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What Octane Fuel are you using in your Firecat?

  • F5 - 87

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  • F5 - 89

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  • F5 - 92

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  • F5 - 93

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  • F5 - 94

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  • F7 - 89

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  • F7 - 92

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  • F7 - 93

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Discussion Starter #1
I have been using 89.
 

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If cat has the engines timed for the 87 why use anything more?? The more octane the cooler the engine runs. Horespower = heat. Use the 87. Maybe if you are out in the boonies at some bar where you suspect the 87 octane to contain about 50% water you would use the premium. :p
Cat S.
 

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Discussion Starter #7
Go back and Re-read those owners manuals. It does not say to use 87 octane. It says to use a MINIMUM of 87 octane. B)
 

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cmscat50, you say if you're in the boonies than you would buy the higher octane because perhaps there is water in the regular. THink about that for a bit. Okay now that you have, wouldn't people up there and perhaps everywhere except at a race track be using more of the regular gas. I mean how many people actually use the high test in there vehicles? If it's my choice, I go with the gas that is most likely replaced more often. ie. regular 87 octane. Throw some isopropyl in there and don't worry. Save your money and buy the cheap stuff. It's all we need.
 

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Originally posted by Doze00F7@Jan 8 2003, 02:51 PM
If it's my choice, I go with the gas that is most likely replaced more often. ie. regular 87 octane.
LOL! I've been in the gasoline business for over twenty years, and been snowmobiling for over thirty, and I'll bet you that any station in a popular snowmobile area that sells both 87 and 92 octane grades of gasoline probably sells much, MUCH more of the 92 than the 87! Now, as more and more sleds are being tuned to run on 87 this trend might change. I use, and plan to ONLY use 87 in my std F7. I've read WAY to many technical articles over the years that state using more octane than the engine was designed for can actually hinder performance slightly. -- Roy
 

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Originally posted by Roy T@Jan 8 2003, 04:02 PM
LOL! I've been in the gasoline business for over twenty years, and been snowmobiling for over thirty, and I'll bet you that any station in a popular snowmobile area that sells both 87 and 92 octane grades of gasoline probably sells much, MUCH more of the 92 than the 87!
Roy, you may be correct...but my guess would be more 87 than 92 gets purchased and thus is fresher once you factor in car gas sales...especially in more remote areas...Marc
 

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I was told that the Firecats were made for 87 octane minimum. Also that 89 octane was the safest choice, but if 89 is unavailable and given a choice between 87 and 92 octane we should take the 87.
 

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Discussion Starter #14
Thanks Rob for that input.

In case anyone missed it, here were the questions and answers to octane related questions to GLS. Sorry, they are a little long, but very informative.


What fuel octane do you advise for the F7? Is Mobile 93 good?

gls on 7/17/2002 7:23:00 AM

Mobile 93 is good fuel, and if you want to continue using that, I think you would have good all around results. I think it may be borderline excesive octane, but I don't think your performance would change by much, except up at 4000 ft. Then I think your acceleration may suffer slightly. It's definitely safer fuel. I guess my opinion would be 87-92 octane, and you should be fine everywhere.

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I am trying to understand optimal compression and octane for performance.and trailability. Is there an advantage to keeping lower (or stock) compression and running lower (87 or 90)hotter faster burning octane gas instead of going high compression and running High octane slower cooler burning fuel? I understand that Higher compression ultimately makes more power.But I have heard and read different opinions on this for trailable performance. Some claim that keeping the compression stock around 125lbs and running lower octane.or a 50/50 MIXTURE of High and regular is as good as or better for than going High Octane with High compression? With performance and reliability in mindwhat is the optimal combination? Is there a relationship or advantage with acceleration or top speed .....with either combination? Also.....why do the stock twins run higher compression vs the stock triples? Thanks.

gls on 7/11/2002 8:40:00 AM

This subject could take a very long time to discuss in detail, as there are so many variables. I will try to give you some answers based on my experience, in the shortest time. First of all you ask if there is an advantage to running higher octane fuels. That depends entirely on what your doing. If you are racing a 500 ft distance, and acceleration is your main objective, lower octane fuel with a hot plug would give you the best results. If you are riding at WOT for long distances, 10-20 miles, then you need the safety of a higher octane fuel, and a colder plug, at the expense of some initial acceleration gains. You will always need to accept this compromise regardless of fuel quality you use. Next, speed of burn does not change much with octane change. It always remains relatively the same regardless of octane number. The temperature required to initiate the burn changes with octane. Your post is telling me that you are asking whether you should increase compression on your sled, and be forced to run a higher octane fuel. You would do this to increase performance. This subject is as difficult to answer, if not more, than the fuel discussion. Every type of motor is different in there reaction to this change, and you almost need to be the designer/developer to know if there's a gain in performance by adding compression to a particular engine. I'll try to explain. You know you need to have correct fuel for your chosen compression ratio, but not overkill on octane. So you have selected that, and hope to see a gain by adding compression. In most all cases, higher compression ratios will give you some gains in low and mid range acceleration or pull. Top speed is another issue. Regarless of the power number from a dyno, higher compression ratio's may not be faster, and in some cases may be slower top speed. This happens because the increased cyl. pressures generate more heat due to, among other things, higher compression and ign. timing advances. This heat is retained for a longer time and soaked in the combustion chamber and other surrounding surfaces. That means less heat in the pipe, and consequenty slower wave speed which is directly proportional to RPM. Also there is some effort lost in simply the pistons ability to compress a higher ratio. So you now have a different motor which requires other calibration changes to many areas, clutching, jetting, timing, pipe design etc. When I design/develop an engine, one of the first parameters to decide is compression ratio. Much of the remaining development items and areas are done around that chosen ratio. If the compression ratio is changed, the design of other components should also change to match the package. One example would be the 900 twin. That pipe makes good power and torque, but power after the peak falls off rather sharply. if compression is added, mid range acceleration may improve, but for reasons mentioned earlier, the power may fall off harder and sooner. So now your cluthcing isn't even close, and your probably going to go slower. And depending on the ratio change, may require an entirely different pipe design. If you want to experiment with this, but don't know the engine inside and out, you need to have some knowledge of clutching, jetting, ignition timing function, and pipe design. And then be willing to burn up a few parts. If you don't want to experiment, then I would run 92 octane for long WOT running, and 87 if you have typical driving habits, and leave the compression ratio alone. I could elaborate much more on the proper ratios versus octane based on cyl bore size, combustion chamber shape, and operating RPM, but I better get working. I generally use 6.3-1--6.5-1 compression ratio for 87 octane regardless of the number of cyls. This is for a liquid cooled engine running at a typical snowmobile engine RPM. I hope I have helped with you question.
 
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I've been using a combo of half and half av gas 107oct and regular 87 oct seems to be wat better on the bottom end not much change on the top compaired to 92 oct out of the pump.
Some guys say avgas burns colder because it burns faster. does anybody know more about this?
 

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I have been running mobile 97 octane with 1 full can of Klotz Octane Booster which adds about 10 or 12 so i am running about 107 or 109 octane and my F7 loves it.
 

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hum..... that sounds like a lot of octane boost. any alcohol in that stuff? :huh:
alcohol burns kinda hot. could melt your rings doing that.
 
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