I see your r has 257psi and was wondering what fuel do you burn? My brothers r has 220psi and i thought that was alot compared to my 185psi on my banshee. You must have incredible throttle response! We both have burned av gas for years with out any problems. I tried vp c-12 and didnt see any difference. You must be using at least 116 motor octane. Got me wondering if i bump my banshee up to about 220-240 what it would run like. But i was told that twins dont like a lot of compression because it will make it run flat at high rpms. Just wondering what your thought was?

 

I run VP C12, as there are other factors involved in a 2 stroke head set-up that will determine the octane required, like the squish band clearance and width.

I don't like to see twins with that much compression. It's not necessary with a twin(or more cyl's). The max typically that I would set-up towards for a gas engine would be around 175 pounds. You're right about it going flat on top with that much compression, especially a Banshee. With 220 pounds you're starting to flirt with being able to run methanol.

I need to update my signature block as since I have tweaked it a little different direction and now only have about 205 PSI cranking. The 257 was real nice, boy she wicked up REAL fast, but started to fall very flat after about 8600, but my target peak power RPM was 8400 so it wasn't that big of a deal. I like it better at around 200 now.

I'm not a big fan of Avgas. There are better fuels, I'm not saying that you'll cause damage to your engine, I just think that after spending alot of time and in most cases alot of money to get your engine dialed in, to try to skimp on a few bucks for gas is not the best, in my opinion at least. I prefer to always set up an engine to run a higher octane fuel, the potential given is much greater then. Premium engines can be set-up well too, but there are seasonal fluctuations in pump gas that can be a tuner's nightmare.

I think that if your head was specifically cut to run C12 then you would notice a difference. Do you know your head set-up as it is. To get 185 PSI something had to be done. Was it re-cut entirely or simply the gasket mating surfacce was machined to bump up the compression. Banshee heads have alot of room for improvement, as well as 250R heads do too!!!

 

Back country, i had my motor ported by duncan racing. I had mid range porting done and rechambered head. When i got it back the squish clearance was .035" and compression was 155. Loren told me to use c-12 so i did for a while. Just happens to be the same fuel i used in my drag car at the time. After the first rebuild i bought a trinty head with 16cc domes. Clearance now is .040 and 185psi. About the only difference was better throttle response. My egt still reads 1090*-1150* at wot with either fuel. I thought that was funny because of the specific gravity differences. Where do you ride i have cousins that live in seattle. Planning on making trip out there this summer and doing some riding.