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6 Mpg

I get 15 city/20 hwy in my stock 1987 Blazer. The only change I made was to install a new 2000 vortec 5.3/4L60E. I will never save enough on gas to pay for the upgrade- but with gas going up at least I feel a little bit better about it.
 
OK with my set up I get a soild 10 mpg in town very little ideling. 15 mpg on highway!

BFG 31/10.5/15; 305 TBI with the spacer plate; K&N air filter; 5w 30 oil; 700r with a shift kit; 3:08 gears; using 87 Octane unleaded

Driving like an old man nice and slow starts!
 
Do you happen to do all mountain driving in Colorado? Even then your milage is still low...

I live in Idaho and if I go East I am in mountains, loaded but no trailer I will get 12 mpg in my 2wd 1990 5.7L Suburban. If I go West I am flat land and get 17 mpg. The worst milage I ever got was 11.5 MPG and that was cold winter starts to drop my son off at school and back home. Truck almost warmed up by the time I got home.
 
I'm with everyone else that says the calculations are off. My '88 K10 Burb 350/700r4/3.42/stock tires got 9mpg while towing a car on a tow dolly from Florida to Ohio- and that was with the timing retarded about 8 degrees! With the timing set correctly, I picked up a few mpg.

Speaking of timing, have you checked yours? It can make a big difference.
 
Metrodps said:
OK with my set up I get a soild 10 mpg in town very little ideling. 15 mpg on highway!

BFG 31/10.5/15; 305 TBI with the spacer plate; K&N air filter; 5w 30 oil; 700r with a shift kit; 3:08 gears; using 87 Octane unleaded

Driving like an old man nice and slow starts!
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I would think that a K5 with high gears would get better than that in town :eek1:

Lowest I've ever gotten in my 'Burb was 10.5 or so... if you saw how I drive it you'd be surprised I get that mileage out of the 6000 pound pig. Needless to say if I wasn't racing(and kicking their ass) Honda's from stop lights I'd probably be doing a lot better :crazy: Highest I've gotten so far has been 13.8 or so and that was doing my best consciously to drive it easy with 70% city/stop 'n go driving.
 
i have no cat i took it off right after emission testing. tomorow at school i'll test my o2 senser. and no mountian drivin it is farlly flat ground
 
bowtieboy4life2000 said:
when mt speedo say 55 in am aculey going 65. acording to the construction sign. but at lower speeds it is 1 to 3 mph off
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that's because it's a ratio. in my truck, i'm always going 20% faster than the speedo says. thus, when my speedo says 50mph, i'm really going 60. when it says 25mph, i'm going 30mph. so, to get an accurate mileage reading, i have to multiply my miles on my odometer by 1.2. i'd bet this is your problem. figure out your exact ratio and rework your figures. don't use those construction sign deals - they're never perfectly accurate. if you've got a GPS unit, or a friend with one, drive with it and see how fast you're going. or, go with a car pacing you where you know the car is accurate...
 
You can also use mile markers on the side of the highway, my '77 Jimmy speedo is off by two tenths of a mile, so I figured it that way. 5.5 mpg with built 454, ouch!!
 
Something is definitely wrong. When my Blazer was in 1 piece and driveable, I was pulling down 10-12 MPG, with a real tired 350 tbi, 33s and 4.10s. Went with the 4.10s to keep the tranny happy, as I found it searching with the 3.73s often.

When all is said and done, my trazer, which may or may not be my DD, will have a carbed and cammed 350/built 700/33s/4.10s. I hoping for at least ten with that setup.
 
Something isn't right here. What were the factory gears and tires?

My stock gears were 3.42 with 31's and I switched to 4.10 with 33's. That change makes the speedometer read 10% faster than my actual speed. So when my speedo says I'm going 50mph I'm actually going 45.

This also means I have to reduce my fuel economy #'s by 10%; so if I calculate 15mpg, I'm actually getting 13.5mpg, which is what I tend to average in the summer months.

bowtieboy4life2000 said:
when mt speedo say 55 in am aculey going 65. acording to the construction sign. but at lower speeds it is 1 to 3 mph off
Click to expand...
 
Just as an example a 29" tall tire has a 91" tread length. So for every rotation it travles 91".

A 33" tall tire has a 104" tread lenth. So for every rotation you actually travel 13" more distance than the odometer is calibrated for.

A 29" tire rotates 696 times in a mile. (this is what the factory odometer is calculating) With 33s you would actually travel 752 feet further for every 1 mile calculated.

Changing gear ratios can obviously will throw this off further.

If we knew EXACTLY what the factory set up was, we could calulate roughly your real mileage.
 
Something's not right.

My 1986 with 4.10 gears, 33" tires and a California Emissions 350 gets a solid 12.5 mpg and that's tank after tank after tank.

The TBI engines should be at least a couple of MPG better.

If your odometer is off, so are your calculations. Figure your odometer error by doing a minimum twenty mile odometer versus mile-marker calibration.

It's not easy when filling up to get the exact same level of "full", which throws off your calculations. For example: A couple of weeks ago my girlfriend and I drove from Utah to Texas to pick up a used boat. Roughly 1,200 miles each way. Our mileage "to" (without a trailer) varied between 22.4 and 17.0 mpg. "From" (with the boat and trailer) varied between 13.2 and 17.4 mpg. Certainly there were many factors: headwinds, tailwinds, elevation changes, etc. but I think the big reason was I was not uniform in "filling the tank".
 
bowtie,

Did you ever figure out the problem? I just figured my mileage on a little highway trip of 125 miles I took. I got 10.1mpg. A little less than I had hoped, but I was bucking a good wind all the way home, I averaged 70mph and I need an oil change!

125 miles/12.2 gallons

This is in a 77' with 98,500 original miles, a 400ci, 3.08's, 400TH, NP203 and an Edelbrock 600 carb.


truck.jpg
 
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This makes me feel alot better. I was just think about posting something about this. About two days after I picked up my blazer ('90 350 tbi/700r4 10's with 3.42's) I threw 35's on it and THEN checked my mileage.. Same thing 6mpg:doah:. But it makes perfect since now that some body mentioned the spedo cable I feel so much better now:D. Well not really because I'm still only getting 8 to 10, but... that's way better than 6. Thank you fourms.. YOU GUYS ROCK!!!!!!!!:bow: But it probably doesn't help that my truck has 250,000 miles. But it still runs strong.
 
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10.64 is the lowest in town flogging it and 13.29 feather footing it, both with crappy 87.
265/75R16 (31.6 X 10.4) 4L80E 4:10
235/85R16 (31.7 X 9.3) stock
 
I think I get around 12-14 hwy with mine. Thats an 87 with a 383, 3.42s, 35s, and 4" lift. I really need to fix my damn gas gauge though. :o
 
Something is wrong for sure. Ive got 84 with 670cfm carb, 700r, 4:11s & 33 x 12.5 x 15 and I get 12-14mpg, my motor as 125k on it.
 
Well, since this is about gas mileage. I have the gm crate 330 horse with TBI, with 454 injectors, a custom prom, turbo 350, 4.10 and 35" bfg. I pulled an 88 2wd burb on my trailer, empty trailer weighs 2k#, plus the weight of the burb. I went from Chandler, AZ to Flagstaff, 90% uphill, and got Almost 8 mpg. I was impressed.
 
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