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PostPosted: Wed Jul 10, 2024 1:29 pm 
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SooperDooperMiniCooper ExpertEngineering
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The attached image is drawn from the Australian Supplement chapter of the Mini Workshop Manual - AKD4935 - 1967 (full manual here: viewtopic.php?f=25&t=84427 ).

It suggests that the timing adjustment for the temporary use of "Super" petrol be adjusted to 10 degrees AFTER top dead center. I always understood Super to be high octane and stable fuel equivalent to 98RON premium fuel. Can anyone provide the context behind the quote?


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PostPosted: Wed Jul 10, 2024 8:55 pm 
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It was common then to add methyl benzene or benzol to the fuel to get about 100 octane. Service stations sold it back then. Wasn't too expensive.
In the mid 60s.
Or you could use avgas even on the street.

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PostPosted: Thu Jul 11, 2024 7:57 am 
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drmini in aust wrote:
It was common then to add methyl benzene or benzol to the fuel to get about 100 octane. Service stations sold it back then. Wasn't too expensive.
In the mid 60s.
Or you could use avgas even on the street.

I bet the Avgas made the cars fly. ;-)

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PostPosted: Thu Jul 11, 2024 8:05 am 
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So "Super" was similar to 91RON or below? Was there a time it was bumped up, as I remember my Coooper S had no trouble running on it in the 90s?

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PostPosted: Thu Jul 11, 2024 8:41 am 
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Super was allegedly 96 or 97 Ron but who knows really. Like 98 it drops with its age.
Standard (aka regular) was 87 Ron.

Edit
I think the ignition timing problem with the Cooper S was mostly due to the tame cam in it. Same valve timing as a Morris 1100 in Mk1 S, 5/45-51/21. Used to ping with its 9.75:1 c/r.
In comparison my 1360 is running at 11.0:1 and doesn't ping, because the 282° sprint cam gives less cylinder filling at low RPM.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:


Last edited by drmini in aust on Thu Jul 11, 2024 9:30 am, edited 1 time in total.

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PostPosted: Thu Jul 11, 2024 9:02 am 
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Then why the big timing jump to 5 deg ATDC in the note. It makes me think Super in 1967 was significantly different, as it thinks it was the more economical fuel to use.

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PostPosted: Thu Jul 11, 2024 9:03 am 
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Perplexity gives me a few good tidbits of information too.
perplexity.ai wrote:
Based on the search results provided, I can offer some information about the fuel options available in Australia in the late 1960s:

1. In 1967, there were two main grades of fuel available:

- Standard fuel, with an octane rating of 92 RON (Research Octane Number)[3].
- Super fuel, with an octane rating of 97 RON[2][3].

2. The octane ratings changed slightly over time:

- In April 1964, Super fuel was upgraded to 97 RON[3].
- In August 1968, Super fuel was further upgraded to 98 RON[3].

3. These fuel grades were leaded petrol, as unleaded petrol was not introduced until much later:

- Unleaded petrol (ULP) was introduced in Australia in January 1986, with a 91 RON rating for Regular ULP[3].
- Premium Unleaded Petrol (PULP) was also introduced in 1986 with a 96 RON rating[3].

4. The compression ratios of engines at the time were designed to work with these fuel grades. For example:

- The 1967 Ford XR GT had a compression ratio of 9.7:1, which was suitable for the Super fuel of that era[2].

It's worth noting that the fuel quality and octane ratings have evolved significantly since the 1960s, with the introduction of unleaded fuels, higher octane ratings, and stricter environmental standards.

Citations:
[1] https://www.energy.gov.au/sites/default ... _2018.xlsx
[2] https://www.fordforums.com.au/showthread.php?t=11486825
[3] http://www.fefcholden.org.au/techinfo/tech003.html
[4] https://www.bitre.gov.au/sites/default/files/is_082.pdf
[5] https://www.aph.gov.au/About_Parliament ... sStandards

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PostPosted: Thu Jul 11, 2024 9:11 am 
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I believe it's not so much the octane rating but the burn time. They would've been more concerned at the high RPM timing needing to be retarded due to an unsuitable advance curve. The unusual low RPM timing is just the result without changing the advance curve.

It's a similar situation with modern fuels.

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PostPosted: Thu Jul 11, 2024 10:12 am 
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They specifically mention under 100 octane isn’t recommended in both the manual and handbook

https://mk1-performance-conversions.co. ... tp766a.pdf

They did try and stress in the handbook it’s not just an ordinary car, it’s a race tuned engine for the road so it needed to be adjusted to meet normal fuel & driving. The road tests for both Mk1 and Mk2 Cooper S often mentioned pinging

The combination of high comp, long advance curve, mild cam, no vacuum advance would have made it a bit temperamental

I remember reading about “5-star” leaded fuel from back then which was 101 octane, so maybe that’s the suggested fuel? Was it available locally or just the UK?

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PostPosted: Thu Jul 11, 2024 8:23 pm 
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We used to have Fleetwing 100 fuel but it wasn't widespread. As I said above all the Boyz used to add Shell methyl benzene or BP benzol to get 100 octane or better.

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