If you go with Ivan's tune, you can drop down to 89 as well. Faster AND cheaper to operate though part of me wonders what he could have gotten out of the N1K if he kept the need for 91 octane.
As Lucky Luciano said in his post, total waste to run the higher octane. Higher octane is could help if you had a turbo motor and running more boost or if you had more ignition timing for stock motor. None of these apply here. Since you aren't bumping up your compression ratio either, not much need there as well.
higher compression needs higher octane. Stock ninjas are fine on pump gas. My CRF450 supermoto has a 12:5/1 piston and stage 2 cam. It will only run on 110 octane. Anything lower and it sounds like a popcorn machine!
I was wondering because the dirt bike guys use VP race fuel on stock engines and see a good power difference.. so I was wondering if the same applied to street bikes.. but I will stick with pump gas since it is a lot easier for the wallet
To be more technical, geometric (aka static) compression alone can not tell you what you need to know about octane requirements. We really need to look at the effective compression ratio. This takes into account cam timing, any sort of forced induction, etc. We also have to take into account thermodynamic effects and ignition timing.
We also have to factor in altitude too. All these effect what sort of octane you need to prevent detonation. Generally any more octane needed than to prevent detonation is wasted. There is a caveat though. That assumes a motor under static load.
So you could assume that an engine listed at 12:1 static CR might require higher octane fuel than one at 11:1 but that isn't always accurate. On general principle yes, but if the second motor (11:1) had cams that allowed more cylinder filling then it could require higher octane fuel. I am used to tuning motors with forced induction so I always err on the safe side. They are much more sensitive to octane than normally aspirated motors. Then again they are a lot more fun for me. Without going way off on a tangent, I'd rather have bppsted motor making 150 HP than a normally aspirated one make 150 if it is properly designed. I totally understand some of the trade offs that can effect the immediacy of throttle action but those can be tuned/designed to be pretty insignificant with some work.
That is correct. They adapt for altitude within the ability of their setup automatically. So at high altitude they aren't running too rich. Or if setup for high altitude and you go lower, they aren't running too lean.
As you've likely noticed at high altitudes, you can't usually find 91 octane fuel, nor is it usually needed. The one exception to this is is you have a turbo'd car/bike that is setup to run a certain amount of PSI (absolute) in the intake as referenced to sea level rather than most that are a relative PSI. I prefer to go with absolute rather than relative is possible.
So a quick example of this is a turbo motor that is running 10 pounds boost. So to see what pressure is in the intake (I am keeping this simple) we'll need to take the 10 + 14.7 (normal atmospheric pressure at sea level (STD)) which equals 24.7 PSI. For absolute and relative boost the numbers would be the same.
Now lets go to 10,000 feet. The atmospheric pressure is ~10 PSI. So with our 10 pounds of boost, we are not at 20 PSI if relative (like most cars/bikes/etc.). As you can see there will be a loss of HP since I am no longer feeding the motor with 24.7 pounds of pressure but only 20. So I've lost about 20% of my HP. But I was not boosted, I'd have lost about 30% (14.7 to 10). So turbo cars/bikes lose less HP with altitude than normally aspirated cars.
Now lets go to my turbo setup where I base everything on absolute pressure. So to have my 24.7 PSI at 10,000 feet means my turbo system will need to provide 14.7 pounds of boost to go with the 10 PSI that I have at altitude. If it can do it, I'll keep my rated HP at altitude and have no power loss. This is the simple look at it. I am not getting into compressor maps and efficiency of the turbo. Normally a dual, small turbo setup can be better in this situation than 1 big one. They will spool up more quickly yet still provide enough boost. Spooling up quickly provides better throttle response. Anyway you probably get the idea for now.
I still have my old t-shirt from drag racing "injection is nice but I'd rather be blown". That pretty much sums it up for me but actually I'll take both now.
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