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K5 Blazer gas mileage thread

83BlazerSM465

83BlazerSM465

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I did a search and found some miscellaneous old posts on this. Curious how everyone is doing currently in terms of efficiency. I know it's pretty hilarious discussing K5s and efficiency, but with high gas prices it's definitely worth thinking about.

I daily drive my 83 K5 about 80 miles per day, so as much as I do it for pure enjoyment, I do keep an eye on mpg as well.

Currently I've found the sweet spot hovering around 15-16 mpg. This is about 90% highway 10% city. I recently adjusted timing to 12 degrees and that's when I hit my record of 16.07 mpg. The average of my last 6 tankfuls is 14.68 with a low of 12.68 when I recently drove it to San Diego from Phoenix. The mountains really killed the mpg...

Specs:
83 K5 305 with manual trans. 33" tires on rally wheels and stock suspension. Single exhaust with high flow cat and flowmaster. Does have a phenolic carb spacer to help with hot starts, but that did not improve mpg. I do have an AEM wideband installed for carb tuning. Idle is around high 13, low 14 AFR. Cruising is in the mid 15s. I try to keep speed steady at around 65-70mph on the freeway.
 
My best ever was 17, under ideal conditions (flat ground, 50MPH, cool, still night, unloaded truck), my average freeway only on flat ground now is 16.

Quickly drops to 10-13 with hills, stop start, etc.

Best ever was carbed, current 16MPG was with TPI on an L31 (Vortec long block), SM465, 3.42's and 33's.

Absolute best non-diesel MPG I've ever heard (that I believe), for sustained periods under normal driving conditions (not just coasting downhill), was 19MPG, and that was a fuel injected Suburban that was tuned for lean cruise.
 
83BlazerSM465 said:
I did a search and found some miscellaneous old posts on this. Curious how everyone is doing currently in terms of efficiency. I know it's pretty hilarious discussing K5s and efficiency, but with high gas prices it's definitely worth thinking about.

I daily drive my 83 K5 about 80 miles per day, so as much as I do it for pure enjoyment, I do keep an eye on mpg as well.

Currently I've found the sweet spot hovering around 15-16 mpg. This is about 90% highway 10% city. I recently adjusted timing to 12 degrees and that's when I hit my record of 16.07 mpg. The average of my last 6 tankfuls is 14.68 with a low of 12.68 when I recently drove it to San Diego from Phoenix. The mountains really killed the mpg...

Specs:
83 K5 305 with manual trans. 33" tires on rally wheels and stock suspension. Single exhaust with high flow cat and flowmaster. Does have a phenolic carb spacer to help with hot starts, but that did not improve mpg. I do have an AEM wideband installed for carb tuning. Idle is around high 13, low 14 AFR. Cruising is in the mid 15s. I try to keep speed steady at around 65-70mph on the freeway.
Click to expand...

What gears do you have? Any lift? Did you change anything on the carb after installing the AEM, like rods, jets, etc?
I get 11mpg 90% street/10% highway 8-12 mile trips. My quadrajet is off of some other vehicle from PO and runs rich all the time. Going to FI soon.
 
Just drove mine from CA to Alaska, 3100 miles. 1988, 3.73, 700r4, stock tires, mild rv cam and conversion to Edelbrock carb/Hei. Towing an empty 26' boat trailer the best I got was around 11 and most tanks were at 8.5 - 9.0. Really killed my travel budget as I thought I'd be in the 15mpg range.
 
Checked mine last weekend and got around 13.. completely stock 85 full convertible running the safari top (not that it probably matters much..). Pretty hilly some stop and go and running 55mph the whole way- it was about a 250 mile trip
 
With a stock LS1, and overdrive tranny, does 20 sound out of the question? With 31-33” tires and 3.73 or 4.10’s
 
muddybuddy said:
With a stock LS1, and overdrive tranny, does 20 sound out of the question? With 31-33” tires and 3.73 or 4.10’s
Click to expand...

Given that the factory 2005 trucks were rated at 21MPG freeway, I suppose it's possible. Not sure what the aerodynamic increase was from our trucks to the newer ones, but the freeway MPG numbers are generally pretty far off IF you know how to drive, so I could get behind believing that under ideal conditions, 20MPG could be possible.
 
muddybuddy said:
With a stock LS1, and overdrive tranny, does 20 sound out of the question? With 31-33” tires and 3.73 or 4.10’s
Click to expand...
Maybe... But probably very optimistic.

My 91 with a stock 5.3, 700r4, 4.10 gearing and 35" tires has hit 20mpg one time prior to the camper going on. Most of the time it was right at 16-17 unloaded. But with loaded for camping and climbing the Rockies it dropped radically.

Camper on, average is 12ish. Depending on speed as the aero drag is brutal.

Just don't have enough stuff to push mine around with the 5.3.

Keep in mind all my data is at 4800 ft of elevation or higher. So it's going to be less than most at lower elevations.
 
I think i average 15sh
Its a dd with 53 miles each way to work
I hit one light the rest is open country road (395 bridgeport Ca)
The mileage doesnt bother me i fill up every 3rd day i work 4 days a week.
I get smiles to the miles.
76 k5 350/th350 on 33's
 
The only time I tried to figure the mileage was over about 550 miles.
The Iron Maiden got 5.5 overlanding with about 60% on road driving.

A9498925-C255-4421-A14C-5D147D059801.jpeg
 
ZooMad75 said:
Maybe... But probably very optimistic.

My 91 with a stock 5.3, 700r4, 4.10 gearing and 35" tires has hit 20mpg one time prior to the camper going on. Most of the time it was right at 16-17 unloaded. But with loaded for camping and climbing the Rockies it dropped radically.

Camper on, average is 12ish. Depending on speed as the aero drag is brutal.

Just don't have enough stuff to push mine around with the 5.3.

Keep in mind all my data is at 4800 ft of elevation or higher. So it's going to be less than most at lower elevations.
Click to expand...
Yes I was going to say that’s my average is 19.5 mpg also with 91 5.3. Is it the tbi? Or just that I drive like a granny? Haha
 
muddybuddy said:
With a stock LS1, and overdrive tranny, does 20 sound out of the question? With 31-33” tires and 3.73 or 4.10’s
Click to expand...
Not out of the question fifteen months now that’s still my average every tank is around 19 mpg
The hills and highways and in town miles seem to balance out even if I do more highways in a tank than the next
 
11mpg
400sb/700
FAST efi
4:88/38s
All flat freeway, except the on ramp
Only time I ever checked. Not a daily
 
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