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OK...3.73 or 4.10

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 89Blazin, Apr 3, 2001.

  1. 89Blazin

    89Blazin 1/2 ton status

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    Well....I got straighten out quick about the myth between a chip and a tranny. Read here before GU6 is 3.42 gearing. Got GU6 in my glovebox. 350TBI, 700R, 33X12.5s. I tow an 18 ft. ski boat, (fishin boat when the kids/grandkids aren't along) and will drop 'er in drive for towing. I got the formulas from a link here that deal with tire size, gearing, etc. No tach....unfimilar with 350 power curve..

    I do a little 4X4.....mainly when deer/pheasant hunting. Some rugged stuff...not too bad. Goin to spend money...

    YOU ARE IN MY BOOTS.....WHAT YA BUYIN? 3.73 or 4.10 ?

    I currently drop from 70 MPH to 55 MPH when going up a slight incline, before she drops down to drive. I am trying to improve THAT plus still tow the boat in drive at a safe (on engine) steady RPM. I haven't a clue what goin from a 3.42 to a 3.73 will do....probably not much if I were to guess, but I really feel I don't need too much change. No idea what goin from a 3.42 to a 4.10 setup will feel like. I guess that's it....I want to know what the formulas can't do for ya....what's the performance feel like with the mentioned various setups?

    85 Burb and an 89 Blazer
    One just for fun, one simply for pleazer
     
  2. Mikee

    Mikee 1/2 ton status

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    Heres my two cents. i've been driving blazers for years. i had a '90 with 3.42 that i sold to my brother. Even with 31's it was definently inadequate.
    Now I have a '90 with 4.56's. However, it origanally had 3.73's. With a new motor and 33's it had plenty of power around town. Down the highway it would go up slight inclines no problem. Due to the power curve it would lug between 60-65 uphill in OD. 70 was fine, 55 fine. For gas mileage I would say 3.73's, they have plenty of umph. For fun 4.10's. I have 4.56's with 35's, thats mabot a 4.10 with 33's. i can catch second with ease. Runs about 2000rpms at 65. If you decide 3.73's, I have the one out of my '90. Brakes are about 65%, rear is totally rebuilt( under 200 miles) I do have the reciept. Thats just my 2 Cents.

    "Got stuck once, hung up on top of a Jeep!"
     
  3. 89Blazin

    89Blazin 1/2 ton status

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    Thanks for your "feel". What kinda RPMs are you turning in drive? Without a tach, I'm curious how many more rpms I'm running when in D vs. O...and the rpm difference at the same speed. My Burb has 4.10 with 350/carb/ TH400. I got use to the feel of that....dissapointed with the Blazer setup. This is my first TBI.. and at first I thought about more h.p. Drivin for a few weeks now....strong engine/tranny....just not geared to suit me.

    85 Burb and an 89 Blazer
    One just for fun, one simply for pleazer
     
  4. mudhog

    mudhog THEGAME Staff Member Super Moderator

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    i would go with 4.10's imho

    77blazer see it at<A target="_blank" HREF=http://community.webshots.com/user/ssmith6333>http://community.webshots.com/user/ssmith6333</A>[​IMG]
     
  5. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    What kind of mileage would I get with 31's and 3.73? I currently have 3.08.
     
  6. Mikee

    Mikee 1/2 ton status

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    Well first I'll try to answer your RPM questions.
    With 3.73's and 33's, in D at 65 you will run about 2450RPMS, in OD you will run about 1750 RPMS.
    With 4.10's and 33's, in D at 65 you'll run roughly 3000 RPMS, probably more like 2800-2900. In OD you'll run about 2000.

    To answer the gas mileage question, in my '90 with a new motor, 31's and 3.73's I'd average 15mpg around town. However this is with a very light right foot. The most I ever got was on a hunting trip down the highway, and that was 18mpg.

    Hope this helps you guys

    "Got stuck once, hung up on top of a Jeep!"
     
  7. Wheels

    Wheels 1/2 ton status

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    Being that you will be towing a boat, 4.10 as a minimum with 33's. Drop the tranny out of OD when towing or you'll shorten the life of the tranny real quick.
     
