[abarnett]

Not in a Chevelle, but my C10. Swapped in a truck 5.3, factory 862 heads, with a Sloppy Stage 2 cam. 585 lift, 228 @ 50. Stock intake and throttle body. Th400 and 373 gears. Running it with Holley Terminator X. Ran it with manifolds for a long time and took it to a dyno to be tuned. Last week switched to long tubes and quieter mufflers. Picked up a lot of grunt from 3000-5000rpm. Was averaging 13mpg when cruising at 60mph with little traffic. My commute has more traffic these days and speeds vary, and my mpg is closer to 10-12mpg. Was hoping headers would help out, but they haven't. I put a couple hundred miles on it this week and transferred over fuel learn table to the base table a couple times to adjust for the headers, and that's gone well. But there must be a way to get fuel efficiency better.

Has anyone put honest effort into tuning for cruise mileage? Initial tune had timing at 36 degrees at WOT, and the same at cruise. Shouldn't cruise want more timing to deal with the lower load? The big block in my Chevelle had cruise timing in the low 50s and ate it up. Cruise AFR is at 14.7, could I get away with 15.0, or higher?

 

[427L88]

t400 and 3.73s maybe the "weak link" for mpg. While i cannot help with AFR tuning, bear in mind the system's limits. My Heavy ass stage 1 LS 6.0 nets out closer to 20, with a 6L80 and lots of OD.

 

[B52bombardier1]

I get 22 MPG on the interstate in my El Camino running 2.73 gears and a nearly bone stock LM7 LS 5.3 liter truck motor with a 4L60E overdrive transmission. Headers are my only mod to the motor.

Rick

 

[Hotwire]

I'm posting in this thread to remind myself to look later today, but I believe your timing is way off. I know I'm at 29 degrees all the way in at wot with 862 on my 6.0.

Have you checked for exhaust leaks? That would trick the o2s into delivering more fuel then needed. Looked at the plugs?

As said above, you're out of gear with th400 and 3.73s. LS motors are better technology and make more power but they're not magic.

 

[69-CHVL]

My last LS swap was a 6.0/th400/3.23 in a mustang and at 14.7 afr on the hwy was something like 16 mpg. This was at 3000 steady state.

around town I could totally imagine 10-12 mpg especially with a stall converter.

 

[jeff swisher]

2 different trucks a 2012 and a 2013 both with 6 speeds and the 5.3. One stock and one with cat back and cold air intake and both get 13 mpg average.
Hook a small trailer with a 1940's jeep to the stock 2013 and hauled it 2 states north and got 8 mpg.

I absolutely hate that small 5.3 Ls engine.
No low end power and horrible MPG in a truck.

Seems these LS engines need to get up in the RPM to make decent steam.
My 350 with 601 heads and a carburetor and TH350 constantly gets better MPG than my buddies 2012 chevy truck.
I ran a 280H magnum cam 3000 stall and 3.00 gears and 750 edelbrock pulling my 20 foot wood deck pontoon with AC on I get a GPS 11.6 mpg. In my 1957 chevy 4 door car. That is not a good tow combo.

My buddies 2018 Ford Ecoboost 3.5 Platinum truck with 10 speed gets 12.1 pulling my pontoon.
So 1/2 MPG better for his new tech truck. I feel I am the winner here.

I think the HP wars took towing and low end power away.
I used to run 455 oldsmobiles in trucks and run J heads I ported and stock camshafts.
Stupid amounts of TQ and always 15 MPG towing or not. NO OD and with a Quadrajet or AFB carb.
The J heads are comparable to a SBC smogger head in runner size.

I think the runners are too large on the LS engine for making good velocity at low speed and the aluminum head does not have the heat of an iron head to help atomize the fuel.

Fuel injection through a plastic or aluminum intake and aluminum head can't atomize fuel as well as a hot iron intake and hot iron cylinder head fed by a carb. That is my opinion.

I think RPM needs to come up to get the fuel atomized in an LS but too much of that RPM hurts MPG.

I may be way off in my thinking it could be as simple as installing a different injector that has the same flow but many more smaller holes to allow the fuel to pass through.

I think there was a Ford injector you could put in the Dodge 318 to get 5 more MPG or it could be the other way around.
It was all about finer mist.

 

[jeff swisher]

I did help a friend build his 6.0 LQ9 and we checked cranking pressure of the stock engine and then took it apart and reground his LQ9 cam using the LT4 hot cam masters which is 218-228 and .492" lift with 1.5 rockers.
We ground this on a 109 LSA and had to buy slightly longer intake pushrods because the lobe got smaller from grinding and pushing it over to 109.

Anyway most cam swaps on the LS I see kill low end TQ but make more top end.
This cam resulted in much more low end power and lots of top end .

It had 15 psi more cranking pressure than the stock LQ9 camshaft.
I always want more cylinder pressure.

