Does anyone have the straight info on this AND how does the 4.6 compare to the 5.4 in mpg?? thanks

 

I don't have any documented info, but I would *think* on 87 octane gas the regular and FFV would get essentially the same mileage, all other things being equal.

In general, I would think with all other things being equal, a 4.6 would get slightly better mileage than a 5.4, but it shouldn't be more than a 1 or 2 mpg difference. I would also think under some conditions a 5.4 would actually get better mileage than a 4.6.

I am basing this on nothing but logic, nothing real world.

 

Acctually the E85 FF will give you less mpg. E85 is not 87 octane gas either it is more like 105.

Here is the thing E85 is not as efficient as normal gas is so it will take burning more of it to get you the same distance if that makes sense.

87, 89, 93 octane hell even 110 octane you are going to get the same MPG either way, the octane rating is the fuels resistance to detonation nothing more. If your truck is made to run on 87 there is no reason on earth to run anything higher unless you just like to give your money to the oil companies.

As for the 4.6 vs 5.4 and mpg it is probably more determined by the driver and their style of driving than the motor itself in the real world.

 

The question was about mileage running 87 octane gas in both, not gas vs. E85. E85 will give you anywhere between 7 and 30% less mileage. This is documented.

 

Sorry guess I mis understood the question

I would not think there would be much difference at all between the two MPG wise. The only difference between FFV and non-FFV is computer tunning and hard system parts i.e. plumbing lines(ethenol is corrosive), non arching fuel pumps(ethenol is conductive as opposed to gas), and possibly bigger injectors to handle the extra 40-50% of pulse width needed.

 

That's my thoughts too. The FFV needs a wider possible range of mixture control and spark timing due to the fact E85 requires a lot richer mixture than gas and can handle a lot more spark advance. Logic tells me with 87 octane gas in both, operational parameters should be identical.