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4.56 Gears

T

themauler

NAXJA Forum User
Location
Va Beach
A while back I posted a thread getting opinions on 4.56 gears with 30" street meats in my 93 4.0 xj. Well i did the swap and the results were different but I am adjusting cruising around town is great but highway speeds aren't very fun. 70mph is max 65 is good cruising speed.

here is the tach at 65 on the highway using my gps as correct speed
IMG_20110517_153240.jpg


I will probably be finding some 32s to help making highway commutes less painful but it sure is nice never leaving OD even on hills :)
 
I bet that thing is pretty quick with 4.56s and 30s lol
 
I am using 4.10 and 30" tires. The 4.0 turns 2350 at 65 MPH which is a bit high for my likeing. However, I think 32" tires will be too big. The next set of tires will be 31" which should bring the RPM down about 100+/- .

When I bought the XJ it had the OEM 225X70 -15 which was about 28" and turned 2075 RPM at 65 MPH. For best highway economy, I would the 4.0 to turn about 100to 150 RPM above the OEM RPM to compensate for the heavier tires.
 
So....did I miss something or do you have a question/problem? I agree with "he probably doesn't have OD". Is your rig an auto? Stick? I'm running 4:56's...and while I haven't taken a pic of the dash while running, my speedo is pretty much spot on (within 5 mph) at highway speeds. If you're 20 mph off, your axle gears must have been 3:07's to begin with...much bigger shift in RPM's vs. speed than I noticed with my Auto (with 3:55's stock).

Enjoy the lower gears...get bigger tires....wheel the heck out of it!
 
^
I have an AW4 so I do have overdrive, and my stock gears were 3.55

the reason i posted was to just show everyone what the rpm's were running 4.56gears+30" tires at highway speed. I couldn't find my original post so I made a new one
 
32s with 4.56 gears are an excellent combination for highway driving. We have this on our expedition XJ. The tachometre reads approximately 2400 RPM at 65MPH, 70 MPH is 2500 RPM, and 80 MPH is 2900 RPM. We average 21 MPG using cruise control at 70 MPH. Speeds and fuel economy were confirmed using a Garmin Quest GPS. The 4.0L L6 enjoys operating at 3000 RPM (+/- 500 RPM). No downshifting on inclines is required using 4.56 gears and 32s from our experience.
 
This is within like 100rpms of driving an AW4 not in OD, 3.55 gears, and 31" tires. I find it a touch buzzy but the power sure is nice. :) With 32's as Badger mentioned, you'll probably be very happy with it.
 
so, with 4.56s and 30s.. what will gas mileage be like for mixed 50/50 city/highway driving?
 
With my 167k mile old O2 sensor I was getting 12mpg. My last tank, involving a lot of wheeling and then some around town driving, with a new O2 sensor, got me 14.5mpg. Best I've seen since getting 33s.
 
So where is the problem? pull the string out and hammer down.


Don't be afraid to run down the highway at 3000 rpm's. high rev's on the 4.0 arent what kill your gas mileage, having to use more throttle to maintain the lower rev's is.. that, and an old o2 sensor, bad air filter, etc.

The 4.0 is most efficient at about 2700 rpm's, but economy shouldnt start to taper off until over 3100.

This isn't a V8. Start thinking about it more like a civic and less like an F150.
 
Darky said:
With my 167k mile old O2 sensor I was getting 12mpg. My last tank, involving a lot of wheeling and then some around town driving, with a new O2 sensor, got me 14.5mpg. Best I've seen since getting 33s.
Click to expand...

cal said:
This isn't a V8. Start thinking about it more like a civic and less like an F150.
Click to expand...
i have a v8 and get the same mileage Darky is getting.. ;)
 
nw-xj-scott said:
i have a v8 and get the same mileage Darky is getting.. ;)
Click to expand...

that sucks. :)

i have a stroker. I got 16.5 going to the last event (~115 miles) and 18 on the way home (mostly downhill on the way home).

it drives like a v8 too, which is nice.
 
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