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Requesting advice on gear selection...

One_Ton_k5

One_Ton_k5

1/2 ton status
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Jan 30, 2003
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Location
St Paul Minnesota USA
Hi all, I am about to buy new gears and ARB lockers for my 14 bff and d60 and I want to get it right the first time.

Here is a little info on my truck:

88 Chevy R30 Crew Cab
93 6.5 Turbo Diesel
93 nv4500
70's era 203
70's era 205
d60 front with leaves
14 bolt full float rear with 4 link

All these parts are in my shop current undergoing full rebuilds.

Now for my question:

I want to get this gearing done right. I used the search function here and elsewhere to try an find as much info as I could and here is what I came up with:

I have the early nv4500 with the 6.34:1 lo range and a .73 OD.
Currently building the setup for an ORD doubler so 1:1, 2:1, 4:1.
My axles currently have 4.56:1's.

I went to 4lo.com and with what I have learned, namely that your final crawl ratio should match the circumference of your tires, and found that 4.88 will be the closest match. Here are the results for crawl and highway uses:

low-range.png


high-range.png


So running 40 inch tires: 40 x 3.14 = 125.64

That also make for 1795 RPM @ 60 MPH.

What do you guys think of these numbers? It is very important to me that the truck handle the on-road as well as the off-road.

Thanks for reading this far. :D
 
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If you already have 4.56 gears than my suggestion would be too leave them alone versus spending the money to go to 4.88. It's just a lot of money to spend for a minimal difference. I've personally driven identical trucks with the exception of a one step difference in gears, and trucks before and after doing this, and I could never tell any "seat of the pants" difference between them.

You definitely don't need to worry about the off-road crawl ratio with the NV4500 and doubler, so just take that out of the equation. In my opinion axle gears only really affect street manners and again I don't think the 7% difference between 4.56 and 4.88 makes a noticable difference.
 
4.56s would drop your street/highway RPMs too low. Even 1800 at 60mph sounds a bit low but I'm not sure what diesels run as far as RPMs go. I'd go 4:88s with 40s at least, if not the next step up.
 
I'm building the diesel and shooting for 300/500 HP/TQ

Even so, I am concerned that the 4.56 may be to high. I'm changing the diffs anyways, so a difference of a few hundred, while substantial enough, isn't enough to stop me from putting in new gears.

I'm just trying to get it right, cost is secondary. ( Within reason ;-)

With that in mind, do the figures look correct?

Thanks.
 
If you think 118 rpm @ 60 mph is worth the cost of new gears front and rear ($400-$500 for parts) then go for it, assuming you would just keep the existing ring and pinions in the diff.
 
Well I was planning new R&P either way as I found metal shavings in the 14 bolt while tearing it down and my "new" 14 bff is a hybrid of three different 14 bolts.

Thing is, I know it's a hard thing to pin down since I'm trying to hit the most efficient power range for the 6.5 to cruise at.

It's pretty much a guess at this point though. If I go to low on the axle gears, I may end up with an unusable overdrive below 80 and that is what I am trying to avoid here.

The 5.3 in my 06 z71 cruises just fine around 1600 on the hwy but the crew cab is much bigger, heavier and has more friction loss in the drivetrain.

Thanks.
 
If you're gonna re-gear anyways go with 5.13's. When you say 40" tires I'm assuming you mean 39.5". Safe to assume at best they're really about 38.75" tall.

60 mph, 5.13's and the NV4500 is 1948 rpm. Ideal sweet spot for a 6.2 or 6.5 is 1800 rpm at freeway speed. This is for max cruising economy. With the larger tires and poor aerodynamics I'd say 1948 rpm at 60 mph is much closer to ideal. Still leaves room for blitzing it up to 75 mph once in a while, but should cruise nicely at 60-65 too.

Rene
 
SInce I know you have had this combo in the past Rene, I will pay close attention to what you say.

What gears did you have in your old k5?

Thanks.
 
I ran 4.56's, and with the SM 465 it was great around town, but got pretty revvy on the highway. I only got about 500 miles on the NV4500/doubler set-up. Around town it was fine as well...but I never used 5th. That was fine for me, I wanted 5th for the highway and didn't need it around town.

I think 4.56-5.13 is gonna be in the right range for you. My opinion is if you have your mind set on swapping gears you may as well go 5.13. It'll be snappier around town, 5th gear would be more useful even on lower speed secondary roads, and freeway speed it'd be within the right range for best economy.

Rene
 
My pleasure!

How about some pics of your truck though?

Rene
 
Well it's not much of a truck at this point as everything is in teardown mode for a complete rebuild. After gears and ARB's at least the axles will be done.

Here's a few pictures anyways....

The first one is the day I bought it. ($400) 2 wheel drive - th400 - TBI 350

After I took the utility box off, I discovered both rear leafs and a u-bolt on each side were completely broken. The 1/4 inch bolts on the spring keepers were the only thing holding it together on both sides. Drove it home 40 miles that way.

Test fitting the 6.5 turbo diesel I got from the 93. I bought the 93 for $350 and drove it home. It needs head gaskets.

After toying with the idea of using the 4l80 that came with the 93, I decided I'd rather have a manual and bought this nv4500 off my local Craigslist.

I'll do a more complete build thread when I have more to show but I have a lot of work to do and money to spend before then.

Thanks again Rene....

first.jpg

springs.jpg

donor.jpg

test-fit.jpg

gears.jpg
 
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It's almost spooky how similar our builds are.

I picked up an 87 R-30 crew cab, with utility box too. My diffs are dirty, but are 'done'...60/14. Have the NV4500/203/205 already. My 6 pack also came with a TBI 350, but had a SM 465.

Still debating engine. I have a decent 6.2 in the Garage which is one option. OTOH I've always wanted a decent big block, and this will never be a commuter. i have lots of time to decide, mine looks quite similar to yours right now. Same reason I don't really have a build thread up either. ;)

Rene
 
You got any pics of yours posted up? It looks more red than orange to me.

What are your plans?

The way I'm going, I seriously think it's going to be too nice of a truck to take off road. Crazy right but maybe after I drive it for a year or two.....

:crazy:
 
The only real pic I have is in my sig. Definitely not pretty, but pretty solid.

My plan roughly is this:

Convert to 4WD. approx 6" of lift up front with some off the shelf kit springs. Rear I want to link, coils and shocks instead of spendy coilovers

Likely a 37" mud radial like the KM2...might push it to 38". Stock steel rims and dog dish hubcaps.

It'll be a short box stepside. That I have been working on already. A '58 GMC stepper. It'll either look good, or not. We'll see.

Engine to be decided, maybe a 6.2, or maybe a rowdy big block. Again haven't decided. Definitely the NV4500 and most likely the doubler too. The mission statement is more of a resto-mod than a hard core wheeler. I'm attempting to make it appear stockish (at least not advertise the mods if possible) The doubler with the triple sticks doesn't fit that, and prolly would be serious overkill for the Crew's ultimate end use.

70's front clip. this rig will see real paint in a pale green metallic.

Bumpers will be premium chrome replacement bumpers, no step bumper in the rear. Likely a hidden winch behind the front.

End use will be comfy mild wheeler, explore, etc. Not a rock crawler or tree basher. Good highway cruiser.

Rene
 
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