700r4/NP208C with 4:88 Gears

[Ozie P]

Truck used to have 37s. Went to 33s on my weld wheels. I’ve heard that low gears and 700r4 trannys don’t get along. Other than high rpms in overdrive, don’t seem to have any issues. Any input?

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[bucket]

They don't like gears that are numerically low. It's probably happy as a clam with those 4:88's.

 

[Ozie P]

They don't like gears that are numerically low. It's probably happy as a clam with those 4:88's.

Feel like I’m turning unnecessary RPMs (25-2600) at 65.


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[bucket]

That's no problem at all for an engine in good condition.

 

[rpcraft]

It's not a matter of what the engine likes actually but more a matter of if you like your engine being at a higher rpm while at cruising speed or at a lower rpm, and possibly at a more fuel efficient running speed. If you get on the highway and rock 33's with 4.88's I imagine your turning a pretty high rpm rate if you are doing 70 to 75 mph and also burning fuel at a pretty low mpg. The optimum engine speed for around 70 mph usually is around 1800 to 2000 rpm, which is also where it is usually most efficient for mpg. If all you do is drive around all day at 45 to 55 mph then you probably don't see the difference.

 

[bucket]

Eh, 1800-2000 rpm at 70 is good in theory. But it's not very efficient with a stockish small block and a 700r4. 2200-2500 makes the trans happy and since the engine isn't lugging, mpg is roughly the same. The most efficient way to push a brick through the wind is power and/or steep gearing.

 

[Ozie P]

Eh, 1800-2000 rpm at 70 is good in theory. But it's not very efficient with a stockish small block and a 700r4. 2200-2500 makes the trans happy and since the engine isn't lugging, mpg is roughly the same. The most efficient way to push a brick through the wind is power and/or steep gearing.

It’s a strongly built 350, and the rpms seem to put it in a great position of power as far as ready to pass or get on it. Just been contemplating on dropping down to 4:10s since it’s more of a street truck/weekend cruiser.


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[bucket]

If you are currently getting 10-11 mpg highway, you won't see any improvement, just less power.

 

[bucket]

But if it makes a bunch of low end grunt, you can pull off taller gears ok.