4.56 gears K2XX 4x4 L83

300 Blackout · September 22, 2018

I am going to repeat my mpg calculation with E85 after I finish this tank of 87 gasoline. There is a noticeable difference between E85 and 87 gasoline in how often the truck goes into V4 mode during city driving. On E85 it almost exclusively traveled in V4. So far, that is not the case with the 87 gas in city driving conditions.

I don’t want to speak too soon, so right now I’m data logging everything on the tuner for an objective comparison and will repeat it again once I fill back up with E85. Then I’ll crunch the numbers and post my results.

It would be fascinating if E85 provided just enough additional torque over 87 gas that the vehicle can switch to V4. I’m very interested to see if this results in E85 getting better fuel efficiency than 87 gas.

300 Blackout · September 22, 2018

300 Blackout · October 1, 2018

15.35 mpg on 87 gasoline hand calculated. That’s a 28% increase over the previous 12 mpg that I was averaging.

Just filled up with E85 so we’ll see how this compares to the gas. Unfortunately, I still had 1.5 gallons of gasoline left in my tank when I filled up so it’s not gonna be as accurate but still will be good for a general idea.

Centex14 · October 1, 2018

Lower gears don't always mean lower mileage. My g37s I stepped up from 3.23's to 4.08's and lost none on the highway and gained slightly in town. My 392 charger I jumped from 3.23 to 3.73's and highway and city mileage never changed. If you've got bigger tires then lowering your gears and giving your engine a better mechanical advantage can very realistically improve mileage. Higher RPM's don't necessarily mean higher load and that's what a lot of folks don't realize or forget. Of course there is a point where you can over gear but I can definitely see where the OP is getting better mileage.

300 Blackout · October 14, 2018

The following fuel efficiency of E85 is not a fair comparison to 87 gasoline because my driving habits were vastly different during this time period. After the gears were broken in at 500 miles I changed the differential fluid and I began testing the capabilities of the truck. In short, I was driving the vehicle much more aggressively compared to when I had 87 gas in it.

E85 averaged 10.25mpg being driven aggressively. Some anecdotal observations are fuel mileage on the instant reading seemed to be similar to 87 gas while driving around town. Freeway driving, however, showed a distinct disadvantage of the E85 in terms of efficiency.

The horsepower gains of E85 are very noticeable. With the stock gearing and bigger tires, E85 was a necessity to help alleviate the sluggish response of the truck. With 4.56 gears and E85, it’s actually quite entertaining how quick the truck is, especially at the shift from first to second at WOT since the engine is right in it’s power-band.

Kmbz71 · October 24, 2019

I got a quick question. I recently bought a 2016 Silverado 1500 z71. Its got all the bells and whistles but after doing some digging i found out the previous owner had 4.56 gears installed. I bought this truck from a Chevrolet dealership and i think they didnt know about the gear swap. Im speculating but do you think the dealership would have wiped out the aftermarket tune for the gear swap and reset it back to default? The truck will get up and go but there are times that if i really hammer on it especially when i go to make a pass the rpms get so high so quick the engine will cut off. Its happened more than id like to admit. The truck has 35's on 22's and drives like a dream otherwise but sometimes i wanna let it sing! Do you think i need to take it to a tune shop? Is this normal with 4.56's? First photo is without tows second photo with tows.

Edited October 24, 2019 by Kmbz71
Had to make a point that I had up dated mirrors.. i shelled out that much $$ everyone is gonna see them

flyingfool · October 24, 2019

you might want to toss the 22's and get 17"-18" rims if your gonna run 35 tires.

I'm running the z71 tahoe rims , 18" whole wheel and tire weighs 64 lbs. origionally truck came with the 20" wagon wheels they weighed about 80lbs. the handling improved dramatically on the z71 wheel set. the shocks actually function now. before the swap , the wagon wheels would bounce multiple times after hitting a bump in the road.

the best rim would be 17" in my opinion.

flyingfool · October 24, 2019

On 9/22/2018 at 1:36 PM, 300 Blackout said:

that gauge isnt accurate, use the average mpg under the milage trip , reset it after a full tank then drive.

