I have an 1989 Iroc that has a 3.08 posi in it and I want to drop a new rear end gear in it to help my acceleration and 1/4 times out. Do you guys think I should go with a 3.42 or 3.73 rear end gear? As of now i'm leaning towards 3.73 because that is what my dad has in his camaro and it still tops out at 140mph and its only a 4 speed.

 

Gear choice should be based on rpm and trap speed. It's really simple to figure out what you want by using an online calculator.

 

A 3.73 gear will get you off the line pretty quick (I know, I have them) but with a TPI motor, I'd suggest the 3.42 gear. A typical TPI motor goes athsmatic after 4500 rpm, but makes truck-loads of torque below that. My 350 is the same way, no top end, and with the 3.73s, it just runs out of gear way too quickly. I think you'd be happier with the 3.42 gears.

 

what would you say about a carb'd L98? mine is bone stock with a 750 duble pumper holley w/ edelbrock performer intake...and i plan on putting in a mild cam. would 3.73's be a good choice for me?

 

you got a stick? hell you could go higher if im not mistaken... my GTA came stock with 3.45s and ive seen people running over 4.**s with their manuals. i think thats with the t-56 though

 

yeah, i have a t-5. i would like to stay somewhat streetable....but ****, i dont mind sacraficing some streetability for some fun . i heard 4:11's were quite streetable as well, but i do believe it was with a t-56. i remember zepher talking about it in a thread a while back. sure id love to get a t-56 but i doubt thats going to happen any time soon. right now my 5th gear popped off the shaft so its a bitch to drive on the highway since im always in 4th. the drone of driving above 3k really get to you, especially since i have no radio heh.

anyway, can 4.xx's go in a 3 series carrier? im running 2.77's right now and i have horrible acceleration. too bad its a 2 series carrier



wow, i just used the RPM calculator to figure out how many rpms the engine wouldat when you're going 65mph with a 4.11 rear in 5th gear (.63:1)...only 2100rpm!! thats totally streetable....who is running anything higher that 4.11's?

 

you see that? i am good for something on this site

 

of course! so does 4.11's go in a 3 series carrier?

edit: is it 4:10's or 4:11's that go in BW 10 bolt rears??

 

honestly i couldnt tell you. im not good on most in depth stuff

 

heh...ok

i'm really just looking for some decently fast gears for a 5 speed...i dunno if it should be 3.73's or 4.1x's. where can i buy gears online? i'm having a tough time finding anything..

 

http://www.ringpinion.com try that site. heard great things about the yukon gears. expensive stuff for the gears and rebuild kit though

 

either, but most are 4.10

 

I have the 3.42's cause I used to have a 700R4, but they work awsome with a T-5 nice acceleration and good all around gear. I spin like crazy even with these so I am glad I don't have 3.73 or deeper. The T-5 has a 2.95 first gear when combined with the 3.42's, is deeper than an old 2.20 muncie with a 4.11 rear. Plus, gook luck finding speedo gears for a 4.10 ratio rear end.

 

You could always do 3.55s, I think they came as stock gear in the vettes(someone correct me if im wrong). And theyre right, 4.10s work best with the T-56, has something to do with the final gear ratios in the tranny causeing it to get better gas mileage or something to that effect....but since you didnt say 3.55s, go 3.42s.

 

Dude, are you sure about those calculations? If you want to stay streetable definatley go with 3.73 or 3.42. 4.11 would be a total pain in the *** on the freeway unless you have a t-56.

Oh and by the way, the New Jersey Devils Suck! It's all about the LA Kings!

 

haha never! devils are a dinasty


anyway, these are numbers i used in the calculations:

rear end gear ratio: 4.11
Transmission Gear Ratio: .63 (5th gear)
MPH: 65
Tire Radius: 12.8

= 2208.9965625 RPM

no?

 

yeah i found that one...but there are no prices.

what rear ends do we have...7.5's...7.65's? i have a 10 bolt BW from my '88 GTA.

also, can i buy 3.73's for a 2 series carrier? i think i have 2.77's...

 

what are you on ? 14" rims or are those REALLY low profile tires?

also, i have the 3.08 2-series carrier and summit sells 3.73's for 2-series, i believe they sell 4.10's as well.. but that might have been another website i saw that at,

 

stock GTA rims...16". ok maybe i miss calculated. this is what i did

my tires are 245/50/16

to get the height of a sidewall (profile):
50% of 245mm = 122.5mm
122.5mm= 4.82 inches
4.82" is the height of one sidewall.

to get the radius of the entire wheel:
4.82" + 8" (the radius of the rim) = 12.82"
12.82" = the radius of the entire wheel.

correct?

 

You need to keep the full sidewall distance in your calculation, do not divide it by 2., so 245 is aprox 9.5 inches, and add that to half your rim which is 8, total is 17.5"

try that in your calculation, that should give you a real rpm range.

 

The stock 245/50/16 tires have a diameter of 25.7 inches so I'de say you are correct.

 

25THRSS: yeah that's what i thought...

TraviZ: if i use both of the sidewalls, that wouldnt be the radius of the wheel...

heres some more calculations...maybe they make a little more sense.

2 sidewalls = 9.64"
9.64" + 16" rim = 25.64"

25.64" would be the entire wheels diameter.

half of that is 12.82", which should be the radius of the wheel.

 

Well, if you got a carb, that takes away much of the top end limitation of the TPI engines.

Assuming the motor is good to around 6000 or so, I'd say 3.73 for auto, and 3.73 or 4.10 for a manual

 

and what about my calculations? can anyone confirm if they are correct?

 

according to http://www.dodgecharger.net/tech/RPM...alculator.html
you are correct.. your overall diameter is 25.65 and at 65 mph you will be running 65 at 2000 with 3.73 and 59 at 2000 with 4.11
if i was you, id go with the 4.10 or 4.11 gear

 

ahhhh i dunno. are 4.1x's a pain in the ***? how are they for driving around town

 

i'm looking to change the gearing in my car too. i am setup with 2.73's in my 91' formula. i am thinking i want to go to the 3.42 because i have heard that you run out of gearing quicker with the 3.73 and i want something left for the highway. also i have heard traction problems comming off the line with the 3.73 or anything geared much higher. i am running the TH700R4
Thanks

 

anyone?

also: on another subject...can one determine the rear end gear ratio by counting the teeth on the speedo gear?

 

4.11's are gonna be hard unless u got a 6 speed

 

It's kind of funny you guys are talking about -speeds handling 3.73 and 4.11 better than auto's. I'm going from .70 to .72 in top gear by going to an 84 5 sp, from a 88 700. Ooops. I didn't really look into that before I bought the parts car. I think I'm going to run 3.43 posi. My 2.73 just doesn't cut it. I'm also going to run 17" wheels though, so I have to be careful. I may need 3.73's.

 

Is anyone running 3.42? I'd like to hear how it runs