4.88s And 33s

35s come stock on a minivan? Or do you mean 35s on stock suspension? That must've been a lot of sawzall blades...

 

Inside joke...
The Expedition Max in my signature was bought when looking for a minivan that could tow a bigger camper. It's basically a minivan body on a f150 chassis with independent rear suspension.
It runs something like 35s from the factory with the right options.

 

I'm not picking on you, but I am going to interject some knowlege and common sense here.
In your final calculation "What you (and I) want" you have 4.88 ratio, 33" tire and .75 final trans drive ratio with a desired speed of 80 MPH.
First off, any advertised 33" tire is only going to be 32.5" tall at best. That puts you are 3027 RPM when traveling 80 mph on a flat and level road without a headwind...... or factoring in the fact that a CJ is less aerodynamic than a jersey cow. 3,000 RPM for extended periods of time is less than ideal for engine life.
80 MPH is fast in a CJ...... I have done it..... actually I have held 90 mph in mine for a mile or so.... on a freshly paved stretch of road in the middle of nowhere. My jeep is extremely well built and almost perfectly square with perfect steering geometry, caster and toe adjustment..... something that 99% of jeeps out there aren't.
Download a GPS speedometer app to your phone and go for a drive. Your stock speedometer is guaranteed to be incorrect.

 

Yep, high speed in a CJ is possible with the right parts assembled in the right way. My 3B has been to 120 mph once and only once. It felt fine and still had more power available but any sudden maneuver wouldn't have ended well. That and the hood hold downs are a bit problematic.

 

I've got 33x12.5-15's with 4.88 gears and I like it. I swapped out the speedometer gear and it isn't far off. I've got enough torque to chirp the tires on pavement, though I'm sure that isn't recommended!

Highway speeds are ok. An overdrive would be nice, but for what I do it is adequate.

 

Thanks for the knowledge. Don't worry about offending me; I'm always looking to learn from those who know more than I do.

I mainly did my calculations at 80 because that's what the post before me was describing, but I'll probably keep it around 65-70 for fear of exploding like a rotten tomato. I should've done it at 65-70 at the first place. When I drove it home after buying it, the speedo was running quite close to my dad's truck, which was in front of me.

I'll re-run some calculations at 65 or 70 with the actual tire size and report back.

 

I have put a lot of hiway and interstate miles on L-134 2A’s and especially the F-134 3B’s.
The 3B with a good condition F head plus overdrive will max out at 81 mph (4000 rpm).
But that’s a white knuckle experience with the Ross steering. Anything above 65 mph sustained is getting iffy in these short wheel base Jeeps having a fairly good Ross box. And yes when in windy conditions your wondering if the hood will stay put.
At least for me if feel comfy at least up to 65mph and would likely go faster with a better engine, better steering and a secured hood. Yeah more speed requires better braking too.
They make a lotta noise between the 5.38 gears, mud tires and the Dana 18.

 

Personally I wouldn't want to run 70 in a 50 year old Jeep. I prefer less than 60.

 

My CJ has the 225, and I could (with 33s) hit 80mph at a little over 3k rpm. Now I probably won't be gutsy/suicidal enough to pull 80+mph, but my Jeep felt good at 65-70 on my first drive on some hills with a medium amount of wind.

 

That's a good approach. Ease into it and see how it holds up. I welded on a permanent tow bar for this exact reason. I live close to the desert and I test my mods before I go further out where recovering it would be harder.

I started with 33s and because of a good deal, moved up to 35s. The extra mass was felt on the highway but offroad I can't really tell the difference with the Dauntless. My Jeep is pretty low geared with the 5.3 axles and the doubling effect of the auto trans. On the highway with OD, you can really feel it. Factor in the condition of the engine. All in all, it gets around pretty good. I hit about 45-50 at 2.5-3k and 55-60 with the OD. Idle up steep stuff no problem.

 

I agree with what others said, 80 mph is scary even in a JEEP that is set up well. My JEEP came stock with 4:88’s and 3 speed and Dad put 31’s on it from the beginning and it ran Hwy fine and worked great off road. In all the years of off roading it went anywhere he wanted it to go, the only issue with axles were blown front spiders, his fault, (his words). I put 33’s on it and switched to the 4 speed. It runs well on the Hwy, (not as zippy) and works great off road even if not using granny low. Unless you drive it off road like your hair is on fire you shouldn’t have any issues with “grenadeing” the axles, as long as they start in good working order and you service them. My motor has been worked over and runs really strong, see: http://www.earlycj5.com/xf_cj5/index.php?threads/118867/
60mph@2400rpms on Hwy 88 6500 foot elevation at 100*

 

The SM420 has a 1-1 ratio in 4th, correct?

That is a clean looking dashboard. I'm not one for white gauges, but those look really good on the black background.

 

I believe it Is the 1-1

 

Gauges are silver face the dash has a black carbon fiber overlay

 

Thanks.

I don't imagine I'll get to that level of fancy on the CJ, but I might throw some of those in a project down the line. What brand are those gauges?

 

Auto Meter

 

Thanks.

 

Yes

 

When I purchased my 71 CJ5 (new) and drove it off the lot I was pleasantly surprised when my RPM seemed quite high...when I got it home I investigated and sure enough, rear tag said 4.89. Within a week I installed a fully synchro warn OD (.7-1) and I felt I had the ideal drivetrain for both off and on road (with the dauntless V6) and I still feel it is ideal with stock tire/wheel dimensions. But then I am old school. In 1987 I installed a crate 231 with an RV cam, headers and tiny 4 bbl holley with vacuum secondary's. A very sweet combo to this day and I love shifting so I routinely run through the 6 gears as I drive on the street...hehe. YMMV.

 

Anyone telling you they drive their Jeep with a 225 at 80MPH for any sustained length of time is FOS. I have an extra 12" of wheel base, PS power disk brakes and no. Just no. 65mph is fast enough to die when some jerk cuts you off..

And yes every single final drive transmission that does not have an OD is 1:1. the last year of the SM 420 is 1967 with some mil variants to 81

Have you ever driven a pre 86 jeep? On the highway? Going more than 35 mph?