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vortec 454 gas mileage?
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Post vortec 454 gas mileage? 
what kind of gas mileage is everyone getting? with a vortec 454?

my 96 3/4 extd cab 4x4 with 265/75/16 tires is getting 7 mpg with the heat and ac going. Mad
strictly highway i get at most 12 mpg.

what can i do to better my mileage?

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Post Re: vortec 454 gas mileage? 
george wrote:
what kind of gas mileage is everyone getting? with a vortec 454?

my 96 3/4 extd cab 4x4 with 265/75/16 tires is getting 7 mpg with the heat and ac going. Mad
strictly highway i get at most 12 mpg.

what can i do to better my mileage?


Let's do this cheapest to most expensive:

What kind of gas do you use? Different vehicles burn different brands with different results. Yes, it all comes from the same place, but the different brands have different additive packages. For example, my 96 Tahoe gets 2MPG better off Shell than anything else in my area, but the wife's 89 GMC Jimmy S15 gets the same regardless of brand. And, at the 10-15MPG range gaining 1MPG is the same as saving 12 cents per gallon, so don't be afraid to spend 2-3 cents a gallon more for the same octane, if you get better mileage.

How is the truck used? If it is a work truck that carries a lot of gear, weight reduces mileage. Remove what you can.

You can add a quart of Marvel Mystery Oil to a full tank of gas. Mileage should decrease for that tank, then increase to more than the decrease on the following tank.

You can get a quart of GM Top Engine Cleaner. It goes in the throttle body slowly, then dump the last 1/3 can in till the engine stalls. Wait 15 minutes, then start. It will superclean everything. When you follow the directions, make sure to do it away from the house. After the 15 minute wait period your truck will smoke like it has a blown head gasket for about 15 minutes, the smoke smells like bad gunpowder and clings. Some folks leave it in overnight. Change the oil immediately after using this as it will contaminate the oil.

Last tuneup? New plugs, wires, cap and rotor, and a new coil, will make sure enough spark is there to burn all the gas. If it's been more than a few years, this needs to be done.

How old are the O2 sensors? They can get lazy after 50K - 100K miles. Changing them can gain up to 5MPG, but only if you are now getting 5MPG less than when new.

A computer reprogram aimed for mileage can make it better.

What rear gears do you gave? Getting a larger (lower numerically) gearset can improve mileage. Don't get tooo wild though, because if you go too far it'll make the engine work too hard. On a SBC 350, 2000 to 2200 is the ideal cruise speed, and gears to put cruise in this RPM bad is best.

Electric fans can add 2MPG or better to your truck. And, it'll make the AC work better in the summer and help the truck warm up faster in the winter. GM is installing them on new trucks now. Make sure to get flow though, because you can overheat easily if you don't have the right fans. You want a setup that flows better than 5000CFM.

A bed cover can improve mileage by reducing drag.

Headers can improve mileage, along with a free flowing exhaust. You must shield the starter if you go this way though, as headers on a big block will cause starting problems. When the solenoid is hot it won't work till the whole works cools down.

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wow, big reply. Very Happy

ok, a few more things about my truck. it's a 96 gmc 3/4 ton 4x4 extd cab short bed. it has a 454 vortec and 4l80e trans and 4:10 gears. the truck has 190k miles on it, BUT about 30k miles ago(when i bought it) i put in a completely new(not rebuilt) motor with all new sensors, injectors, intake manifold, throttlebody, distributor, coil, o2 sensors, radiator, banks cat back exhaust. actually the only thing i never changed was the MAF sensor.
the truck ran alright before i did all this, but it had a little coolant leak, some piston slap, and took a few seconds with the starter to get it started. so i decided to redo it all.

i usually use 87 octane and i purchase gas from all places. i dont really notice much difference by using better gas.

the truck is almost always empty, never haul anything. the truck does have a 3" bodylift along with the 265/75/16 tires, and yes i have a bed cover.

it seems like my mileage and performance go down with the hotter weather. one time i drove to florida(from IL) in the middle of winter and i calculated 14mpg. that was the only time that happened.
does warmer weather alter performance and mileage? lately it's been in the 90's here and i average 7-8 mpg mostly city.

oh and here are a couple of pics of my truck: Cool




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I have a 96 K2500 Suburban with 454/4L80E and 4.10's 2 1/4 duals from the cats back which are the only not stock items on it. My is used as a daily comuter here in Hawaii with occasional family hauler duties and it gets right around 8 mpg with all of the stop & go traffic and A/C on constantly. When I was in Louisania it would get around 10 mpg no matter around town or road trip, the best it ever got as an amazing 12.5 mpg on a trip from Louisania to Pennsylvania and back. I've just come to accept that something with a 454 that weighs over 6000 lbs will never get good gas mileage.

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Post So you've done most of it already then... 
The only thing I can really suggest is do the computer then, and the electric fans. Gears would also help some. Since the mileage on the engine is low, some folks have reported a mileage improvement on synthetic oil. If you are using dino oil now it might be worth trying. On the fuel, the only way to determine if one brand is better than another is by running five tanks of one brand at a time, then do a 5 tank average off it. If you fill up somewhere different every time then you never will see a difference. As ALS454 says though, you'll never get good mileage out of a 454, that just isn't what they're for.

