Where does the LS engine get it's efficiency from?

[C-10 simplex]

Where does the LS engine get it's efficiency from as compared to gen1, gen 2 smallblocks? They get about 20-21 in a fullsize truck which is pretty good.

You can put, as did the factory, EFI and distributorless ignition on a gen 1 smallblock and it still does not match the LS, so i don't think the bulk of the efficiency is coming from there?

Better tolerances=less friction? Higher compression?

[cableguy0]

ITs no 1 thing. Its the overall package. Roller cam. individual coils for each plug. The latest tech in fuel injection. Tighter engine tolerances. Better head design. Its the whole thing that makes it better theres no 1 thing to point out and say thats what makes it more efficient.

[Super73]

I'd say the biggest things on the mileage:

Head design
Cam Profile
OD trans with lock up converter

[TR65]

I don't pretend to know for sure and I think all the above points are pretty valid.

I would add: Oxygen sensors allow optimum air/fuel ratio under all conditions. Knock sensors allow higher compression and max timing.

TR

[LEEVON]

They're definitely more efficient than older small blocks, but 20 mpg and above has never been a reality for any of the 5 GEN III's and IV's that I've owned or any of my family members (another 10 or so) which all average 14-16mpg. 6.0L's are worse (heavier trucks and trannys) at 12-14mpg. My old 305 TBI engine could do 15mpg all day long. The only full size truck I ever saw 20mpg in was a '92 4.3L / 5-speed. It had optimal gearing and the efficient 4.3L, routinely went 450 miles on a tank of gas.

Contributing factors in the LS motors:

Efficient intakes, heads (huge improvement), ehaust, tighter tolerances, PCMs that monitors volumetric efficiency, etc at a faster rate than before. Possibly the biggest improvement is the individual coils. Waaay better than a distributor.

I'm really curious to see how well my carbureted 5.3L does for efficiency.

They're damn good engines.

[68GMCCustom]

Better breathing heads
more efficient internals - cam, rockers, ring tol., cylinder honing, etc.
lower cruise rpm's with an o/d trans.


my '01 Sierra C3 (4dr ext. cab SB) with 325hp 6.0L LQ4, 4L60eHD, full time AWD, and 3.73 gears averaged around 12-14mpg but could get 17-18mpg on the hwy.

[glock35ipsc]

My old 2003 5.3L ECSB eeked out 21 mpg on the highway on the last road trip I took it on, it averaged 18-19 going to work and back. I got the same with and without the blower, as long as I kept my foot out of it! It had a W4M tune along with bolt-ons.

The 5.3 in my 85 gets 18-19 normally, and 20-21 on the highway on the last 3 road trips I've had it on. It has been dyno tuned.

The best I ever saw out of my 2002 1500HD 6.0L on a road trip, not pulling, was 16.5. Average was 14, and pulling was 10-12. It also had a W4M tune along with bolt-ons.

I love these engines so much I don't ever see myself building or installing another Gen I or II into anything.

[Super73]

My wifes awd tbss gets 18.5 on the freeway.. To say 20 isnt possible is just wrong. Bone stock, no, but with a little tuning, electric fans ect, it's possible. I will tell you on 87, it only gets about 14.5 on the freeway.

[68GMCCustom]

we run nothing but 93 octane in our TBSS, and have never gotten better then 17mpg or so with it. Those 4.10 gears have as much to do with it as the aerodynamics...or lack of.

Next June our warranty ends...and it will get dual electric fans. Have you ever monitored your TBSS's trans temp? I've got an Aeroforce scan gauge and have seen temps over 215* depending on length of trip. It just climbs...the longer you drive like the cooler isn't doing a thing. Our trans was rebuilt once already (heard that story more then once)...guessing its not just the LS2's power thats killing the transmissions in these things.

[TR65]

For the past 10 years or so I have averaged from 21-23 mpg driving back and forth to work in Corvettes (34 mi/day, 22 mi highway, 6 mi urban, 6 mi suburban). My old C5 Z06 averaged 26-28 mpg on the highway.

So the goal for my 65 C10 with LS2 was 20+ (same gearing as the Vette, 1800 RPM @ 70 mph). After several weeks of driving, it is close to 20. I am making careful measurements so in a week or so I should have some stable numbers to report.

