Gas Mileage

[L31MaxExpress]

But we’re talking about an 88 Full Size Blazer, that brand new, only got 11-16 mpg, but now 36 years later is getting “in the 20’s” with 33” tires.

I will also add that strictly highway running, my 99 4 door Tahoe LT with 3.42s rolling on 32" tall P305/50R20s was very good on fuel. It hated hills and would downshift to 3rd on anything more than the slightest grade but on level road with the engine only turning 1,700 rpm at 70 mph it would get 22-23 mpg. The 8.1L/4L80E in it would get 18+ mpg turning ~1,850 @ 70.

 

[Caman96]

To me, when mileage is mentioned, city or highway are the only caveats I consider. Perfect conditions like flat straight roads or downhill with tailwinds and such aren’t realistic scenarios. My mother bought a brand new square body Blazer back in the day and “New” with my mother driving, it never saw mileage in “the 20’s”. Whatever that even means: 21? 24? 28?

 

[Nick88]

The 33” Mud Terrains and 3.73 gearing have me questioning this. Who adjusted pcm for tire size?

Its a 700r4 so its all governor/ throttle valve controlled. I need (I believe) something more like an S10 governor to have closer to regular shifts. Again it shifts early because of bigger tires and gears which probably helps my case, when im trying to get good economy the truck barely ever hits even 2k rpm.

 

[Nick88]

To me, when mileage is mentioned, city or highway are the only caveats I consider. Perfect conditions like flat straight roads or downhill with tailwinds and such aren’t realistic scenarios. My mother bought a brand new square body Blazer back in the day and “New” with my mother driving, it never saw mileage in “the 20’s”. Whatever that even means: 21? 24? 28?

I always just go off of however the conditions are when Im driving around testing it, never really have seeked out any particular, it just is what it is. Also mostly lower 20's think like 20- if I had a good tail wind and lots of downhill maybe 24, but like you said thats not a very realistic scenario, thats also being a granny on the gas to the point of people passing me. Again despite the tires and gearing, the mechanical trans shift points due to the different size really help by shifting at lower rpm.

What is the factory tire size for your truck? If your OE tire is originally a 30, or 30.5 or 31 inch. And you now have 33 on.
And if your using your stock speedo/ odometer , it is in no way correct. Taller tire , less revolutions per mile. Therefore indicating lower vehicle speed than actual ground speed. Using that as your mpg reference your math is wrong.

Im using maps to calculate miles, truck came with 31s then whoever swapped in 3.73s changed speedo gear for that, it is about 2-3 mph off, but I dont use that I use maps and adhere strictly to those routes then fill up and divide.

still waiting on proof from OP. spoiler, it won't happen because he's not getting 20s mpg

this is as bad as the cummins guys claiming 20mpg while towing

What proof would you like, Ill provide. Also you think thats bad, I used to work with a guy that said his 12 valve got 40 mpg unloaded and high 20s towing, I got a good laugh

IDK, but an “88 Squarebody” full size Blazer from what I see got 11/city - 16/highway and came with 235/75/15’s. So can 33” tires, 3.73 gears, new plugs, Acdelco plug wires, Accell coil and a K&N oiled air filter gain you 5-7 mpg on a 36 year old truck? Remember, having new clean fuel lines is irrelevant compared to a brand new one, that when new, only got 11-16 mpg.

I have a picture somewhere, Id have to look for it of an 89 or 90 fullsize dealership window sticker that was rated higher, maybe 18 highway? Again Id have to look for it, it was of a original factory car with like 7 miles being auctioned, went for insane money.

I have seen them double their fuel milage correcting running issues. It is very easy to lose 5 mpg. Failing front brake hoses and the resulting warped front rotors from brake drag had my highway fuel mileage on my 97 down about 7 mpg at one point. Power wise felt like I was dragging a bus. Discovered the problem after I parked it after a 30 minute highway drive and both front wheels were smoking.

I have also seen a dead knock sensor kill 3-5 mpg and about 50 hp. The truck was a 95 and the PCM was running at maximum knock retard the moment the PCM enabled the knock sensors ability to retard timing. The truck struggled to get to 80 mph even at WOT.

Extremely true, when I bought my truck both front brakes were locked up, I would do a couple laps of my block and be able to see the fuel gauge move considerably!!

