I have a question regarding the difference in average mpg between the 4:10 rear end and the 3:73 rear end. I don't do much heavy towing maybe 3000lbs for about 2 thousand miles a year . I got the truck off the lot and over looked the rear end gears and was curious how much a difference it will make with the 2004 crew cab 5.3l . Right now I am getting about 15.5 mpg by hand but I only have 900 miles on it. Thanks Steve








2004 cc 5.3 4 x 4

This is a touchy subject but what they heck. There is a mind set with most that lower RPMs is best for MPG but this is only true to a point. You have a 5000lbs + truck with stock 31's or biggers and a 5.3. 3.73's is tall in my book for this combo for best overall performance and mileage. When overdrive is engaged your final drive ratio is about 2.61 and that 5.3 will be straining a bit to use it and will suffer badly in head winds and small grades. Also, gas V8's tend to be more efficent at higher RPMs (less fuel used for HP/hr delivered) so there is nothing really gained with lugging it. GM puts tall gears in that truck (yes 3.73 is tall with OD in that combo) to squeak max possible MPG out on EPA dyno tech, not for you to get best performance. If they can get another .1 MPG in that test, they will do it. Problem is that test does not relate to real world very good. A 5.3 likes to rev a bit to make its power and with 4.10 it will run better and most likely get better MPG to especailly around town. Whether it is worth the cost to you to make the swap is something you have to decide yourself.

Snowman is right, you can get 10 different answers from 10 different people on this subject.

I took an Impala SS, which is near the equiv of a 1/2 ton truck, slapped on added cooling, 3.73s gears, upgraded driveshaft and programming (and a large list of other odds and ends) and I was able to tow 6,300lbs without ANY issues, even towing up some significant grades. Granted I could tell the 4L60E didn't like the added weights on the grades, but in the end, I towed very successfully with that car. Mostly because I drove like I wasn't in a stock car race when towing.

You're 5.3L will work just fine with either set of gears towing 3000lbs. If you look at the numbers Chevy puts out about the 5.3L, you'd see that the tuck in 1/2 ton form is rated at anywhere from 6800lbs to 7800lbs (approx) with 3.73 gears and upwards of 9000lbs with 4.10s. That is trailer weight, not gross combined vehicle weight. 3000lbs, provided you don't have an additional ton or two in the pickup bed will be nothing more than an afterthought. The 4L60E in the 1500 series will be just fine with 3000lbs for 2000 miles.

I would suggest that you do two things if you find you don't have them.

1) Get a trans temp gauge. Priceless when towing and a must have. I didn't have one in the Impala, but installed one later. A must for anyone towing.

2) Make sure you have a trans cooler. Nothing can kill a trans faster than excessive heat.

As for MPG, my view is pretty simple. You didn't buy a truck to get an instant membership into Greenpeace, you bought one and found an honorary membership in OPEC! . http://www.dieselplace.com/forum/smileys/HiHi.gif Anything over 10mpg towing is awesome. Over 13 mpg not towing, a gift! I've gotten bad MPG with 3.73s and bad MPG with 4.10s both towing and not. If you're looking for great gas mileage, get a Prius, but the reality is that it won't tow very well. Anything that's got guts, costs money to operate.

RPMs are somthing to look at too as they can translate into better or worse MPG and delivery of power from the engine. Usually, higher RPMs equal better HP output, but HP costs money and that translates into more fuel costs. However, in your stated situation, 3000lbs for 2000 miles a year, it might not warrant a drastic change of swapping a rear end to 4.10s given the fact that with 3.73s and a 5.3L you are using half the GM stated tow capacity for that truck.

Now if down the road you come back and say I've got 5000lbs, or plan on getting a 5th wheel or something similar, all bets are off, but with 3k lbs....enjoy your truck as it is. http://www.dieselplace.com/forum/smileys/Big Smile.gif

Yeah but if you ever plan on upgrading to bigger tires, 3.73's and a 5.3 would suck so if tire are in your future, you better make gears too.

I just want o say thanks guys for your views on the situation . I have been reading topics from this entire forum and I am amazed and impressed with the wealth of knowledge and more importantly the willingness of everyone to help each other. Thanks for the help Steve.





