what rpm's ?

[ladytex70]

What rpm's are your guys burbs running at when your going 70mph? What are you guys getting on gas mileage? I have a 98 burb 4x4.

[beastofburban]

96 / 140k Miles / 4x4 / 454 Vortec / 4l80e Automatic / 3.73 limited slip, dual exhaust, airraid filter, MSD 8.5 mm Wires, and stock (245/75/16) tires.
70 mph = 2150 rpm.
Only had the truck about three weeks, Haven't been on freeway more than 5 miles yet. First tank of gas around town before tune up and dual exhaust = 10.53 mpg
Will check back after holidays and let you know how it did on freeways as we are going from Seattle to San Diego and back over christmas.

[The_Cheese]

'96 350 vortec 4x4
70mph = 2000rpm+/-
bout 16.5 mpg

[beastofburban]

96 Burb 143k 4x4 k2500 7.4L Vortec 3.73 LS 4l80e Auto 245/75/16 tires, Dual ex, Airraid Filter, MSD 8.5mm wires

Just returned from 3k mile trip. Average 14.3 mpg mostly freeway. Could have been better but had to place auto tranny in lower gear (w/4x4 in high) during blizzard over passes for better traction. Maybe the fact that I cruised closer to 80 mph than 70 mph for majority of trip seems to have hurt a little too. That's the real world for ya. No complaints.

Best = 15.4 at 70 mph
Worst = 11.5 mpg at varying speeds of 0.01 mph to 25 mph in Blizzard

[ladytex70]

98 350 Vortec 4x4 102234 miles 55mph @ 2k 65 @ 2500. I'm sure that I have something going on because I have seen other burbs run at 500 rpms less then mine at 65. I get about 10.5 in the city. with a 44 gal tank it about 448 or so. I use to get about 600 to a tank. I really think that it has something to do with the bosch plugs that i'm useing. I did have an exhuast leak that I had the rpm's drop a little when i had that fixed.

[Fireplug]

1997 350 engine 105,500 miles 13 mpg around town.
42 gal tank 90 bucks to fill tank

[beastofburban]

Originally Posted by ladytex70

98 350 Vortec 4x4 102234 miles 55mph @ 2k 65 @ 2500. I'm sure that I have something going on because I have seen other burbs run at 500 rpms less then mine at 65. I get about 10.5 in the city. with a 44 gal tank it about 448 or so. I use to get about 600 to a tank. I really think that it has something to do with the bosch plugs that i'm useing. I did have an exhuast leak that I had the rpm's drop a little when i had that fixed.

Sounds like you have 4.11 gears which would account for higher rpm. Search previous forums on gear ratios. Simple check is basically to compare axle revolutions to tire revolution. You could also check your RPO codes for what axle ratio came with vehicle.
Don't think fuel milage is excessive for 350 around town but you should do better than that on freeway driving. I did some minor mods to try and improve performance/economy that may have helped some (see above) but cannot say for sure as did them all right after purchase.
Try getting rid of Bosch plugs. Have heard several complaints in forums about these but no personal experience. Recently installed AC Platinum Plugs and have had no problems.
I see you are running close to empty on fuel tank. Try not to run fuel below 1/4 tank and change fuel filter at every other oil change. Bad things happen to fuel pump which is located inside gas tank, when pump does not have fuel around/over it to keep it cool or has to work to hard to pump fuel through dirty filter.

When in doubt compare the additional 30k you are not paying for a new rig against current fuel milage. If a new rig got half again your current milage it would pay for itself in a mear 450,000 miles at $2.00 a gallon. Thats about 30 years of seat time for me, if I live that long.
When in doubt, I just enjoy the ride.

[gregory914]

I have a 97 K1500 w/5.7, 3.42 gears, K&N on factory "high capacity air filter", with 110k miles and only Mobil 1 every 5k and usualy Premium fuel.

City= 12-13.5(best),
Hi-Way=16.5-17.9(best)

I almost always use Premium and over the years have documented a 2MPG increase in city and a 2.5-3.2 increase on the hi-way @ 80-90MPH.

The fill-ups suck but it does improve the performance too !

[ladytex70]

I have been told that I should use some slick 50 and that would lower my rpm's and get me better gas mileage. I have wanted to use the slick 50 but don't know if I should. I plan on putting in better exhaust. I already have the K & N. I don't always go to empty I just want to see if I was get the same milage at half as I would at empty (near empty). I always fill at or before half tank.

[ladytex70]

anyone use slick 50?

[1BADGTO]

I think Slick 50 is a waste of money. Best thing you can do - oil changes every 3k miles. I like fram filters and Mystic Jt8 oil. At least 750k miles in various vehicles using this combo and never any sludge or premature wear. I have also used prolong transmission treatment in several automatics (TH400, TH350, 700R4 and Chrysler 42RE) with VERY GOOD results. In fact my 95 Grand Cherokee with the 42RE is going on 270K and is all original - no rebuilds. I've tried the prolong engine treatment recently (Jeep) but too early to tell anything.

Anyway, the expensive way to decrease engine RPM is to change gears. The cheap way is to increase tire size then go to a driveshaft specialty shop and let them recalibrate your speedometer. Did that with my Chevy dually.

Best way to improve gas mileage: don't accelerate and drive 65. LOL. I've found that headers and aftermarket "performance parts" will increase power but do very little for gas mileage - unless you can improve the efficiency of the combustion so that less fuel is used...ie direct port fuel injecting, superchargers etc. An engine has a fixed displacement, therefore will require an amount of fuel to maintain the desired air/fuel ratio at given rpm's. Slap on an intake and headers thinking you'll get 3-5 mpg increase cause that's what the add says and in reality you get .5 mpg. Why? Your engine is still the same displacement and your still sucking the same amount of fuel and air as before. Now, at 5000 rpm there is probably an improvement but we don't drive at that rpm for long periods of time. So.....that's my 2 cents. Good Luck! Chad

[san fran crisco]

If the RPMs for a given speed have CHANGED verses what they used to be, and nothing was modified related to tires or gears, isn't it possible that the torque converter is not locking? That might account for about 500RPM. Do these machines have locking TC's?

[Eggert]

Hi,
do NOT use slick50 on a high mileage engine !!!
I did that on my VW Jetta and one month later I needed new piston rings.
As for gas mileage, or the lack of it (this thing weighs 6,600lbs with me and a full tank):
2001 YXL K2500 6.0 liter, 4.10 rear - Hiway 14, City 10, Towing 7. I think 2,300RPM @65MpH.
Take care, Eggert

[sassee]

After seeing some of you guys mileage, I actually feel a lot better!

1997 GMC ' Burb, 2500, 2WD, 7.4L, Stock as sold, 265/75/16's, 4.11 rear gear with 150,000 miles!

18.3 Hwy -best (avg is 17.8)
15.2 city
And YES! I tend to run it hard when i'm driving.