 

[abarnett]

I understand they're not magic. I'm not expecting Toyota Corolla mileage. I just expect something more than I'm getting. Was hoping someone here has spent some time actually working with their tune in that cruise area of the timing and fueling tables.

I'm posting in this thread to remind myself to look later today, but I believe your timing is way off. I know I'm at 29 degrees all the way in at wot with 862 on my 6.0.

Have you checked for exhaust leaks? That would trick the o2s into delivering more fuel then needed. Looked at the plugs?

As said above, you're out of gear with th400 and 3.73s. LS motors are better technology and make more power but they're not magic.

862 heads on a 6.0 will bring up compression considerably, they're 10cc less than the 317s they normally come with. That might be the limiting factor on your timing.
We did several dyno pulls and 36 up top was the winner. Any higher and it didn't gain anything. Never had knock running pisswater 87 octane and regularly winding it up to 6200rpm

No exhaust leaks. Haven't pulled plugs since putting in the headers. Before the headers they were all the same and beautiful.

 

[Hotwire]

Sorry man, I know you know what you're doing, I misspoke on the points above. The 5.3 w/ small displacement should get better mpg, but Holley is about hp. I understand trying to tweak their box tunes. Also I am running an LQ4 with the low compression 317 heads, I was wrong on 2 fronts.

Looking over my datalogs I'm 30 degrees up at 6000+, 31-33 degrees cruising normally with little throttle (20ish%), that's most likely stock tune coming through as I haven't messed with that area much. ECM is looking for 14.7 while cruising, bounces around from 13.5 - 15.0. I am using a stock green/blue 0411 ecm and hptuners.

Just remember, you're taching 3k+ cruising with the throttle pedal damn near 50% if not more, work that area in the holley tune, you might be transitioning into wot tuning while just cruising causing mpg loss. Besides pushing a barn door down the road. 😁 I have 4 door handles and rain gutters sticking out in the wind, I can say that.

How do your datalogs look?

 

[abarnett]

All good. If only there was a Quadrajet ECU...
That tune is pretty close to what I'm doing at cruise. If you haven't played with the cruise area on your tune, something my internet surfing keeps digging up is people mentioning factory tunes are contending with emissions as well, which don't always correlate to efficiency. 14.7 is best for NOx emissions, but leaner will improve economy. I'm cruising right around 3200 most of the time, throttle pedal around 25%. 71 is definitely a brick going down the road. At least it looks good!

My thought is that at WOT, cylinder is at maximum full-ness (extra scientific words here). So timing will have a given limit for that. At cruise, cylinder will be a lot less full, and load is lower, so I should be able to run more timing, and a leaner mixture. If this approach works on a carb'd, distributor motor, an LS isn't radically different, the same principles should still apply.

Haven't pulled logs yet. Need to do that, it'll give me more data on what vacuum I'm at during cruise so I can focus on that area a bit more.

 

[396325]

There is a reason that all cars and trucks have overdrive transmissions and lock up converters. I’m guessing that well over half of mpg gains is due to what’s behind the engine and not tuning tricks.

 

[abarnett]

There is a reason that all cars and trucks have overdrive transmissions and lock up converters. I’m guessing that well over half of mpg gains is due to what’s behind the engine and not tuning tricks.

Well aware of that fact, but it's far easier and far cheaper to adjust fueling and timing than it is to drop an OD transmission in.

 

[drivejunk]

I think Gene nailed it in the first sentence of the first reply. On top of that, the "pushing a barn door" effect Hotwire mentioned.

Just the drip rail design alone on a 67-72 Chevy truck has to be like half a dozen ping pong paddles as far as drag. Look how mirrors and windshield angles have changed, between trucks that came with LS engines and what you have one in.

Even a six banger would be thirsty.

Drop the tailgate and the MPG quest, its an old truck with old running gear. The engine has to work much harder than it did in it's original habitat. Cooler styling is the benefit you are paying extra gas for.

IMHO, 5.3 mild modern liters just isn't enough displacement to operate in a thrifty manner shoving 2 1/2 tons of brick wall against a constant headwind but they do well in the trucks LS's were made for. Seven or eight liters is better suited to the job.

My post is entirely speculation but is based on fundamental observations.

Oh but wait, theres more. Is the truck lifted or lowered? Big fat tires or pizza cutters? You could experiment with tires if you are genuinely hunting for clues.

 

[67 Mistress]

Call ANDREW. He’s also known as Dr EFI he does remote tuning is the best message me if you want info he’s great to deal with and very honest. I feel remote tuning as best so they don’t beat the hell out of your motor on the Dyno

 

[69-CHVL]

Not in a Chevelle, but my C10. Swapped in a truck 5.3, factory 862 heads, with a Sloppy Stage 2 cam. 585 lift, 228 @ 50. Stock intake and throttle body. Th400 and 373 gears. Running it with Holley Terminator X. Ran it with manifolds for a long time and took it to a dyno to be tuned. Last week switched to long tubes and quieter mufflers. Picked up a lot of grunt from 3000-5000rpm. Was averaging 13mpg when cruising at 60mph with little traffic. My commute has more traffic these days and speeds vary, and my mpg is closer to 10-12mpg. Was hoping headers would help out, but they haven't. I put a couple hundred miles on it this week and transferred over fuel learn table to the base table a couple times to adjust for the headers, and that's gone well. But there must be a way to get fuel efficiency better.