Since you reminded me yea the bigger tires are coming in the future. So I guess I will love and hug my 4:10's.

We have are moments, all of us... If you plan to go real big like 35's or so you might consider 4.56's. Good Luck and welcome! http://www.dieselplace.com/forum/smileys/Hug.gif Edited by: snoman

Just some added info. I have a 2003 GMC ext cab, 5.3L, Quadrasteer with the 4.10 rear end. 90% of my driving is city. I got and average of 13.6. Have just over 20,000 miles on the truck. In town, the 4.10 has good get up and go from a stop and pulls trailers with ATVs or firewood or bass boat with no problems. Best MPG is around 65 mph. Get up to 80 and it drops down to around 15. I some added weight from front and rear reciever hitches and a toolbox full of tools, an under rear seat storage box with equipent, a front grill guard, and a winch on many days.

I recently added a Westers 89/93 tune and my city is now right at 15 with much more acceleration.

If you drive a lot on the highway, I would get the higher gearing. Just depends upon what you are wanting. Good luck on your choices.

If you drive a lot on the highway, I would get the higher gearing. Just depends upon what you are wanting. Good luck on your choices.

Not really because as you exceed 65 or so it is more than just a "gearing" issue. The faster you go, the more drag there is and the more drag there is, the more fuel you burn per mile unless you as in a vaccum riding on zero friction bearing which is not a SUV or 4x4 P/U!

But, with two identical trucks and one is turning higher revs, it will get worse mpg. I have a friend with almost the same truck and configuration, except for the 3.73 and 4.10 gears. He gets 19-21, whereas I get 18-mid 19's, both being all highway driving at 70 or so, no trailer or loads. The wind resistance will increase exponentially, thus my dramatic drop at 80 vs 65.

But, with two identical trucks and one is turning higher revs, it will get worse mpg. I have a friend with almost the same truck and configuration, except for the 3.73 and 4.10 gears. He gets 19-21, whereas I get 18-mid 19's, both being all highway driving at 70 or so, no trailer or loads. The wind resistance will increase exponentially, thus my dramatic drop at 80 vs 65.

Not always so, even with to identical trucks there is differences (the driver for one) Over Drive really take the bite out of a 4.10 axle ratio and along with 31's or so, it is pretty tall. You must remember that a V8 likes to turn some RPM to be its most effiecent (HP hrs per gallon of fuel) and when you compare a 3.73 vs a 4.10 in OD, the engine has to produce atleast 12% more torque to cruise than with 4.10's ans since it is runs about 2 to 300 RPM slower, it is out of the power curve it will have less availbe torqe at say 1800 or 1900rpm than it will at 21 or 2200 RPM and less HP is availible at 65 in OD with 3.73's than with 4.10 (HP is basically HP x RPM with a twist. We are not talking about a streamlined light weight car here but a 5000lb plus truck with areodynamics little better than a brick with rounded corners.

The trucks I am referring to have the same setup (except where noted after taking initial measurements)--stock--no tire changes--same engines, exhaust, intakes, no tire changes from stock. Almost identical weight, setups, engine, transmission, accessories, tires (even brands and model). The main difference is the rear end ratios. The results shown are not with towing, racing, etc., just driving with a light foot on the pedal attempting to get an accurate comparison. I've tried running in tow haul, and in 3rd, etc. Best gas mileage came staying below 70 on the highway for me and in OD.


Just real results, not theoretical losses due to stance of the truck, transmission friction, oil, wind, humidity, fuel loads, fuel temps, air temps, coefficient of friction differences due to surface or tire compound, waxes used, etc. Just a real world comparision of two almost identical trucks that articbouncer inquired about, with the main difference being the rear end ratios.

