426 fuel

11 replies to this topic
  • jaybird67k

Posted October 26, 2000 - 05:23 PM


Why is no one talking about fuel ? I am curious as to what octane the majority of people are running in a 12.5 to 1 compression engine. A race car with that C.R. would require at least 110 octane to stop pre-detonation in the cylinder. Please enlighten me to the correct fuel to use.

  • YZThumpa

Posted October 26, 2000 - 06:17 PM


Strictly an amateur here, but I use your basic convenience store bought 93 octane and she purrs like a kitten on steroids.

  • Boit

Posted October 26, 2000 - 08:21 PM


I use Sunoco GT Plus which has a pump octane of 104 that is recommended for CR's of up to 14:1. I use it because of quality consistency, and the anti-knock characteristics along with a cooler running engine. Is it an improvement over typical gas station gas? I wouldn't know, but what research I've done points to insurance against engine damage due to predetonation.

  • Numpsy

Posted October 26, 2000 - 11:16 PM


I use AG RF102. This is a synthetic Acetylate fuel (like Sunoca I think).
This is cleaner, contains 1,8 % oxygen and burns better.
This makes the engine run cooler, better powerband and gets a few hours more out of Your spark plug.


  • Tim

Posted October 27, 2000 - 07:26 AM


I just use plain old Premium 92 or 93 octane. I do make sure it is fresh (one or two days old), normal gas does start to break down rather quick. I also have enhanced the compression in my street bike and it also runs fine @ 12:1 with pump gas. If your bike is not pinging, I feel there is no reason to spend the extra money and pain in the butt to put anything more than premium in the bike.
Hope this helps

  • ART

Posted October 27, 2000 - 07:28 AM


I had a similar question that was posted under the topic "95 octane vs. 95 octane". Two links were posted with good information.

I use 92 octane pump gas with no problems.

I also pulled out an old Dirt Rider that had an article with first test of the '98 YZ400. It noted that the high compression motor was designed to run on premium pump gas.

[This message has been edited by ART (edited 10-27-2000).]

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  • MikeOK

Posted October 27, 2000 - 12:17 PM


The manual calls for at least 95 octane but I've used premium 93 pump gas a couple times in a pinch with no pinging. I normally use pump 93 with a quality octane booster added just for peace of mind...


  • chill63

Posted October 27, 2000 - 12:49 PM


I run 93 octane pump gas. I have noticed some confusion on this in the past because the manual specifies unleaded fuel with a research octane number of 95. The 93 octane on the pump is obtained by the average of two methods, research and motor. You will usually see somewhere on the octane sticker R+M/2. In most cases the research number is higher than the motor number. The bottom line is if your engine is not pinging on 93 octane pump gas, then you will not gain anything by using high octane race gas, except a thinner wallet.

  • MikeOK

Posted October 27, 2000 - 01:49 PM


Chris- interesting, I have seen that sticker and wondered but do any of you know what "research" and "motor" actually mean?

  • chill63

Posted October 27, 2000 - 02:08 PM


MikeOK - What does the Motor Octane rating measure?
The conditions of the Motor method represent severe, sustained high speed, high load driving. For most hydrocarbon fuels, including those with either lead or oxygenates, the motor octane number (MON) will be lower than the research octane number (RON).

What does the Research Octane rating measure?
The Research method settings represent typical mild driving, without consistent heavy loads on the engine.

I "borrowed" the above from http://www.seansa4pa...ce/octane.html. This is just a little snip. The faq has a lot more detail.

What is the effect of engine speed?
Faster engine speed means there is less time for the pre-flame reactions in the end gases to occur, thus reducing the tendency to knock.
- this was also on there. Which is probably one reason why the 426 may be able to get away with the lower octane fuel. I've heard that some high revving engines do not run well on a fuel with too high of an octane because the fuel is too slow to burn.


  • holeshot

Posted October 27, 2000 - 02:20 PM


92 octane pump gas will typically have a Research Octane Number (RON) of 96 to 97 approx., so you should be safe, provided the gas you're getting is actually 92 octane.

  • jaybird67k

Posted October 27, 2000 - 05:36 PM


I sure appreciate all of the input on the fuel question. I just recived an e-mail from sunoco and they said if I'm using it stictly for racing they recommend using sunoco standard, which is a leaded fuel with a rating of 110 octane.(purple in color)Thumper racing also recommends a leaded fuel between 100 and 110 octane. The lead has alot of lubricating properties, hence longer engine life.

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