Old question but..MPG and building a motor?? Tbi to Carb etc.

[olllie]

Looking at upgrading my new purchase 1987 2wd, tbi 350 700r 3.42 rear,

Any input from would be great.

Im going with what should be the original engine. so I think its an L05. Still need to check the numbers. but was told its original... 392000km !!! still runs strong

Stock heads... I'm pretty sure tbi heads off 87's are not too bad, maybe I can find an old writeup on getting them to breath better. Use Mid length headers, I currently have an h pipe and dual out.

Small cam keeping the power low, maybe a "mild thumper" or another comp product. need to read up on cam numbers for this build still. Upgrade the springs to match the cam, rest of the valve train would be refreshed but stock. Bottom end would be gone over but basically stock, stock pan & pump etc. oversize if needed.

Dual plane Intake, 650cfm carb (Qjet?), nice hei (in cap coil) vac and mechanical advance, ditch the the computer. I would use a lock up box for the 700r and use a fuel regulator with the current pumps.
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I did start a mpg log on my truck and I'm seeing about 12.6mpg (us gallon) playing with gap and advance. The best I've seen is 15.8mpg. I do drive hard at times but its in short bursts seem that the truck always smells rich at the pipes but it does have 390k and the valve seals are not doing well.

So big question is with the above build, would my mpg go down or up?? and what kind up power could i expect? guessing on a good day, I now maybe see 150hp (crank) Im just looking to make it a nice "strong" daily driver. But 150hp is not cutting it.

I know tbi can make 300hp but Im not a big fan of early injection and obd1.