Commandos and fuel octane rating

Mike40M said:
Interesting and confirms what what others says. Though ethanol burns slower so ignition timing adjusted might change outcome.
My main reason to prefer non E fuel in road bikes is short best before date. Living in a country where half of the year is too cold for pleasant riding.
Click to expand...
Although I prefer E10, I agree that the shelf life is a problem. In those areas where you can buy unleaded E0 I have no issue with it being used - it is meant for the road. My issue is using leaded avgas or race fuel which are clearly not for the road and unless you're running really high compression, are a piss-poor fuels as the octane is too high. Not to mention that lead in the atmosphere is really bad for us all and especially bad for the rider.

"Only seven states (Louisiana, Minnesota, Missouri, Montana, Oregon, Pennsylvania, and Washington) have mandates that require ethanol to be blended with the fuel supply. Louisiana and Washington require ethanol to make up 2 percent of the total volume of fuel sold, while the other states specify E10 (a blend of 10 percent ethanol and 90 percent gasoline)."

Still, in Northern Virginia, it is not easy to find E0, in Southern Virginia it is easy but getting harder. AFAIK, leaded gas in Northern Virginia is simply not available.
 
ashman said:
Well all I know is my Norton runs better on 98 premium non E10 fuel and same with my Yammy 30hp two stroke outboard motor, my Thruxton well it runs great on any fuel I use but I will stick with the 98 as they seen to run a bit cleaner and I get more mileage to a tank full and as I always say each bike/owner is different and in Aus we don't get the best quality fuels here.

Ashley
Click to expand...
Your Thruxton probably has an engine management system which copes with the fuel changes. A thing which many people might not think about is the calorific value of the fuel, When ignition advance, compression ratio, and jetting are optimised, you can get the most power out of your fuel. However, you cannot have what is not there to be had. The fastest Triumph 650 in the 1960s in Australian road racing was the Jesser Triumph which Ken Blake rode. From memory, the fuel was 60% toluene and the rest was methanol and nitromethane. Mixing nitro with hydrocarbons is not wise, but it seemed to work. At one meeting the bike brought down four riders when the motor spread it's guts. Aromatic hydrocarbons usually have the highest energy content. However benzene can cause leukaemia.
I suggest the perfect fuel for racing might be 60% toluene 30% methanol and 10 % acetone. However mixing and handling it would be a problem. All this stuff about octane rating is probably bullshit - when everything is optimised, you don't get detonation, regardless of the octane rating of the fuel.
The problem of getting more power out of petrol, is related to carburation. I do not believe normal carbs are ever adequate for petrol. I use methanol which hides up the tuning errors - the jets flow twice as much, so the errors are halved.
Methanol has about 0.8 times the calorific value of petrol, but you use twice as much of it and because of that, it is easier to get right. The latent heat of vaporisation effect, probably does not contribute as much as we might believe. A small amount of methanol is probably all that is needed to get the supercharging effect.
 
Last edited:
When I was jetting my 850 for methanol, the difference between fast and slow was half a thousandth of an inch in the needle jets. When you use the same MK2 Amal carbs for petrol, the half a thou becomes a quarter of a thou. How can you control that ? When you lower the needle in an Amak carb, you should be able to induce the motor to miss - raising the needle one notch should give best power.
 
acotrel said:
When I was jetting my 850 for methanol, the difference between fast and slow was half a thousandth of an inch in the needle jets. When you use the same MK2 Amal carbs for petrol, the half a thou becomes a quarter of a thou. How can you control that ? When you lower the needle in an Amal carb, you should be able to induce the motor to miss - raising the needle one notch should give best power.
Click to expand...
 
Al its not all about racing as most on here only ride on the roads, my Norton is always well tuned and with the Joe Hunt and jetted right for my motor, same as every Triumph I have owned, but the new Thruxtons are controlled by the ECU and fuel injection, I installed a Meerkat x-pipe and opened up the mufflers to let the exhaust out quicker, when I did this the bike ran very lean on the first 20 minute ride and shut down before the ECU adapted to the change, the next ride the bike ran a lot better and runs a great colour out of the pipes, that was 6 years ago and is still running great, open the throttle up and it will run without missing a beat to the rev limiter through all gears without any hesitation at all, you can buy tunes for the ECU but my bike is running great with just the stock tune as the ECU adapted to the changes.
With my hot Norton the carbs were jetted to the cam and head work and starts first kick every time with the Joe Hunt magneto and depends on the mileage I replace the needles and jets every 3 years and a good clean out of all passages, I mucked around with other carbs on my Norton, Delortos pumper carbs, PWK carbs from Jim jetted right for my motor but I have gone back to my Amals and my Norton has run the best it has in its whole 47+ years I owned it the Amals and Joe Hunt magneto works so well together, it tuned and runs well from putting around the suburbs to full on opening the throttle without missing a beat or any hesitation and it just gets up there pretty quickly.
I do all my own work, I am no carb expert but I do know my own Norton, I have never used a timing light and I get long life out of my plugs, I tune by ear and feel, set my timing till I get a little kick back and just back it off ever so slightly till no kick back, my Joe Hunt runs at full advance as I have no advance/retard unit, the JH works great without it, from low revs to flat out open throttle, it starts first kick every time.
I always run 98 premium fuel or 95 premium if they don't have the high 98, 91 octane my motor just pings and doesn't like it at all.
I just know my own bikes and what is best for each one, just the new models you just do general maintenance on them, but my Norton has always been a good reliable road going bike that I keep it running the best it can and to spend the time to keep it running great, but that is very rare I have to make changes or touch it except for oil changes and chain maintenance when needed and of course tyres lol.
Patting the tank and thanking it for a great ride/day out has helped, as it never lets me down, well not for a long time anyway lol, (only failed EIs, dead batteries and 2 broken chains have ever let me down in 47+ years), not bad really.

