Octane rating for Nortons?

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I tried an octane booster/lead sub when I first got this old gal going again a couple of years ago and stopped using it as soon as I found flakes collecting on my plugs. Stopped use and flakes went away.
I've thought about getting some race gas and seeing what happens. Don't want to poke it with a stick too much though, but a little experimenting can't hurt anything..... Can it?
 
jbruney said:
I tried an octane booster/lead sub when I first got this old gal going again a couple of years ago and stopped using it as soon as I found flakes collecting on my plugs. Stopped use and flakes went away.
I've thought about getting some race gas and seeing what happens. Don't want to poke it with a stick too much though, but a little experimenting can't hurt anything..... Can it?
Click to expand...
Street [engines] usually have static compression ratios of between 8:1 and upwards of 11:1, and usually in the 9:1 and 10:1 area on most performance "street" engines. The problem running race gas is that if you don't have the compression to compress the fuel and air enough, you'll actually run SLOWER! I see this happen all of the time at the race track where during the Wednesday night drags, people with bone stock cars will go fuel-up with 110 or 114 octane race gas and wonder why they aren't running as quick, or as fast, as usual.

Contrary to popular belief, the more octane in gas, the COOLER and SLOWER the burn is, and more importantly, the more compression is required to get that fuel to release its energy. What happens to regular gas if you have too much compression or too much timing? You ping (detonate). How do you remedy that? You use fuel with a higher octane rating to get that uncontrolled burn back under control.

Can I Run Race Gas In My Street Car?

Bad-Ass Racing Engines specializes in building some of the baddest street and race engines around!
www.badasscars.com www.badasscars.com

I run 95 RON (91AKI) in my 9.5:1 motor with Maney repro exhaust. But I have bigger jets.

I have found the motor doesnt run any better on 98 RON.
 
gortnipper said:
Street [engines] usually have static compression ratios of between 8:1 and upwards of 11:1, and usually in the 9:1 and 10:1 area on most performance "street" engines. The problem running race gas is that if you don't have the compression to compress the fuel and air enough, you'll actually run SLOWER! I see this happen all of the time at the race track where during the Wednesday night drags, people with bone stock cars will go fuel-up with 110 or 114 octane race gas and wonder why they aren't running as quick, or as fast, as usual.

Contrary to popular belief, the more octane in gas, the COOLER and SLOWER the burn is, and more importantly, the more compression is required to get that fuel to release its energy. What happens to regular gas if you have too much compression or too much timing? You ping (detonate). How do you remedy that? You use fuel with a higher octane rating to get that uncontrolled burn back under control.

Can I Run Race Gas In My Street Car?

Bad-Ass Racing Engines specializes in building some of the baddest street and race engines around!
www.badasscars.com www.badasscars.com

I run 95 RON (91AKI) in my 9.5:1 motor with Maney repro exhaust. But I have bigger jets.

I have found the motor doesnt run any better on 98 RON.
Click to expand...
Gort, that is very interesting. It is one of the reasons I started this thread. I wondered whether were any drawbacks to using very high octane fuel.

Thanks,
Ed
 
There is no advantage to using fuel of higher octane than whatever octane will not ping in the engine. It's the same thing as the old shade tree method of setting optimum timing - advance till it pings, back off 2 degrees. With gas, it's the other way round - have the timing wherever you want it and "advance" (increase) the octane until it doesn't ping. If 87 (USA) does that, paying for 93 is a waste of money.

FWIW, 89 pump gas from any station works fine in my stock-engined 850, timing at 32 degrees (6400 ft altitude) and 250 main jets/peashooters.
 
Just worth remembering that that article above is talking about drag race fuel of 114 octane… it’s not talking about ‘super’ pump fuel vs none super.

The performance loss due to the slower burn of super pump fuel will be tiny IMHO, but I’ve never dyno’d it to compare.

But too low an octane causes detonation that can wreck an engine.

Engine tune, as well as ambient temperature and riding style / use can all impact on whether an engine suffers detonation or not.

I know this thread is about the possible down sides of using super pump fuel, but we should not ignore the risks of using a too low octane either, as the risks of this are more serious (ie wrecked engine).
 
Absolutely right; severe pinging (detonation) can destroy an engine. OTOH, once there is no pinging (sufficient octane) for the engine setup, using higher octane (more expensive) fuel can't reduce the pinging to less than 'none." :)
 
Fast Eddie said:
Just worth remembering that that article above is talking about drag race fuel of 114 octane… it’s not talking about ‘super’ pump fuel vs none super.

The performance loss due to the slower burn of super pump fuel will be tiny IMHO, but I’ve never dyno’d it to compare.

But too low an octane causes detonation that can wreck an engine.

