Mpg
 

Just started driving my LS1 transplant. What kind of of gas mileage are you getting on normal driving? Just curious.

Re: Mpg
 

My 84 Stepside 6.0 gets 18-20 mpg. It has 3.73 and the tune is from a box truck.

My 86 longbed 6.0 gets 16-18 mpg. It has 3.73 and a Van tune. I did just change the injectors this weekend and it seems to be running better.

Re: Mpg
 

A friend I had at my old apt block had a 5.3 swapped C10 rcsb. He said untuned he would routinely be around 24mpg highway. He had the same gear ration my truck had which was 3.23, but I had a 07 rcsb. With a 6/8 drop. I could get 21-22 cruising the highway to work. I am sure with a few tricks he could get the same at higher speeds. His engine did not have the dod.

The truck he had was a 74? with a 4/7 drop roughly with something like 255/60/15 on all 4 corners.

It was kind of weird how much more larger my truck was with out offering better interior space.

If your concerned about mpg. Gear it so the engine is hitting the torque band at the speed you intend to cruise. If your going for big wheels or heavy wheels. Shoot for 2500 or so it is firmly in its power band to drive the heavy running gear.

Re: Mpg
 

Need some more info, trans, rear gear, stock or modified ls1, tire size, vehicle?

Re: Mpg
 

1980 C10. Basically no options. No AC, no radio, no insulation, thin layer of outdoor carpeting, no dash pad. I weigh about 260lbs. Haven't weighed the truck.

flip kit rear, 2.5" drop spindles in the front, worn out stock springs
275/60/17 rear tire (cheap SUV tire)
235/60/17 front tire (cheap SUV tire)

Stock 2006 L59 (5.3L,) dual 2.5" exhaust (mostly, one side the "tail pipe" section is made with some 2.25" piping because its what I had on hand and wanted it done... need to fix it) with 28" Glasspacks, no cross over, turned out before the rear wheels. Stock 2006 Yukon air intake tract/filter housing/etc.

2005 4L80E out of a van. PCM adjusted for the rear tire size/transmission

Stock open 2.76 12 bolt rear.

Currently running semi rich, fuel trims in the -10% range.

Best I've done was 25mpg at 70mph on relatively flat interstate (Maine, so lots of hills, but no mountains)
Normally I get around 19-20mpg around town, with a mix of short interstate and city driving (again, Maine, so "city".) 18 if I get feisty through a tank of fuel.

Runs 74mph through the 1/8. ET is almost irrelevant because the tire was spinning the entire way.

My truck was my daily driver all summer long, so feel free to ask any questions. I'd still be driving it, but need to register it. Its currently my most reliable/leak free/best fuel economy vehicle, in a fleet that includes a Honda Accord. Trans/Rear gear/rear tire size is all wrong - wants to cruise at 50 or 70, not in between, and 1st gear gets me past 60mph at WOT.

Re: Mpg
 

my 6000lb C30 with LQ9/NV4500 and 4.10s with 30in tires gets just over 16 if I keep my foot out of it....

Re: Mpg
 

2001 Camaro ss 5,7 460e all stock, 370 rear end tires are stock 15 inch steel rims all disguised as a 1978 c10

Re: Mpg
 

You should be able to get in the low mid 20's I would guess, depending on rear gear. Open up the intake and exhaust and maybe a slight tune should pick up some...but you'll have to keep your foot out of it.

Re: Mpg
 

4:10's in my 68 LS6/4l60E. Best on the highway at 60 mph with no wind was 23 mpg. Around town I'm guessing about 18 mpg.

Re: Mpg
 

Don't get your hopes up about getting mid 20's in a square body, it probably won't happen. I am getting 17mpg in the city, which is where I do most of my driving, and only slightly better on the highway. My truck is a '71 short bed, 2004 5.3/4l60e with 3:08 gears. I feel like the gear hurts me some in town, but should help on the highway, but on my longest trip I've made in it, 1200 miles of interstate in one day, I only averaged about 19-20, with the cruise set, although I was doing 77ish MPH for a lot of it. :lol:

Re: Mpg
 

My 70C10 with 5.3 and 65e got 21 on a trip recently from Columbia, SC to Atlanta - driving 60ish on back roads. Has 373 and 17" rims.

I kinda figure it would go down driving 80ish on freeway with wind resistance. Probably has same aerodynamics as house going down road.

Re: Mpg
 

There's two significant factors involved in fuel mileage. Height of the truck, and weight of the truck.

These older trucks are typically several thousand pounds lighter than the modern Tahoes and Silverados that we're pulling engines from. This bumps our mileage up a little bit.

More importantly, a c10 sits much lower than a modern truck, which significantly reduces the wind resistance. Lower a c10, and the effect is even more pronounced. Jack up a k10, and the mileage will suffer a lot. The actual shape of the front end is much less important than the overall height of the truck.

Re: Mpg
 

LS trucks didn't get great mileage, why would think they would do better in a truck shaped like a brick?? The newer trucks have better aerodynamics than older ones, that has alot to with mileage. Weight and gearing plays in too....I got hi teens in my brick shaped 4 door tahoe with the stock 205k Tahoe doing 90....

Re: Mpg
 

I disagree with this. There's not much difference in aerodynamics between a 1970's truck and a 2000's truck. Look at a 2012 Silverado HD. There's nothing aerodynamic about it!

Most of the aerodynamic drag comes from the rear of the vehicle. As you drive, a dreadful "windstorm" occurs behind your truck, creating a pocket of low pressure. If you had a hypothetical vehicle with one end completely blunt and the other end tapered out to a fine point, the blunt end should go first. When a vehicle travels through a mass of air, that air splits apart a lot more cleanly than it comes back together again. By having a long tapered rear, you're allowing the air to recombine cleanly after you pass through it.

This phenomenon is not lost on vehicle designers. Every small SUV has a downward slope to the rear roof-line. This is an attempt to taper the back of the vehicle. The new Tesla truck is obviously targeting this tapered rear as well.

I've heard many accounts of folks getting much higher mileage in swapped vehicles, compared to the same engine in the donor vehicle. Most of these cases involved a lowered c10. A few were in slightly jacked k10's though. Enough so, that it's safe to say that the weight reduction made a difference.

Another difference that shows up, is in the engine tune. Tunes are always compromises between Emissions, Economy, and Performance. Many tuners will completely ignore emissions, and focus on the other two.

Re: Mpg
 

Look at the side windows. Notice how on newer trucks they are flush with the body? Not so with squares. Now this doesn't sound like a big deal, but its still turbulence. Not to mention wind noise. I totally agree with the tune tho. I'm not sold on LSs. Maybe when my garage goes up and have room I'll mess with one. Right now it's just easier to pull motor, drop in another, and not have to change mounts, wires, etc. etc.