Speed question

Speed question

I have a 1964 CJ 5 stock Hurricane F134 motor, stock 3-speed transmission, stock Dana 18 with over-drive.
I have been told that I can go 60 mph with the over-drive all day long without blowing it up.
I also have been told that 55 mph is the max. What is the max cruising speed without blowing up the Jeep?
nelson haha

 

Depends on what you are comfortable with, and the condition of the engine.

How tall are your tires? With 28" tires, 5.38s and an overdrive, your theoretical top speed at 4000 RPM is 83 mph. However, you will definitely not have enough power to go that fast.

http://www.film.queensu.ca/cj3b/Tech/EngineDyno.html

If the engine were in good condition, I would probably be comfortable at a constant 3000 RPM, which is 62 mph.

 

I have a 69 with the same set up I have drove mine as fast as 72 by my gps. sustained speed is tricky depending on terrain but at constant interstate driving for as long as an hour I have drove 60 -66mph but I keep rpms under 3000 unless passing, who am I kidding I pass no one. I have noticed I go fastest with top off and windshield down.next fastest is top on and slowest is top off windshield up. I also keep a close eye on oil pressure and temp and have seen no problems. I will say cruising a 2 lane at 55 is no worries at all. hope this helps

 

Long history of this debate here in the past.


Before anyone else needs to say it, the F-head is a great engine.

But it is a long stroke and doesn't like high RPM. In modern traffic it is way too easy to feel "too slow" and get pressured to keep pressing the accelerator just a little more.
It was 40 years ago but I will never forget the sound of all the rod bearings knocking and the look on my Dad's face when I came home with his Jeep after a highway run.

For the sake of engine longevity, I personally feel 55mph is a maximum speed for a "used" F-head without o/d. For sustained cruise I feel it better to stay under 50mph. Others will differ.

Safety is a matter for consideration, too.

 

My F-head has no problem with 60 mph cruising rpms wise. The road better be flat though. Around here, with all the hills we have, the best I can do is anywhere between 45 and 65, depending on whether I'm going up or down! I've got overdrive as well as 4.27s in the differentials. I have 28" tires with some fairly mild tread, otherwise high speeds would probably be much more difficult to achieve.

 

The Warn 25% O.D. became a Willys approved option in Sept of 1964.
At that time Willys Motors specifically stated that the O.D. was only intended for use with 4.88 and 5.38 final drive ratios (FDR's)

I've tried a strong running Hurricane with 4.88 FDR with O.D. and it's much worse than 5.38 with O.D.
4.88 with O.D. is actually slower than 5.38 with O.D.

5.38 x 25% O.D. = 4.03 compound FDR.
The F-134 simply does not produce enough power to run any ratio higher than a 4.03 compound FDR.

I have run my stock Hurricane with O.D. up to 82 MPH @ 4000 RPM.
I prefer to cruise 62 MPH or slower.

For in depth study see: http://z4.invisionfree.com/CJ3B_Bulletin_Board/index.php?showtopic=2427

 

I don't have the overdrive.
My '60 runs along happily at 50 to 55 at around 3100 rpm. On 5.38's and 28.5 street tires. I stay away from the freeways and the higher speed highways.
(We actually have highways in this state that the speed limit is 50 or 55 mph. The heavily traveled ones are limited to 65 and 75 mph)

 

Yes 1964 CJ's were standard with 4.27 FDR.
5.38 FDR was an option in 1964.

 

I have a goo Hurricane, rebuilt, works well but I don't push it too much by respect... and because at "high speed" I want to stay on the road.

The CJ5 is quite high and it is well known that it is a car specialist of roll-over. So I believe that max speed must stay a calculation.

Except if you have a good flat place to test the speed.