3.73's or 4.10's

[Chaz]

What gears would you guys prefer in a mostly street/highway daily driven 89 suburban with occasional off road duty. 5.7 tbi motor, th400, np241, lifted on 35 inch bfg's (they actually measure 34 inch on the ground). It had 4.56's on it when I got it. I drove it that way for a while and it was ridiculous on the highway. Those gears were awesome off road though!! I replaced the rear axle with a 14bolt ff cuz the sf I had the bearings went bad. I finally took the diff cover off and confirmed the ff has the 3.73's. I've been driving it this way for bout 6 months not knowing the gear ratio and I told myself I don't think I can go any lower on it now cuz rpm's are still like 25-26k at 65 mph. Basically what I want to know is does anyone run 4.10's on a daily driver with the th400. I don't want to go to the expense of installing 4.10's and then hate driving it later due to excessive rpm's on the freeway and possibly worse gas mileage. I still have the 2.73 low with the np241 for offroad but I don't want a weak ass 4x4 either.

 

[MrMarty51]

I would like to split the difference on My 93 GMC 1500.
It has the 3:73s and I think it would be just about right with a set of about 3:90 or somewhere close to that.
I dont think it would shift down as much on the hills and I think it would get better fuel mileage too.
Of course though, remember, Mine has the 700R4 trans instead of the TH400.
I think for Your Burb,and the 400 trans; You are better off with the 3:73s

 

[Tyger13us]

I would like to split the difference on My 93 GMC 1500.
It has the 3:73s and I think it would be just about right with a set of about 3:90 or somewhere close to that.
I dont think it would shift down as much on the hills and I think it would get better fuel mileage too.
Of course though, remember, Mine has the 700R4 trans instead of the TH400.
I think for Your Burb,and the 400 trans; You are better off with the 3:73s

X2..

 

[Chaz]

Ya that's the main issue,,,,no overdrive,,,,,if I had overdrive I'd rock on with the 4.56's,,,,this truck had 3.73 stock with the th400,,,,and I think they did have a 4.10 option too with the stock tires so I would think id be ok with 4.10's,,,,,Id just like to hear from someone who runs that setup and can tell me if it sucks like the 4.56 did or is it gonna be ok for the highway,,,,and or murder me at the pump,,,,,

 

[Tyger13us]

Ya that's the main issue,,,,no overdrive,,,,,if I had overdrive I'd rock on with the 4.56's,,,,this truck had 3.73 stock with the th400,,,,and I think they did have a 4.10 option too with the stock tires so I would think id be ok with 4.10's,,,,,Id just like to hear from someone who runs that setup and can tell me if it sucks like the 4.56 did or is it gonna be ok for the highway,,,,and or murder me at the pump,,,,,

my 78 4x4 gets 18mpg with 3.73's and i cry every-time i go to fuel her up..

3k rpms @ 70mph.....

 

[Chaz]

18mpg sounds really good to me lol,,,,, I cant figure mine cuz odometer is broke,,,,drinks gas like no tomorrow,,,,,

 

[jake wells]

i dont have a burb but i cry everytime i fill it up i can squeeze 217 miles out of a 20 gallon tank 4spd 350 4bbl 4:11

 

[Driver4r]

WHEN i had my 4.11's in the rear, rolling on 32"s. I cruised at 3.1k roughly 60mph.....

I usually pull about 6mpg

 

[skysurfer]

I'm going to differ with the others and say 4.10's are a better choice if you're running 35's. I have the Th400 & 35's with a factory 4.10 rear end. At 2600 rpm's I'm doing 66 mph.

With 373's & the same revs I would be doing 72.5 mph. Dropping back to a more reasonable pace to avoid tickets puts the rpm's at 2375 and a speed of 66.2 mph.

Look at the attached link, it uses a 1.1 final drive as an example so it's spot on for a Th400. At 2375 you're well out of the window for "economy" and flirting with "lugging the engine" territory. A 454 might be happy at that pace but not a 5.7

http://auto.howstuffworks.com/auto-...wing/maneuvers/gear-ratio-tire-size-chart.htm

 

[Driver4r]

I'm going to differ with the others and say 4.10's are a better choice if you're running 35's. I have the Th400 & 35's with a factory 4.10 rear end. At 2600 rpm's I'm doing 66 mph.

With 373's & the same revs I would be doing 72.5 mph. Dropping back to a more reasonable pace to avoid tickets puts the rpm's at 2375 and a speed of 66.2 mph.

Look at the attached link, it uses a 1.1 final drive as an example so it's spot on for a Th400. At 2375 you're well out of the window for "economy" and flirting with "lugging the engine" territory. A 454 might be happy at that pace but not a 5.7

http://auto.howstuffworks.com/auto-...wing/maneuvers/gear-ratio-tire-size-chart.htm

It also matters of your camshafts happy spot and how your engine is built to run.
My L79 cam is 4deg. advanced, so my effective range is rougly 1800-6500, At 2375 my engine would love that for a cruising rpm.

And as far as economy goes, i put 3.08's in the rear end to lower the rpm( i had the axle, so in it went). I just took a 90-100mile round trip a couple weeks ago, I pulled 18ish mpg out of My hopped up 355/th350.

And for your chart, theres hundreds of those out there which have a wider rance then 1 space. For example.

You must be registered for see images

the difference between 3.73:1 and 3.91:1 is so little in affective rpm that he coule easily run 3.73's and still have pep.

Sorry for the long post and i hope you dont feel like im trying to bash you, but heres my opinion.

 

[skysurfer]

Sorry for the long post and i hope you dont feel like im trying to bash you, but heres my opinion.

That's what this forum is for, stating opinions.

Your chart, my chart, it doesn't matter, both show that 35's and 373 gears are outside of the optimum range. I don't doubt that engines can be built to cruise at lower rpm's, but we're talking about a stock tbi motor. I couldn't find a chart showing the sweet spot in the hp and torqe curves but it's more than 2375 rpm's based upon the factory specs.

1990 5.7L TBI: Standard (VIN "A") 190 HP @ 4000 RPM, ft-lb torque 300 @ 2400 RPM.
Optional (VIN "K") 210 HP @ 4000 RPM, torque same @ 2800 RPM.

 

[MrMarty51]

Now You fuggers making Me want to go and spend a bunch of money, foolishley, on a tach.

 

[Driver4r]

I got my 70's Speed Pro tach for 2$ on a garage sale, and my truck is the 2nd vehicle its been in.

 

[MrMarty51]

I got my 70's Speed Pro tach for 2$ on a garage sale, and my truck is the 2nd vehicle its been in.

Yeah MAN, if I had one of those, I`d not be for letting it go either.
If You happen to come acrost another one at that price, gimmee a shout, I`ll double Yuhr money. Heck, I`ll even top it with paying for the postage.

 

[Chaz]

Skysurfer,,,,,so you're telling me you like running the 4.10,s on your burban with the 35's,,,,,??? The only question I have is are you sure you have 4.10,s because I think im runnin around 2600 rpm at about 65 in my truck with the 3.73???? My speedo could be off though but it feels like I dont want to go deeper gears for any highway driving.... I think I just want 4.10 for cool factor anyway,,,,,,naw i really want my 4.56's back,,,,