I hear that - I've got a Fold-A-Cover sitting in the box on the floor of my garage. Getting tired of tripping over it, so who knows ... maybe I'll get off my lazy *** some day soon.

 

That's hilarious! Mine is only sitting in the garage because I'm out of town on business. I ordered it from my hotel, and it arrived (along with my new K&N filter) on Monday.

 

I posted in another thread and then found this one. Are any of the posters that swapped to either 3.90 or 4.10 still around? Still happy with the swap? I have a 2010 ecsb 5.3 2wd. Engine is stock. No CAI. No tune. No headers. Current gears are 3.42. Considering going to 3.90 or 4.10. Tires will be 285/45r22.

 

I bought a barely used 2011 4wd 5.3 6l80 truck in 2012. My first mod was swapping to 4.11 after a few months of owning. I now have a cam, converter, headers and a few other minor things, but the gears made the most in-town impact that made a huge driveability impact, if that's a word. Just better all around in town. And Hwy for that matter. I gained about .5mpg both in town and Hwy going from 3.08 to 4.11. I'd do it again, first thing. All daily driving this truck in town other than 5-6 Hwy trips a year. Don't hesitate on going 4.10/4.11 with the 5.3, especially on a heavy truck. I also have stock 20s and factory ride height, minus the rear lift blocks. And yes, this thread was a factor in my decision. This heavy truck jumps off the line, but I've never raced it.

 

 

Thanks KC_kid! I was hoping to hear from someone that actually made the swap. Speculation is fine but real world experience is much more valuable (IMO). Looks like you've got a great helper too.

When I spoke to a shop here, they said I would probably be spinning around 2050 in OD on the freeway at 70 mph with 4.10 gears. That doesn't sound that bad too me... My main concern with 4.10 is that 1st gear might be too quick vs 3.90. Do you find that you almost skip (for lack of a better word) through 1st?

I don't know if I mentioned that I live in the communist state of Kalifornia, so I can't do headers, cam, etc. And even things with a CARB EO# are a pain in the a$$! So I like stealth mods like gears. And a tune. I could get a tuner because I can reload the stock tune easily enough. But in general, a lot of people say a tune won't do much if I don't do the other things (CAI, CAM, headers, etc)... So if anyone has experience with adding a Diablosport tune to a stock engine lemme know.

 

A tune will be huge difference, very much worth it. I had an autocal tune from Black Bear (see sponsor list on the right) before I had a local tune and that is the "lowest" level of tuning that I would recommend. From what I've heard, diablosport or other off-the-shelf tuning products are not worth it, but I have no experience with that.

I like the short first gear, it gets this truck moving better with less effort from the engine. I probably shift out of first around 10mph with regular driving, 20mph if I floor it. If you hit the gas hard with this low first gear, truck jumps hard, which can be fun.

You can calculate your RPM very easily. As mentioned before in this thread, choose a RPM you are comfortable turning at your typical highway speed and then back calc your gear ratio. 6th gear is a ratio of 0.67. Your tire height for 285/45r22 is 32.1". Use a constant of 336.13.
RPM = (MPH*trans ratio*gear ratio*constant) / tire diameter.
RPM = (70*.67*4.10*336.13) / 32.1 = 2,013 RPM.
IMO you'll get good MPG turning 5.3 at 2050.

There is a guy on here that went 4.56 on a 6.2 crew cab with factory tire size, called it his "highway truck" and loved it. Don't fear the gear! I couldn't go 3.90 cause they don't make it for the front diff, so I went 4.11 and love it.

 

Thanks! Yeah I need to keep repeating that mantra "don't fear the gear." TBH I am getting pretty close to pulling the trigger...

 

What he said. One has to understand how gearing works and it's purpose. The reason engineers use gear ratios is to multiply torque input. That is accomplished by allowing the input rotation to turn more frequently in one revolution than the output rotation. Axle 4.10 rotations of input for 1 rotation of output. When you further multiply the input through transmission gear manipulation, you further multiply the torque potential.

Trailblazer SS's come standard with 4.10 gears. With the 6L90 in it, my first gear is programmed to upshift between 5 and 9 mph with normal driving and redline at 20 mph, but it isn't something that will cause alarm in the day to day. More importantly it gets you up and moving with heavy loads quickly and you can program the trans to take off in 2nd if you have a heavy foot and are concerned about blowing out the tires. Mine is AWD, so I rarely have that problem and even in the rain/snow, that's what traction control is for.

The key is to know what your effective ratio is. A 4.10 geared 6L80 has a 2nd gear like a 3.90 gear 4L80 1st gear. But now you have the advantage of a 1st gear that is even better than a 4.56 geared 4L70 1st gear to get your weight moving quickly; and less engine strain. Remember engine load is what burns gas, not just engine RPM. Numerically high gearing allows you to do more with less power. If you already have a lot of power, THAT'S when you spin tires. But we have the advantage of traction control which moderates so that we can have as much power as we can make in the engine and still be able to get JUST enough down to the tires to maximize acceleration. Sometimes that means using less of your gearing than is available, but that's a good thing when you don't have to wind out your engine.


(6L80) 4.10 :1
Gear Ratios Eff Ratio
4.03 16.523
2.36 9.676
1.53 6.273
1.15 4.715
0.85 3.485
0.67 2.747

(6L80) 3.42 :1
Gear Ratios Eff Ratio
4.03 13.7826
2.36 8.0712
1.53 5.2326
1.15 3.933
0.85 2.907
0.67 2.2914


(4L70) 4.56 :1
Gear Ratios Eff Ratio
3.07 13.9992
1.63 7.4328
1 4.56
0.7 3.192


(4L80) 3.90 :1
Gear Ratios Eff Ratio
2.48 9.672
1.48 5.772
1 3.9
0.75 2.925

 

Thanks TrueBlueGTO for the detailed response. I did not know the TBSS came with 4.10 gears... That fact. your analysis, KC_kids experience and all of the anecdotal evidence seems to support 4.10 gears (or at the very least 3.90). TBH I don't actually expect the MPG to increase but I do expect the DFF (Driving Fun Factor) to increase. :-)