That might be true for some makes, but in my experience with GM and other domestic manufacturers, there’s no difference between flex or non flex injectors - they’re all built with the same size injectors and the capabilities are either turned on or off within the PCM. However there is a difference between port and direct injector sizes.

I don’t know for sure on the fuel pressure except to say that every fuel has a different ideal (stoichiometric) air-fuel ratio. Gasoline is approximately 14.7:1 whereas alcohol is much lower - somewhere around 10:1. It’s possible that ratio can’t be maintained by adjusting injector pulse width alone, so modulation of the fuel pump could be utilized to reduce the pressure.

 

I daily drove that '60 in 1994 and 1995.

Just FWIW, while I've only run this 1994 G20 with a 4.3 about 250 miles, it seems to get around 20 highway. It only used about half the 14-ish gallons I put in it to go 150 miles home. But it hangs around the half mark forever and given all the sitting it did who knows if the gauge works right.

 

If you look up part numbers for both FFV and non FFV GM vehicles you will see alot of different part numbers. Several things are beefed up to handle the ethanol. In the hot rod world, alot of people tuning LS engines use the factory FFV injectors when adding superchargers and the like. I can tell you from a fleet manager's perspective when we started seeing FFV GM and Ford vehicles show up (2008 up Crown Victoria 4.6L) (lastest gen Caprice 6.0L) fuel pump failures almost became non existent especially for vehicles that end up sitting around for a year with no use.

 

I know GM has made changes to some FFV components out of necessity. The most recent example I can think of is the high pressure fuel pump on their direct injected engines - the earliest versions started leaking ethanol through the pump seals and into the crankcase - so I suppose changes to other components has been necessary as well.

Maybe I just haven’t had to look for parts where being flex vs. non-flex made a difference.

 

If fuel economy is a driving factor get it chipped. If you are smart about it, I've average 10 percent across most vehicles. I've done diesel and gas. There are some cautionary tales out there but I've been installing and using them for the last 10 years and had some good success with it .

 

Sharing some road trip mileage data for my 2000 3500 with a 5.7L and 3.73 gears. On multiple fall & winter trips back and forth from the PNW to Utah I averaged between 15.5 and 16.00 MPG. This route includes climbs through many mountain passes and cruising at 80 MPH in parts of ID and UT where the speed limit is that high. The best mileage I've seen was on a trip between Atlanta and Virginia Beach in July at 18.1 MPG and then 18.3 MPG from VA Beach north on US-13 which is completely flat and has a 50 MPH speed limit for much of it. I don't have mileage numbers for in-town driving.