Fuel milage poll

[85burb]

Ok so i want to see what kind of milage the 6.0s are getting in bigger vehicles. I have a 6.0 with 700r4 and 4.10s with 33 and am getting 6-8 with mixed driving. It has carb on it and was thinking of going to efi. But if i only will pick up a few mps it does not seem worth it to me. Only 6.0s too i know the little motors do great on gas. And Bigger trucks. Thanks.

[Clyde65]

burb, is yours an LQ4 or LQ9?

[BR3W CITY]

a lot of factors at work on this, and I'm not sure how much has to do with it being a 6.0
Carb will be slightly less mpg than efi, the taller tires and the additional rotating mass also will cause mileage drops. I also see your are running 4.10's to turn those big tires, also a mileage killer. I think any of the lsx engines in your combo (big truck, 4wd, big tires, steep gears) will fall right into the same ballpark. Hell my mild 355 didn't see a ton better and thats on a 2wd truck half the size.

[Super73]

Well I have 2 vehicles with late model motors. I did not add to the poll but could if you want.

Wife drives a 2007 Trailblazer SS AWD. It has an LS2 in it. Prior to installing an Electric fan, it was getting an average of 14.4-14.7mpg and the best long trip drive was 15.5mpg. After the fan swap and some shift point settings/converter lock up adjustments, it averages 15.5-16.0mpg and has knocked down the same long trip mentioned above at 18.6mpg. Here TBSS weighs 4,900lbs with out driver and a half tank of gas.

My 63 with the 347/4L80E, big cam, 4,500 rpm verter, 4.56's and 30" tire was getting 12.5-13mpg on the freeway. Truck at it's lightest weighed in at 3,525 but I didn't really notice a mileage change from the 3,900 lbs it once was. I'm not too sure with the new 418/powerglide combo.

[Clyde65]

burb, why are we even discussing this? if you wanted MPG's you should have gotten a Honda....Opps, did that just come out of my mouth? dont shoot me yall!

[85burb]

I have to drive it everyday now and was trying to decide if efi would be worth the money to swap or not. Not looking for 30 just double didgets would be nice. It is a lq4. I work 12 miles or so from my house so i use like 3 gallons a day. Tank i only use 18 gallons out of the tank so that is only about 6 days of driving bettwen fillups. I am trying to not have to swap burb for wifes 98 avalon. Gets over 20 mpg but after driving my burb it so such a let down to drive the avalon....

[85burb]

With the set up i have it is 1500-1750 rpm locked up on hiway speed between 65-75 mostly 65. How ever fast i have to go to keep up with the morning 5 or 6 cars on hiway. In town it is at like 11-1200 rpm at 45-50 or so. Speedo is way off. When it says 55 i am infact 65 mph....Ask me how i know

[Super73]

The number one killer for milage is wind resistance. Going to be hard to overcome the frontal area of your Burb with out major changes.

Number 2 is rolling resistance. Tires and any other friction cuased by the wheels turning.

RPM believe it or not is less of a factor.

If your carb is tuned well, going EFI will not gain you a ton. My advice, spend $200 on a wideband and dial in the carb for part throttle driving (high 14 to low 15 AFR) and it is there also to aid tuning WOT.

Just my 2 cents worth.

[85burb]

I have a wideband analog(sp) gauge. Crusein it does 13-15 depending on the cruse speed. But if i just tip in the throttle like when going down hill to keep speed but not accel it is way over to 9.9-10.8 to 1. If i give it gas on the hiway it goes lean like 16-18 to 1 then recovers to 14 or so. My 670 street avenger has 69 mains, 33 pump nozzel and factory rear jets in it. I am not sure about the timing thing with the msd box working all that i have the number 2 timing pill in it right now. Has i think 22-36 degrees of timing in it i think. The vaccum advance is wierd also. Not sure what it needs to be set at so i left it alone.

[matthew20061]

With my Silverado SS truck I daily drive with AWD and 4.10 gears and a stock LQ9 I get right around 12.5 to 13.5+ in the city depending on how easy I am on it. Just to give you an idea.

[Super73]

Originally Posted by 85burb

I have a wideband analog(sp) gauge. Crusein it does 13-15 depending on the cruse speed. But if i just tip in the throttle like when going down hill to keep speed but not accel it is way over to 9.9-10.8 to 1. If i give it gas on the hiway it goes lean like 16-18 to 1 then recovers to 14 or so. My 670 street avenger has 69 mains, 33 pump nozzel and factory rear jets in it. I am not sure about the timing thing with the msd box working all that i have the number 2 timing pill in it right now. Has i think 22-36 degrees of timing in it i think. The vaccum advance is wierd also. Not sure what it needs to be set at so i left it alone.