The ONLY way to get a real world valid test would be same truck, same driver, same route, different gearing. Personally, I would not own a 4x4 truck with a OD tranny without at least 4.10's in it to begin with because I buy it for a truck, not a car. Edited by: snoman

I have a question regarding the difference in average mpg between the 4:10 rear end and the 3:73 rear end. I don't do much heavy towing maybe 3000lbs for about 2 thousand miles a year . I got the truck off the lot and over looked the rear end gears and was curious how much a difference it will make with the 2004 crew cab 5.3l . Right now I am getting about 15.5 mpg by hand but I only have 900 miles on it. Thanks Steve


2004 cc 5.3 4 x 4





I agree with SNOMAN. My brother has a 99 4x4 w/5.3L and it came with 3.73s. He tows a TT when he goes camping or hunting and the truck really strained on the hills with downshifting all the way to low gear at times. He contemplated programmers, but decided on a gear change. He swapped the 3.73's for 4.10's and tells me it's the best thing he ever did to the truck. Not only can he tow in overdrive, it rarely shifts down lower than 3rd. In addition he has picked up 1.5 mpg in around town driving. He goes on and on about improved acceleration and all around performance since the change. The downside, if you consider it a downside, is that both front and rear gear sets need to be changed and it will require a PCM program change. This change cannot be done at the dealership unless you have a dealer that is in to hot rodding. Your best bet is going with a vendor like www.pcmforless.com (http://www.pcmforless.com) Bryan Herter is pretty sharp on this stuff, but I'm sure there are other good tuners out there. Anyways, good luck and keep us posted on what you decide.
JP

The dealer can do it if they want to (reprogram ECM) becaue 4.10 is a factory option. All else fails, Hypertech for one will let you program for different tires and axle ratios as many times as you want.

The dealer can do it if they want to (reprogram ECM) becaue 4.10 is a factory option.


Well, I hope he has better luck than my brother did. His dealer changed tire size to accomodate the gear change...Ha. Anyways, I think you'll be happy with the 4.10's and the PCM programming has many options to enhance your truck's performance.


JP

Got to find a dealer that the service manager is kinda laid back. Not all of them will do it but a bigger dealer that sells and services fleet truck so do it. The one that does it here is into fleet sales.

I totally agree. Some dealers will do it, if the vehicle had the option from the factory. In northern Illinois, Lattoff is one of those kind of Chevy dealers.
Edited by: Silvertwinkie

If you drive a lot on the highway, I would get the higher gearing. Just depends upon what you are wanting. Good luck on your choices.

Not really because as you exceed 65 or so it is more than just a "gearing" issue. The faster you go, the more drag there is and the more drag there is, the more fuel you burn per mile unless you as in a vaccum riding on zero friction bearing which is not a SUV or 4x4 P/U!


i get just over 20 mpg when driving at 80 with the cruise on and some times 85. when i do 70-75 mt milage is 18 almost 19 mpg and 65-70 is back to 20 and the slower i go untill 50 the better gasmilage i get. so how come my truck gets better gasmileage at 8-85 than 70-75? also i got 19 mpg towing a car trailor unloaded with 2 axles at 75-80mph


my truck in completly stock. and these are just hand caluations. them figuares are all on the same highway going to the same place every time.


i believe once a engine gets into a rythem it runs the best. thats why we got cruise control. also i think that the reason it gets better the faster i go is because when it comes to a hill its got the momentom to get to the top with out straining.


but i think 3:73 would be better if he does any type of highway driveing. 3000 pounds is nothing. i put 3000 pounds in my bed. i think you should get 3:73's and be happy. how much bigger tires are you gona put on? 285's are the biggst you can go on stock suspention.

i get just over 20 mpg when driving at 80 with the cruise on and some times 85. when i do 70-75 mt milage is 18 almost 19 mpg and 65-70 is back to 20 and the slower i go untill 50 the better gasmilage i get. so how come my truck gets better gasmileage at 8-85 than 70-75? also i got 19 mpg towing a car trailor unloaded with 2 axles at 75-80mph


my truck in completly stock. and these are just hand caluations. them figuares are all on the same highway going to the same place every time.


i believe once a engine gets into a rythem it runs the best. thats why we got cruise control. also i think that the reason it gets better the faster i go is because when it comes to a hill its got the momentom to get to the top with out straining.


but i think 3:73 would be better if he does any type of highway driveing. 3000 pounds is nothing. i put 3000 pounds in my bed. i think you should get 3:73's and be happy. how much bigger tires are you gona put on? 285's are the biggst you can go on stock suspention.

