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Topspeed with 4.88's

I

Imjosh

NAXJA Forum User
Location
Dacula GA
aight my friend and I are arguing about how fast my cherokee could run with a 4.0 aw4 and 4.88's with 33's down the highway so any insight would be helpful. I'm sayin 70 or so he says no way in hell so thanks for any help.
 
well when I had 4.56s and 31s I could run 80 and I am sure 90 would not have hurt anything. The auto likes the gearing and so does the 4.0.
 
I run 3,000 RPM back and forth to Johnson Valley, which is 10 hours from my house. No worries, other than the fuel consumption. (4.88's, 35's, NV 4500)

BTW, my rig has 212,000 miles on the original 4.0, and it's a Renix, which is much less high RPM oriented than an H.O. motor.

CRASH
 
Don't try this at home, kids:

I was following a co-worker down a deserted strech of interstate after work one day and he claims we were right around 100. This was in my doorless MJ with 4.56:1 & 33"s, 89 4.0l/5spd. IIRC I was tachin about 4000.

3000 rpms = approx 80 indicated with the above setup, could (and did) run that all day a few times.

3000 rpms = approx 75 with your #s

the math for speed @ is:
rpm x tire diameter / axle gear x drive gear x (low range for crawl speed) x 336

<edit> the #s lie a little...they don't allow for air drag/other parasitic losses. Also to be closer to 'true', disregard what's stamped on the sidewall and use the working radius (hub center to ground) of your rear tires at your happy tire pressure x 2 for a 'true' diameter.
 
Last edited:
Good i win i like to be right
 
I have 33's and 4.88's...it cruises nicely at 3 grand...thats about 60MPH with a non-od auto trans. And it will pull over 4 grand easily..I figure thats way to fast for a lifted XJ on mud tires.
 
I've had my 4.56, auto, 4.0, 31's up to 85....

Nothin like the Autobahn at rushhour :D


(I mean I-696 near detroit.....)
 
I have 4.88's with 35's, and I've run at 80+ with my old '88. Of course, it will only do that under ideal conditions....flat ground and no headwind. :D

When I drive from CA to Moab or CO I run between 70 and 80 most of the way.
 
I had mine up to 108mph last week but I also had my 235's on but with the lift and everything that's still fast.
 
i had my buddy on his street bike pace me at 120 mph. mine is a aw4 4.0 31 with 4.11 gears. it pulls 85 at 2950 rpm down the highway. also what is my jeep governed at. when i was doing this my speedometer went past the 85 mark and to the M on the mph writting on the gauge. when i went past that mark my jeep scared the s**t out of me and the engine just reved down and then i remebered i have a govener. anyone know the speed the governer on a 91 is set at.
 
4.88's, 35's and AW4.....I run it up to 80 mph all the time, but don't like it much past that......

Speedo is 'calibrated' via checking against the GPS so I think I'm pretty accurate.
 
It amazes me how some people can have similar set ups and run different rpms for the same speed. With the exception of different trannys, and tire sizes (relative) they should be similar.

I have a non-ho 4.0 with AW4 auto 4.88's and 33x12.5's. I cruise at about 65-70 most of the time at very close to 2700 rpm's. When I get to 3000rpm's I am doing very close to 75 and I do not like to push it above that without a really good reason. I am sure that it could do 80+ but I would prefer not to test it with the jeep.

Just to keep up with the other posts, how about 145 mph on a crotch rocket with a young lady on the back (dusk in Arizona).

Michael
 
CRASH said:
I run 3,000 RPM back and forth to Johnson Valley, which is 10 hours from my house. No worries, other than the fuel consumption. (4.88's, 35's, NV 4500)

BTW, my rig has 212,000 miles on the original 4.0, and it's a Renix, which is much less high RPM oriented than an H.O. motor.

CRASH
Click to expand...

Are you in 4th gear or are you going 85?
 
A relatively small difference in tire diameter makes a difference...my "33's" are actually 32" tall...some brands of tire are actually taller than their advertised size...Interco tires according to the data on their website are a good example...other factors can be tire growth at speed and on auto trans vehicles, possibly some torque converter slip under load.
 
I run 3,000 RPM back and forth to Johnson Valley, which is 10 hours from my house. No worries, other than the fuel consumption. (4.88's, 35's, NV 4500)

BTW, my rig has 212,000 miles on the original 4.0, and it's a Renix, which is much less high RPM oriented than an H.O. motor.

CRASH
Click to expand...

Yes, that's in 5th, right around 75 - 80 mph. I don't have a speedo, so I have no idea how fast I'm going. I just keep up with traffic on I-5.

BTW, I saw your rig at Riebes in Auburn the other day, but wasn't sure who you were. I was in a rush, so I couldn't wait around.

CRASH
 
CRASH said:
Yes, that's in 5th, right around 75 - 80 mph. I don't have a speedo, so I have no idea how fast I'm going. I just keep up with traffic on I-5.

BTW, I saw your rig at Riebes in Auburn the other day, but wasn't sure who you were. I was in a rush, so I couldn't wait around.

CRASH
Click to expand...

Yeah, you probably would have been waiting a while, I was digging through one of those 5 inch thick books and rummaging through the back trying to find a stupid brake line adapter to put a Toy 8" under my MJ. Finally just decided to redo the lines with a double flare tool.

Toy 8", Waggy 44, and front leaves going in this week :D :D
 
You gonna be ready to run some trails soon?

CRASH
 
I had a write up about it at one time.....got to rummage around to find it.

Fairly simple, the most difficult part is the crossmember. I used the OEM bellhousing, and then an adaptor plate from AA. The 231 bolted right up after adding a longer 23 spline input shaft (I had a Peugot tranny that used a 21 spline unit). I bought my tranny, rebuilt with a 23 spline output from a 3/4 ton Dodge 5.9 V-8, and a 6.3 to 1 first gear from National Drivetrain, for $1499. That was 5 years ago, though.

Some floor cutting is required to get the tranny in there, as it is a wide mofo.

CRASH
 
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