Gears

I've been thinking about moving up to 33" from 31". How much of a difference can I expect on the low end with the bigger diameter. I have a '67 Muncie car trans, M2?, without any type of granny with a D18. I've got the Saturn OD and 4:88 gears. With the OD it does just fine on the highway, but I would like a little lower in 4WL. Time for 5:?? gears. I don't know the the first gear ratio for the trans. I know with the bigger tires I'm going the wrong way, but how far?
Thanks

 

which motor? 4cyl im not sure v-6 then you should be fine in my humble opinion

 

D'oh!

283 Chevy

 

here's some numbers for you to mull over;

63-77 m21 and m22 = 2.20 first gear

66-74 m20 = 2.52 first gear

ok at 60mph in forth gear no od

30" tires and 4.88 = 3279 rpm

33" " " " = 2981 rpm

first gear equals 2.52 and 4.88 rear end at 10 mph

30" tires = 1377 rpm

33" tires = 1252 rpm

these numbers were arrived at using one of the rpm and mph calculators found on the web.


for fun; with a first gear ratio of 3.42 and 4.88 rear end at 10mph

30" tires= 1869 rpm

33" tires= 1699 rpm

now just what the h*ll this all means; your guess is as good as mine :

 

I doubt if you'll notice much of a differance except for merging on the freeway. Otherwise that combo should work fine. If not, add some NOS! :twisted:

 

I had the saginaw car 4 speed in mine. I switched over to the 465 for the lower first gear. I run 5:38's with the overdrive on the freeway fine with 31's. About 3200 rpm. I just wasn't happy with the 4 low in the dirt, with the car trans. BTW i'm running 4.3 chevy V6.

 

John - I see what you mean. I'm not real happy with the 4 low and with the bigger tires, albiet a small difference, will be even worse. Maybe 5:35's are the way to go. Thanks

Dan - Very little highway driving. When not in the dirt, just around town, 55 mph tops. Thanks

Don - Wow! Thanks for all the numbers. Any idea what that comes to in 4 low?

 

I mean 5:38.

 

I would be more apt to swap to a granny low trans, than to put 5:38's in. Probably the same cost wise, but the 4 speed will give you a better crawl ratio while maintaining your highway drivability. I think with the 465, and the 5:38's you get a crawl ratio of close to 100. I don't think swapping only to 5:38's is going to increase your ratio by that much. I know the 4 speed I had, was similar in ratio to your muncie and even with 5:38's the crawl ratio was crappy.

 

Crawl ratio is easy:
2.20*2.42*4.88=26:1 - what you have now
2.20*2.42*5.38=29:1 - change axle ratio
2.20*3.01*4.88=32:1 - with Tera low range gears
6.55*2.42*4.88=77:1 - add the SM465 only
6.55*3.01*5.38=106:1 - SM465, Tera gears, change axles

Changing the close ratio Muncie for a wide ratio transmission will give you almost 3x the crawl ratio (a 200% change). Changing the axle ratio (5.38/4.88 - 1) * 100% = 10% change, while the Tera gears (3.01/2.42 - 1) * 100% = 25% change. There's no comparison if you are looking for go-slow capability.

Plus, with the SM465, you're likely to get back some of your investment if you ever need or decide to sell your Jeep.

 

four low huh! ok here's some

2.52 first 2.43 low at 5mph = 30" 1695 rpm

" 33" 1541 rpm

for fun.... 2.52 first 2.43 low with 5.38 at 5 mph= 30" 1868 rpm

33" 1698 rpm

one step more ..... 2.52 first 3.15 terra low with 4.88 at 5 mph = 30" 2170 rpm

33" 1973 rpm


and last but not least what i would do! the reason this would be my choice is i also have a bad case of hot rod iduss! swap out the munice for a t10 with 3.42 first gear and never look back!


3.42 first gear 2.43 low with 4.88 at 5 mph = 30" 2276 rpm

33" 2065 rpm

if your inclined and want the real low crawl rates i'd take john's advie and go with the granny low of the 465...............good luck

 

Another way to picture this ... with your current setup, at idle in lowest gear, you'll move forward about 42 ft in 10 sec, or a little more than 4ft/sec. Adding the SM465 makes your slowest forward speed about 14 feet in 10 sec, or 1'5"/sec.

 

If you want to hot rod it, you might consider a WC T5 with GM V8 gears and a D300 with 4:1 Tera gears. Big bucks, but a hot rod close ratio 5-speed with a great crawl ratio; 4*4*4.88=78.

 

All this number crunching is giving me a headache :? Plus you guys have way to much time on your hands R) R) R) R) R) R) R) R)

 

yes sir!

ok it's sunny high 70's...tops off the jeep...........going to go hop in and good cruisin now

oh and did i mention have a few

 

Wow! I guess the 465 is the way to go. At least it should mount right up the motor. Thanks for all the info guys. Guess I'll start looking for one.

Now where's the asprin??