Ashley
 
Any real dyno HP numbers for a classic Norton 10:1 compression engine running 91 octane premium pump gas versus 100 octane race fuel in a controlled indoor engine dyno testing environment? The engine would be tuned optimally for the 91 octane pump gas to help determine if the race fuel makes any real difference without changing the tune.

Race fuels are going Green now, so who knows what the results would be?

Gonna go see if I can one pull start my generator with year old fuel and Sta-Bil in it. ;)
 
Last edited:
I just ride my bike up the big hill full bore and see what happens. The results are very repeatable.
Sometimes dyno results aren't!

High Octane fuels have a bit less energy per unit of fuel.
The phrase high Octane has come to mean high powered but really it's just the opposite.
You made the motor into a high compression, high powered thing so now you'll need to use some slightly lower powered gasoline to make it work!
Al made a suggestion that Octane ratings are bullshit. I don't think they are.
Some here might recall some of the high performance v8s from the 60s. We had a Factory 11.0 to 1 cr 429 engine in a 69 T bird. If you were a silly cheap teenager and tried to run it on regular, the pinging/pinking sounds were incredible.
On high Octane fuel there was none of that.
As has been stated earlier, there is no reason to use fuel with a higher Octane rating than needed. You will lose a bit of power in running extra high Octane fuel as it slows the burn, that is how it prevents pre-ignition.

Glen
 
Last edited:
worntorn said:
I just ride my bike up the big hill full bore and see what happens. The results are very repeatable.
Sometimes dyno results aren't!

High Octane fuels have a bit less energy per unit of fuel.
The phrase high Octane has come to mean high powered but really it's just the opposite.
You made the motor into a high compression, high powered thing so now you'll need to use some slightly lower powered gasoline to make it work!
Al made a suggestion that Octane ratings are bullshit. I don't think they are.
Some here might recall some of the high performance v8s from the 60s. We had a Factory 11.0 to 1 cr 429 engine in a 69 T bird. If you were a silly cheap teenager and tried to run it on regular, the pinging/pinking sounds were incredible.
On high Octane fuel there was none of that.
As has been stated earlier, there is no reason to use fuel with a higher Octane rating than needed. You will lose a bit of power in running extra high Octane fuel as it slows the burn, that is how it prevents pre-ignition.

Glen
Click to expand...
In New Zealand anyway octane differences are real. Baring screwups of course.

Companies are legally required to meet consumer law standards and the AA and Consumer organisations sample and test fuels.

I imagine most other countries are the same

Information about fuel - Fuel Quality Monitoring Monitoring the quality of automotive and marine fuel

This page contains information for consumers about fuel makeup, quality and measurement.
fuelquality.tradingstandards.govt.nz fuelquality.tradingstandards.govt.nz
 
johnm said:
In New Zealand anyway octane differences are real. Baring screwups of course.

Companies are legally required to meet consumer law standards and the AA and Consumer organisations sample and test fuels.

I imagine most other countries are the same

Information about fuel - Fuel Quality Monitoring Monitoring the quality of automotive and marine fuel

This page contains information for consumers about fuel makeup, quality and measurement.
fuelquality.tradingstandards.govt.nz fuelquality.tradingstandards.govt.nz
Click to expand...
AFAIK, all US states actually test gas taken from the pumps. There is a sticker on pumps showing when tested. A problem for a public international forum like this is that the methods of determining octane differ. For instance:

"In the U.S., unleaded gasoline typically has octane ratings of 87 (regular), 88–90 (midgrade), and 91–94 (premium). Gasoline with an octane rating of 85 is available in some high-elevation areas of the U.S"

This is not to say that other countries with 91, 95, and 98 such as NZ have higher octane - just the measurement system is different.

