Better gas mileage and performance.

[Pinger]

Reduces pumping losses and puts the engine where it has the highest volumetric efficiency thus the best brake specific fuel consumption. It goes hand in hand.

A lot of people can't get their head round half throttle being full throttle (as the engine sees it) at half rpm of maximum power (where the torque is). Roughly speaking that is.

The stock Vortecs will not dip into power enrichment until you get to 90% and beyond throttle opening.

So up to half the rpm of maximum power, half throttle gives the engine all the air it needs without dipping into fuel enrichment strategies.

 

[L31MaxExpress]

A lot of people can't get their head round half throttle being full throttle (as the engine sees it) at half rpm of maximum power (where the torque is). Roughly speaking that is.

So up to half the rpm of maximum power, half throttle gives the engine all the air it needs without dipping into fuel enrichment strategies.

That is the general idea. You could open the throttle to 75% and still not enter fuel enrichment, but that will drive the shift points higher than optimal for mileage driving. When I drove a Q-Jet vehicle, I found they delivered excellent fuel mileage as long as you stayed out of the last 1" of pedal travel. The Q-Jet model of 700r4 would also not activate the WOT kickdown unless you pushed the throttle fully to the floor.

 

[Pinger]

That is the general idea. You could open the throttle to 75% and still not enter fuel enrichment, but that will drive the shift points higher than optimal for mileage driving. When I drove a Q-Jet vehicle, I found they delivered excellent fuel mileage as long as you stayed out of the last 1" of pedal travel.

Yep, that last bit of throttle travel is as much to do with fuel delivery as air supply. A signal to call up enrichment.
Re shift points - if I'm into the pedal hard enough that the upshift is being - or is going to be - delayed, a momentary 'lift' enables the upshift at a point of my choosing.

 

[L31MaxExpress]

Climbing a ~6-7% grade into a headwind in the van at low rpm. MAP is near ambient but the throttle is only 1/2 open. It also pays back in fuel mileage to maintain speed on a grade as well, versus letting the vehicle slow down to where it has to unlock the converter or downshift to keep climbing said grade.

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[L31MaxExpress]

Yep, that last bit of throttle travel is as much to do with fuel delivery as air supply. A signal to call up enrichment.
Re shift points - if I'm into the pedal hard enough that the upshift is being - or is going to be - delayed, a momentary 'lift' enables the upshift at a point of my choosing.

A slight lift will generally enable an upshift where you want it. However since I do my own tuning, I just set the upshifts and downshifts to match my driving style. My shift tables are nowhere near what GM used except maybe under 25% throttle. I actually make use of a part-throttle 2-1 downshift without having to floor the pedal or manually downshift as well.

 

[L31MaxExpress]

Yep, that last bit of throttle travel is as much to do with fuel delivery as air supply. A signal to call up enrichment.
Re shift points - if I'm into the pedal hard enough that the upshift is being - or is going to be - delayed, a momentary 'lift' enables the upshift at a point of my choosing.

I once liked to bring the enrichment as well as added timing advance for power enrichment in earlier. I have since discovered that it is better to unlock the converter and downshift out of a load than trying to make the engine slug it out against higher loading. Engine bearings, piston rings live longer with less cylinder pressure and the combustion chamber stays much cleaner operating near stoich.

 

[L31MaxExpress]

My converter unlocks at a TPS just above the previous screen shot and a downshift to 3rd is only 10-15% higher TPS than that. The MPG number is a calculated instantaneous value I created with a math function. You can easily see why it is better to get the converter locked as soon as you can when the added torque multiplication of having it unlocked is not needed.

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[HotWheelsBurban]

I'll answer this question, FWIU Fry's and Krogers are not Top Tier stations, at least not here in AZ. Maybe Hot Wheels can confirm this in her area...

Not sure about this. I've never seen the tanker there, to see the name on it. We have so many refineries in the Houston area, no telling who makes it. Knock on wood, I've never had bad gas from them in either truck. I'm picky where I get gas in town; used to buy from Shell but they only give you 10¢ a gallon discount. I've used Raceway a few times, when they were cheaper than Shell and it made a difference cause we had to fill up before payday. No issues with their gas either. I know Vortecs are picky about what they drink, learned that on our old '99 Burb. Walmart gas did a number on the fuel injection on it, cost over a grand to fix it. Now my '90 TBI 350 would run on anybody's gas.....

 

[SentandBent4x4]

Yeah, and on these trucks, to get the worst mileage possible, use crude control on a hilly road! It's sucks on these old trucks!

 

[HotWheelsBurban]

Interesting... I had the opposite experience in my '97s (before any tuning). I tried running 91 octane in both of them and got noticeably worse mileage, plus they felt like they were a little down on power for some reason. Granted this wasn't really an apples to apples comparison as the main reason I tried this was to attempt to run ethanol free 91 from a non top tier station. After switching back to top tier 87 octane the MPG and power came back.

Did you fuel up at a top tier certified station? If so that might have something to do with it. I also went up four points in octane vs your two so that could be part of the difference.

When it was cooler days , the truck would have less of the roughness and surging in the idle. This was a little worse when it started getting warmer. I have the vented distributor cap so I think inside it should be dry....
But Mom and I both noticed after changing grades, that it runs better, rain or shine. Big rainstorm while we were out this afternoon, and it ran great during this. Same as yesterday when it was dry and in the mid 90s.... The gas change has made as much difference as the tune up (cap/rotor/plugs) did. Remember, when we got this one, it had been sitting around a lot, and I had to run a couple tanks and Berrymans B12 Chemtool to get the nasty old gas through it. It's always run strong on acceleration, and quick off the line, but it's never enjoyed idling. Like it's saying, "Mom....you know I wanna get out and stretch my legs, not sit around doing nothing...."