By what reason or logic do you compare the gearing requirements of a diesel to a gas engine????? A gasser has a completly different power curve. A diesel power peaks by 3000rpm and torque peaks well before that so it needs to turn slower. A gasser peaks a lot higher and needs to turn faster to get in its sweet spot where efficiency is it highest (torque peak). Also, you could put 4.56 gears in a gasser and still do 120mph or more, put those same gears in a diesel and you wil never see much over 85 or 90. To completely different animals. 4.10's with OD play best with a gasser in a big truck with OD for overall performance and MPG with 4.56's doing best for very serious towing with gassers. Edited by: snoman

So since peak torque RPM for the 5.3 is 4,000 I should get my best efficiency by running at 62 MPH in 2nd gear (which is right at 4,000 RPM with my 3.73s). I don't think I'm going to try that.


I'll admit that at 55 MPH mine downshifts for every significant hill, but even at 1800 RPM (62 MPH in O/D) it'll climb most hills without shifting.


Peak efficiency for a gasser in terms of horsepower hours per gallon of fuel consumed does occur at or very near peak torque RPM AT WIDE OPEN THROTTLE. For producing a particular amount of torque at the rear wheels the gearing that will result in the widest throttle opening is generally the most efficient. That's because it takes a certain amount of air and fuel to produce a certain amount of HP, so the mass airflow (and fuel flow) of an engine turning slowly with a wide throttle opening and near ambient manifold pressure producing a certain amount of power is similar to the mass airflow of an engine turning faster with a smaller throttle opening and lower manifold pressure (higher vacuum). The difference is that the pumping losses are much higher for the higher RPM = higher vacuum situation so a lower percentage the power produced in the cylinders is available at the wheels. Since we started by saying that the power at the wheels was a constant that means more air and fuel will be consumed by the higher RPM, small throttle opening combination.


All of the above discussion assumes constant air/fuel ratio, that cylinder pressures are not excessive enough to require retarded ignition timing and that there isn't enough valve overlap to let unburned charge to reach the exhaust manifold at the lower RPM. None of those assumptions are even close to correct for hot rod engines with carbs, but all are pretty good assumptions for a port fuel-injected, ODB-II, roller cam emissions motor like the 5.3.

Oh yeah . . . peak efficiency for a normally asspirated diesel . . no contest, it's always at best torque RPM because that's where the engine breathes the best (achieves peak cylinder filling). With no throttle valve to complicate things the best filling happens at the same RPM regardless of the fuel rate.


Peak efficiency RPM in a turbodiesel, that's between God and the camshaft and turbo designers. It varies with load. Generally the lower the load the lower the optimum RPM . . . at higher loads low RPM results in low boost over-fueling . . .peak efficiency arrives when airflow is just sufficient to burn the fuel required to produce the specified power cleanly. Higher than necessary RPM increases friction, and due to the slow burning nature of diesel, wastes more of the "push" later in the stroke.


The moral of the story for TDs is that very tall gearing is good for light load fuel economy, but downshifting is more efficient than smoking along at low RPM for the heavy load/steep hill combination, even if it "can" climb it in overdrive. For stock D-maxes the Mass Air Flow (MAF) sensor and ECM "smoke map) won't allow over fueling at low RPM, low boost, so the highest gear it will pull the load in is the most efficient. For those of you who modify . . .smoke is fuel that didn't make power, you figure it out.

So since peak torque RPM for the 5.3 is 4,000
I should get my best efficiency by running at 62 MPH in 2nd gear (which
is right at 4,000 RPM with my 3.73s). I don't think I'm going to
try that.


I'll admit that at 55 MPH mine downshifts for every significant
hill, but even at 1800 RPM (62 MPH in O/D) it'll climb most hills
without shifting.


Peak efficiency for a gasser in terms of horsepower hours per
gallon of fuel consumed does occur at or very near peak torque RPM AT WIDE OPEN THROTTLE.



Not reallly on the peak efficiency at WOT. Maximum HP hours per gallon
of fuel is below that setting. As far as crusing RPM, while a 5.3 peaks
at 4000 rpm in theory, in practice it is closer to 3500 RPM or so good
compromise for a cruising rpm is 2100 to 2600 RPM (depending on ground
speed ie, 60 to 75mph) is a good cruise in OD for stock tires in a big
P/U and if you down shift to drive with a load on a hill it puts you
near or in the engines torque peak so that it can give you its best
effort. With big rubber add a few hundred RPM to that figure.