Engine tune, as well as ambient temperature and riding style / use can all impact on whether an engine suffers detonation or not.

I know this thread is about the possible down sides of using super pump fuel, but we should not ignore the risks of using a too low octane either, as the risks of this are more serious (ie wrecked engine).
Click to expand...
OP asked of up to 112 race fuel too.
 
If you use high octane fuel and raise compression without increasing ignition advance, you will probably jet to compensate for the higher compression with larger jets. So theoretically, you get more horsepower or torque by using more fuel. But in practice, I think you don't get the increase in power you might expect. There is a quenching effect and some of the excess fuel is used to expand and drive the piston because the combustion temperatures are higher..
 
I think the main advantage in using race fuel lies in it's consistent quality. If you are jetting a race bike, it is one less variable to contend with. It is one of the things with using methanol - it does not usually vary from batch to batch.
 
Most of the time I run my Nortons on 91 octane, but if its hot, and I am working the bike hard, I put in 96 octane. Have never really had any trouble, but one time in a traffic jam on the Auckland motorway, my bike started pinking when I took off, so I then decided to ride down between the lanes of traffic like all the mad Auckland riders do. { That was on the way to a NZ rally. Now I add the 96 before going to Auckland, then add the 91 later to cover both options. }
 
Yeah, only time mine pinked was heading to Welly out of the hot going up the hills.after Desert Rd fully loaded. That was before I rejetted.
 
APRRSV said:
I have read many posts concerning alternative gas (petrol) options for Nortons. but I have a few questions concerning what is good and what is not good.

snipped

b) Is there any danger with using 100+ octane fuel (leaded or unleaded) in our Nortons (other than the legality of using leaded fuel)?
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Ed, Aviation 100LL [LL stands for low lead, a relative term, as it contains 4 grams per gallon of tetra-ethyl lead. It's only low compared to Aviation 130 octane] requires the use of special "Aviation" engine oils to deal with the lead. Aviation oils are not detergent oils, as used in cars, trucks and motorcycles. These oils are referred to as "ashless dispersent" oils. Ask any local aircraft mechanic what the inside of a Lycoming or Continental engine looks like upon tear down. There is a gray film of lead on everything. Of course, that Sunoco fuel may contain less lead. I'd advise that you find out how much before using it. Spark plug fouling is much more common when using leaded fuel. Use of unleaded fuel burns cleaner, combustion chamber & valves stay cleaner, keeps the oil cleaner and extends the engine life. I suggest you will have better results using the high octane unleaded fuel.
 
joe czech said:
FWIW, running 89 non-ethanol in my 74 Mk2 - cant say I've noticed any pinging or problems. some may have issues for me though....
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Joe,
Yes, the standard 850s with 8.5 [or 8.75] to 1 compression ratio call for 89 octane using the RON + Motor / 2 method used here in the USA.
 
MexicoMike said:
There is no advantage to using fuel of higher octane than whatever octane will not ping in the engine. It's the same thing as the old shade tree method of setting optimum timing - advance till it pings, back off 2 degrees. With gas, it's the other way round - have the timing wherever you want it and "advance" (increase) the octane until it doesn't ping. If 87 (USA) does that, paying for 93 is a waste of money.

FWIW, 89 pump gas from any station works fine in my stock-engined 850, timing at 32 degrees (6400 ft altitude) and 250 main jets/peashooters.
Click to expand...
I would not use pinging to set the octane rating of the fuel I would use. I'd just find the highest rated, best quality fuel and adjust my motor to run it's best with that. If the motor pings, it is either way too lean, has too much ignition advance or the comp. ratio is too high. The ping is easily fixed and should never happen. Best power is well back from that. But not so far back that the jetting is slightly too rich. When I tune, i use fixed comp. ratio, fixed ignition advance, fixed fuel type - and I adjust the jetting.
With most fuels, choosing comp. ratio and ignition advance is a matter of judgement. You usually know what other people have done in the past and what you have done yourself. You only usually change only one variable at a time.
 
i run 90 (MON+RON/2) octane non-ethanol in my 70 roadster, because it still has a fibrglas tank. no detonation that i can detect with that, but it's not a modified motor and not tuned to a sharp edge. at the end of the summer i usually have a can or two of VP C12 leaded racing gasoline, 108 MON, and i use that too. definitely no detonation with that stuff.
 
If you get detonation, stop and fix the bike. - raise the needles. If you continue to ride it, you might get a hole through a piston.
 
gortnipper said:
I ran 92/3 in Seattle for almost 20 years before I moved to NZ. All it did was wear out a soft lobed cam. Guys at Pokes told me not to use octane booster. Can't recall why.
Click to expand...
Speaking of shops in Seattle….Deweys was just north of Poke’s. All gone now.
 

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