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Those with 38"+ tires and non-OD trannies...

Re: Those with 38\"+ tires and non-OD trannies...

I have a slush box TH350/NP203 ans 4:56's and 38's. 4:88's will be fine for freeway 5:13's would be the limit, you'd be the slowest rig on the freeway as not to over rev you motor. But with larger tires you'd be ok.
Bill
 
Re: Those with 38\"+ tires and non-OD trannies...

350/TH350/203/205/5.13's/39.5's

try telling the rocks that they gears are good for the freeway /forums/images/graemlins/waytogo.gif
 
Re: Those with 38\"+ tires and non-OD trannies...

I ran 39.5" tires with 3.73's for a few years. I ran them with a manual and an automatic. The problem I had was bad lower gearing in the hills and due to the high gearing the drivetrain was loaded up all the time. I went through drivelines, trasfercase adapters and broke the rear of one tranny. After I went to 5.13's, I have not broken anything at all. I would at least go to 4.56 gears.
 
Re: Those with 38\"+ tires and non-OD trannies...

Im running 4.10's a TH350 NP205 and 38X12.50 SX's.......Im planning on a Doubler next year but I do wish I had 4.56's now. Its too high geared on the rocks and the street. Ive only got a wimpy 350 engine though....
 
Re: Those with 38\"+ tires and non-OD trannies...

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turning 3350 rpm at 70 with 5.13's and 38's

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I'm ok with that. My /forums/images/graemlins/k5.gif isn't my DD and really, a sbc should be able to run in between 2800 - 3500 rpm all day long and be fine. Mine was designed to run that way and I have noticed that if I lug it, it sucks gas like there's no tomorrow. I am currently still running my 3.73's and really wish I had 5.13's, 4:88's at the least.
 
Re: Those with 38\"+ tires and non-OD trannies...

I have a 700R with a non-lockup converter, 5.13's, and 39.5's and it will run down the freeway and keep up with traffic. I can't really go much faster because the tires are....well.....swampers.
 
Re: Those with 38\"+ tires and non-OD trannies...

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i have the sm465np205 4:10 39.5 combo and i really wish i had 4:88's-5:13's

[/ QUOTE ]

Or a Doubler...
 
Re: Those with 38\"+ tires and non-OD trannies...

[ QUOTE ]
Thanks for the ideas, all, but geez...sounds like you guys have no problem with running an engine at 3,050 rpm on the freeway (1.0 tranny gear, 5.13 axles, 39.5" tires).
Personally, I'm not comfortable doing that, I'd rather be below 2500. (With 4.10's I'd be at 2400)

Looks like right now I should be thinking about the 700R4-5.13 or NV4500-5.13 setup.

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I run my small block at 2700-3000 RPM down the highway with 33" tires and 4.10 gears and still get 13-15 mpg empty. This is in a 3/4 ton longbed pickup too. The small block is made to make peak torque around 2500 RPM (but that can change depending on modifications). You will find your best mpg is when you keep your motor in its peak torque band on the freeway. /forums/images/graemlins/thumb.gif Plus you still have some power left over for passing.
 
Re: Those with 38\"+ tires and non-OD trannies...

I run a 350/th400/241 and 37's with 4:10's. I can cruise 70 all day which is nice but it needs more grunt for wheeling on rocks. The engine is tired and stock. I plan to cure the low range problem with an Atlas. Only reason for doing the Atlas is it will be cheaper to do then the Doubler. Reason for it being cheaper is add up everything to do the Doubler, rebuilt trans, rebuilt t case, Doubler adapter, crossmembers, driveshaft mods, output flanges, triple stick, and other parts. I can do an Atlas with 1350 CV flanges on both sides for less then $2200 up and running.
 
Re: Those with 38\"+ tires and non-OD trannies...

Holy shnikes! 4.56 for 35", really? I'll tell you now that this is NOT a rock crawling K5, I'll save that for my 'yota... I drive my K5 45 miles every day to and from work, and at least 2 times a month I make a 300 mile round trip to my hunting cabin. The only wheeling my K5 sees is on old skid roads/logging trails and improved dirt roads. I will be making a trip from SF to Bend, Oregon this summer to visit my bro, and I plan on doing that trip at least once, if not twice a year. My 350 is a Targetmaster crate, the only performance mods I have are the E-brock performer intake and 600cfm carb. What I am looking for is something that will not leave me feeling underpowered when I take off at a stop sign(currently 33" w/3.08, oof /forums/images/graemlins/doah.gif), yet still give me good cruising ability at 70-75mph(33 w/ 3.08 /forums/images/graemlins/thumb.gif). Last night after my first post, I went and crunched the numbers and figured that 4.11 would be the ticket. Now, I am doubting myself again. As soon as my tax return comes in, I am buying new tires, rims, and gears, so I am trying to figure out what EXACTLY I wanna get. It looks like this is something that cannot be nailed down to a definite answer, and 4.11 might just be the happy medium when looking for that "takeoff from stop 'oomph', and that cruising at 75mph 'zing'". I am definitely open to more oponions on this. /forums/images/graemlins/ears.gif

