Yes. Even 108 or 110 octane will detonate the hell out of it unless it's jetted on the rich side. The best fuel to use is something with at least 112 octane like VP C12. You can also use VP MR8 or Nutec GP2 but they're oxygenated so richen up your jetting accordingly. But, since you won't get that much gain out of using the oxygenated fuels on your 94 model, the best bang for the buck is the C12. --Chris
I ran Sunoco 110 for 2 seasons on a 94 and a 95 and never had a detonation problem. Set squish at .030 and even ran a split fire plug at on time. (serious budget) Won 2 Regional Championships and had a blast. I would not run anything less than 110.
What about Sunoco Red. A lot of guys on the coast are using it. 7-8 buck a galon. Love to go with nuetec just not the nuetec price. Any one local try it?
Hmm, the TZ runs just fine on Sunoco 104. Maybe THATs why it's slower? Maybe I need to lower the deck a bit. Hmmmmmm (rusty wheels turning in head). Jack
I have been using Sunoco Purple (108) octane. I also run A-747 oil. I do get detonation as I am running a Yamaha and I am running a little lean to get every last ounce of power. I have a practice head and a race head. When the detonation gets bad on the race head I send the practice head out to be reshaped and recycle. Octane cannot hurt and is good protection from detonation, however do not go crazy with super high octane fuel unless you have a tuner to dial the motor in. High octane fuel burns slower and requires more timing advance. Even with as Chris Pyles stated C-12 I would bump the timing just a bit. Bill Cole WERA#72
I'm in process of purchasing a 96 RS 125 so I'm also wondering about fuels to use. Found something while searching about fuels that is interesting. Maybe someone here who has more knowledge on the subject can check this out and reply. www.hotrodheaven.com/comments/messages/11933.html www.vtr.org/maintain/gasoline-octane.html
I have to agree with Chis P. This issue has been around the block and back a few times and always leads to the same conclusion. First off use a fuel that you have access to. You want to pick a fuel and stay with it. Jetting for fuels can very a few sizes. For example Sunoco Maximal runs real lean. 3-4 sizes thank Purple. If you were running Maximal (as I was) and got used to the jetting with it and then put purple in (as I did) it will be to lean. Find out if you have a VP or Sunoco racing fuels dealer near your house and stay with it. Also stay with major manufacturers. VP, Sunoco, nutec etc. You want consistancy in every barrel of fuel. Things like Power Mist are OK for 4 strokers but do not have the consistancy of the malor manufacturers. I highly recommend VP-C-12 or Sunoco Purple. If you have the money get Nutec. These fuels are VERY consistant and you will be able to jet with your eyes closed once you know how they react. Side Note... Chris I saw a weird label on your fuel can this past weekend. Are you trying that new VP Grand Prix gas.... How is it? Bill C WERA #72
Hey Bill, Where do you send your heads to get reworked? Kevin Murray? Also, what sort of profile do you get cut? Do you use the stock top hat profile or a hemispherical one? I've had some detonation on mine and have been thinking of doing what you're doing, finding a thrashed spare and reprofiling it. Chris Doktor WERA Southeast #73
Another thing about different types of gas, some have a hotter exhaust temp than others. This effects pipe tuning. I'd never thought of this before until recently. My good friend and tuning guru Duncan Paul wanted me to buy some av gas and mix it with pump stuff, 50/50 and take some lap times to compare with straight pump on the KX (it'll run on pump gas). When I inquired as to why, he said that the av/pump would run about 75 degrees hotter exhaust temp. This would effectively shorten the pipe as the pressure wave would travel faster in the hotter gasses. He'd compare times taken with the 50/50 to straight gas and get an idea if fiddling with exhaust tuning would help. His dyno is toast or he'd do the tests on it. I would expect that different gasoline blends and burn rates would vary in exhaust gas temp and could effect pipe tuning in this way. Jack
Chris, Yes Kevin does all my work. I have the stock profile reshaped for the fuel I run. It is my opinion that a little detonation is OK. Tells me I am jetting a far as I can. I do not run alot of extra timing so to me it is an indication of my jetting. They two head swaping really works for me. Bill C
So is it a top hat or a hemisphere? I don't need dimensions or anything. I've just been wondering why yamaha used the top hat combustion chamber in the first place, since it is not the best design heat transferwise. I'm planning on recutting mine as a hemispherical profile and I was just wondering if others have done the same.