 

[Nick88]

Sorry for the long reply Ive been off the forum for a couple days. Nonetheless, again take it all with a grain of salt, Im not asking anyone to believe me, Im just happy with what I got and maybe it will help someone else, many people are taking it all out of context and not considering the full picture. They are 33's that are worn so probably closer to 31-32, but because of this the trans shifts much sooner with the gears as well, meaning my engine is shifting at low rpm and considering these engines are very low geared, I dont need to use more gas by turning the motor faster, it is a truck not a camaro. Also the low gearing helps me come out of stops using less gas, which I rill nice and slow into it to try to get the best economy possible. Once again, this is what has worked for me, I think a lot of people underestimate how much some minor mods can seriously bump mpg. Consider if the truck is rated for 16 or 17 highway... thats only 4-3 miles per gallon from 20. Some guys claim to get an extra mpg or two from just an injector or tbi spacer. Also many times driving lighter can help gain even a mpg over factory rating- if your willing to get passed by people often haha. Overall, believe it or dont believe it, wont keep me up at night, but when you think about it, it really isn't too hard to believe.

 

[RichLo]

hahahahaha what a joke on a side note being serious I have all ways been a little curious about those e3 plugs never tried them though

I'm surprised nobody has brought up 'Indexing' normal plugs yet in here.

It used to be common practice where plugs even came with shims to get them indexed correctly.

Aim the open side of the 'U' part of the ground strap toward the intake valve. I can tell you that it does help cold starting a kick-start only Ironhead Harley. I'm not sure if it helps at all with a new engine running at operating temp but cold starts sure helped my knee.

Take those stupid E3s out of your engine and install old-school full copper plugs that will erode after 30k miles and index them correctly!

 

[L31MaxExpress]

I have had very good results using NGK Nickel V-Power plugs. Inexpensive and easier to read the plug correctly.

I took a lesson from the old flathead briggs kart racer guys and use a surface gap plug in my tiller. My old Mercury 1150 2-stroke inline 6 tower of power used the same plugs. I may swap a set of surface gap plugs in the 383 at some point as a test.

 

[Pinger]

I have owned several TBIs. Every single one was better on fuel than the EPA estimates on long trips. My Vortec was better than the EPA estimates as well. That was running 70-75 mph as well. I find 55-65 mph actually kills fuel mileage compared to 70-75 in the typical undergeared modern vehicle.

When you say 'undergeared', do you mean numerically lower FD - eg, a 3.42FD is more undergeared than a 4.11?

 

[Erik the Awful]

You might be able to squeeze out a little efficiency here and there, but does anyone believe GM would leave 5 mpg on the table when they could just run a different air filter or put a different spring in something?

The world is run by C students and engineers are no exception. What do you call a guy who graduates engineering school at the bottom of his class? An engineer.

Testing different air filters and tuning takes time, and the engineers are just as eager to get home on Friday as you are. They're given so many days to complete their task load, and if they don't get it optimized, some dude like L31MaxExpress is going to find it dorking around in his spare time years later.

on a side note being serious I have all ways been a little curious about those e3 plugs never tried them though

They're a gimmick plugs, like the old Splitfires. Your plugs will never gain gas mileage, but you can definitely hurt it with the wrong plug. Get an AC or NGK plug and you won't have to worry about plugs.

Back in the day RX-7s had funky 4-prong plugs, but it was done to extend the life of the plug. As one prong wore away the spark would begin jumping from a different ground strap.

 

[0xDEADBEEF]

The world is run by C students and engineers are no exception. What do you call a guy who graduates engineering school at the bottom of his class? An engineer.

Testing different air filters and tuning takes time, and the engineers are just as eager to get home on Friday as you are. They're given so many days to complete their task load, and if they don't get it optimized, some dude like L31MaxExpress is going to find it dorking around in his spare time years later.

Do you know the GPA of the engineers who did the work or the amount of time they spent or the amount of validation it required to mass produce a vehicle for US purchase? I don't. It's a lot more effort than one person can do though, I'm confident of that.

There are definitely gains you can make if you don't care about ROI, warranty, EPA, NVH, running on 87 octane for all conditions, etc., but those gains are not 5 MPG. You're not going to take an engine that was 18% thermally efficient new and make it 25% efficient with air filters and a coil and whatever else you can bolt on.