4.0 head vs. 4.56 gears

Srambler83

Legacy Registered User
City
Houston
State
TX
#1
I have a question that maybe most of you all heard over and over and over but here is goes anyway. I know I will get probably about 10 different ways I should go about it, and thats ok. What I am trying to accomplish is a direction I should follow based on experience or current set up.
I currently have cj-8 258 with amc20 and dana 30 w/ 3.73 . I will be putting on 35" or 36". I am very light off road/ back road, dunes and occasionally jumping the median on traffic day.

1. Should I stay with the 3.73 gears and add the 4.0 head?
2. Should I stay with the 258 stock and change both gears to 4.56.

With out going into too much detail what are the pros and cons.:shrug:
 

Rosco1974

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
West Haven
State
UT
#2
GEARS!!! GEARS!!! GEARS!!!

In all my jeep tinkering, it has always been the best bang for the buck. Think of it this way. Changing the gear ratio re-aligns the motors torque curve (at a given RPM) where it was from the factory or better. If you keep the 3.73 ratios with the 35's, it would be the equivilent of running 3.08'ish gears. It would be an absolute dog and only slightly better with the 4.0 head. Play with the calculator at http://www.ringpinion.com/Calc_RPM.aspx to see where the factory ratios are and try to keep it to factory or better.

IMO: I would run 4.88 gears with 35's (3000rpm @ 80mph).
 

Rosco1974

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
West Haven
State
UT
#4
Be sure to do the trans ratio portion and think of how you want to drive it. Options between 4.27/4.30 and 4.88 will work well. If its on the highway alot, the 4.30/4.56's are good. Offroad, the 4.88's will be best.
 

Srambler83

Legacy Registered User
City
Houston
State
TX
#5
Rosco,

It will be mostly used for the road. I was thinking going with the 4.56. 80% on road- 20% off road. Any other suggestions regarding my set up. I should be able the use my overdrive with the 4.56 gears right? From researching on here and speaking to other guy I would not have a problem using my overdirve on my T5.
 

zeeksta

Legacy Registered User
City
essex
State
ct
#6
4.88s if you have overdrive..... all those charts are for 1.1 ratio, you will have the best of both worlds with overdrive, just be gentle with that t5 4.88 gears and sticky 35s will tear that thing apart if you pound on it.....
 

Srambler83

Legacy Registered User
City
Houston
State
TX
#7
zeeksta,

I do not want to go to that extreme where I will be tearing apart my T5. Will the 4.56 not turn those 35 or 36? Mostly street driven/trips. Don't want to down shift on every over pass either. Tell me your 2 cents.
 

ineedajeep

Scrambler Junkie
LIFETIME
CJ-8.com Member
SOA Member
City
Lake Charles
State
LA
#8
I have 4.56 gears in mine and have a stock motor with a Weber carb. It is fine for in town driving and highway use. I go over a bridge every time I use my CJ8 to go to work and it will take the bridge fine in fifth gear. If you live in Houston yours should do just fine also. If you go much steeper with gears you might not be able to use fourth gear as a passing gear on the highways when needed.
 

ben8jamin

SOA Member & PROUD of it!
City
St. Simons Island
State
GA
#9
im going through the exact same dilemma. i've been researching and researching. i have the same set up as you. i just decided to go the gear route, i got some 4.56s and im working on getting them in this week. i'll post an update as soon as it's done. i think, like rosco said, gears are going to be the best route.
 

Srambler83

Legacy Registered User
City
Houston
State
TX
#10
thanks guy for your help. I am in the houston area aswell 4.56 it is . Ben8jamin let me know how your t5 runs with 4.56 . I have heard the 4.56 should do the trick for t5 road and a bit of fun off road.
 

Scramblerman84

Legacy Registered User
City
Lansing
State
MI
#11
I had 4.56's in mine with a T5 and a 258 with a 4 barrel carb. When the trans wasnt broken...it worked well, I could cruise on the highway no problem and cruise the dunes easily.
 

ben8jamin

SOA Member & PROUD of it!
City
St. Simons Island
State
GA
#12
thanks guy for your help. I am in the houston area aswell 4.56 it is . Ben8jamin let me know how your t5 runs with 4.56 . I have heard the 4.56 should do the trick for t5 road and a bit of fun off road.
i don't a t5, i have the t176, but i'll keep you up to date on it...
 

Srambler83

Legacy Registered User
City
Houston
State
TX
#14
Anyone know where I can purchase a good set of 4.56 gears for both the dana30 and the amc 20? Anything in particular I should look for when purchase 4.56 gears? I suggestions or comments welcome. How is the quality of gears from 4 wheel parts or Quadratec? Thanks
 
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