I have been doing a bunch of research and reading when it comes to EFI systems. Its up to me to make my final decision.

Its down to two systems
Holly EFI
Fast EFI 2.0

they both have pros and cons but I really like the Fast only because of the e85 capability. I have read with fast you will need a different o2 and that is fine with me.

the holly requires a different fuel table and that really scares me if I botch it up on the initial setup. it scares me because I have never sat in front of a laptop and changed fuel curves, for some its very easy for others no so much.

what it all comes down to is me making my decision.

Now for the real question I have, and sorry for it being a stupid one.

If I run one of the two efi systems will I still need to run race fuel or a fuel of 100 plus octane, can the system learn a lesser octane and compensate without spark knock?

I only want to spend the money once. but I am getting very excited about efi the more research I do.

any and all comments are welcome, and if there is a different system out there that someone has used with real experience

Kiddart

EFI is great. And no it does NOT require you use fuel of higher octane than the engine needs with a carb. Now if you have a 13:1 engine EFI will not let it run on pump gas either. EFI is not magic it's just a diff way to fuel the engine. All of them will use the O2 sensor to keep the fuel mixture in an acceptable range while they autolearn....After it learns your engine, theres little need to make changes.

when i first bought my holley hp i had buyers "remorse." that has changed. holley is very very customizable. buy the holley. that is all

So your question is , will the efi system recognize using a higher octane on occasion & will the efi automatically adjust timing for the better fuel?

I'm going to go with Megasquirt 3 Pro - which supports everything you listed, but may be more in-depth than you'd like to go. It even supports OEM flex fuel sensors that can determine the ethanol level and blend the fuel tables.

I mostly chose to go that direction because the computer w/harness for a splashproof computer is $1200, which is significantly cheaper, and I can use my choice of sensors, which allows you to use combinations of quite accurate setups. Mine will have all GM sensors short of the Crank position sensor (Ford with 36-1 crank wheel - $51 worth of target and $11 worth of sensors), and a cut down 5.2/5.9 Magnum distributor for the cam sensor. All OE tested sensors and easy to find should they go bad.

I am also going coil-near-plug from an LSx GM engine mostly because they have great spark output, no worries about distributor caps or bouncy timing, and they are very, very cheap. It's just some extra wiring.

A lot of people including myself are going the ms3 route. If you don't mind a little learning curve these ecus can do miles of things beyond the average for a very small price tag in comparison

I just received my FAST XFI 2.0 with the data logger, but not the traction control. It comes with the wide band O2 sensor. Still waiting for the harness. I was originally thinking of adapting my Edelbrock XT harness, but decided to leave it alone so I can use the XT EFI o something else down the road.
It is pretty pricy at $1846.03 + 364.27 for the main harness, and another 127.37 for the injector harness. Plus I opted for the dual sync dist for another $393.92. I'm not sure if I still need the fuel pump and fan harness which is another 69.60?