Gas Mileage

[Nick88]

This isn't hard to figure out, surely you've kept a log or something of your fillups if you're actually getting in the 20s because that is unheard of...hence my skepticism

and driving a 40 mile round trip while being intentionally easy on the gas pedal and returning to fill up isn't exactly an accurate representation of your fuel mileage

got a log you've kept from the last 5-6 fillups where you've used the majority of the fuel in the tank each time?

as said earlier, this mileage claim is a steaming pile of horse s h i t e. if you're going to exaggerate at least make it believable. i'd believe you and even be jealous if you had claimed 17

I don't think its in accurate, I often drive extremely light because of volatile gas prices, one week ill fill up 3.60 a gallon another 3.40 a gallon. I dont log often because I only really do it at fillups as that is my way of tracking and I dont fill up very often, making logging much harder, say logging an entire week compared to a day or two. Again, Im not asking you to believe me and I have absolutely zero to gain from lying about my mileage. I dont think its too hard to believe that a 40 year old motor that was originally rated for around 17 would be able to get in the 20s. For just one example is the exhaust. Factory was 2.25 extremely restrictive y pipe to a super fat bead cat and a 3 chamber muffler.... not too efficient to say the least. I have 3 inch true duals and an H pipe, lots more efficient. Also say timing, for many this is a touchy subject but these trucks came with 0* baseline, which in my opinion and the opinion of many others is very conservative. I bumped mine to 3*-4* to help a bit with mpg. In my opinion also every little bit counts even certain things like using synthetic oil instead of conventional and adding even an injector spacer. Also with lower gearing and bigger tires my 700r4 with OD shifts much earlier, meaning Im always at low rpm, and when Im cruising on the parkway not tryna set a speed record... I'm probably sitting around 1000-1500 rpm, not a whole lot of rpms. Id understand if you decided not to believe it, but I will try to get a log next time I fill up.

 

[Nick88]

I said 5,300 lbs empty as in curb weight. Just looked up a V-Blazer on GM Heritage, closest I saw was a 1989. They show it as 6,100 GVW and show a 1,579 lbs cargo capacity based off curb weight. 6,100-1,579 puts it at 4,521.

You must be registered for see images attach

Agreed, every piece of literature I could find put it around 4500-4600 pounds, I believe it is registered 45(something) thats before you subtract the rust of course haha

 

[Nick88]

wait a sec... you are using a map, and not the odometer, to measure distance?

Google maps or ways, not odometer because odometer is slightly off, so to get most accurate I dont use it.. speedo is about 2mph off (bigger tires)

 

[L31MaxExpress]

Google maps or ways, not odometer because odometer is slightly off, so to get most accurate I dont use it.. speedo is about 2mph off (bigger tires)

My dad and I checked the odometer on that old 83 back when interstates frequently had mile posts years before cheap GPS was even a thing. The factory tire size was P225/75R15 and it had P235/75R15s on it for years. IIRC that van actually went nearly 17 miles for every 16 miles the odometer logged, speedo was off a bit too, 70 mph was like 66 mph on the speedo. I also prefer using GPS log for mileage driven as most vehicles are off a bit. Those old mileage logs were purely off the odometer. 17/16 = 1.0625 x 17.25 = 18.32 mpg corrected for odometer error.

 

[L31MaxExpress]

Google maps or ways, not odometer because odometer is slightly off, so to get most accurate I dont use it.. speedo is about 2mph off (bigger tires)

I have also figured out programming speedo calibrations in these GM vehicles, using the mathematical tire size calculators is never accurate. I have had better accuracy measuring from the ground to the center of the wheel and doubling it as it usually works out much more closely in real world than the math off the tire size numbers. With the vehicle load on a properly inflated tire, the loaded sidewall of the tire is always shorter than the math works out. Perfect example, the 10 ply LT245/75R16s on my Express show to be 30.5", but in real world they are 29.6" measured from the ground to the center of the wheel and doubled. Interestingly GM used the same tire height on the newer Express 2500 and 3500s in the OE calibration.

 

[L31MaxExpress]

Speaking of speedo calibration, I need to see if I can come up with a speedo gear for the TH400 in the 87. I need to pull the gear to find which one is in it, but I have a feeling it was changed out for the wrong one at some point. The speedo is off quite a bit even though it has never been regeared and the tire size is close to stock height wise.

 

[Road Trip]

My dad and I checked the odometer on that old 83 back when interstates frequently had mile posts years before cheap GPS was even a thing.

Back when I was in the hunt for the big MPG #'s, I started off by using a pair of mile markers to get a rough
idea about the odo accuracy. I eventually found out that this was a rookie error, for (I think) in the old Ecomodders
forum their standard of accuracy was to use *10* mile markers at a time. This way, every tenth of a mile deviation = 1% error.
If your odo claimed 10.3 miles had elapsed right when you passed the 10th marker then you knew that your odo was off
by 3%. You could get a pretty accurate feel for the odo error over 10 miles. (Then when we arrived home we
would rub 2 sticks together and get the fire started for dinner. It was a different time in the pre-GPS days. :0)

I always checked the accuracy of the odometers in any car I was tweaking, and was sure to share the 'corrected'
MPG when comparing notes with others. Attached is another pic of a different used Insight that my daughter
Steph & I retrieved from Tucson for her use after graduating college. It would get the rated 70 mpg at 60-65,
but the MPG would droop a little when making time. (Note: The last gas tank bar went out right as we neared
the exit. We cut it close, but I wanted the shot for posterity. :0)

BTW, the refill took 9.7 gallons, (10 gallon tank) ...and yes I had already verified an accurate odo via the 10-mile
marker trick...so it ended up being a 63.5 MPG tank.

Sure, those old 2-seater Insights might have been homely on the outside, but at the same time there some serious
beauty to be had in the vicinity of the instrument cluster.

 

[0xDEADBEEF]

Any C level or better mpg engineers want to get me an extra 5 mpg on my Tahoe? I'll report the 100% truth. Might be a fun forum thing.

 

[Caman96]

Any C level or better mpg engineers want to get me an extra 5 mpg on my Tahoe? I'll report the 100% truth. Might be a fun forum thing.

Are you willing to drive exclusively at the Bonneville Salt Flats?

 

[0xDEADBEEF]

Are you willing to drive exclusively at the Bonneville Salt Flats?

No, she's rust free on the bottom and I would like to keep it that way. I'm willing to drive those speeds though ... for the sake of science of course.