I'm basically a very sick man, and my illness has metastasized into an obsession with inappropriate uses of forced-induction LS motors. My daily driver is a 1979 Olds Delta 88 Royale Brougham coupé with a TVS 2300 blower on a 30-over LQ4 with a 4L80E transmission and a 3.73 Eaton True-Trac, but it's too rowdy for road trips with the family.

Now, like any allegedly grown-ass man, I need a FAMILY CAR. My fantasy is a 1990-1996 GM B-body wagon - a Caprice Classic, Roadmaster, or Vista Cruiser. It doesn't need to be fast, but I'm wondering what kind of fuel economy I could get with a well-designed build. I think that de-stroking an aluminum 5.3 with a 4.8 crank, adding a turbo that is spooled by 1500 rpm, and running really tall gears would be the way to go, but I don't know a lot about turbos. Anyone have any ideas? Am I on the right track?

 

Why destroke? If changing cranks, i'd stroke the the 5.3 for some low speed torque. A couple comments.... I don't see the economy thing panning out as most any properly tuned forced induction engine runs with a higher bsfc than na. If you just want to turbo it, that's cool, but enough boost at 1500 rpm to make a good amount of torque is going to be tough on engine parts, especially as you get near peak torque. Not saying it can't be done, but it has it's own challenges, and will require a proper tune. I'd also want a 4 speed (or more) trans with lockup.

 

Spool by 1500? you can always swap in a dirtymax or chummins lol. Fuel economy you can always swap in a turbo ecotec 2.0 lol. If you keep your boost low on the 4.8/5.3 and not drive it like you stole it all the time(I know it’s tough) the fuel economy shouldn’t be bad

 

A very mild build with a tiny economy cam, 8 or 10 speed trans and a turbo that doesn't spool until the top end for the fun factor would be a better bet.

Boost is artificial increase in displacement, a 4.8l at 14.7 psi is acting like a 9.6l, and consuming equivalent fuel plus about 10% for BSFC. You need to figure out how to use this to your advantage for economy. You want to be cruising with the smallest displacement possible, then use the boost to make the engine act bigger for power when you need it.

Turbo + small displacement and lots of gears = good economy.

Turbo + V8 and 4 speed = mediocre to bad economy.

Look at the current truck engines to see where you can optimize. The Ford 2.7l v6 TT is a good example, tiny engine with enough boost to keep the truck moving, 10 speed transmission. They will get over 30mpg highway if you keep out of the turbos and keep it just barely in 10th (around 60mph), still get around 25mpg at 75mph, but still produce enough torque to warrant a 9000lb tow rating.

 

Thanks - you guys definitely know this better than I do.

I figured destroking, and reducing displacement, would make for more efficient highway cruising - same reason I thought of a 5.3 over a 6.0 or 6.2. The 5.3 makes 50 more horsepower than the original 5.7, and the same peak torque, with 25 fewer inches to feed and a more efficient engine architecture. Any idea what kind of economy gain I'd see from swapping in a stock but well-tuned 5.3 Or 4.8, for that matter?

 

Gains should be pretty good, your getting a significant upgrade in cylinder heads, intake path, engine management, possibly a significant transmission upgrade depending on which year you select. The extra meat in the curve would allow you to run taller rear gear without being gutless.