AX15/NP231 swap?

[Atla]

Has anyone done this swap? From what I understand it bolts right up to the 258, as long as the spline count is correct... 23 spline?

I'm pretty big into the TJ Wrangler world, so finding one being swapped out is pretty do-able.

Just wondering if it would pay off in power/mpg/etc for a daily driver compared to my T177/NP208 set up.

[tgreese]

Has anyone done this swap? From what I understand it bolts right up to the 258, as long as the spline count is correct... 23 spline?

I'm pretty big into the TJ Wrangler world, so finding one being swapped out is pretty do-able.

Just wondering if it would pay off in power/mpg/etc for a daily driver compared to my T177/NP208 set up.

Not sure it would give you much over the T17x. You likely have axle ratios that would make the overdrive gear impractical on anything but level highway.

There's not much difference in the NP208 and NP231 ratios.

If you went to a higher (numeric) axle ratio it might be worthwhile.

[carnuck]

It depends what ratio you have now. The O/D is .79 and works well with 27" tires and 3.07 ratio if you have EFI. What tire size? What's the current ratio?

PS: I would only do it if you freeway drive a lot (like me)

[Stuka]

If you plan on regearing, then it would be great. I know I could use a over drive in my J10 with its 4.56's.

[Atla]

33" tires with 3.15 gears.

I have a 50 mile round trip to work, all freeway. :/

[fulsizjeep]

If gears are factory now, they would be 2.72 or 3.31. With either gear set, 33s and an OD, I doubt you would use OD at all.

[rocklaurence]

Its a great setup and I think it would do well/better behind a V8. Talk to t he guys with the 258 and T5--OD doesnt happen with 31" tires and up

[tgreese]

It's pretty easy to run the numbers. Here's the Novak gearing calculator: http://www.novak-adapt.com/knowledge/gearing.htm

If you have 3.31s with 33s, at 70 mph gives 2300 RPM. To me, that's low for the highway. So it's hard to justify all the work for an overdrive gear.

I think you'd be better off with a 4.0L HO swap than worrying about the transmission. That should improve your fuel economy a lot and give you much better performance on the highway. If the noise bothers you, insulate the floors, and go with quiet tires and exhaust. If you have a fixed fan, that's very noisy. A fan with a thermal clutch or an electric fan will be much quieter.

Is there something about driving the T17x that you don't like? Maybe the shifting? I recall it's an easy shifter when not worn out.

[Stuka]

33" tires with 3.15 gears.

I have a 50 mile round trip to work, all freeway. :/

What fuel economy are you getting right now?

When my J10 was stock with 2.73's, 31's (Mud tires at that), with the 258/T176 I could get 17MPG HWy doing 70mph.

Engine had a few mods. Full 2.5" exhaust, Weber Carb, TFI Ignition, rest was stock.

[brielly]

I have a 258 w/ mopar efi, 3.31 gears and a T5. I do around 2200 rpm's at 75 mph. My old rig w/t176 and the same gears spun 3000 rpm's at the same speed. I've noticed very little if any difference in the gas mileage between the two setups. The t5 is ok on the hwy as long as their are no hills and you aren't trying to overtake another vehicle. If you live in a hilly area or the mountains a gear swap will most likely be in order.