The US uses: "The (R+M)/2 you see on the label refers to the average of the research octane number (RON) and the motor octane number (MON) ratings. To determine the RON, the fuel is tested under engine idle conditions with a low air temperature and slow engine speed. To determine the MON the fuel is tested under the more stressful conditions of higher air temperature and engine speed."

My German car built for the US specifies RON ROZ 95, 91 minimum. ROZ is a 3rd measurement system. When you first see that sticker in the filler area, you wonder where you'll get gas. For a Mercedes marked 95, 89 is the US equivalent so premium is not required and regular is well above the minimum requirement!
 
Have to agree with Ashley on low octane not being the best for a theoretically higher performance Norton engine. Especially in high ambient temperatures. With low enough compression like the pre-Commandos engines had (7:1 on some) with the dished pistons, you could probably run on E10 87 octane regular as long as you didn't short shift climbing long mountain passes in 100F degree weather. Engine would probably ping in that scenario. Unless it was Al's optimally tuned Seeley obviously. :)

If I could afford to run race gas in my Norton 750, I would just for the exhaust smell. 🤣
 
I always ran the Chevron Supreme 94 EZero in all of my bikes, at least around here and for winter storage. Sometimes out on the road you have to take whatever you can get. I have been in some backwoods places where only reg gas was available.
After I tested the Coop e zero 91 octane on dyno hill and found that the bike ran consistently a bit stronger up there with the 91 vs the 94, I switched to the 91. The bike doesn't ping at all on the 91 but it is just a standard compression 8.5 to one engine. My 11 to 1 1360 also runs nicely on the same 91 Octane, but that has twin plug special heads with huge squish/quench area.
And now I think of it, the 920 is just under 10 to 1 with a single plug and no effective squish, but it runs fine on the 91 as well, no pinging.
The only bike I have that pings is my lowest powered machine, the 9 to 1 Super Rocket. It pinged on the 94 Octane as well. I just have to be careful not to lug it. It seems crazy to buy race gas for something with about 28 rwhp!

I don't know how much longer the 91 e zero will be available as the pump is now labelled " May contain up to 10% ethanol"
After that label went on I called the Coop Petroleum division to see if they would offer an E0 product of any Octane level. The answer was " No, but you could test the 91. It does not show as having ethanol added on the Bills of Lading"
I asked if the other types of fuel showed ethanol content on those Bills of Lading.
The lady answered " Definitely, every load shows the ethanol content on the Bill of Lading and have done so for years now"
Sure enough, when I tested the 91 it was Ethanol free.
I'll keep using it as long as it stays that way but I'll have to test every time as the label indicates ethanol may be present.

Glen
 
marshg246 said:
AFAIK, all US states actually test gas taken from the pumps. There is a sticker on pumps showing when tested. A problem for a public international forum like this is that the methods of determining octane differ. For instance:

"In the U.S., unleaded gasoline typically has octane ratings of 87 (regular), 88–90 (midgrade), and 91–94 (premium). Gasoline with an octane rating of 85 is available in some high-elevation areas of the U.S"

This is not to say that other countries with 91, 95, and 98 such as NZ have higher octane - just the measurement system is different.

The US uses: "The (R+M)/2 you see on the label refers to the average of the research octane number (RON) and the motor octane number (MON) ratings. To determine the RON, the fuel is tested under engine idle conditions with a low air temperature and slow engine speed. To determine the MON the fuel is tested under the more stressful conditions of higher air temperature and engine speed."

My German car built for the US specifies RON ROZ 95, 91 minimum. ROZ is a 3rd measurement system. When you first see that sticker in the filler area, you wonder where you'll get gas. For a Mercedes marked 95, 89 is the US equivalent so premium is not required and regular is well above the minimum requirement!
Click to expand...
Nz fuel is reported in RON.
 
Pretty simple really, just use what works best for you and if you believe what the fuel companies advertise the premium fuel runs cleaner with added additives to keep valves cleaner and so on for carbon build up and another thing lower octane fuel goes off quicker than premium fuel if stored, my plugs are always clean when I check the plugs, being retired now I am not riding everyday like I use too when working and my LR Defender lives on diesel.
When I installed the JH magneto on 14+ years now and new NY7C plugs at the same time I just recently returned to Amal carbs so I put a new set of plugs in, the old plugs after 14 years and over 30k miles on then still looked as good as the day I first put them in, bigger spark and cleaner premium fuel seems to work pretty good in my Norton.

Ashley
 
ashman said:
Pretty simple really, just use what works best for you...

