Gearing advice

M

MudDawg

New member
1053783

I have a 85 Chief... 2.5...auto trans...running 12.5 x 33's. currently with 3.73 gearing...my calculator says somewhere around 4.56 should be about right. Still flings mud pretty good in low range, but its kinda puny on the road...make that real puny..lol
I use it to go puddle jumpin and to haul my Jon Boat in and out of the trails and steep dirt boat ramps in the local phosphate pits... :-D I want to be able to cruise along at 55-60 MPH. My upcoming motor should be in the sweet range at around 3,000 to 3,500 RPM.

Dawg






Flingin Mud 'n Kickin Bass 8-)

edited by: MudDawg, Feb 05, 2003 - 10:30 AM[addsig]
 

1053785

I´ve always figured 3.73 with 31´s (sometimes 4.11), but I´ve never had a four banger. The four banger usually makes peak torque at a little higher RPM than the six´s or eights. 4.56 sounds about right to me, depends some on the gear sets available for your rear end. Some of the other guys, with more knowledge, about the 2.5 can give you some more specific advice.
As a rough calculation, I use one gear set, for every two inches over stock tire. Stock tires are usually set up to run, at near peak torque, at 55 in overdrive. I´ve rarley seen two, RPM-tire size tables that were the same.
Most of the guys go with 4.88 with 35´s but seeing as you want to run, about 700-900 RPM over stock, peak torque, you might think about the 4.88`s.
Just thinking out loud, hope I didin´t confuse you (or me).



edited by: MudderChuck, Feb 05, 2003 - 01:09 PM[addsig]
 
1053794

My upcoming motor should be in the sweet range at around 3,000 to 3,500 RPM.
Click to expand...

what motor will you have? if you're getting a V8 you won't need as high of a gear because the motor will have more power..................
[addsig]
 
1053874

Thanks Chuck and Dingus... the motor will be a 2.5 four banger...the AMC version...basically 2/3's of a 4.0 with a shorter stroke...there are some pretty nice goodies available for the little buzzer. I resectioned the stock intake and installed a dual-jet rochester (basically 1/2 of a quadrajet) flows around 230 CFM.. adding .030 over pistons,blueprinted shotpeened rods with SPS bolts, SS valves, HD springs, .440 lift 240 degree cam, header, have a recurved distributor... general port cleanup and bowl reshaping...(sigh) wish i could build a motor for my dragbike this big....and a 50 HP shot of NOS just for grins and giggles (leftover from my dragbike program).

Dawg


[addsig]
 

1053892

I am putting 33x12.5 on my 2.5 L TJ, does this mean that I am going to have to change my 4.11 gear???? :-? :-? :-? [addsig]
 
1055068

I'm running a four banger in my YJ, and find that my choice of 4.88 gears is the only way to go. For the amount of money you're going to spend, you might as well do it right the first time. 4.56 gears are popular and 4.10 gears have been around for a while so this is what you typically see swapped in. But the newer 4.88 gears that are available don'nt cost that much more and give you a better crawl ratio and better highway manners to boot! I've found that my jeep runs about the same or better at highway speeds (and in 5th gear) with the 35x12.50BFG Muds and 4.88 gears as it did when I had 31x10.50 road tires and 4.10 gears. The arguement of high RPMs cannot be denied, but at 65mph I'm still around 2500; which is'nt that bad. The only thing to remember is that with those low gears you'll have to take it easywhen in first gear (peeling out will become pretty easy to do). If you upgrade to some larger tires (you said you are running 31's) you won't have any regrets about going with the lower gears. -Also, if you're going to be towing heavy loads, the 4.88's will give some relief to always downshiftning into 4th on hills. :-) [addsig]
 
1055102

Thanks for the input, I appreciate it...I have a Dana 30 and a AMC 20...i was told that 4.56 is the lowest gear to fit both ends...and the new motor should have no problem cruising along at 3K...its not my daily driver anyways...just to go fishin and foolin around...speakin of crawlin...in florida yah gotta substitute Toyotas :evil: .. we dont have rocks....lol....sand....mud....no rocks except the ones in our heads....LOL



Dawg




[addsig]
 
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