unleaded or super unleaded??

[Rich C]

Hello again all. Was wondering which is the best to use normal unleaded or super unleaded?? Have tried search but still not sure. Many thanks Rich

[knackeredMk1]

Super unleaded is only beneficial if you have raised the compression ratio significantly by skimming the head quite a bit or installing a Mugen head.

[xander]

I'd have to disagree. I've always run my bikes on super unleaded and having used it in a car as well I'd say it definitely runs better. I know it's hardly scientific but I do think it makes a difference after a couple of tanks. Also I seem to remember Audi ran a car with one half of its engine on normal fuel and one on 99RON. After a while they took it apart and you could see it was a lot less coked up. I would assume this is benificial on a 2 stroke that burns oil as well since it would help stop it coking up. Finally it definitely imporved the MPG on my car compared to normal fuel.

[knackeredMk1]

The only difference between Super and Standard Unleaded is the degree of resistance to knock or pre-ignition. There is no difference in the calorific values (how much power they give). So you would only find a difference between them if your engine verged on pre-ignition if it was badly set up or you have raised the compression ratio. In evidence I would bring up several recent reports in the motoring press (cars & M/cs) that have tested power on a dyno with Standard and Super Unleaded. Between each session they reset the ECUs on the vehicles. In gereral they found no significant differences between the fuels. The only cars that showed differences were those cars that had 'learning ECUs' and could exploit the differences in the fuels. They were mostly, if not exclusively , high performance turbo charged engines.

The difference in 'coking' would be down to the different detergents and additives that the fuel manufacturer had put in. Pays your money and takes your choice between brands.

In the CRM world this would also be down to the brand and type of two stroke oil you used. Some fully synthetic two stroke oils burn very little on their way through the engine whilst cheap non-synthetics burn much more readily. This also ultimately effects jetting, meaning that in general, cheap oils lead towards needing leaner jetting as some of the oxygen in the intake charge is taken up burning the oil and not the petrol.

[Gammakeith]

Its certainly worth using for highly tuned 2 strokes as it may not make more power but as Knackered says it reduces the resistance to pre-ignition and gives you a margin of safety. I had a piston eaten away with detonation on my RG a few years back that caused a seize. I never did find a cause but I suspected a poor batch of petrol. I've used Super-unleaded ever since and had no further problems. Not worth it for stock CRMs though!!

Keith

[xander77]

Don`t forget the placebo effect, don`t know about the tech side, but if I put it in my road bike, it "seems" to run better, I might not be able to actually judge the change, but I kid myself I can and the bike runs better!!! well feels like it does!!

[Mudfacetony]

I'd have to disagree. I've always run my bikes on super unleaded and having used it in a car as well I'd say it definitely runs better. I know it's hardly scientific but I do think it makes a difference after a couple of tanks. Also I seem to remember Audi ran a car with one half of its engine on normal fuel and one on 99RON. After a while they took it apart and you could see it was a lot less coked up. I would assume this is benificial on a 2 stroke that burns oil as well since it would help stop it coking up. Finally it definitely imporved the MPG on my car compared to normal fuel.

I would agree with Knack'd. I used to use super in my KTM 200 for H&H and it makes no difference as the bike is much to good for my ability. In rallies with my CRM it makes no noticable difference at all that i can notice. There is more in the mind - you think it is quicker, therefore it is. Spend the money on sorting your suspension