I like the way my K5 cruises at 75-80 with the 3.08's and 33's, but I want a bit more "grrrr" when acceleratin from a stop, especially here in hilly San Francisco. So I plugged my current values into the 4lo.com calculator, and then changed the tire size to 34.8 (actual dia. of a BFG mud terrain) at the same rpms and checked what gear ratio it came up with. 3.27 is what it said, so I figured that 3.73 would give me that oomph I was looking for. TRhen I come back today and read this post, and once again I wonder what it is I really need. /forums/images/graemlins/dunno.gif Now I am thinking "What did that 700r4 that rifguitar and hi-pinion got cost?" OHHH nooo! I only want tires and gears, not spend even mo' money! Eh, by the time i get my $$$$ I hope to have it all figgered out. /forums/images/graemlins/whistling.gif
 
Re: Those with 38\"+ tires and non-OD trannies...

Gear/Tire Ratio Chart

Check out this chart it might help you ake your decision. I have 3.08 and 33's on my /forums/images/graemlins/burb.gif with a 700-R4 and I really wish I had 3.73's in it. 3.08's are just too tall for it. Remember, when you keep your stuff close to factory ratio, you get similar to factory performance for torque and rpms where you need them to be. If you over gear, you'll rev your eng. too high, if you under gear you make your tranny slip till it eats itself up. My 700-R4 was $1300 to have rebuilt and I had it "bullet proofed". I will still be changing my gears to 3.73's pretty soon. But what you need to decide on is WHAT WORKS FOR YOU. Like I said before, there are many opinions and not every one works for every person. So, do the research and figure out what works for you and your driving needs. I personally don't like running 35's with 3.73's, but thats just me! /forums/images/graemlins/grin.gif
 
Re: Those with 38\"+ tires and non-OD trannies...

Try this gear calculator - Calculator Since the original poster asked for input from those who don't have OD trannies I didn't chime in, but since a few have, I'll add my 2 cents worth.

We recently went to 5.13's with 38's, 700R4, NP241, all behind our 383. My son and I recently made a little road trip in the to see Tim @ 4x4 Iron, which was almost a 400 mi round trip. I was extemely happy we were able to get 15 mpg for the trip. Without the OD the 5.13's are a little to much on the highway, but off-road you won't be disapointed.
 
Re: Those with 38\"+ tires and non-OD trannies...

I just looked up the calculator. If I read it right, then my /forums/images/graemlins/k5.gif with it's TH350/3.73 gears/38" tires is running at 5200 rpm at 70mph in 2nd gear?? /forums/images/graemlins/yikes.gif That can't be right. There are times on the freeway when I manually down shift into 2nd to pass and I know I'm nowhere near those rpm's. In my previous post, I was referring to his mention of 3.07's and 33's. I run 3.08's and 33's on my /forums/images/graemlins/burb.gif and very rarely do I get a chance to use OD. Only on the long straight flat stretches, otherwise it bogs down too much. Even with the cruise on, it doesn't spend much time in OD..and that's the computer doing it not me /forums/images/graemlins/histerical.gif
 
Re: Those with 38\"+ tires and non-OD trannies...

Remember being mad while driving into the wind, getting bad mileage and listening to the tranny hunt around? Putting you Burb higher into the wind and adding fatter tires is going to greatly increase the wind drag. One thing will help overcome the drag. Torque. Either from the motor, or better gearing. PREFERRABLY both. /forums/images/graemlins/waytogo.gif

The deeper gears mentioned here will cure that....If I knew the 700R4 would live forever, I would run 5.38's in my 'Burb with the planned 36" tires. Why you ask?

I feel the gearing gives me more freedom to build the motor I want. I do not need to run 80 mph anywhere in the 'Burb with larger tires. Is saving 15 mins THAT important on the trips to Green Bay? I will bet you waste the 15 mins with an extra gas stop anyway /forums/images/graemlins/dunno.gif /forums/images/graemlins/dunno.gif

With trying to specialize the truck more, more compromises are to be done. Without a lot more gear choices (tranny/T-case) the 0-80 mph range you are expecting great performance from will leave a compromise at one end or the other. Just the nature of the beast....

Remember a motor is most efficient at it's torque peak.

All these decisions would be easier if GM hadn't put in such a deep OD gear. I believe a 30% OD ratio is just to steep. I think many of the gearing/burning up trannies issues would have been solved if the OD ratio was a little more friendly, like 15 or 20%.

My .01 cent /forums/images/graemlins/waytogo.gif
 
Re: Those with 38\"+ tires and non-OD trannies...

Using the calculator I provided above, your rpm's at 70 in 2nd gear w/3.73 & TH350 would be 3509, which seems a little more realistic than the 5200+ rpms.
 
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