Kmbz71 · October 24, 2019

42 minutes ago, flyingfool said:

you might want to toss the 22's and get 17"-18" rims if your gonna run 35 tires.

I'm running the z71 tahoe rims , 18" whole wheel and tire weighs 64 lbs. origionally truck came with the 20" wagon wheels they weighed about 80lbs. the handling improved dramatically on the z71 wheel set. the shocks actually function now. before the swap , the wagon wheels would bounce multiple times after hitting a bump in the road.

the best rim would be 17" in my opinion.

Are you replying to me? If so i didnt ask for anybody's opinion on my wheel and tire combo. I was asking if the previous owners custom tune and calibration for the 4.56 gears may have been restored to a factory tune by the chevrolet dealship i bought it from. The truck drives great. The only thing is when i accelerate [WOT] to go out and pass someone my truck will cut off because of the rpms get up so high so quick. Im wondering if its doing this because its not properly tuned for the gear ratio or asking if this is normal.

KARNUT · October 24, 2019

Are you replying to me? If so i didnt ask for anybody's opinion on my wheel and tire combo. I was asking if the previous owners custom tune and calibration for the 4.56 gears may have been restored to a factory tune by the chevrolet dealship i bought it from. The truck drives great. The only thing is when i accelerate [WOT] to go out and pass someone my truck will cut off because of the rpms get up so high so quick. Im wondering if its doing this because its not properly tuned for the gear ratio or asking if this is normal.

I’ve used lots of tunes. It possible to set the shift points too high and cause the truck to cut off. Usually it will go ahead and shift. Sounds like some fine tuning is in order. You could alway manually shift it just before cut off. Us old dude’s use have to drive that way.

Sent from my iPhone using Tapatalk

Jacoby · October 25, 2019

On 10/23/2019 at 7:13 PM, Kmbz71 said:

I got a quick question. I recently bought a 2016 Silverado 1500 z71. Its got all the bells and whistles but after doing some digging i found out the previous owner had 4.56 gears installed. I bought this truck from a Chevrolet dealership and i think they didnt know about the gear swap. Im speculating but do you think the dealership would have wiped out the aftermarket tune for the gear swap and reset it back to default? The truck will get up and go but there are times that if i really hammer on it especially when i go to make a pass the rpms get so high so quick the engine will cut off. Its happened more than id like to admit. The truck has 35's on 22's and drives like a dream otherwise but sometimes i wanna let it sing! Do you think i need to take it to a tune shop? Is this normal with 4.56's? First photo is without tows second photo with tows.

All the dealer did was take that truck in on trade, get it detailed and put it right out on the lot. They didn’t reflash anything. If they had flashed it back to stock then the speedo would be waaaayyyyy off. What sucks is if you don’t have the tuner that was used your kinda screwed and in reality need the dealer to flash it back to stock. That way you can go out and get a proper tune.

jumpinjoe · October 25, 2019

On 9/21/2018 at 12:56 AM, 300 Blackout said:

Grumpy - so far it seems to be functioning fine. I haven’t adjusted any shift points on the tuner, it’s still the stock settings. It’s not searching for gears. Downshifts are much more noticeable and effective to slow the vehicle down.

Ski - I haven’t taken it on the freeway yet. Right now I don’t drive more than 20 miles before letting it cool down. I’ll take a short trip on the freeway tomorrow and get back to you.

Centex - If you found a shop that is willing to install your own parts you could probably get it done for a little bit cheaper. The cost of my parts through the shop was over $1200 and labor was just over a grand. I probably could have bought the parts online for $800. To me it was worth it to have this particular shop do the install and give them the ability to order exactly what they needed. Everything is warranted by them for a year and I get peace of mind that the job was done right along with knowing the money went somewhere local.

