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Discussion Starter #1
I am fairly new here and I am sure this isnt the first time the question has been asked, but I looking for ways to improve my milage on my 04 Silverado 2500 HD, 6.0 gas. Here are some of my low cost ideas:

K&N air filter - how much improvement?

tonneau cover - clean up the air flow, how much is it good for?

4.10 -> 3.73 gears - towing not a huge concern and wont affect it anyway.

Also with the gear swap, do you change out the front axle as well? Its a push botton 4wheel drive system. This is the 1st 4x4 I have owned where I considered a gear swap. So if it sounds stupid, forgive me.
 

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There is pro's and con's to K&N filter, I'm not convinced the flow difference is worth it. I've heard it lets more contaminates in and leaves a messy residue in there. Tonneau cover wouldn't hurt, soft/hard. Gear swap would be at a hideous cost. No you wouldn't have to change axles though.

Exhaust flow, chip/programmer might be better options IMO
 

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Tire pressure-40 psi-narrower tires

I'm new to Chevy trucks(98 suburban), but have given FE lots of thought.
K&N-or a CAI of any type won't increase part throttle FE in a modern vehicle.If it does decrease the resistance thru the air filter, the throttle plate just closes more so you get the same total resistance to flow.
Almost the same story on exhaust changes-different reasons-change the resistance,and you foul up the part throttle exhaust tuning.
At 70 mph, you probably only "use"about 50-60 hp-not even 20% of wot.
Your best bet is to work on rolling resistance, weight,and aero stuff-GM has done a pretty good job on the motor efficiency-etc.You can't improve the intake,exhaust tuning in respect to part throttle FE.
1)Tire pressure. Go to 40 PSI-mine rides so soft that 40 psi causes a couple more rattles, but no loss in comfort.
2)When you get new tires,check CR for rolling resistance.Soon, tires might have that on the tire-like a load rating. Consumer Reports does tire reviews,and they measure it.
3) You can go to a thinner tire.It could adversely affect braking, handling,so...
4)You can go to a thinner,taller tire.This will effectively give you taller gearing,fewer RPMs.However, it will raise the vehicle, increase the drag a bit.At lower,city speeds, it might improve FE, but at hy speeds, it will decrease FE. Pass on this.
5)Go to taller gearing-yes, it would have to be ft and rear.It would cost a lot-but it would work-.You might get 1/2 mpg at hy speeds-19 mpg at 65mph instead of 18.5mpg.
6)Drop the truck a couple of inches,and skirt it a bit.You could probably fabricate some sort of spring loaded skirt/spoiler so it would still have reasonable ground clearance.This would be worth something-a couple of percent maybe-at hy speeds. Lotta work,and the truck is less capable because of the loss of ground clearance.
7)Go to lighter wheels/tires. Centerline Forged wheels in the same size as stock,are generally 5 lbs less per wheel relative to OEM aluminum wheels,and 11 lb less than an OEM steel wheel(yes,I weighed them)..This will improve city mpg, but maybe not enough to measure easily.I have seen a few reports of failed Centerline wheels.It is hard to beat OEM for reliability.
Bottom line, only the tire pressure is for reasonable folks.The light wheels aren't a bad idea if you are going aftermarket anyway.
Changing the gearing will work, but pricy-maybe $3000 to pay someone to change ft and rear.
Some FE folks pull the rear seats,dump their spare,turn the ignition key off and glide up to redlights(no kidding,they claim they retain a bit of braking for 3-4 seconds-;steering -not for me)
Pulse and glide is a FE trick the hybrid types use,and it works on normal cars also.You basically briskly accelerate up to about 5 mph above the speed limit(none of this driving with an egg under your foot crap).Then just completely let off the gas,and let it glide to about 5-10 mph under the limit-repeat,repeat... It works. My 98 seems to glide forever.At 30 mph it will glide for maybe 40 seconds before it drops to 26 mph.The auto trans just doesn't allow any engine braking to speak of.Don't put it in N-some folks do, but it doesn't seem to matter,and you might accidently slip it in R(not sure if it will actually try to shift into R-probably not-lotta auto prevents on modern vehicles)
Tire pressure,and Pulse and glide are about it for practical purposes.Sorry to run on.
Luck,
Charlie
 

