almost at 140,000 on the ol' LG4 now and i was wondering what my MGP are at cause im about to head on a road from southern cali to denver colorado. The only mod's are a open element air cleaner with an airhog high flow air filter, 3" high-flow cat, 3" mid-piping, and a 3" single in / duel out flowmaster......... any ideas?!?!

 

Yup...

1. Fill up the tank to the top.
2. Reset trip odometer. If its broken, record actual odometer milage.
3. Go drive granny-like until about 1/4 of your tank is left.
4. Fill up to the top again. Use the same station, even the same pump if possible for the most accurate results.
5. Time for math... Milage on trip odometer divided by gallons needed to fill it up equals MPG.
6. Don't forget to reset the milage so you can measure again on the next tank.
7. For a more accurate number, repeat 5 times and average results together.

Nobody can guess your milage. The amount of variables, including how you drive, condition of engine, and current state of tune makes it impossible to lay down a flat number of what you will get.
The gearing(which apparently your to lazy to figure out) in your axle is another of the dizzying amount of factors.

I've got an LO3 with 176,000 and similar mods as yours. I get about 20 mpg combined. And I've got a pretty light foot in that car. I gotta save my gas money for flooring the other, faster car.

I'd be shocked if you could break 23mpg. But that's just my opinion, its possible to do better, but not easy.

 

20 mpg is what I get on the highway at about 80 mph.

 

Burn reg. gas. New plugs, 70-80 MPH. 22 + mpg. Highway. That's what I get, And my cruise doesn't work.