One thing I found out is that it takes at least 4 times the power to push our trucks through the air than a Vette, 2X the frontal area and 2X the drag coefficient. The difference in coasting distance between the truck and Vette is amazing.

I understand that a Tonneau cover is good for 1.5 mpg or so. I am looking for a good one.

TR

[LEEVON]

I'd like to see a bonified 20mpg in a truck with mixed driving. It's another thing to drive 100 miles on the freeway and monitor the instant mileage. I've had trucks with all the goodies, even had one with a mileage only tune. My current DD has 3.23 gears and 4.8 and my mileage never tops 16, even on long highway trips. I'm sure it's largely driving style but I just don't see a REAL 20mpg.

I rode in a modified Honda hybrid with a couple of guys who were pioneers in the solar/electric car competitions and they are "hyper-milers". It was very, very interesting to see how they drive and what they monitor. It's taken to an extreme. I could never drive that way though.

[Super73]

Average mileage her TBSS get's about 15.8-16.2.. But, I drive it once or twice a week.. I'm sure it'd be a pinch better it I stayed out of the drivers seat

I towed my 63 to the track with the TBSS the last time I went. It was HOT out (for us that's over 80 degrees). When climbing hills with no trans cooler just the factory radiator trans cooler, Trans temps went up to 230. But, I have modified the tune where the verter is locked under little to medium loads. If there is nothing being towed, it stays in the 180-190 range as does the coolant. I'd like to put a real trans cooler on it.

[Ratpowerd67]

if i remember right, the rings are low tension?

[68GMCCustom]

I think this write up explains it.......

motown_ls_crate_engine

[glock35ipsc]

Originally Posted by LEEVON

I'd like to see a bonified 20mpg in a truck with mixed driving. It's another thing to drive 100 miles on the freeway and monitor the instant mileage. I've had trucks with all the goodies, even had one with a mileage only tune. My current DD has 3.23 gears and 4.8 and my mileage never tops 16, even on long highway trips. I'm sure it's largely driving style but I just don't see a REAL 20mpg.

I'm sure driving style plays the largest role in mileage. Mine is a genuine 18-19 driving back and forth to work, which is about 16 miles of 'highway' and 2 miles of in-town roads. My 85 doesn't have the instant mileage thingy , but the calculator doesn't lie. Practically the same with my old 2003 ECSB 5.3. But yeah, between here and Denver it's 20-21 based off the refill gallons and actual miles driven.

A board member in CA recently drove his 6.0 GTO (370 hp dyno'd at the tires) out to Colorado and IIRC, got around 26-28 (actual, calculated) on the way out.

[68GMCCustom]

another things is where you live. Here in Dallas (and a lot of TX for that matter) in relatively flat...and easy to get reasonable mileage if you keep your foot out of it. If you live at a high altitude, or in an area with lots of elevation changes, etc....would impact your mileage.

[glock35ipsc]

FWIW, I filled up today:

Odometer at fill-up today: 76,121
Odometer at last fill-up: 75,888
233 miles / 11.677 gallons = 19.953

I'll go ahead and round that up to 20.

[Clyde65]

Cheater! HA, Ha, that is good mileage, mostly hiway?

[glock35ipsc]

Lol, mostly highway. I live in a rural area, so my drive to work is about 6 miles of county roads at 60-65, 10 miles of interstate at 75, and a couple miles through town.

[Thealien]

Best I'm getting is 15 but that is no highway. And I am having fun driving it?

[C-10 simplex]

PT.2:

If the engine was outfitted with all forged rotating assembly---namely pistons, would it still get the same mileage?

[99-LS1-SS]

Originally Posted by Super73

I'd say the biggest things on the mileage:

Head design
Cam Profile
OD trans with lock up converter

This ^

[swb85]

Originally Posted by C-10 simplex

PT.2:

If the engine was outfitted with all forged rotating assembly---namely pistons, would it still get the same mileage?

All else the same, yes. Piston material has no bearing on mileage.

[BR3W CITY]

forged pistons would be more rotation mass, so TECHNICALLY it would TAKE more power to turn the assembly. That being said, I'm not sure you'd notice the difference. AND if your running a forged assembly, your looking to build big power and don't care about mileage lol

[5150.4.67]

I believe most forged performance pistons for LS engines are lighter than their cast brothers these days......
Agreed, won't make any noticeable difference in efficiency.