so I have a 1999 Chevy blazer ZR2 Ls with the 4.3L on 33s I'm wanting to upgrade my gears I'm pretty sure I want run the 4.56. Everything under the hood is stock right now.


I plan on doing some upgrades but nothing major(air intake, exhaust, intake manifold...etc) it will probably be a bit on that. I want to do my gears first so I can get my MPG back.


My first question is what kind of MPG do you think I can get before my upgrades(stock) with the 4.56 gear?
And second once I do my upgrading will those gear still be enough?

 

mostly highway or stop and go driving? those gears would help to get the blazer going but will hurt you on the highway. 4.10's would be close to stock performance.


if you were at ~2600 rpm with 31's and 3.73's, you would be a little over 3000 rpm with 33's and 4.56's and ~2700 rpm with 33's and 4.10's


I'm getting around 14 mpg on average with 3.73's, 33's, and max energy tuner programmed for more power.

 

+1 on what Jamaroon said. Unless you do mostly city & offroad driving I think the 4.10 gears would be better all around for mileage. I have the 3.73 gears with 32" tires. I find that around town this setup is ok, great on the highway, and a little too tall offroad. My commute is about 60 miles per day on the highway with very little city driving, and I average about 16mpg with my setup. My drivetrain is basically stock, with the same Hypertech tuner as Jamaroon.

Just for fun, my Dodge Durango is great with 3.73 gears and 32" tires, but that 5.7L Hemi pushes a lot harder than the 4.3 Vortec.

 

yea mostly city. Very rarely does it see highway. Also I have the 3.73 or so I was told because I have the ZR2 package? Is that right? If so I'm getting really crappy MPG with those gears.

 

Yes you should have the 3.73s in your truck now. If you are really concerned about your mpg perhaps you should consider a smaller tire like the 31s it came with factory. I haven't spent any time looking for gears for a factory front diff for these things cause I just don't really think its worth the time but I don't believe there is much in the way of aftermarket gear selections to fit these things

 

I agree with these guys, your mileage goes for a shat as soon as you install bigger tires and even a minor lift. I have 4.88 and 35" tires(equivalent to 33" and 4.56) and on the highway i get about 15mpg and about 12mpg in town if I'm gentle. All around I think it's about as good as I could hope for. On the highway, it would be nicer to have the RPM slightly lower, but then the engine would be out of it's power range, which it needs to be in to keep it moving in overdrive lockup. On the trails it's great, but 5.29(4.88 with 33's) would be better mind you.

I think you should go with 4.56.

 

Well after thinking about it I'm probably just going to try and get more power from the motor I'm not really that worried about it but would like to at least get 14-15mpg or so because right now I'll be lucky if I'm getting maybe 10 haven't checked don't really know but it's bad so I probably try some minor stuff first like an air intake and exhaust Or should I just go straight for a programmer?

 

Programmer is going to be best bang for your buck or better yet a pcm tune.

 

pcm tune? I would take it to a shop and have them tune it?

 

What is a good programmer to use with the 4.3l?