Ran 100 octane for the first time. Wow

[d55dave]

Whitepunkonnitro is spot on. People love to think things are better because they cost more.

In 25 years in aviation. I can honestly say that I have never seen anything other than 100 octane low lead. They higher octane fuels were phased out years ago. Granted my career has mostly been around helicopters with turbine engines. Even the 100 low lead should not be run straight up in an automotive engine as it has significantly more lead than good old leadded auto fuel used to. It will cause lead deposits and possibly foul plugs in an automotive engine.

 

[clinteg]

BTW, would it be prudent/benificial to re-time the motor if you changed your regular fuel usage significantly (from pump gas to av) gas ? Does this resistance to detonation help if the mix is leaned out?

I thought ethanol added resistance to detonation/octane, like E85 {15% 87 octane, 85% ethanol} has a 110?? octane rating. Why would an apparent change in motor performance be noticable then? Do you mean pure as in less inpurities?

If you HAVE to back your timing way off to run pump gas to prevent knocking due to higher CR's, then yes advancing your timing and running 100+ octane will give you more power (in most cases I would say). Example: I have mine turned back to 28 degrees total to run 91 at the moment with an iron headed 11:1 motor. I've ran it from 0-110 mph with the foot down to the floor the whole time on 91 (probably with ethanol in it too) and heard no ill effects from the motor. I've beat on it and beat on it and it doesn't seem to care. It pulls hard. At the track, race fuel will get put in and will probably run somewhere around 34 degrees total and go from there. It should be pulling even harder with the timing change.

It is true that ethanol will resist detonation better than pump gas. The problem lies in the fact that ethanol does not have as much energy in it as gasoline (per the same amount of fuel). Therefore, that is why E85 systems have to run about 30% more fuel than gas because it takes about that amount more to get the same effect of gasoline. BUT when you feed it the right amount of E85 that it needs, it's like running race fuel since it resists detonation very well while also running cooler and reaps very good benefits from that. But if you add ethanol in the mix of pump gas and your fuel system isn't tuned for it, that 10% of ethanol that's replaced the gasoline doesn't have the energy that the 10% gasoline did. So that fuel technically doesn't quite have the energy that it did before. That is the mostly the reason people claim to lose power when running it. On the flex fuel cars, the fuel systems test the ethanol in the fuel and compensates accordingly. Hence why they get worse mileage with the higher ethanol levels.