  8. 87JIMMY

    87JIMMY Registered Member

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    I run 33's w/4.10s and I love the combo. Around town it's very "snappy" even w/a very tired 350 (260k). On long trips (200 miles freeway) towing my boat I sometimes wish I had a gear between D & OD though. It seems like I'm over-reving for too long in drive and I won't tow in OD. I guess it depends on how much towing compared to regular driving you do. Hope I didn't add more confusion.

    Scott 87JIMMY
     
  9. Emmettology 101

    Emmettology 101 3/4 ton status

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    4.10's would be best, but will reduce MPG.... If you are really concerned about MPG go with the 3.73's And like someone else said, dont tow in OD..

    Also, Run a big cooler on that to keep your 700r4 happy.


    <font color=green><A target="_blank" HREF=http://emmett.coloradok5.com>http://emmett.coloradok5.com</A></font color=green>[​IMG]
     
  10. 89Blazin

    89Blazin 1/2 ton status

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    87 JIMMY....you didn't confuse me more...you shined a little light. I tow the boat 10 times or so a year....200 miles or more. One of my concerns, you hit on the head. Running long, loaded down, runnin higher RPMs than I feel real comfy with.

    Appreciate all the posts...if I was younger (sigh...when I couldn't afford a boat and wanted to play around town), 4.10s sound like the ticket.

    Not needing to much more umph, I think 3.73s are lookin like the setup I want. I'll read some more input...

    85 Burb and an 89 Blazer
    One just for fun, one simply for pleazer
     
  11. muddin4fun

    muddin4fun 3/4 ton status

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    I'm gonna go 4.10's when I put 33's on. I used it to tow a lot.

    [​IMG]
    <A target="_blank" HREF=http://k5chevyblazer.homestead.com/home.html>http://k5chevyblazer.homestead.com/home.html</A>
     
  12. Sparky

    Sparky 1/2 ton status

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    Go 4.10's. If you want to tow with 33s in Drive (assume you mean overdrive or 4th gear). 700r4s are netorious for burning up that way. If you dont get 4.10s you will be shifting in and out of 3rd and 4th all the time. In the mean time... tow in 3rd gear unless you are doing 75 plus. Also, the 4.10s will probably actually help your city mileage while they might hurt you a little on the highway. I say its a trade off for gasmileage.

    sparly

    When all else fails... Check the blinker fluid.
    78 K-5
     
  13. gokartergo

    gokartergo 3/4 ton status Staff Member Moderator

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    Go to <A target="_blank" HREF=http://www.ring-pinion.com/>http://www.ring-pinion.com/</A> They have a caculator for your engine and what ever tire sizes you have to what gears you want and it figures out your rpm. I was going to go with 4.10's untill I did this calculation. I decided to go with 4.56's.

    Become one nature..........Then marinate it..
     
  14. muddin4fun

    muddin4fun 3/4 ton status

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    Ummm...on a 700R4, they last a lot longer if you say out of overdrive when you tow. I had a pick up with a 700R4 and when I put any weight on it, it would down shift to third constantly and there is just too much slipping when driving in OD for towing. Even with a cooler, it will get too hot. 700R4's are very heat sensitive so when you tow, keep it in third...just my opinion. [​IMG]

    [​IMG]
    <A target="_blank" HREF=http://k5chevyblazer.homestead.com/home.html>http://k5chevyblazer.homestead.com/home.html</A>
     
  15. Daveytree

    Daveytree Registered Member

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    I ran 33 in. tires with a 410 setup for a little while. It was very snappy around town. It also had quite a bit of torque. When I was on the highway it felt like it was running too high in the r.p.m.'s. I didn't like that. When I was running bigger tires it was more comfortable. Be careful with that tranny. I had a B&M tranny cooler in mine (the best they make). I also didn't tow in O.D. My tranny blew when I was towing up an incline. Tranny fluid caught fire and burned my truck up. I wouldn't want the same thing to happen to anyone else. Just use caution.
     
  16. 87 mid canada k5

    87 mid canada k5 1/2 ton status

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    Had my 4.10's for two days now,running 33's, switched from 3.42's. Sure feels good around town peppier off the line and generally feels like the motor is in it's proper range. Took it on the highway a little, first time I've used o.d. in years, the tach is definetly going a bit higher and I can see I will think twice about speeding it would get costly on gas. Also gonna have to do something about that speedo, it must be close to 10 mph over now, over all so far I'm glad I did it!

    Denis
     

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