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Choosing gear ratio

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nixit

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Bridgport, TX
I'm having trouble deciding what gears to run. Any input would help.
This will be a DD with light to medium trail use... but mostly highway if we are being honest

Mild Fuel injected LQ4 / 4L80E / 14bolt SimiFloat / 10bolt / 37's
grimmjeeper.com says
5.13 2620rpms @ 75 / 1922 @ 55
4.56 2329rpms @ 75 / 1708 @ 55
Are 5.13's to much for highway? How much difference in MPG is it negligible compared to the lift, tires, cage, roof rack, and my right foot?
 
Mostly highway I vote 4.56's. The LQ4 should have more than enough tq at light throttle and ~2000 rpm to move your truck down the road, and @75 it's still not too buzzy.
 
Yes lots of highway I'm building this for more overlanding/family vacation vs ripping trails
4.88 would be 2493 @ 75 / 1828 @ 55
I guess I can go with that, I just wonder if I'll ever wish I had went with 5.13's
 
Why are you concerned with MPG? Not to be a jerk about it, but with what you are talking, you'll probably be in the 12's or so at best? 1MPG difference is an 8% increase in economy, which is equivalent to a $.04 increase per gallon of gas if you are paying $2/gallon, which I saw last I was down there.

When you figure the rig is, at the cheapest, costing you $.10/mile (federal figure is around $.50/mile) a $.003 increase is negligible. Before anyone beats me up over that cost per mile figure, go ahead and add up every bit of expenditure on your rig, to include things like oil changes, tire replacements, routine repairs, insurance and acquisition cost, and spread that over a 100,000 mile lifetime. It only gets worse the fewer miles you drive.

If MPG is a concern, slowing down is going to net you way more "bang for your buck" than choosing gears trying to optimize for economy, not to mention most people are happier with numerically lower gear sets off road.
 
Fastereddie said:
4.56's and a doubler. Best of both worlds.
Click to expand...

That's the plan with my similarily set up burb. I'm only on 35s(for now) but the 4.56s are fine for town and highway, but not low enough for trail use. This is also my first auto off road, but I not sure that 5.13s would have been enough for me either. This big body needs to move real slow when the going gets tight.
 
dyeager535 said:
Why are you concerned with MPG? Not to be a jerk about it, but with what you are talking, you'll probably be in the 12's or so at best? 1MPG difference is an 8% increase in economy, which is equivalent to a $.04 increase per gallon of gas if you are paying $2/gallon, which I saw last I was down there.

When you figure the rig is, at the cheapest, costing you $.10/mile (federal figure is around $.50/mile) a $.003 increase is negligible. Before anyone beats me up over that cost per mile figure, go ahead and add up every bit of expenditure on your rig, to include things like oil changes, tire replacements, routine repairs, insurance and acquisition cost, and spread that over a 100,000 mile lifetime. It only gets worse the fewer miles you drive.

If MPG is a concern, slowing down is going to net you way more "bang for your buck" than choosing gears trying to optimize for economy, not to mention most people are happier with numerically lower gear sets off road.
Click to expand...

Heck if it gets 12 - 13 I'll be very pleased, I was thinking it would be more like 10 or less. Im not overly concerned, but it's always in the back of my mind.

I would like a doubler but there are so many other areas I would like to improve on also
 
Is this a K5 , or a burb??
I would think 4:88 or 5:13 with the 37s.

@azblazer
Granted, elevation makes a difference.
 
Well up here, I would go to the lower ratio due to mountains and air starvation....
I have 4:56s in my '70 big block truck and I liked it when it had 33's. Now with 35's there is less pep..
Keep in mind how much it takes to push a brick through the wind.
Now maybe, at your elevation, the 4:88s will be good.
But I definitely wouldn't go 4:56....
 
I will be spending some time up there, Love the logging roads. I've wasted allot of time daydreaming about moving to CO or northern NM.
 
Obviously we are all biased one way or another. If it's a daily driver, and you expect it to be so for 10 years, and you put 12K a year on it, ok, might be worth trying to ratchet the MPG up 1 or 2. Which in that case another vehicle that gets 30+ MPG may actually save you money. 12000 miles at 12MPG is 1000 gallons, for $2000 in fuel cost, a 30MPG car has a cost of $800.

Really boils down to what you need and want you think is most important. I tend to think the 4:88's are a decent compromise from the ranges you've given, but will you ever "need" them, vs. 4.10's?

What gears are they now? Pretty sure 4.10's aren't uncommon in the 14SF, that might save you a bundle right there, if you already have, or can get and use as-is a complete 14SF.

And on another note, while more difficult I assume, you could certainly try it (without using 4WD if front/rear ratios don't match of course) out as-is, and see how you like whatever gears are in it. I'd think 3.73's or numerically lower would be fairly bad with 37's.

Looks to me like 4.10's and 37's are nearly equivalent to what I run with 3.42's and 33's. I'm sure there is more acceleration or towing power to be had, but I don't feel it's a bad compromise between engine speed and felt power.
 
The donor truck had 33's and 4.10s and I wasn't really impressed. I noticed a big loss of acceleration when I went from 27 to 33's. and coming down the mountain required allot more braking or 4lo.
 
I'm going with 5.13's.
compared to the stock tire size on the donor with 4.10's.
At 75 5.13 will run 77 rpm higher / 4.88's will run 50 rpm lower not a huge difference either way
 
nixit said:
I'm going with 5.13's.
compared to the stock tire size on the donor with 4.10's.
At 75 5.13 will run 77 rpm higher / 4.88's will run 50 rpm lower not a huge difference either way
Click to expand...

This is a good choice you will never be able to tell the difference in the buzziness or vibration of the motor.

I was gonna say 5.13s. you'll love em
 
With od 5.13 would be good. But with a lot of highway driving I might not want that deep of gears. Small blocks like to be in the 2000-2500 range for good cruising. I kinda wish sometimes I hadn't gone so deep on mine but off road was a huge difference. The blazer will never get good gas milage but I also don't want to scream down the road at high rpm either. You lose efficiency every mph you go over 55. But most roads are now 70 limit anymore. With od you will be fine more than likely at 5.13.
 
LS motors can make better MPG than older SBC. The LQ4 likes to be under 2000 rpm to do it, though. That's the only reason I would consider 4.88, for freeway driving. Also remember that 4L80 doesn't have as low of a 1st gear as 4L60.
 
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