hey guys. I'm new on here but want some input on some questions I want to ask. First off I'll explain my truck. '97 silverado, ext cab short bed, 4x4, ...

hey guys. I'm new on here but want some input on some questions I want to ask. First off I'll explain my truck. '97 silverado, ext cab short bed, 4x4, z71 package, 5.0 vortec, 4l60e tranny, 167,000 miles on the clock and counting. I'll start with my first question... It currently has a 3.42 gear ratio in the differentials. Would I benefit by swapping in 3.73's? And I'm not just talking mpg either. Just all around performance. I realize the 305 is by no means a tire shredder but the 3.42's seem to put it well out of it's rpm range... What do you guys think?

3.73s would give better acceleration and towing performance, but would suck down more gas. Just depends on what you want....

The taller your tires are, the less 3.73s would hurt mileage. But if you're gonna swap, go right to 4.10s. It's difficult to feel much difference just going 3.42 to 3.73.
It'd be cheaper to swap a 350 engine than to swap front and rear axle gears.

Thanks fellas. That was going to be my next question. I am going to swap in a 350 some time from now. Do I need to change computers or anything brain box wise for the 350 or drop it in and go? I'm anxious to see how she runs with the 350 and 3.42 gears.

You didnt say anything about what size tire you have now. I think you would get more bang for the buck if you upgraded to a 350 engine. A stock one for that truck might not cost that much and after you change your gears your old engine will be running faster than it is now. Maybe even pushing it to the grave sooner!

green97z71 wrote:Thanks fellas. That was going to be my next question. I am going to swap in a 350 some time from now. Do I need to change computers or anything brain box wise for the 350 or drop it in and go? I'm anxious to see how she runs with the 350 and 3.42 gears.

Probably best to call a tuning shop like Nelson Performance, and discuss the options with someone who has done these things many times.
The engine you should be installing is the L31, you can get a new long-block, with a GM warranty, for around $2300. But that option is more $ than swapping axle ratios.
It certainly is capable of driving your 3.42:1 gears, but it really likes more gear. It's a bit more rev-happy than your L30, because it has the high flowing heads.
If you're going to swap in an L31, you may as well get some long tube headers while you're at it.
The L31 will be a dramatic improvement, but so will 4.10:1 gears. Do both, with headers, you should be running with the stock 6.0L guys.

The truck currently has 265-75/16 tires on it. I plan on keeping this size tire.

if you are keeping the stock tire size---I recomend the gear change before engine swap

Thanks guys.

Really doesn't matter which you do first.
When you do pull the 305, please remember to PM me the casting number of the heads, I may want to buy them from you.