In reply to Robbie (Forum Supporter) :
The short answer is availability. Where I live, only about 1 in 10 gas stations have E85.
Manufacturers started doing flex fuel so that you could run gasoline which is ubiquitous, or when you encounter E85 you can choose to run it as an environmentally friendlier choice.
The use of avgas in the old wheezers was primarily in response to the loss of TEL in automotive fuels. If you had an old iron-headed muscle car with 10.5:1 and terrible chamber designs, when 1975 rolled around you were kinda screwed. Avgas was more of a choice to be able to operate your vehicle without damaging it rather than a performance fuel choice. I think the myth survived because "more octane must be good."
Robbie (Forum Supporter) said:
this is the article im referencing. With dyno tuning on an otherwise mostly stock miata, 100 and 105 octane race gas nets essentially 0 power benefit over pump 93, but e85 shows a real improvement (in a motor that was definitely not designed as a 'flex fuel' vehicle).
Admittedly they did not test avgas, but I think that it would be very close to the 105 octane race gas.
https://grassrootsmotorsports.com/articles/fuel-truth/
If you have to modify your engine to maximize the potential of race fuel, why wouldn't you instead modify your engine to maximize the potential of e85?
Not being a Miata expert, I don't really have any thoughts. If it is truly not a flex fuel vehicle, the O2 sensors would be trying to fight to keep things stoich for gasoline. It would richen a little on E85 since ethanol carries some of its own oxygen. Let me read that article and get back to you.
Ok, after reading the article, they had complete control over fuel ratios and timing, so that explains some of my questions.
My only thought is that the cam, compression, head flow, and other engineering factors of that particular engine and tuning system they were able to squeeze 7 hp out of it.
My question would be... could they have squeezed that same 7 hp out of gasoline if they had put the effort into that as part of the baseline.
The math part of it (just looking at BTUs and fuel ratios) it's pretty much a wash. What the tuner and the engine DOES with it can favor one fuel over another.
You can fudge E85 fueling just by injector size (50% larger ie a 20lb/hr to a 30lb/hr) with no other changes (assuming the fuel system is up to the task). It will still target lambda 1 in closed loop and WOT will depend on if it's narrowband or full time wideband control. Usually I see better power on slightly richer mixtures with E85 compared to race gasoline. Though the E85 does fine on the leaner mixtures and still makes more power than gasoline.
03Panther said:
I’ve never personally bought any Av gas; I assume there are also different grades of av gas available?
i also do not know what 100LL is. Have heard it mentioned before, but would not know where to get it.
There used to be some places that had Cam2 at the pump, but it’s been many a year since I’ve seen that
Av gas also comes in 115/145 which I could get free any time the squadron was forced to drain a tank in an airplane. They cannot reuse "contaminated fuel" so I'd pull my Cameo pickup with 4 MGA gas tanks in the fenders plus the original 22 gallon tank behind the drivers seat. That plus a few 5 gallon gas cans would get me out to Holtville race track and back again.
Yeh, I'd have to clean the plugs after the weekend but I'd clean them every 3000 miles anyway. ( and reset the points )
Having run a 93/100LL mix in my car, about the only 'definite' difference I noticed (was convinced by a bunch of the older generation gear heads from the drag racing club to give it a try) was the smell of the exhaust.
Butt-dyno wants to say it felt a difference in the mid range and I ran faster at the strip BUT ambient temperatures probably played a much larger role than the fuel did that day.
