mpg?

[GalaxieJeff]

About 1 to 1.5 more maybe 1.75.
Depending on the car the mpg increase between E-10 and straight gasoline is 5-15%.

[Bat out of Hell]

Thanks, I always wondered how the older blends of gas would do. What modifications would it take to get a car as old as mine to run on E85, and What was the recommended octane for cars like LTDs in the late 70s?

[GalaxieJeff]

Originally Posted by Bat out of Hell

Thanks, I always wondered how the older blends of gas would do. What modifications would it take to get a car as old as mine to run on E85, and What was the recommended octane for cars like LTDs in the late 70s?

Too many! I wouldn't do it. Much lower BTUs per gallon of e85, you'd have to fatten up the jetting in the carb for starters, might also have to recurve the distributor as well as jump up in heat range with the spark plugs. Your mileage will really drop off as well. Then there is the problem with older rubber, plastic and gaskets in the fuel system, that 85% ethanol blend will eat them up.

Late '70s were low compression no performance engines. You could pee in your gas tank after a couple beers and it'll run...well ok not really, but the lowest stuff out their today is more then enough.

That said, there is a misconception that todays gas is junk compared to "the good old days". Back in the '60s gas was rated only by the ROM (reaserch octane method) which was pretty high. Some time in the early '70s IIRC, is when they rated it the AVERAGE of the ROM and the MOM (method octane method) which was lower. On the pumps you will see the octane sticker also note "ROM+MOM/". There is even way more to it then that, 2 fuels with identicle ROM+MOM/ rating can have much different properties as to how they perform over a given range.
Anyhow, todays premium 92/93 will run just fine in an engine from the '60s that calls for 98 octane.

Some people have found they need to run mid grade or even primum in their older cars that originally only needed regular grade back then. But thats usually due to the engine having carbon deposites or other problems, out of tune, worn, etc.
My Galaxies 302, .030 over with original small chamber 289 heads runs close to 10.5:1 compression. It will run fine on 87 but with 89/90 midgrade I can advance the timing a couple degrees and pick up some performance. I tried using premium and playing with the tune more but there were no further gains, so back to midgrade. When she was 100% bone stock she ran perfect on regular 86/87, no gains from higher octane. Stock was I think 9:1 or 9.25:1 compression ratio.