Ashley
Click to expand...
True, before it was stolen in 1970, my Triumph 66 T100C rebuilt as T100R was way over "hot rodded". 13.5:1 compression, race cams, 650 racing valves and springs, dual 900-series Amal carbs, etc. Sonoco 260 wasn't getting it. Airport gas would just. What worked best was Sonoco 260 and some added Alcohol. Was it stupid to do all that to a Triumph 500 - of course it was. But, I did odd jobs in a Triumph dealership for free and they had fun providing more power to the dumb kid - like most here, I didn't know better while a teenager. When they put the big valves and springs in, the rockers hit the spring collars so of course I spent hours with a file on the rockers to get clearance.

So, my experience with alcohol added to gas started long ago and is why I don't hate it today.
 
In the old days when we ran leaded petrol we only had standard and super fuel here in Aus, standard being the low octane fuel and super being high octane but was only the older cars that would run with standard fuel, the super was pinkish in colour and had a very strong smell to it (the petrol sniffers would have loved that), todays fuel have a different colour as well smell to it.
I miss the old super leaded fuel it burned a lot better than the crap we run our bikes on today, bring back the days of no additives added lol.
Leaded fuel had no affect on me o_O🤪🤣
 
worntorn said:
I just ride my bike up the big hill full bore and see what happens. The results are very repeatable.
Sometimes dyno results aren't!

High Octane fuels have a bit less energy per unit of fuel.
The phrase high Octane has come to mean high powered but really it's just the opposite.
You made the motor into a high compression, high powered thing so now you'll need to use some slightly lower powered gasoline to make it work!
Al made a suggestion that Octane ratings are bullshit. I don't think they are.
Some here might recall some of the high performance v8s from the 60s. We had a Factory 11.0 to 1 cr 429 engine in a 69 T bird. If you were a silly cheap teenager and tried to run it on regular, the pinging/pinking sounds were incredible.
On high Octane fuel there was none of that.
As has been stated earlier, there is no reason to use fuel with a higher Octane rating than needed. You will lose a bit of power in running extra high Octane fuel as it slows the burn, that is how it prevents pre-ignition.

Glen
Click to expand...
A good point, well put.

My old T140 with 10.5:1 Powermax pistons needed 5-star leaded petrol (those were the days!), otherwise it tinkled like a small jack-hammer.
The modern solution is to run Tetra-Boost as an octane improver & lead additive.
Sadly I can't use this in my little race engine because the regulations forbid it, which is a shame.

Running tuned motors to their maximum potential is all about management of detonation, and F1 teams spend a lot of money on this.
My Subaru requires 99 RON fuel as standard, and the aftermarket is swamped with knock detection/indication systems to go with all those boost gauges, extra clocks and radar warning systems.
 
Last edited:
B+Bogus said:
A good point, well put.

My old T140 with 10.5:1 Powermax pistons needed 5-star leaded petrol (those were the days!), otherwise it tinkled like a small jack-hammer.

Running tuned motors to their maximum potential is all about management of detonation, and F1 teams spend a lot of money on this.
My Subaru requires 99 RON fuel as standard, and the aftermarket is swamped with knock detection/indication systems to go with all those boost gauges, extra clocks and radar warning systems.
Click to expand...
I fitted those powermax pistons to my t140 e
It ran really well until it got hot
Then it just pinked like crazy no matter how much I backed off the timing and richened it up
 
Last edited:
baz said:
I fitted those powermax pistons to my t140 e
It ran really well until it got hot
Then it just picked like crazy no matter how much I backed off the timing and richened it up
Click to expand...
Just edited my post regarding fuel improvers
 
An effective squish band seems to be king when it comes to this topic.

I ran my 840cc Triton at 11.2:1 and it ran fine on Super Unleaded (97 or 98 depending where it was bought) because it had a Degens modified squished head.

Actually, late T140Es (the parallel port heads) had a reasonably good squish band machined into the head and pistons, but the factory assembled with the gap too big! Some careful measuring and assembling (on mine I simply had to delete the base gasket) to tighten this up raises the CR a little and gets the squish working well and bingo, no more pinking.

My 920 Commando is also 11:1 and also runs perfectly fine on Super Unleaded. It may run fine on 95, but I haven’t tried it. Again, I put this down to it having a decent working squish (helped by the increase in bore size of course). Same story with the 1330 Vin motor.

My 1007 motor doesn’t have a squish (CR would be way too high). I run that on 110 octane race fuel purely to protect against detonation. I experimented on the dyno with 98 octane Super Unleaded and there was no difference between them at all. Thats a BIG difference in octane, with zero measurable power difference. So I continue to use the race fuel as a safety factor (it is a track only bike).
 

Similar threads

A
  • Locked
Octane rating for Nortons?
2 3
Replies
46
Views
3,684
acotrel
acotrel
1up3down
  • Locked
Commandos and Higher Octane Gas
2 3 4
Replies
77
Views
8,219
Mark
M
Back
Top