454 Mileage

[montess85]

I got 12.4 mph all highway with mine. I have 285s with 4.10s. Also mine is running a little lean with the check engine light on. Honestly 285s might be a bit much for 3.73s and lowering engine rpm doesnt always mean better miliage. I have a Saturn SL2 with a 5 speed and I swapped out the 5th gear in the trans for a better one. Dropped my RPM at 70 from 3100 to about 2650. I got slightely worse miliage at 70. The car wasnt in its power band and had to lug to maintain speed. Also a friend of mine has a Super Duty with a V-10. He had 4.10s and swapped them out for 4.30s. Increase his miliage about 1 mpg. Truck was about to maintain overdrive more with those gears.

 

[dr_goodwrench66]

Alignment is spot on. New idler and pitman arm. Tires inflated to 50PSI all 4 corners. Turns out I may have to part with the ole girl if I cant get better than 10! PCM reflashed with EFI Live for larger tires. Speedo is also correct and verified via GPS.

 

[great white]

count your lucky stars if you top 13 in the summer on the highway at 55 mph.....

 

[454cid]

He changed from stock sized 245's to 285/75/16 BFGarbage tires since he though that turning the engine slower would net better fuel economy.... Sure the engine turned lower RPM for the same speed... but the mileage dropped by 2mpg.

Install the stock tires, back came the 2mpg lost.

I thought you meant that he thought the 285s were causing him to run too high RPM. He was likely getting worse mileage for the same reasons I mentioned to the OP....... higher wind resistance, and too little gear for the tire (taking the engine out of it's power band on the low side).

 

[great white]

Both you guys told me I was wrong, and then agreed with me???

You guys are forgetting that the taller tires means he traveled further. Unless the computer is adjusted for the tires, the odometer is off, so mileage is always higher than calculated.

nah, you just read my reply from the wrong perspective.

Taller tires do reduce your overall effective ratio which leads to lower engine rpm. That is correct, but it doesn't mean better MPG.

The cumulative/system effect it has is what matters on fuel mileage. That lowering of rpm (and incorrect speedometer reading) can mean less time in converter lockup, or the shift scheme being off just enough, or operating below the torque peak of the engine. The calibration files are cut and dry numbers. There is no "about this" the converter locks up. It's a number. Like 45 MPH. If the speedometer doesn't see 45 MPH, it will not lock. Even though you actual road speed is 45 MPH. Same with shifting. It's a cut and dry number. For both upshifting and down shifting. It's like giving the PCM the wrong O2 data because the sensor is old and lazy and expecting it to tailor the fuel properly. Won't happen. It will always be "off" just enough to waste fuel or give rough running. Same deal with the wrong speedometer info to the PCM.

Then there's the higher rolling resistance of slightly wider tires, not to mention putting weight were it will do its absolute worst on MPG (further out from center is more leverage on the rotating center, has a multiplying effect becasue of the lever/fulcrum thingy).

There's also a penalty in a slightly taller vehicle and resulting drag, but it's minimal in this case.

The change in odometer reading due to the disparity between actual miles traveled and odometer miles traveled (as you mention) is also another error factor.


So you see, I didn't say you were wrong. Just that it wasn't the whole picture.

 

[454cid]

nah, you just read my reply from the wrong perspective.

Possibly

Taller tires do reduce your overall effective ratio which leads to lower engine rpm. That is correct, but it doesn't mean better MPG.

Show me where I said that it means better mileage.

The cumulative effect is what matters on fuel mileage. That lowering can mean less time in converter lockup, or the shift scheme being off just enough, or operating below the torque peak of the engine.

Then there's the higher rolling resistance of slightly wider tires, not to mention putting weight were it will do its absolute worst on MPG (further out from center is more leverage on the rotating center, has a multiplying effect becasue of the lever/fulcrum thingy).

There's also a penalty in a slightly taller vehicle and resulting drag, but it's minimal in this case.

The change in odometer reading due to the disparity between actual miles traveled and odometer miles traveled (as you mention) is also another error factor.


So you see, I didn't say you were wrong. Just that it wasn't the whole picture.

If you go back and read my posts, you'll see I mentioned those things to the OP, at least implicitly.

 

[great white]

Possibly



Show me where I said that it means better mileage.




If you go back and read my posts, you'll see I mentioned all those things to the OP.

Whatever bub.

I'm not here to argue with you.

 

[454cid]

We were posting at the same time........


When I said his mileage, was better, I meant than whatever he's calculating....... due to the odometer error.

 

[454cid]

Whatever bub.

I'm not here to argue with you.

Nor I with you, and I don't see what you're disagreeing with......... you and I have basically told the OP the same things!

 

[great white]

Nor I with you, and I don't see what you're disagreeing with......... you and I have basically told the OP the same things!

Like I said: not here to argue.

have a nice day