CCSB Engine Swap Questions

Hey guys. I'm new to fuel injection performance and as such I'm still debating doing something like this to my DD. I've been throwing around ideas of doing a 7.4l or 8.1L swap into my 00 OBS CCSB GMC. The 5.7L makes ok power for it as I don't tow alot, but guys with the bigger engines have me by over a hundred horses and still get the same 12mpg I'm having to deal with.

So, I got to thinking. The 5.7L, 6.0L, 7.4L, and 8.1L trucks all get about 12mpg. With Ford's success with their EcoBoost V6's and the fact that my truck has nearly a 2000RPM stall and 4.10 gears already, I was wondering if a turbo charged 4.8L or 5.3L would do any better on fuel mileage and still make good power. I don't need low end grunt because the torque converter is already stalled pretty high and even the first 5.3L's (LM7?) makes about the same torque numbers as my old 5.7L does.

I'm not looking for earth shaking performance and I've generally been against a power adder on a daily driven vehicle, so somewhere in the 4-7psi range where I won't need to do a lot of internal changes or super building to get it to live, but enough to actually notice the power gain. Since my truck turns about 2000RPM (with converter locked) at 60, I think with what very little I know about turbos at the moment that it could be a lively combo for this truck.

I was just wondering what the more experienced guys thought about it. I'm hoping for some power gains but mainly economy gains but I do understand that if you put more air in, you have to have more fuel. However, guys with 5.3L CC 1/2 ton stuff are getting 17-18, why can't I get a little more from what I have?

Any input or suggestions on this, even if it is a forget about it and go with the big block would be appreciated.

Simply adding a turbo will not increase your MPG. The reason the Ford Ecoboost does so well is it's a smaller engine. That's where turbos do well. They allow a smaller engine to be more fuel efficient at low power demands, and then when it's needed, they can make the same HP as a larger NA engine.

From what you've said I think you would be better off with an NA 4.8 or 5.3 and dropping the gear down a bit. A 5.3 with small Crane cam will make 100+ more HP than your current 350 will and more torque as well, PLUS gets you up around 20mpg.

I realise that the turbo doesn't do it alone, but I wondered if the added efficiency if properly tuned would help.

I've been looking into a 6.2LDoD/6L80E swap since posting this. I need to do some more looking at the transmission to see if my T-case is compatible and to see if a towing mode is available or even possible at this point.

I don't tow a lot, but if I do it'll be a 50hp 4wd tractor or my full body K5 off road rig so the gearing can't be changed. This is all just food for thought right now unless I pop the engine or something.