ForkHorn

Doing a little bit of math.... the difference at 65 mph between 4.11's and 4.56's is roughly 200 rpms. Approximately 1778 vs 1972 using the 6l80e trans and my 285/75/17 tires for calculations.

How big of a difference on MPG does that make? I honestly have no idea.

Now we look at the performance side of it...
Over the stock 3.42's in my truck, 4.11's are worth about a 20% increase in torque.
4.56's on the other hand are worth about a 33.3% increase in torque over the 3.42's and about a 11% increase over the 4.11's.

These are all mechanical torque calculations based on gear torque multiplication theory.

The downfalls are that your driveshaft is now going to be spinning a lot more and an upgrade may be needed, in addition to the extra 200 rpms of the 4.56's vs 4.11's. Each gear will also be a lot shorter. However I checked and with my tires, I would still be able to pull off 110 mph by about 5750 rpms in 4th gear with the 4.56's.

Decisions decisions....

ForkHorn

I forgot to add where some sort of trutrac or locker was borderline needed with the 4.11's, I imagine it may be downright required for the 4.56's. Lol


If my math is right... if you have a 5.3 like me and assume 300 ft lbs of torque... swapping to 4.56's is equivalent to having 400 ft lbs of torque with the stock 3.42 gears.

JRENIGAR

iTrader: (20)

Just an 09 ccsb 4x4 LTZ 5.3ff A6 tranny with factory california style 20'
s and 275/55/20 tires I believe. The 55 on the tires might be wrong, cant remember. I bought truck used at local dealer so the wheels may not be stock for this truck but they are GM 20's is all I know.

KC_kid

iTrader: (5)

mpg difference at that rpm? not noticeable. torque difference between 4.11 & 4.56? very noticeable. and from what I've read, the 4x4s don't have the drive shaft critical speed issues as much as the 2 wheel drive trucks

hog

If assuming 300lb/ft engine torque and assuming ZERO torque multiplication from a TC and 1:1 ratio in 4th gear
with 3.42's=1026 lb/ft at the rear tires
with 4.56's=1368 lb/ft at the rear tires
for a net gain of 343lb/ft at the wheels

In 1st gear same assumptions with 4.03 1st gear ratio
3.42=4134lb/ft
4.56-5513lb/ft
for a gain of 1379 lb/ft at the tires.

3.42 gear
70 mph cruise with 33" tire/3.42 gear/ 0.67:1 6th gear OD requires 1625rpm (1875rpm@80mph) That is WAY too low of a cruise rpm for any truck, esp with a GEN 4 5.3/6.2 engine. Even pulling down from 6th gear down into 5th gear raises the 70mph cruise up to 2075 with is bearable. But towing could be improved.

4.10 gear
70mph/33"tire/4.10 gear/0.67 OD ratio need 1975rpm*2250rpm@80)
Pull down inro 5th gear and 70mph cruise rpm is 2500rpm *2850rpm=80mph)

4.56 gear
70mph/33" tire/4.56gear/0.67:1 OD requires 2175 rpm(2425@80mph)
Pull down into 5th gear and you'll be revving 2775rpm at 70mph(3160rpm@80mph). Just in case you need a bump up for that hill.

These 6l80e/90e transmissions share the highest geared OD ratio with the 200R4 with its 0.67:1. Theyare coupling these trans gears with the tallest tires ever offered stock, teh trucks are at their heaviest and biggest(aero) ever, yet they expect the trucks to comfortably cruise down the highway at 1500rpm using engines that simply arent that strong at these rpms.

4.56 gears sound like a low gear, but not once you stop and think about the high trans OD ratios, the tall stock tires(compounded by taller aftermarket tires) A 275/55/20 stock tire is a 31" tire, a 235/70/15 tire from the 90's is 27" tall.
For a 6l80e/90e trans with its 0.67:1 OD and a 33" tire, 4.56 is a good suggestion. Just beware, the 4.03:1 1st gear ratio, coupled with the 4.56:1 rear gear gives you a 1st gear final drive ratio of 18.4:1 that is a short short 1st gear and 5800rpm gives only 31mph. Just remember that the C6 ZO6 will do 60mph in 1st gear. And if you are making 340lb/ft of engine torque through a 4.03 1st gear and 4.56 drive ratio makes for 6250 lb/ft of torque at the rear axle. That is a LOT of twist. Throw in a shift to 4LOW and you are pulling down houses at idle.

Gearing is great.

peace
Hog

hog

That would only be due to the taller tires typically on 4wd trucks, possibly the shorter length of the 4wd as well.

With all the standard tire sizes:

P245/70R17 all season, blackwall or white letter (29.62")
P265/70R17 AL2, blackwall or white letter (30.69")
P265/70R17 on/off road, blackwall or white letter (30.69")
P265/65R18 all season, blackwall or white letter (30.64")
P275/55R20 AL2 touring blackwall (30.98")
22-inch TBD (dealer installed)

All being within 1-1.5" of 30" getting in danger zones within reasonable speeds is unlikely.

4000 rpm with a 4.56 gear/0.67:1 gear/30.5" tire gives 119mph which makes for 5320 d/s rpm.
5000rpm makes for 148mph and 6650 d/s rpm.

All these numbers are for worst case scenario GMT900 trucks as all stock tires are taller(thus lowering d/s rpm per mph) and all stock gear ratios are higher thus again lower d/s rpm per mph.

I would suggest d/s loops and aftermarket shafts for any combo that raises d/s rpm much over stock. I had a d/s come apart on the freeway and it tore off the extension housing, the trans output shaft, split a catalytic in 2, and bent a cross member. Scary experience as I was worried about teh traffic around me and seeing that I was in the passing lane and needed to get over 4 lanes in traffic spewing smoke like a jet at an airshow.

I now sport custom steel shafts and dont speed much.

peace
Hog

HAMMER!

iTrader: (1)

Love my 4:10's with my 6l80e! On stock tires it's still good and on my 35's it's awsome! As my truck came with the 4:10's I can't compare from another gear but was a huge difference going from a 4spd to 6spd!
Now have a tad more power than the stock 6L but would imagine it would be better with 4:30's or 4:56's if you plan on staying around stock to mild power levels. If you plan on 400rwhp or more then 4:10's are fine.

hog

The difference between the 4l60e/65e/70e 4 speed auto and the 6 speed auto with 35" tires/4.10s at 70mph with both in highest gear is 75rpm.
1850 rpm for the 6l80e at 70mph
1925rpm for the older 4 speed auto at 70mph

I bet accelerating from a stock is way different with the 6 speed(4.03:1 ratio)) compared to the 4 speed (3.06:1 1st gear)

I just dont like the even greater rpm drop on the 1-2 upshift the 6 speed has, its even a greater drop than the 4 speed auto. TC would halp that though.

peace
Hog

craigsix

i just solved my fuel mileage issues i got a 2013 nissan sentra 1.8 double wizbang. 40+mpg for dd. my truck will be for playin and racin.

daves10denali

So I have a 2010 Denali 6.2 awd 3:42 gears and Im thinking of doing a gear change to 4:56 but Im not sure if it can be done without spending big dollars to do it. I know that 4:10s can be done but was hoping for the 4:56 as I have a 35 foot travel trailer that I tow Any information would be great

Thanks Guys