Gas Mileage

[Caman96]

The world is run by C students and engineers

This is the only thing I commented on.

Nope, but I work with quite a few(no idea how many

Ok, maybe you do. Remember though, there just might be some unknown quantity who just might consider you one. It goes both ways. And I’m just pointing out that aside from bottom feeding points on door handles or JB3 brakes(like any and all manufacturers don’t have these problems), these trucks, and this is not my opinion alone, Google it, are known for their engineering. And it’s unknown how many C students were part of that, but from what’s generally understood now, they were known for exceptional engineering. I don’t think the engineers who “ran” that project were C students. Maybe you misunderstood.

 

[Keeper]

If you give me a way to provide proof I will gladyly provide, but if I do what I normally do, fillup, drive from the gas station to an area I know the mileage away, loop back and fillup then divide, I can give you exact numbers from a fillup, but you probably still wouldnt believe it. If you can think of a way to provide concrete evidence I will gladly do it!!

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

 

[L31MaxExpress]

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

We recorded fuel mileage for years to keep track fuel ups. The old worn out, 200+K mile Q-Jet carbureted 305 in the 1983 G20 completely stock, turning both air injection pumps and the massive old power hungry A6 compressor still managed better than 17 mpg. This was running 70-75 mph in a 5,300 lbs empty conversion van, loaded down with a family of 5 and all the luggage we carried with us. Probably 6,500+ lbs if I had to take a guess. If a heavy carbureted van can get 17 mpg, a TBI 350 in a lighter Blazer with less frontal area can certainly do better. You can tell the first fillup on 6/10 was prior to heading out of town and the subsequent fill ups through 6/13 were on the same roadtrip. 428.6 miles / 24.844 gallons is 17.25 mpg. The more efficient L31 350 in my 97 Express despite that van being heavier and having 3.42 gears rather than 3.08s always managed 18-19+ mpg on every tank and that was stock.

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[Caman96]

a TBI 350 in a lighter Blazer

They were heavier than you think.

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[L31MaxExpress]

I'm planning on a 65HD, we sell Interstate batteries at work and I may be able to get a slight deal. 850 CCA, 1000 CA.

The cheapest 550 cca battery turns the 10.25:1 350 over effortlessly in the 87. Excuse the water, just had a storm blow in here and I left the hood partially open during it.

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[L31MaxExpress]

They were heavier than you think.

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Still lighter than a 6,600 GVW conversion van with 5 people and all their luggage for a long weekend road trip packed inside. I would be surprised if that Blazer is even 5,000 lbs curb weight. Even with the heavy 20s that were on it, an 8100 and 4L80E, a heavy brush gaurd and westin steel side bars my 99 4 door Tahoe LT was right at 5,500 lbs on the CAT scale.

 

[Caman96]

Still lighter than a 6,600 GVW conversion van with 5 people and all their luggage for a long weekend road trip packed inside. I would be surprised if that Blazer is even 5,000 lbs curb weight. Even with the heavy 20s that were on it, an 8100 and 4L80E, a heavy brush gaurd and westin steel side bars my 99 4 door Tahoe LT was right at 5,500 lbs on the CAT scale.

You said it was 5300 GVW. If you added the 1200 lbs. of luggage/people to a 6100 GVW Blazer you’d have 7300 lbs.

 

[Road Trip]

The cheapest 550 cca battery turns the 10.25:1 350 over effortlessly in the 87.

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The fact that the ICM basically sets the timing to 0° during cranking (before handing timing control off to the ECU > 400 rpm)
makes these EFI SBCs turn over a lot easier than the primitive old days where I had a handful of base timing cranked into the
dizzy housing, leading to the strained 'whoa whoa whoa' cranking by the starter.

Especially after a good heat soaking from the headers. :0)

You know, there actually are several good things to be had with a TBI or Vortec setup over the way we used to do things.

And that's coming from an old school Q-Jet / big cap HEI devo. :0)

And with those spring-loaded metering rods & high signal strength from those small, triple-venturi primaries
allowed GM to combine unsurpassed lean cruise metering with good driveability back in the stone age carburetor
daze. Between the jets in the floor, the tapered metering rods, the different springs underneath the
metering rod hanger, etc., once you figured out the interrelationships you could make a good thing even better.
(Note: I learned all this way back during the 1st Arab Oil Embargo and the resulting price shock at the pumps.
Man I'm getting old. :0)

So, yeah, I absolutely believe in the numbers from that notepad in reply #83. I'm just hoping to recreate some
of that Q-Jet highway lean-cruise excellence via some quality time in a 0411 tune...and be able to do so guilt-free,
thanks to the retention of the O2 driven Closed Loop, GM 0411 ECU, & 3-way cats so that they can help keep any
resulting NOx in check.

(attachment credit: https://67-72chevytrucks.com/vboard/showthread.php?t=820133, eric peters auto, ebay auction)

 

[L31MaxExpress]

You said it was 5300 GVW. If you added the 1200 lbs. of luggage/people to a 6100 GVW Blazer you’d have 7300 lbs.

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.

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[L31MaxExpress]

The fact that the ICM basically sets the timing to 0° during cranking (before handing timing control off to the ECU > 400 rpm)
makes these EFI SBCs turn over a lot easier than the primitive old days where I had a handful of base timing cranked into the
dizzy housing, leading to the strained 'whoa whoa whoa' cranking by the starter.

Especially after a good heat soaking from the headers. :0)

You know, there are several good things to be had with a TBI or Vortec setup over the way we used to do things.

And that's coming from an old school Q-Jet / big cap HEI devo. :0)

And with those spring-loaded metering rods & high signal strength from those small, triple-venturi primaries
allowed GM to combine unsurpassed lean cruise metering with good driveability back in the stone age carburetor
daze. Between the jets in the floor, the different diameter metering rods, the different springs underneath the
metering rod hanger, etc., once you figured out the interrelationships you could make a good thing even better.
(Note: I learned all this way back during the 1st Arab Oil Embargo. Man I'm getting old. :0)

So, yeah, I absolutely believe in the numbers from that notepad in reply #83. I'm just hoping to recreate some
of that Q-Jet excellence via some quality time in a 0411 tune...and be able to do so guilt-free, thanks to the
retention of the 3-way cats so that they can help keep any resulting NOx in check.

(attachment credit: https://67-72chevytrucks.com/vboard/showthread.php?t=820133)

Funny you mention the base timing at Zero. That is one reason I always liked more inital advance on TBI and TPI setups. I usually ran 10* and set the Initial timing value to 10* in the ECM so that the ECM had an accurate point of reference. It helped what I call a cold start windmill effect as the engine spins over ans over for a while before catching and firing. It also allowed me to run the 46-52° of cruise timing needed for running lean cruise with them since the distributor is limited to ~42°. Lean burn especially with EGR use likes a lot of timing and a lot of HEIs in the vacuum advance days had an equal amount of cruise timing.

I started using the little Vortec PMGR mini starters over 20 years ago and one of the first conversion to that starter was the carbureted 305 in that G20. It would crank that 305 over at 12* initial without a single complaint and that was heat soaked with headers. The stock style starter struggled at the stock spec of 4* to crank it over hot.

I added 3-way cats to the 87 because why not. I do not like the smell of catless exhauat and know the thing runs cleaner now with the sequential port injection and OBD2 grade 3 way cats than it ever did with the TBI and Pelletbox cat.

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