My 63 when tuning the 347ci motor for better street manners, it ran best with a part throttle AFR of high 14 to low 16. Now this motor had a big cam in it with a lot of overlap for it's cubic inches and I'm sure there was a lot of reversion. I'm assuming the leaner AFR help compansate and reduced the poluted intake. But I found that it was not an issue running at low 16 to 1 for very light load. For medium load I was running high 14 to low 15. For high load (WOT) 12.6-12.8, but that doesn't save mileage.

If you can't get the carb to clean up, then EFI is probably a good choice. Since you can adjust AFR based on manifold pressure and RPM (with a powere enrichment at a given RPM) you can really nail the AFR where you want it. The other thing is there is DFCO (Deceleration Fuel Cut Off) that you can enable once you get everything else where you want it. Not only does it cut fuel down big hills, but it also works a little like an engine brake in doing so.

Here is a screen shot of HP tuners to give you an idea of how the fuel map works.

First one shows 3 different screens:
Power Enrichment table (RPM)
Primary VE ie Fuel Map (KPA/RPM)
VE Multiplier (Throttle/RPM)



What trans do you have in the truck? I'm assuming not an 80E. If you are going to add EFI, you might consider adding an OD trans at the same time since the controller is already there.

[85burb]

Oh sorry it is the engine and trans in my sig. A 700r4 with locking converter. It is semi fresh. Had it in about a year and half but only drivin it daily past 6 months. Dont want to change it. Spent way too much on it to change it and i really like it. Shifts hard when i get on it and firm when i am not. My motor does not like any leaner then about 15. Idles at 12.5. Runs like carp leaner. Smell like fuel idleing but i am told it is due to the cam. Am not sure how to lean up the rich section cause it is when the throttle is just bearly open at all. Like if i am going under 5 mph in parking lot. But if i give it more it leans to 13-14. Does not smoke at all. Is not fouling plugs. Not reallly sure on carb fine tuning.

[Arekusu]

I'll just throw out a carbed number out there for you.

350 sb light cam
MSD Al6 box and msd distributor
3.73 rear
TKO 500 Transmission
Holley 650 cfm spread bore carb
26'' tire

Best highway mileage at 65mph = 23


There has got to be a way to get those injected engines better numbers.

Alex

[CamaroChris]

My parents 02 chev ECSB with a camper gets 18 with 4.10's there has to be something wrong here. My ls1 camaro gets 26 on highway with a4 and 3.23s I just started my 6.0 swap in a 86' burb. I'm hoping for better then 6-8 miles. thats like old school 454 numbers. Check your tuning again maybe.

[dznucks]

I have a wideband analog(sp) gauge. Crusein it does 13-15 depending on the cruse speed. But if i just tip in the throttle like when going down hill to keep speed but not accel it is way over to 9.9-10.8 to 1. If i give it gas on the hiway it goes lean like 16-18 to 1 then recovers to 14 or so. My 670 street avenger has 69 mains, 33 pump nozzel and factory rear jets in it. I am not sure about the timing thing with the msd box working all that i have the number 2 timing pill in it right now. Has i think 22-36 degrees of timing in it i think. The vaccum advance is wierd also. Not sure what it needs to be set at so i left it alone.

I am no expert but I just finished teaching myself how to tune my demon with a A/F gage and a vacuum gage. I think you can squeeze out a few more mpg's by fine tuning that carb.

You say your primaries are 69 and the secondaries are stock. Did you raise or lower the primaries? what were they stock? What is your idle A/F?

When you say you give it gas on the highway and it goes lean to 16-18, is this when you just barely tip into the throttle or it goes that lean before the power vavle and/or secondaies open up?
Do you know your idle vacuum reading? might want to swap your power valve to a 8.5" or 10.5" if you have a high idle vacuum to cover that lean spike.

What happens at WOT? are you pig rich or is it perfect.

Here are some target numbers that Holley recommends when tuning with an A/F gage. I was getting numbers like you until I got my power valve, accel pump cam, and secondary spring right. now i get numbers like these.


Stock and Moderate Performance Engines
Idle and Cruise: 14:1 to 15.5:1
Moderate Load: 13:1 to 14:1
Wide-Open Throttle: 12.2:1 to13:1


Large Cams and Race Engines
Idle and Cruise: 13:1 to 14:1
Moderate Load: 12.5:1 to 13.5:1
Wide-Open Throttle: Typically 12.5:1 to 12.7:1 at peak torque and 13 to 13.2:1 at peak HP

[dznucks]

One more thing to keep in mind when fine tuning a carb, you need to keep it balanced front to back and side to side.