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my 502 ramjet in a 5600 lb 2wd tahoe with a 4L80E, 4.10's on 29 or 31 inch tires seems to only want to get about 6-8 mpg most of the time. I think its just the nature of the beast with these damn big blocks.

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Post 1996 3/4 ton Sub K3500/7.4L/4.1s +150K miles 
with LT265/75R16 E's on 16x10 Alcoa's, so the "real" diff ratio is around 3.9.



10-12.5 MPG city and 11.5-15.4 highway.

Depends on what time of year and the various gas blends available.

Get 15.4 MPG often enough to claim, but not often enough to count.

[edit]....when I had a 8,500 lb boat/trailer it got 7-8MPG going up from sea level to +6.5K feet (Lake Tahoe). Some times 9MPG, but not often.

7,400 lbs with me, toolbox and misc stuff. Also get 15.4 MPG with my volleyball tourney team & stuffed to the gills (must be about 9,000 lbs).

Tires are aired up to 80PSI most of the time. I don't care for "ride quality" much and prefer performance.

I reset the computer at each gas reblend (spring and fall) so that the computer will relearn HOW2 manage the fuel (lesser BTUs during the winter blend). Fuel injector cleaner (Techron) for two tanks around then too (double dosage in each 42 gallon fillup).

Have sprial wound "wire" ignition wires by Taylor. Next time will get brass inserts for the dist cap (present is Delco aluminum inserts).

MagnaFlow dual in/out with custom dual 2.25" dia out the passenger side (OEM location). Next time considering change to single 3" dia, as this setup lost a "bit" off the line, but the top end is FUN!!!!



Ram cold air mod scoop:


I'm going to be changing plugs more often, as the picture below shows Delco Platinums with worn ground electriods at around 50K miles. The first set after about 80K miles had the hockey pucks gone on over half of the plugs. I'm also considering just plain jane plugs modified as shown in the second picture.



Modified CR43TS shown (for my 1980 Silverado C10 350), or might try colder CR42TS for next time.


PS....note that our era big block controls has the computer dump extra fuel to cool the CATs if they should get too hot. That alone drops a few MPG. I'm going to change out the O2's soon, as they have +150K miles and it's time....

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ben, i find it hard to believe the mileage you are getting. and your truck should weigh more too. Confused are you sure your calculator is working right? Wink
what could be affected by temperature? cause like i said, performance and mileage go down with hotter temps.

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Did you recal for the larger dia tires?

Your 4.1's is more like 3.86, so about a 6% difference, or 6% more MPG. Plus your speedo is off by 6%.

Did say that the 15.4 MPG is often enough to claim, but not often enough to be "regular". Plus MPG's are at the low end during the winter fuel blend.

Over at the Suburban forum many with big blocks report 13-14-15 MPG on a "regular" basis. includes the 8.1L.

My Suburban is GMC SLT, the hightest trim, so heavier than most Sub's. Plus it has more glass/sheetmetal/rugs/insulation/etc than any pickup. On top of that, my toolbox weighs in at +200 lbs plus the other misc stuff (about another 50-75 lbs).

What tire pressure do you run? My fronts are at 80PSI and rears at 55PSI, plus the fronts are E rated and rears C rated (less rolling resistance).

My thermostat is a modified 180*F (has a 3/32" dia hole drilled on the flange, in addition to the OEM one already there). Then with the severe duty fan clutch, the dash gauge rarely goes over 210*F, and when it does, drops like a rock when the RPMs goes over 1,000RPMs.

Synthetics in everything, but thinking of going back to dino ATF.

I have the OEM HD air filte (NAPA), in the stock filter box. It's about 2 inches larger in dia over the standard duty, so less restriction. I'll not go K&N though.

Finally, your lift affects the aerodynamics, which means more drag than mine. Both larger frontal area and more air underneath .

[edit]....disconnect your battery ground for 10-20 minutes to reset the computer. It's summer blend gasoline and higher BTUs, so the computer needs to relearn HOW2 manage the new fuel. Double dosage of Techron injector cleaner too. Consider a bumper chin air dam to negate the lift, somewhat.

I'm thinking of cleaning the various sensors, especially the MAF grid. That should help a bit, as these all do, a "bit".

Battery "ground", as the positive connection has rich history of causing failures in the alternator, battery, + cable and even wick acid down to ruin the start.

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i've occasionaly reset the computer by pulling the ecm fuses. is that good enough?
lately i've been using the fram airhog filter, and i've cleaned my maf sensor at least a few times.
also, last oil change was switched to synthetic.
i think my tire pressure is around 40 psi. if i air them up too much, i notice accelerated wear down the middle.

any other ideas?
will the lower thermostat mess with the computer?
what is the website of the suburban forum you mentioned?

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Don't know. There might be some backfeed and will have to check the schematics to make sure.

I'm not f fan of anything Fram anymore. Here's a picture of the standard vs HD from NAPA (OEM is similar). Notice the difference in dia, but fits into the OEM filter box.