If you’re going to do 4.56, you may want to consider a new driveshaft. With 33.5” tires (actual measured diameter, not factory new specs), the driveshaft will self-destruct around 95mph. The reasons why someone would be traveling that speed are another topic, just know, if you hit that speed, it’s almost certain the shaft will catastrophically fail.

I'm really curious .... if you went to 4.56 gears in the rear and made no changes to your tranny shift points, even with 33.5 Dia. tires, just what kinda RPM are you seeing on your engine as you go through the gears? Not knowing what truck you drive, I don't know what tranny you're running either. I'll assume high gear is 1:1 unless there's an OD involved. Thanks.

Regards,

jumpinjoe

300 Blackout · October 25, 2019

I'm really curious .... if you went to 4.56 gears in the rear and made no changes to your tranny shift points, even with 33.5 Dia. tires, just what kinda RPM are you seeing on your engine as you go through the gears? Not knowing what truck you drive, I don't know what tranny you're running either. I'll assume high gear is 1:1 unless there's an OD involved. Thanks.

Regards,
jumpinjoe

A lot has been done to the truck since the gears but I’ll try to fill in some blanks. 5.3L L83. Trans is a 6L80. The truck is a 4x4 and it’s original gears were 3.42.

After the 4.56 gears were installed, I used a TruXP tuner (rebranded Superchips) to reflash the ECM to let it know I had 33.5” tires and 4.56 gears. I didn’t adjust anything else in the calibration, however, it is probable that TruXP automatically recalculated my transmission shift MPH to accommodate the gears and tires.

There’s a couple reasons I think the TruXP must have adjusted the TCM calibration when I updated my gear ratio and tire size. My transmission shift RPMs didn’t change. At the time I thought the TCM shifted the trans based upon engine RPM. When I saw the shifts occurring at close to the same RPMs, I assumed the trans calibration was still stock. Now I know the trans shifts based upon MPH at a given throttle %.

Also, the truck never redlined no matter how hard I pushed it. It never cut off the spark and always shifted appropriately.

I now have 7,000+ miles on the gears and I still believe it’s one of the best investments I’ve made. I gave up on maximizing my fuel economy and decided to install a supercharger instead. So....yeah...4.56 gears + 4x4 + supercharger means she jumps off the line like a rabbit but fizzles out shortly thereafter. Tons of torque in the low and midrange (570lbs-ft according to the ECM) but the high RPM power of a blower just can’t compare to a turbo. And, with 4.56 gears, the truck gets into the high RPM range much faster than with 3.42s, so, I might have chosen the wrong power-adder for my gearing, but it’s still awesome.

jumpinjoe · October 25, 2019

The reason I asked is that way......back in about 1970, my brother and I built an exact (part# specific) duplicate of a 1969 Z28 small block Chevy motor to put in my bright 'GTO' orange '55 Chevy 210. It was known around town as pretty bad before that, but after the Z28 motor went in I really liked it.

Then my bro suggested we should drop to a lower gear to really get the best out of that small block from light to light. So, we put in a 4.56. Big mistake!

Before the gear swap and with a 3.73, I could light the tires in 3 or 4 gears and actually pull the front tires up in 2 of those, so it was no slouch. But then I could drive normally around town and the RPMs of the motor were sensible. After the 4.56 went in, and running a Muncie 4 speed tranny, even in high gear the RPMs would be up around 4200 as I recall at 55 mph. My folks lived about 3 hours away at the time so it was a hard pull for my car to make that trip very often. Obviously it was stupid to kill a good engine like that so went back to the 3.73's and continued to tear up most of the local draggers until I sold the car in about 1973-4. BTW, I never was a really big 'light to light' racer, I always much preferred the circle track.

Now I don't remember exactly what size and type of tires I had at the time (probably something like7.50- 7.80/15 or maybe 8.00-8.25/15, but certainly they were not 33.5" in dia so that played a big part in my RPMs and yours with your truck. But I was just curious just how bad it did affect you after the change out.

Thanks for the come back and info.

Regards,

jumpinjoe