Improve gas milage

Discussion in 'Performance & Fuel' started by iraceIHRA, Jul 25, 2007.

  1. iraceIHRA

    iraceIHRA New Member

    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.
  2. Cableguy

    Cableguy Epic Member 5+ Years ROTM Winner 1000 Posts

    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
  3. Cableguy

    Cableguy Epic Member 5+ Years ROTM Winner 1000 Posts

  4. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    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.
    Last edited: Sep 7, 2007
  5. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    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....
  6. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    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.
    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!
    Last edited: Jul 26, 2007
  7. iraceIHRA

    iraceIHRA New Member

    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.
  8. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    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.
  9. iraceIHRA

    iraceIHRA New Member

    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
  10. davzog

    davzog New Member

    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 the sound, but gained ZERO performance or 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 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 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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