If you raise or lower the primaries, you need to do the same with the secondaries. All your idle mixture screws need to be the same number of turns out from fully seated as well. If you adjust one screw a fraction of a turn, adjust them all the same amount.

I did not do this when i first started tuning and i wasted alot of time getting wierd A/F numbers.

[85burb]

Originally Posted by dznucks

I am no expert but I just finished teaching myself how to tune my demon with a A/F gage and a vacuum gage. I think you can squeeze out a few more mpg's by fine tuning that carb.

You say your primaries are 69 and the secondaries are stock. Did you raise or lower the primaries? what were they stock? What is your idle A/F?

When you say you give it gas on the highway and it goes lean to 16-18, is this when you just barely tip into the throttle or it goes that lean before the power vavle and/or secondaies open up?
Do you know your idle vacuum reading? might want to swap your power valve to a 8.5" or 10.5" if you have a high idle vacuum to cover that lean spike.

What happens at WOT? are you pig rich or is it perfect.

Here are some target numbers that Holley recommends when tuning with an A/F gage. I was getting numbers like you until I got my power valve, accel pump cam, and secondary spring right. now i get numbers like these.


Stock and Moderate Performance Engines
Idle and Cruise: 14:1 to 15.5:1
Moderate Load: 13:1 to 14:1
Wide-Open Throttle: 12.2:1 to13:1


Large Cams and Race Engines
Idle and Cruise: 13:1 to 14:1
Moderate Load: 12.5:1 to 13.5:1
Wide-Open Throttle: Typically 12.5:1 to 12.7:1 at peak torque and 13 to 13.2:1 at peak HP

I went up from 65 to 69 on the mains. Think it idles at close to 16-18 in park. Not sure about in gear. My engine will not idle leaner the about 13.5 deff not 14 or 15. My cam wount alow that. WOT is 12-13 and cruise is like 9.9 to 15. It is all over depending on how fast i am going. If i am only steping on peadle lightly and going 5 mph it is 9 something. Same if i am going down hill and just ever so soft toutch the peadle to keep speed steady and not accel or decell it is 9 or so. But if i push it little more it goes to 13 or so. Idle and wot and most cruse air fuel is ok but it is that 9 to 1 that kills me. Also smell like fuel at idle i guess due to cam. But it is not even that big of a cam.

[dznucks]

some of what you are seeing is normal. when the engine is braking the vehicle, your butterflys are closed but the engine is still pulling fuel and when you slightly tip into the throttle it will pull more fuel...going rich on your gage.

i also think some of your problem is that you made such a big jump in primary and didnt move secondary jets. The secondaries provide fuel at idle and start opening sooner than you think. With your engine relying so much on the primaries, your front cylinders will be richer than the rears. this also will affect the transition of you secondaries giving you funny fluctuations in A/F.

I would drop two sizes in the primaries and go up two in the secondaries and see what happens.

Also make sure all your idle mixture screws are the same number of turns out. Mine, for example, are all just over 3/4 of a turn out from fully seated.

How much of your secondary transfer slot is exposed? it should be slightly exposed.


This is a great read on tuning...
http://www.bob2000.com/carb.htm

[85burb]

Originally Posted by dznucks

some of what you are seeing is normal. when the engine is braking the vehicle, your butterflys are closed but the engine is still pulling fuel and when you slightly tip into the throttle it will pull more fuel...going rich on your gage.

i also think some of your problem is that you made such a big jump in primary and didnt move secondary jets. The secondaries provide fuel at idle and start opening sooner than you think. With your engine relying so much on the primaries, your front cylinders will be richer than the rears. this also will affect the transition of you secondaries giving you funny fluctuations in A/F.

I would drop two sizes in the primaries and go up two in the secondaries and see what happens.

Also make sure all your idle mixture screws are the same number of turns out. Mine, for example, are all just over 3/4 of a turn out from fully seated.

How much of your secondary transfer slot is exposed? it should be slightly exposed.


This is a great read on tuning...
http://www.bob2000.com/carb.htm

I understand kinda the rich going down hill but just putting threw the parking lot i dont understand why it is so rich. It had same exact problem with the factory jets. The only thing the jet size cange did was making it more drivable. With it factory it would be way over on the lean side anytime i would put any more throtte in it it would pop and buck. I have not played with the secondarys at all. So i cant tell you how much of the slot is showing. I have made extra sure that the idle screws are exactly the same out.