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Mythbusters did a special on increasing fuel economy with pickups by changing the bed configuration. Nothing except for the "net gate" type tailgate increase fuel mileage any from the stock tailgate being up. Dropping the tailgate decreases fuel mileage because there is a pressure differential that occurs and creates a "continuation of the cab" to the wind, keeping good aerodynamics. They didn't include a camper top into the test, but I suspect it would have given similar results to the tailgate up. They did test the tonneu covers, and they didn't help any....
 

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Crawdaddy Cableguy-right-tailgate,weight

Crawdaddy and Cableguy are dead on. The dropped tailgate idea just doesn't work, but ANY WEIGHT LOSS is free FE.Via eyeball, it sure looks like the dropped tailgate should work, but you just can't use your eyeball to judge complicated aerodynamics.
One idea,I didn't mention, is a chin spoiler.I've noticed that many of the older Suburbans have factory chin spoilers.I'm sure they aren't their for looks-they must work.Now, on a work truck you really want your ground clearance.Maybe you can install a fairly tall/deep spoiler(within about 4" of the highway), but make it spring loaded-in several sections,so it doesn't hurt ground clearance.
GM tends to make their trucks lower than Ford,and Dodge to begin with-a big plus in my opinion-but more chin spoiler to keep the air from going under the vehicle at speed would probably be worth a bit.
Any weight you can lose-on the truck, or the pilot, is free FE-just like Cableguy says. Some folks go so far as to never carry more than 1/2 tank of gas-save >100 lbs.This is kinda inconvenient,especially in hurricane season,so I don't do it.It will work. City mpg is pretty much inversely proportional to weight-drop 5%-FE improves 5%.This is why the older Tacomas-2800 lbs-got almost twice the FE(20 vs 12 in the city) of big V-8 trucks(5000 lbs).Toyota doesn't have any motor magic over GM(probably none in respect to V-8's-Toyota does make better 4 cyl, but Honda is even better). Toyota did make a light small truck with an efficient 4 cyl(better and lighter than the GM 4 cyl).Now the Toyota Tacoma weights about what the Colo weighs-the FE are closer.GMs doesn't expend much effort on small gasoline motors-they don't make any money on them.Overseas they make,and sell very efficient small diesels(traded them to Honda for Honda's V-6 not long ago).Maybe they will import those small Diesels.Right now GM doesn't think they can sell them at a profit(their little mini mini van-the Zafira-gets 40 mpg hy, but it costs about $28,000- modern 4 valve diesel -it is about the size of Mazda's 5 minivan-3 rows,2 seats)
Weight is king in the city.
Tire pressure, weight loss,and pulse and glide are about it for practical FE mods.
Luck,
Charlie
PS I have spent way too much time trying to outdo the factories.It is close to impossible while still driving like a normal person(P&G),and not taking a comfort hit(tire pressure)-or eating less!I'm guessing your 2500 is stiffly suspended and 40 psi won't hep the ride quality. Suburbans are so softly suspended that 40 psi is no problem-they ride like a huge 1968 Caddy-soft,and smoth!
 

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Discussion Starter #7
Thank you guys for the info and advice. I knew about the tailgate down theory. I keep it up. The tire pressure is up there I belive 60 psi in front and 80 in the rear. So it rolls pretty well. I am going to put a tonneau on it, I need one any way, if it helps it helps if not oh well. I didnt buy this thing for its FE, but it'd be nice to "beat the system" and improve it a little. Thanks again for your time.
 

