4.11s or 3.73s?

[Mudsport96]

I think you'll find it easier to locate 4.10s as they use a 10 tooth pinion gear and 41 tooth ring gear common with the 3.42s and 3.73s for the front and rear.

The 4.11s use a 9/37 pinion/ring gear and I don't see them much for the front differential anymore. Yukon Gear might have ring and pinions in that ratio for both ends though.

I miss 3.90s.

Id hit junkyards and start looking in suburban wrecks. I thought about swapping the wifes 3.42s for 4.10s and found ( in my area anyway) it was more common to find steeper gears in the burbs. And if you do find them, you can get a matched front too

 

[EddieC]

And then there is the effect on gas mileage

 

[swathdiver]

And then there is the effect on gas mileage

Should be better around town and it might not go down on the highway. The rpms will be higher but the load on the motor should be less (at normal highway speeds) because of the gears doing more work.

I'm channeling thoughts I've had that were confirmed by this fellow's experiences just last night:

Advance to about 9:38 for the relevent part about mileage, the whole thing is worth watching IMO.

 

[Mudsport96]

And then there is the effect on gas mileage

Invalid as he is putting a rowdy thumpy cam in and going to probably lose mpg from the music the skunny pedal will be making.

 

[Mudsport96]

Should be better around town and it might not go down on the highway. The rpms will be higher but the load on the motor should be less (at normal highway speeds) because of the gears doing more work.

I'm channeling thoughts I've had that were confirmed by this fellow's experiences just last night:

Advance to about 9:38 for the relevent part about mileage, the whole thing is worth watching IMO.

The newer stuff i haven't seen much experimentation with as a whole. But, on my 9th gen fseries forum, multiple members have seen a 2 to 3 mpg gain on the 300 i6 and 302 trucks by swapping from 3.08s and 3.31s to a minimum of 3.73s and some even 4.11s. And it comes down to not lugging the engine at highway speed.
Hell, my own 5.0 truck gets the same mpg at 60 mph in 4th and 5th. On the vacuum gauge in 4th at 60 it pulls 19 in/mg at 2200 and 5th it has 5in/mg at 1700. So rpm is down and load is up, negating any fuel savings from the lower rpm. It is a fine line though. If i bump it to 62ish in 4th it drops 2mpg. But only lose 1mpg for 5th.

 

[EddieC]

Invalid as he is putting a rowdy thumpy cam in and going to probably lose mpg from the music the skunny pedal will be making.

Seems like misguided effort for such a heavy vehicle. As youngsters we used to think that Thrush muffler noise represented something other than it was.

 

[Alex_M]

Tighter LSA on your cam leading to more intake/exhaust overlap is what causes your engine to lope, but is also responsible for better low end torque production. Can certainly be a benefit in a heavier vehicle if the duration and lift are designed to benefit the same cause. Most of the time this is not the case, but in a truck specific cam there is no reason for the cam to not have a tighter LSA other than idle quality.

There's so much to cam science. I'm far from an expert, but it a topic that I absolutely love.

 

[OR VietVet]

Should be better around town and it might not go down on the highway. The rpms will be higher but the load on the motor should be less (at normal highway speeds) because of the gears doing more work.

I'm channeling thoughts I've had that were confirmed by this fellow's experiences just last night:

Advance to about 9:38 for the relevent part about mileage, the whole thing is worth watching IMO.

I used to run a shop, in Eugene, Or., that catered a lot to off roaders. They came in for very low geared gear swaps and then we saw them back with breakage, at the pinion gear. That is why I preach the smaller pinion size means a chance to increase or accelerate damage. It would have to be extreme, as shown with the 4.88 gears pinion example he showed. I did learn something about the fuel mileage though. In the case of the OP we are not talking about much of a gear difference in the swap. Go for it and have fun and "spend that money".

 

[Mudsport96]

I used to run a shop, in Eugene, Or., that catered a lot to off roaders. They came in for very low geared gear swaps and then we saw them back with breakage, at the pinion gear. That is why I preach the smaller pinion size means a chance to increase or accelerate damage. It would have to be extreme, as shown with the 4.88 gears pinion example he showed. I did learn something about the fuel mileage though. In the case of the OP we are not talking about much of a gear difference in the swap. Go for it and have fun and "spend that money".

You are definitely correct concerning pinion size. But at the power level basic bolt-ons provide, and not ramrodding in low range the 8.5/8.6 in these rigs will be fine. I think problems start around the 5.00 numbers on this specific rearend. I have personal experience with 4.56s in an 8.5 behind a 454 on 35s. It broke, but it was probably definitely the wheel hop that started during a burnout when the transmission went into 3rd gear.

 

[RAMurphy]

I was going to change my gear ratio but after significant research I decided it was not really worth it from my perspective. My current 5.3 with an upgraded cam, TBSS, headers (I too have a volant CAI), and the earlier mentioned BBP tune is pretty impressive. But HP/torque is like a drug - so I'm building a 6.0L engine in place of the gear ratio change.