the detriment of our cars, but to the detriment of our tired wallets at the very least.

A few years ago, I chatted with Phil Allen of Britcar, who was a BL factory rep in Canada and later opened his own service station specialising in British cars. When asked this same question, he recalled that most owners of these cars in the '60s used regular gas, which was typically octane 95, but would occaissionally 'treat' their car to 100 or 103, which were commonly available at the time. Typically, he recommends moving to a higher octane when carbon fouling becomes a problem and it is not alleviated by carb and/or ignition adjustment. If octane is way too low, pinging is the triggger to move to a higher octane, but if too low only by a few points, carbon fouling is an indicator that higher octane is needed.

Steve
 
SteveHall64Healey said:
Gents, can anyone advise on the correct octane rating to be used in a BJ8? I'm in Canada, and have been starting with Sunoco 94 and then adding 3-4 points using an MMT-based octane boost.
thanks,
steve
Click to expand...

The highest octane you can find and leaded if it is available in your area.
 
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I started this post in a quest for the 'right' level of octane. I will respectfully disagree with the assertion of 'the higher the better' because our engines are not high compression and the extra cost of the highest octane at the pump plus booster is just not money well-spent.


Last month, while reading an old review of the BJ8 (AutoCar 1964), I noted that the performance test on the car was conducted with the 'recommended grade of fuel', per the attached photo. The recommended grade is 97 octane RM. In North America, fuel is graded by the (RM+M)/2 standard. From other reading, I've learned that octane measured by the 'M' method (Motor octane versus Research Method) is typically 8-9 points lower than the RM scale. So, if RM should be 97, then M is 89, and (R+M)/2 is about 93. In Canada, the highest readily available octane pump gas is 94 (Sunoco), which exceeds the required 93.

Does this ring true gents? My days of buying octane booster are done!
image.jpg

PS: note the oil consumption spec in the photo!
 
Does this ring true gents? My days of buying octane booster are done! It is generally accepted that this is a waste of $$$$$$$
 
For the Europeans; oil consumption 1 L each 1500 km
 
Use the lowest grade that doesn't cause pinging ('pinking'). I run 91 (R+M/2) in my BJ8, but it has low nominal compression. We run 87 in our 100M, with 140-145lbs on all 4 with no issues (yet).
 
The answer to this question will not be the same for all owners/cars. Have you had your block bored and your head decked during a rebuild? If so, your compression is higher than stock. Does your "original" engine have 75K or more miles on it? If so, your compression is probably lower than stock. I would do a compression check and see how your particular car compares to stock. If it is close to stock, you then may be able to get away with 91 or 89 octane. I would never drop down to the 87 "regular."

I recommend tuning the car to run properly with the highest readily available grade of fuel in your part of the world, (unless you have access to some really high stuff). In the US, I recommend 93 (California is less, unfortunately). Unless you are putting 10s of thousands of miles on your car every year, the higher octane will hold up better between uses. If all gas loses some percentage of its octane over time, why not start with the highest grade? Also, as temps go up, the likelihood of pinging and run-on increases. The higher grade of octane will reduce that problem. I run 93 and use a gas stabilizer.
 
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