Modern Vespa

I used the P200 in September at the races at Daytona as a service vehicle, running errands in town, etc. A racing buddy bought some Sunoco 260 GTX fuel for a back to back comparison in his Formula Vee on track. Bottom line, the 98 octane unleaded was slower than the 110 octane in his race car. I was the lucky recipient of the unwanted 98 which I have used in the P200 for past couple of months. It is probably my imagination, but since I have gone back to the 90 octane alcohol free fuel, the P200 seems slower on acceleration. Does anyone have experience with race fuel in their scooter?

I've never tried high-octane race fuel, but it is common knowledge that extra octane provides absolutely no advantage unless your engine is detonating or pre-igniting on the lower octane fuel.

Does your P200 have a higher-than-stock compression ratio that would require higher-octane fuel? Is the timing advanced beyond the stock spec? Is your cylinder head heavily carboned up? If these are not the case, then it is your imagination.

EDIT -- if the 90-octane stuff had ethanol, that might have explained the difference, but you say it was alcohol-free.

It is a stock engine, with less than 2000 miles, I have put about half of those on in the year that I have owned it. I think it sat for a couple of decades.

http://www.racegas.com/fuel/8

What is the Piaggio-recommended octane rating for the P200?

It's possible that it has something to do with it being a fast burning fuel. I read your link but I'm no expert.

I believe hi octane fuel burns slower and has lower BTUs ( energy) per unit, the reason low octane fuel can cause knock is it burns faster. Hi octane allows an advance in spark timing and higher compression which can help engine output. It's more complicated than just advancing the spark. And with everything bring equal, no changes except for octane, going from 92 to 100 octane will not increase performance on its own. I have a Mazda CX-5, 13 to 1 compression ratio and runs on 87 octane.

Please read the info(all of it) in the hyperlink that DucatiSS posted.
This is a small part of the Tech Corner.

However, for most race fuels, a lower specific gravity suggests a faster-burning fuel, while a higher specific gravity suggests a fuel is slower-burning. This is because most light hydrocarbons used to make a race fuel are faster burning than most heavier hydrocarbons. This matters because faster-burning fuels usually require less spark advance than slower-burning fuels.

The link is a good read

Some more quotes from other sites.


"The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites."



"What are octane ratings? Octane ratings will tell you how resistant the fuel is to burning."



The second quote refers to flash point.

With a lack of a Ph.D. In chemical engineering and a masters in mechanical engineering, I'll say there are so many variables and additives in gasoline and actual engine design/condition that unless the engine was designed for hi octane fuel use, the performance decrease you experienced was imagination, or wishful thinking. Engine design and performance gains over the years is interesting reading. Now...where is my 76 Buick that would run forever with the ignition off? Or wouldnt start because they never gave me a key to unlock the vapor?

On multi-cylinder vechicles the higher octane fuel produces more power-because the ECU can jack up the Ignition timing with out hitting the preignition range. many auto manufactures list different HP ratings for same engine on the lower and higher octane rated fuels. The ECU getting information back from sensors in the engine allow this timimg increase ( but they also change cam timing using solonoids and oil pressure to do so. Where the vespa single cyl engine is capable of changing the Ignition timing, the cam does not (not capable). I have always used premuim in my bikes, and at least middle grade in my vechicles. I had to cut my teeth on fuel injection back in the early/mid 1980's lots of drivability problems. A lot of those stemmed from fuel quality. No a days the fuel is great low or high grade. the higher grades (depending on the vendor) usually have better detergent packages. There is a base detergent package that they all have to comply with. Combine with a higher octane is a better package IMO.