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Forgot About 3/4 Ton Tire Pressure

I forgot about those 3/4 ton trucks ride on very high tire pressure-and 6-8 ply tires?-already.Not much you can do there-you already ride on bricks.
The pulse and glide really works,and it doesn't slow you down in the city.
Just lay back at red lights-let the guy in frontget about 8 car lengths,then gun it up to maybe 5 miles faster than his expected speed-Lift completely off the throttle and glide until you have lost about 8 mph-repeat,repeat.
Luck,
Charlie
 

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Discussion Starter #9
Yeah Charlie, the TP is up there. I am pretty easy on the gas so it looks like I am living with the 13mpg average.

Jamie I have the weight down, 150#, lost about 13# from beg of summer. Alot of water weight. :lol: cutting lawns in 90 deg heat
 

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I have a 2007 Classic Silverado HD 2500 with the 6.0 and 4.10 gears...4x2. From day one I got 14.4 to 14.6 mpg....

First if you cahnge gears to 3.73 you absolutely have to change both axles, otherwise the front wheels would be running faster than the rear...ugh!! The coust is between $1200 and $2000 to switch both axles gear sets...ouch!

THe difference in mpg is almost nothing and you do lose towing power.

I added a Flowmaster BB series 50 muffler...love the sound, but gained ZERO performance or mpg....at least that I can tell....still gets 14.4 - 14.6

I then added an AME Brute Force dry CAI - sounds throaty under WOT, and in combination withthe Flowmaster, I actually did pick up about 1/2 mpg....of course, this might be attributed to the fact that I also switched gas stations and now use QT fuel instead of BP....dunno...now gets 15.1 - 15.5 wow!!

Then I went from the puny 245x75x16 tires to 265x70x17 (on chrome Hummer H2 rims)...difference in tire height is about an inch...looks great, handles a little better, power does not seem to change, but lost 1.5 mpg...no getting a pretty consistent 13.6 - 14.1.

These engine are tuned pretty tight from the factory, and there is not too much more that can be done to affect much, short of adding a supercharger or turbo.

I have talked to a lot of folks that have the programmers and most agree that $300-$500 was pretty much a waste especially when you have to use premium (@ $.30 a gallon more) to get the full effect from them...
 

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Pardon me, but I disagree on tonneau cover...

I had a '93 ext. cab with 5,7 and now a 2000 ext cab with 5.3 and 125,000 miles. I put tonneau cover on both trucks and can tell you without hesitation it accomplishes two primary objectives:

1. Gas mileage did improve on both trucks; 1.5-2.0 mpg at 70 mph. I tested this with the '93 in identical conditions on a 250 mile trip one week apart. First trip in stock condition and second trip with tonneau cover.

2. Improved crosswind stability. Very noticable reduction in crosswind effects on truck with tonneau cover. It prevents wind from entering bed and pushing on side of truck.

I have the Access soft cover.
 

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I am fairly new here and I am sure this isnt the first time the question has been asked, but I looking for ways to improve my milage on my 04 Silverado 2500 HD, 6.0 gas. Here are some of my low cost ideas:

K&N air filter - how much improvement?

tonneau cover - clean up the air flow, how much is it good for?

4.10 -> 3.73 gears - towing not a huge concern and wont affect it anyway.

Also with the gear swap, do you change out the front axle as well? Its a push botton 4wheel drive system. This is the 1st 4x4 I have owned where I considered a gear swap. So if it sounds stupid, forgive me.
On a 4X4 whatever you do to one axle you MUST do to the other. Meaning, if you swap out the gears in the rear end, You must swap the front end with the same gears.

YOU WILL DESTROY YOUR TRANSFER CASE IF YOU DO NOT GEAR EACH AXLE THE SAME!!!!!!!

I don't know about your financial situation, but spending $2500 on a new t/c because you didn't want to spend $200 on a new ring and pinion for the front sounds crazy.