Is your 3 inch lift a suspension lift? If so, then the drive line angles has been increases, therefore less power being delivered to the pavement. That alone might explain the higher throttle settings you need in order to move.

Exact same everything, but suspension lift will have less power delivered to the pavement. Increased U-Joint wear. Mystery vibrations from the drive train, etc. I don't like suspension lifts as a general thing, though I've done that on my old 73 K5.

The lower thermostat temp has power mode available most all times. Once the temp goes into the +200*F range, the computer backs off of power mode (timing, air-fuel ratio, etc). The other guys can chime in on this, but remember reading that the computer comes out of open loop and into closed loop around 170*F and above.

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the truck has a 3" bodylift, not suspension lift. the driveline is all stock.
i doubt the fram airhog filter would give any problems. this filter is designed like the k&n filters and is washable and reusable. i have cleaned my maf sensor a few times after installing the filter, just incase any oil from the filter got on the maf sensor.
i've used brake cleaner to clean the maf sensor, is that alright? how can you test the maf sensor to make sure it is giving the right signal?

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Post Ben - 
Unless your computer is set for it, the 180 thermostat will kill economy. The 195 the computer expects will improve economy as it isn't so close to the open loop cold mode.

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Post Re: vortec 454 gas mileage? 
Speeder wrote:
george wrote:
what kind of gas mileage is everyone getting? with a vortec 454?

my 96 3/4 extd cab 4x4 with 265/75/16 tires is getting 7 mpg with the heat and ac going. Mad
strictly highway i get at most 12 mpg.

what can i do to better my mileage?


Let's do this cheapest to most expensive:

What kind of gas do you use? Different vehicles burn different brands with different results. Yes, it all comes from the same place, but the different brands have different additive packages. For example, my 96 Tahoe gets 2MPG better off Shell than anything else in my area, but the wife's 89 GMC Jimmy S15 gets the same regardless of brand. And, at the 10-15MPG range gaining 1MPG is the same as saving 12 cents per gallon, so don't be afraid to spend 2-3 cents a gallon more for the same octane, if you get better mileage.

How is the truck used? If it is a work truck that carries a lot of gear, weight reduces mileage. Remove what you can.



You can add a quart of Marvel Mystery Oil to a full tank of gas. Mileage should decrease for that tank, then increase to more than the decrease on the following tank.

You can get a quart of GM Top Engine Cleaner. It goes in the throttle body slowly, then dump the last 1/3 can in till the engine stalls. Wait 15 minutes, then start. It will superclean everything. When you follow the directions, make sure to do it away from the house. After the 15 minute wait period your truck will smoke like it has a blown head gasket for about 15 minutes, the smoke smells like bad gunpowder and clings. Some folks leave it in overnight. Change the oil immediately after using this as it will contaminate the oil.

Last tuneup? New plugs, wires, cap and rotor, and a new coil, will make sure enough spark is there to burn all the gas. If it's been more than a few years, this needs to be done.

How old are the O2 sensors? They can get lazy after 50K - 100K miles. Changing them can gain up to 5MPG, but only if you are now getting 5MPG less than when new.

A computer reprogram aimed for mileage can make it better.

What rear gears do you gave? Getting a larger (lower numerically) gearset can improve mileage. Don't get tooo wild though, because if you go too far it'll make the engine work too hard. On a SBC 350, 2000 to 2200 is the ideal cruise speed, and gears to put cruise in this RPM bad is best.

Electric fans can add 2MPG or better to your truck. And, it'll make the AC work better in the summer and help the truck warm up faster in the winter. GM is installing them on new trucks now. Make sure to get flow though, because you can overheat easily if you don't have the right fans. You want a setup that flows better than 5000CFM.

A bed cover can improve mileage by reducing drag.

Headers can improve mileage, along with a free flowing exhaust. You must shield the starter if you go this way though, as headers on a big block will cause starting problems. When the solenoid is hot it won't work till the whole works cools down.







Hope ya know that the bed cover would actually hurt gas mileage and cause drag!!! it sounds realistic but looking but it is the same as having the tailgate down and that also hurts performance... i just skipped through this forum but i did see a pic of a air filter and i don't know if this was also gas milage oriented but to bust the part stores balls this is also not true a clean filter on a mass air engine (if it is so i am not a 100% cause mine has no accessories) measure the air coming into the engine and the less air the less fuel so dont buy into the commercial's on the radio. it is good to have a clean air filter due to keeping contaminants out of your oil but the gas mileage is worse with a better flowing filter... over n out rubber ducky the young gun might know his shit son

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i've seen articles where the bedcover doesn't reduce drag that much since the wind never hits the tailgate anyway,just adds weight.

Electric fans are the first mod I usually do to anything,makes a big difference in mileage and acceleration relatively.
I would do them first,as well as a smaller/lighter tire setup if you aren't hooked on the meats.
And go back to the stock thermo,hotter is better for mileage.
If you're done with engine mods than get a pcm tune done.
TCC lockup and DFCO can be tuned for better mileage as i understand,though i've played with it myself very little.

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Odd,this came up when I hit "unread posts since last visit".
Never even thought to check the date.

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Yes, the fellow before you was responsible.

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