4.stupid

03 to early 07 trucks seem to get shitty mileage no matter what you do to them...at least from what I've seen.

Anyway, figuring out RPMs is super easy. Just need the OD ratio, gear ratio, speed, and actual tire size.

Mounted and with weight on them, pull a tape on the rear tires. It's probably somewhere between 33.5 and 34.5" tall, truth be told. Different manufacturers actual height varies quite a bit...even with the same size tire. We'll use 35" for math purposes to show worst case.

The formula is as follows:

- 336 (the constant) x gear ratio x speed
- Divide that by the tire size
- This number is RPMs at whatever speed in 1:1 gear
- Take that and multiply by OD ratio (.69 in your case)

336 x 3.73 x 65 = 81,463.2
81,463.2 / 35 = 2,327.52
2,327.52 x .69 = 1,605.99

So, now, you're running 1,606 rpm at 65. Give or take a few. Actual tire size will make it vary some. If the tires are 33.5-ish...it could be as high as 1,680 rpm.

Now then, with 4.10s, we're talking 1,765 to 1,844 rpm....again, depending on actual tire height.

So, you'll go from 1,650 rpm to 1,800 rpm. 150 rpm difference. THIS is why everyone says to not worry about regearing it. You'll blow 2,000 bucks out of the water between parts, labor, and gear oil for 150 rpm. Probably more, depending on how much they charge for labor and where you buy the parts from.

You've got a stock turbo and it'll still spool perfectly fine at those RPMs. Tuning changes fuel delivery, timing, boost curves, and throttle input amongst several other things. It'll generally make more power and get better mileage as a result. However, the stock torque converter probably sucks and is just soaking up more power with the larger tires.

With all that being said, I'd save the money for now and do the transmission build and tuning first. If you still feel like it has to be regeared, by all means, go for it. Anything bigger than a 35, I definitely would if it were me. In my case, I went from a stock 30.5" tire to a 32.5" tire AND a 67mm non-VGT turbo. I want 4.10s too, but I still have a stock transmission and converter. The majority of my lackluster feelings stem from the horribly loose stock torque converter, its inefficiency, and inability to drive the turbo like it needs to be. After the transmission, if it still needs it, I'll gear to 4.10 and do a 6th gear conversion so I can still run 80 down the interstates.


Hopefully that helps and proves some points!
 
All this talk about spending multiple thousands of dollars on a well used truck and won't pony up to fix a $200 gauge cluster.

What a waste of time for everyone

Sent from my moto g fast using Tapatalk
Not even, $150 for it.

 
I still stand behind my first statement that a good tuner on a 30-50HP setting will do everything the OP wants, including slightly better fuel mileage.

I think Smarty is a great canned tune. EFI live can be fantastic but that’s all up to the tuner and I would stay far, far away from SMR Diesel in Colfax.
 
I still stand behind my first statement that a good tuner on a 30-50HP setting will do everything the OP wants, including slightly better fuel mileage.

I think Smarty is a great canned tune. EFI live can be fantastic but that’s all up to the tuner and I would stay far, far away from SMR Diesel in Colfax.
It's hard to know that you know it all if you know at all you're a know it all. ;)
 
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