Gearing

[A1971Blazer]

More pondering...just loooking at available axle ratios it seems as if the 44 and 12 bolt matching ratios jump from 3.08 to 3.73 both have some in between choices yet they don't match up on any of them.

Running the 4L60E with 33" tires I suppose the 3.08 will be the best all around? I can always use 4L if I need some low end grunt (pulling my boat up some steep boat ramps?) and then have the high gear for interstate cruising?
Give me some opinions....It's got 3.08 now so if I look at "easiest" 3.08 it is...?


Gonna rebuild both ends probably tru-trac the rear

 

[Greg72]

Without running the math but just thinking in general terms, it seems like 3.08 is going to be too tall for an overdrive transmission. It will probably hunt in and out of OD pretty bad.

With a heavy truck, you have to be careful not to go too tall in the axles..... It will be a total dog off the line, and won't be very fun to drive around town. My guess is that you're going to end up in the 3.73 or 4.10 range with the OD....

-G

 

[A1971Blazer]

Without running the math but just thinking in general terms, it seems like 3.08 is going to be too tall for an overdrive transmission. It will probably hunt in and out of OD pretty bad.

With a heavy truck, you have to be careful not to go too tall in the axles..... It will be a total dog off the line, and won't be very fun to drive around town. My guess is that you're going to end up in the 3.73 or 4.10 range with the OD....

-G

Greg,
that may very well be the case.....I was surprised that this thing had 3.08 gears with the 4 speed manual. Was this the case on most of them?
Never drove it but I can imagine with the 465 it also had to be a dog in anything but granny gear...until you got it up to speed.

I guess it will be time to sit down with the calculator soon.

on edit:ran the math
33" tires 65 mph .7:1 OD

3.73=1210 RPM
4.10=1330 RPM
4.56=1480 RPM

 

[Greg72]

sM465 is a 1:1 ratio in 4th if I remember correctly.

With a small factory height tire, it would work fine. Once you start going to larger tires and OD transmissions the axle gears MUST get deeper to compensate.

There are a few online calculators to play with.... You'll get it figured out pretty quick.

If not, I'll be looking out for ya!


-G

 

[A1971Blazer]

sM465 is a 1:1 ratio in 4th if I remember correctly.

With a small factory height tire, it would work fine. Once you start going to larger tires and OD transmissions the axle gears MUST get deeper to compensate.

There are a few online calculators to play with.... You'll get it figured out pretty quick.

If not, I'll be looking out for ya!


-G

You have a knack for spotting the "greenhorns" huh?.....
I've done all this before, but back then I was looking for the lowest possible crawl ratio for my Jeep build, 5.13 with Atlas 3.8:1, and 39½" tires
Now I'm looking for good power with driveability.

I would think with the LS1 stock, 4L60E, and 4.56 gears, this thing will be a tire smoker from a standing start.............and still cruise with decent fuel mileage.

rest assured, I will be picking your brain along with everyone else willing.....thanks to all for all the info so far

 

[Greg72]

Do some Googling on that new engine you bought and see if you can find a HP/TQ graph for it....

Best highway efficiency is when you are cruising at the RPM that is near the torque peak of the engine. Basically the motor is most lightly loaded at that RPM so it's fuel consumption is at it's lowest.

As before, we'll work it backwards from the tires (and transmission) to figure out a good matching axle ratio.

You might be in the ballpark at 4.56.... I forget what size tire are you planning again?


-G

 

[A1971Blazer]

Do some Googling on that new engine you bought and see if you can find a HP/TQ graph for it....

Best highway efficiency is when you are cruising at the RPM that is near the torque peak of the engine. Basically the motor is most lightly loaded at that RPM so it's fuel consumption is at it's lowest.

As before, we'll work it backwards from the tires (and transmission) to figure out a good matching axle ratio.

You might be in the ballpark at 4.56.... I forget what size tire are you planning again?


-G

whatever will fit with a 4" lift...33" was the number, which leads to another question of wheel size/backspacing.

Good place to start I can look up the LS1 specs, I will likely just leave it stock. I had one in an '02 Vette........nice motor


on edit:
HP....310 @ 5200 RPM, 320 @ 5800 RPM
TQ....340 @ 4000 RPM, 330 @ 4400 RPM

 

[AJs72K5]

whatever will fit with a 4" lift...33" was the number, which leads to another question of wheel size/backspacing.

Good place to start I can look up the LS1 specs, I will likely just leave it stock. I had one in an '02 Vette........nice motor


on edit:
HP....310 @ 5200 RPM, 320 @ 5800 RPM
TQ....340 @ 4000 RPM, 330 @ 4400 RPM

Once you decide on tire size, rim size become more a matter of what "look" you're trying to accomplish. Cost of the desired tire at said rim size may vary greatly and is another factor.

For me, I'm geared at 4.10 with 35s and a 700r4. I'm dropping in a 450+ HP big block and seriously thinking about going 4.56s as most of my driving will be around town. The highway driving I will do won't be bad with the overdrive. Need to get the dang thing running first tho....

 

[A1971Blazer]

I've re-geared several Jeep TJs that went to 33" tires with the 4.0L6...some were 4.56 but I always recommended 4.88
My Z06/LS7 will cruise at 65........about 1350 rpm... 26 MPG ...!

 

[Greg72]

I've re-geared several Jeep TJs that went to 33" tires with the 4.0L6...some were 4.56 but I always recommended 4.88
My Z06/LS7 will cruise at 65........about 1350 rpm... 26 MPG ...!

Heavy truck does not equal light Corvette (or Jeep)!!!

Corvette will get away with super tall gearing because it weighs 1/2 of what a Blazer does..... jeeps need deep gears to overcome a weak motor (relative to a V8). If the motor can make lots of low end TQ, you can gear it a bit tall.... If the motor is tired or weak, a deeper gear can help wake things up!

-G

 

[ekajkrats]

33s can fit with zero lift. Mine can attest to that. I have done only mild wheeling (no locker yet, so that should give you an idea when I say mild and still running the common 3.07 gears) and have rubbed once. The corners of my wheel wells are turned in a bit in the back of the front wheel wells. If you are only street driving, 35s may fit if you can center the wheels properly in the wells. My 2 cents on fitting tires.

 

[A1971Blazer]

33s can fit with zero lift. Mine can attest to that. I have done only mild wheeling (no locker yet, so that should give you an idea when I say mild and still running the common 3.07 gears) and have rubbed once. The corners of my wheel wells are turned in a bit in the back of the front wheel wells. If you are only street driving, 35s may fit if you can center the wheels properly in the wells. My 2 cents on fitting tires.

What about the correct backspacing? should it be 4½ or will 3½ work and not rub the springs?

 

[6.2Blazer]

3.08 gears with the 4 speed were fairly common. The granny low first gave plenty of grunt but the 3.08 axle gears allowed decent highway RPM. However with the 4L60 and 33" tires I think the 3.08 will be way too high to use the overdrive gear very often. Keep in mind that even going to 4.10 axle gears would give you lower RPM on the highway with the 4L60 as compared to a non-OD trans like the SM465 or TH350.

 

[vtblazer]

If you plan on keeping it drivable a reasonable formula that seems to always work out well is to start with your 'intended' tire size and work the RPM's backwards from there gearing towards streetability. (highway travel)

3.08's with an overdrive tranny and larger tires would make for a seriously 'not fun' truck to drive around.