Race Gas

[robinson373]

I am hopefully going to get my banshee back together now after having the crank come apart and was wondering if i should be running race fuel. I had the crank welded and trued, and now have these mods; 21cc domes, vforce reeds, cylinders bored 20 over, k&n with no airbox lid, and T-5s. The guy who did my machine work recommended 50/50 race gas to 97 octane, is this needed? And also where should I start with my jetting? 1900 ft, 65 degrees. Any help would be appreciated.

[SYRacingInc.]

Run it with 93 octane and check for detonation. If it is detonating tt will sound like little gremlins are inside your cylinder beating it with a hammer. I highly doubt youll require anything more then 93 octane.

 

For jetting.......be safe. Start with 300 mains, stock pilots, and put the needle in the middle.

[Mud Pilot]

I was running 110 High Octane and now i just got done rebuilding the top end. I would run lower octane like 93 or 87. But that's just my two sense.

[Stuff]

Your compression ratio is what dictates what octane you should run. Higher compression means higher octane. Running higher octane usually will not increase power but it does smell good

[.]

get yourself a compression gauge. I'd have to say that you probably wont need race fuel to run, but I know when you do run race fuel, its a cleaner burning fuel and it will make your bike a little bit faster.

 

In general though, if you could get a very clean pump gas, the closer the octane level is to what is needed for your compression, the better.

 

I know my buddy on his atc250R, I can beat him by quite a bit when he uses regular fuel, but when he runs race fuel we're dead even or he's even beating me by a little bit.

[boonman]

You will not need race fuel on 21cc domes. Unless you have a custom piston of some sort. Which I doubt. High octane fuel is not cleaner burning. All the octane number tells you is it's resistance to detonation. It is a long going debate on here. High octane "racing" fuels are nothing more than to resist detonation in a higher compression engine. Not much more, nothing less. Now, there are oxygenated fuels. but, we won't discuss that. Run some 91 octane through it, and listen for detonation. Check the plugs. If there are silver specs, than it is detonating. Run a little higher octane. Do not run more than you need. Higher octane fuels NEED COMPRESSION to burn. It's a fact. If you don't have the compression, you won't be doing aything but draining your wallet uselessly.

[Bigairee]

I was reading on this subject yesterday. Here is some interesting reading.

http://www.2strokeheads.com/Compression_and_octane.html

[stu35]

That was an interesting link.

[Ducman]

Good link, important info to consider after geting port work. My $0.02 on the race fuel is that the expensive leaded stuff with additives do a good deal to help protect a 4 stroke valve train but really nothing for a 2 stroke due to the oil added to the fuel for lube and wears out plugs faster. A waste of money unless your compression dictates the need for a really high octane or you are addicted to the lovely perfume it creates when burned. Adding lead to fuel is a less expensive way for the manufacturer to bump up a fuels octane rating and provides added valve train lubrication which shee don't got. On the other hand, unleaded high octane fuel like some of the unleaded AV gas, or like the fuel like I buy from Northern Evergy in CA, unleaded 98 octane for $3/gal, are just more highly refined resulting in a fuel that burns a lot cleaner and has a way better shelf life. There is a huge difference in the large quantity of black soot that regular ol' 91 pump gas leaves VS the small amount of light gray colored soot left with the unleaded 98 in the pipes on my Ducati 996. Also if for some reason while your out riding and come into a lean running condition on your 2 stroke ie. temp drops by several degrees, jets get partially clogged or dirty and restricts flow, whatever, then you may run into a detonation problem where none existed before if you are running the lowest possible octane. 3 main factors contribute to a detonating temp inside the cylendar; actual temp of the piston/head/cylendar itself giving off heat to the gasses flowing through the combustion chamber, dynamic and statick compressions (pv=nrt), and the ability of the fuel in the A/F mixture to absorb heat. Dump enough fuel, even low octane and you will absorb the heat and not detonate (the later resulting in shee's too rich to run right). Some turbo cars even inject small amounts of water in with the A/F to absorb the heat to prevent detonation under high boost when not enough fuel can be dumped to cool the intake charge. Lean conditions (and other factors causing high cylendar temps) go hand in hand with detonation by causing higher cylender temps. I think if you can get this fuel the extra $1 per galon is well worth it for cheap insurance in the short run to protect in the event of conditions which could result in detonation (if your piston doesn't melt first at least you might not poke holes in it) and extend the engines life by keeping the cylendar and exhaust track cleaner in the long run. Wow that $0.02 was more like $1.02, sorry for the long wind!