The only way you can do that (and I know people who have) is do the rear end first, until you save up for the front, and in the mean time, disconnect the front driveshaft.

Also, what size tires are you running?

I believe for an automatic 4X4 truck, stock, 4.10 is really good ratio. If you drop to 3.73 ratio, you engine will bog in overdrive and you will actually lower your MPG.

Check out this chart:
hXXp://www.quadratec.com/jeep_knowledgebase/article-26.htm

(replace XX with tt)
 

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[Gear swap would be at a hideous cost. No you wouldn't have to change axles though.] [/QUOTE]

i think cableguy misunderstood your question about the front axle GEARS. yes you do have to change the front GEARS if you change the rear. incase you decide to go this route.
 

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[Gear swap would be at a hideous cost. No you wouldn't have to change axles though.]
i think cableguy misunderstood your question about the front axle GEARS. yes you do have to change the front GEARS if you change the rear. incase you decide to go this route.[/quote]

Your absolutely right I did read that wrong between axles and gears, Thanks...Carry on good work guys :great:
 

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Gear swaps are not a hideous cost. You can get a front and rear R&P for +/- $300 and it includes all the bearings. And gears are not that hard to install. Just time consuming and setting the proper backlash. Any weekend mechanic can do it. Look here for replacement parts www.gmpartsclub.com
 

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Gas Mileage

Just a few comments from the cheap seats.

I travel quite a bit at my previous truck was a 99 c3500 crew cab lwb with a 454 and 4.10 gears. I put over 140k miles on the straight flat roads of West Texas at speeds of between 65 and 95 mph but mainly cruised at 75. Yes it drank gas, but luckily it was a company truck.

When it was brand new and stock I did install a set of aluminum wheels so I shed probably 100 pounds right there. Drove it for awhile and got 13 to 13.5 on the highway. Put a snug top bed cover on and saw virtually no difference in FE. Installed K&N air filter. No difference, although money was saved as it was the only one on the truck for it's whole life. Then installed a pair of Flowmasters with dual tail pipes. Mileage did go up to 14 to 14.5 and sometimes to 15.

There was an RPM threshold where things went from really good to okay to real bad. If I could stay below 2000 RPM, which I think was 65mph, it could do 15mpg. Over 75mph and I could watch the gas gauge move.

While I agree weight reduction will help alot, I also believe slowing the engine down helps the most. I experience the same type results when I slow down my current truck.

I hope to prove my point when I put a 6-speed (double overdrive) in place of the 4-speed in my Trans Am. Heh heh yeah it will increase top end speed as well. Hell, look at a late model Z-28 or Trans Am with the same transmission - 27mpg on the highway and a top end in excess of 150mph.
 

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Motorhead,
I have been a mpg nut for years,and I have to agree about the RPMs being pretty critical. I have driven thru W Tex maybe 40 times over the years on the way to Flagstaff AZ or Denver from New Orleans.I usually took HY287 to I-40-the last few times I took the southern route-I-10.What a nice surprise to find a 80 mph speed limit on I-10 west of San Antonio-didn't help our MPG much!!
Back to RPMs and weight; weight loss helps city mpg-but it doesn't make any difference for hy/trip/interstate type driving.On the hy is is RPMs and drag.
1)My Tundra 4.7 couldn't get better than 18 mpg hy despite driving like a candy ass and not going over 60 mph.It was because it turned 2000 rpms at 60 mph.-It would get about 13.5 mpg city and 18 hy-weight 4400 lbs
2)Honda Pilot-4400 lbs-3.5 liter V-6- 1650 RPMS at 60 mph- 14mpg city and 23mpg highway.
3)Nissan Titan-4800 lbs-5.6 V-8 just 1550 rpms at 60 mph-13.5mpg city 20.5 mpg highway-beats both of the smaller motored,lighter vehicles on the highway because of the tall gearing.
4)1998 Suburban 2wd 5.7 V-8 5400 LBS- 1675 RPMs at 60mph-12.5 mpg city but 19 mpg hy-it beats the Tundra on the highway despite being 1000 lbs heavier-and it is close in hy mpg to the Titan despite being a lot heavier,and older(200,000 miles). Most surprising is that lb for lb it is at least as good as the more modern vehicles in city driving.If it weighed 4400 lbs-you would expect 15 mpg city with it-beating the 3 4 valve vehicles that "should/could" have a slightly more efficient combustion chamber.Apparently GM has really spent a lot of time fine tuning its small block for efficiency.I would have never guessed it could do so well on the hy. All these mpg numbers are driven with mpg in mind.At 80 mph on I-10the pilot dropped below 20 mpg.I usually drive to get good mpg-city and hy.
RPMs matter-and so does long term R&D on a mature product.
Thanks,
Charlie