Has anyone put honest effort into tuning for cruise mileage? Initial tune had timing at 36 degrees at WOT, and the same at cruise. Shouldn't cruise want more timing to deal with the lower load? The big block in my Chevelle had cruise timing in the low 50s and ate it up. Cruise AFR is at 14.7, could I get away with 15.0, or higher?

not faulting you at all to try and squeeze a bit more mpg out of it. But just to put things in perspective, my 07 5.3 Yukon would get about 11-12 around town. So if your close to that with a much bigger cam and gears, I think your in the ballpark.

if you have a laptop hooked up in the car you can add some timing at cruise and see if your tps is less or lbs/hr of fuel is reduced. But that won’t do much for your around town mpg unfortunately.

 

[abarnett]

Added 4 degrees at cruise for a total of 40 from 40-55kpa, 2750-3500rpm. Smoothed that out into the rest of the table. Changed AFR at cruise to 15.0 and drove it about 5 miles. No issues, so bumped afr up to 15.2, still no problems. Looks like it's trimmed a little out on injector duty cycle, and vacuum still hovers right around 50kpa (approximately 14-15inHg).

Not a fan of what Holley calls "cruise" on their basic fuel afr table, it goes all the way up to 80kPa, approximately 6inHg. Think I'm going to get more granular on that to help avoid any pre-ignition on all the small hills on my commute.

This is really fun. Brings some of the hot rodding/tuning aspect into my daily commute, where I can't enjoy the normal fun parts of WOT and tire smoke. Might have to buy HPT to tweak on the 4200 in my Chevelle.

Edit: Went ahead and changed it a bit. So yesterday I'd added timing at idle from 12 to 20 degrees. Checked the learn table, it's already trimming fuel there. Figured it would. Added another 5 just now and it's trimming some more. Think exhaust is smelling less gassy, but could be placebo. We'll run it some more and see.

Changed the afr table to a full adjustable table. Set it to 15.2 at cruise of 2500-3750rpm (36-58kpa, approximately 19-12.5inHg) and blended it out from there.

Left cruise timing at 40, but set that to only be between 2500-3750rpm at 39-61kpa, approximately 19 to 11.8inHg. Blended it out from there.

We'll see how that does tomorrow. Think I'm going to start taking a longer, but less travelled 2 lane blacktop to work. That will take some of the stop and go out of the commute, and honestly I'll enjoy it a lot more, it has some curves and better scenery in it. Won't be true apples to apples on mpg, but I can still use it for a control going forward. Nice thing is the 3.5" screen shows me vacuum, duty cycle, estimated flow rate, afr, timing, etc. Very useful for this type of work.

 

[abarnett]

Filled it up yesterday after work. It was a mixed tank (some before, some after tuning), showed 10.5mpg.

Went ahead and bumped up tire pressure from 30 front 32 back to 35 front 40 back. While I was adding air, it occurred to me that I made another change a few weeks ago; put the rear bumper back on. This is a heavy, old school steel treadplate bumper, probably 80lbs. More importantly, underneath it is a giant scoop grabbing air underneath the truck. Makes me wonder if this isn't the source of some of the newer bad fuel economy. Thinking of tacking in some thin sheet metal to divert air down and below the bumper.

Drove to work and back today, 42 miles. Filled again. 2.687 gallons. 15.6mpg. That was after hearing the first click and doing another one, which only added .04 gallons (these pumps have been pumping really slow lately). One 42 mile trip isn't much of a sample pool, but it's only a 13 gallon fuel cell, and it cavitates on corners when it gets below half a tank, so I'll be filling up frequently. We'll drive it throughout the rest of the week and see how it trends.

 

[69-CHVL]

If you drive this a lot and want to see a real difference how about dropping gears to say 3.42 or 3.23 etc, if you feel the engine has the power for it. If you can get a 500 rpm drop you def get an improvement for fairly cheap.

 

[abarnett]

Unfortunately with the 3.73 gear and carrier, I'm stuck with 3.73 or higher w/o changing carrier.
Drove very conservatively and filled up yesterday and it showed 9.9mpg. Huh?
Drove faster, did a couple 2 gear pulls, and filled up today, 13.8 mpg. Had the hood open checking fluids while filing (all of 2.8 gallons) and my vacuum cap on the intake had cracked and ripped in half as soon as I touched it. Put a new cap on. So we'll see what tomorrow brings.