I now this is a very odd question for a truck LS swapped Camaro. However I am trying to see if it's worth going to the 6.0 liter lq9 versus a 5.3 liter lm7. For thoes who did the swap, what fuel economy do you get? I'm hoping to road trip a 91-92 camaro so it matters a little to me what I get, yes this isn't the thing you do if your worried about mpg. However...

The 5.3/6.0 will be stock, truck everything for now. Paired with a 4l80.

Bonus, hows the fuel economy if i say screw it and throw a lsa supercharger on the engine? (I know its a loaded question. Not looking for exacts)

 

I haven't done the swap you're saying, but have swapped a 305 for a 350, then later, to a 400. That car got the same highway mpg w/all three engines. The CAR should take the same amount of energy to go the same speed on the same road regardless of engine. Set up matters, but adding 700cc's shouldn't make a meaningful impact on highway mpg.

The supercharge may, with it's added drag/belt etc.

 

I agree with Tom that they should get the same cruising MPG. I would say it is realistic to get 25+ MPG with either motor. I am running an LS3 making north of 600hp and my best cruising MPG (with a 6spd and 3.42 rear) was 24mpg. All around normal non spirited driving I average 18-20. Then again, I can also get 0 mpg as well.

 

If youre able to get the tune dialed back under cruise it can drive very well. Ive gotten a best of 28 with a 6 speed with 411s, I swapped a stock 5.3 into a gta with a 60e and 3.27 rear and its gotten a best of 22 untuned, just the factory ecm running as if it was in the truck.

 

I've got a 370 LQ4 80mm turbo 4l80e 3.25 gear in my 9" and I'm getting right around 20-22 mpg BUT when I'm full tilt I get closer to 0.7 mpg. I run a Holley Dominator