There was an RPM threshold where things went from really good to okay to real bad. If I could stay below 2000 RPM, which I think was 65mph, it could do 15mpg. Over 75mph and I could watch the gas gauge move.

While I agree weight reduction will help alot, I also believe slowing the engine down helps the most. I experience the same type results when I slow down my current truck.
 

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Try this one...

Tape an egg to the gas pedal.

j/k, although it'll definately work, might be a little messy when it breaks.


Do the basic and obvious things.

1. Tonneau cover - (I've driven a 99 Sierra with one, it got 23 on the highway.
2. Pump your tires up to max recommended pressure
3. Drive the speedlimit - to keep the RPMs down
4. Set the cruise control - but let it slow down on the hills a little, then set it again
5. Accelerate slower - egg on the gas pedal thing
6. Don't let it idle for more than a minute - turn it off saves gas
7. On the highway, put the windows up
8. Take any extra weight out
9. Replace your air filter(or keep it clean) and fuel filter
10. Replace your engine/tranny/diff fluids with synthetic
11. Buy the brand name gas (Exxon, Shell) - the cheap stuff sometimes hurts mileage

Those should help

I've done most of these things with our vehicles (on trips at least)
2000 Olds Silhouette Premier 3.4 V6, loaded at 4800 lbs - have gotten 30+ on more than 6 trips
2004 Suburban 2500 8100 4.10s - empty have gotten 15.1 once and low to mid 14s a few times(usually I drive fast), and pulling a flat car trailer with '70 Camaro netted 11.7, (going speed limit)
 

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Try Pulse and Glide in city-Suburbans really glide well

Wayne S,
The mpg fanatics have popularized the Pulse and Glide- you accelerate fairly briskly to about the speed limit(or about 3 mph above it),then completely let off and glide to about 5mph below the speed limit.My 1998 Suburban has so little engine braking(one good thing about automatics) that I can glide about 4 seconds for every mph from 34mph to 25mph.It works, but frankly,I just am not sure why it does.I would have thought that very gently accel to 30 mph,and holding it there would work better, but it doesn't.I have checked ity with my scangauge-the P&G wins.
Now the P&G is only useful in city driving(you could do it on the HY-and some do-but I don't.You hang back a little bit at a redlight-let the guy ahead of you get a jump-then you accel to just a bit faster than him,and completely let off.In the city,you usually willl be able to glide to the next stop.I think it is worth about 1-2 mpg on big V-8s(that get 10-13 city) in city driving.
It is easier to do it than write it-and you don't piss folks off like the very slow driving some folks do.
Charlie
 

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Phoebeisis,

That sounds like something that I sorta do in my Suburban. They do drift pretty easily. Another thing I do once in a while is on long down grades I shift into Neutral. Just letting off the gas (at around 65-70) shows the intant MPG at 35-45, going down hill off of the gas, but if you shift into Neutral, it goes to 99 MPG, and when the hills are 2-3 miles long, it certainly helps even out the mileage, especially from the long uphills.:great:

Another thing I noticed is drafting big rigs on the interstate helps a lot too.
 
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