Would a 3.42 posi be too big of a change from 3.08 open. i thinking about doing swap of entire rear, keeping drums and switching over my new hardware from brakes. Eventually i want to do Lt1 swap. until then would running 3.42 posi kill my power and mpg?

 

the power is the same no matter what rear end you put in but a lower gear like a 3.42 will give you more pull at the line or lower speeds but the rpm's will be higher on the highway causing less mpg and the speedo will be off.

 

yeah i just dont know how it will change 1/4 et. slower? taller gear. my tires only spin alittle now, at launch.

 

don't get 3.42's with a T-5, 3.73's will be better for you. trust me. if you had an auto the 3.42's would be perfect. as for the gas mileage my intown mileage got BETTER with the 3.42's. I didn't have to put much foot into the gas pedal to get going. the speedo isn't that far off. maybe alittle.

 

Not sure what mods you have...

But my TPI 305 5 speed with Hooker 2055's and 3" exhaust, etc...
Stock 3.42 gears is great...

Your gas mileage will go down going from 3.08 to 3.73...
The other thing to note will be traction...
I can smoke all of 1st, half of second and chirp 3rd...

If your motor is powerful, traction will be even harder with 3.73...
And for TPI's (which doesn't apply so much to TBI) most don't recommend anything above 3.42 cuz of the power curve / band...

Raf

 

why would 3.73 be better for t-5? i can get 3.43 complete shipped w/ ship $550. i dont know how to change gears out to 3 series carrier but how much would it cost to switch the 3.08 open to 3.73 posi?

 

The 3.73's are just a better gear for a T-5. You have a whole other gear to play with unlike us auto guys. I had a friend with a 89 tbi T-5 car and he went from 3.08's to 3.73's and it became a completely different car. His car definately pulled alot better in 5th gear and his gas mileage really didn't change that much as long as he didn't floor it all the time.

 

still looking for more explanation why? of course 3.73 is taller better gear.

 

You have a 3.08 now, going to a 3:42 or a 3:73 will give you better acceleration because you are starting with a lower gear (only higher numerically)

You will notice an improvement in acceleration with the 3.42, it would just be exaggerated with the 3.73. I think what others are trying to tell you is that with a 5-speed you have the flexibility of going with the lower gears, without suffering a substantial loss in fuel mileage or driveability because of the higher gearing you have with the manual 5 speed.

Hope this helps.....

 

Thats the setup I'm running in my 88, T5 with a 98 3.42 posi rear. You might loose a miniscule amount of power to the wheels cause the new diff has more moving parts and slightly more friction which equal a little parasitic power loss. That being said it is definetly worth it, for the traction you gain from the posi diff. I have 2.73 in the car before that axle and it made the car a lot more fun to drive. Oh and i have a mild 355 TPI in my car. Normally at the track I run a high 12 on sticky tires and cross the line at about 5500 RPM in 4th which is just at the end of my power band. So I would recomend the straight swap if you can get a good deal on a complete axle you won't see a major gain going from 3.42 to 3.73. Also the overdrive in most T5s is .70 if my memory is correct and a 700 is .74 so your not going to notice a difference between the 2 the nice thing about the T5 is 4th gear is a 1:1 ratio where as 3rd on a 700 is 1:1.32 I think. So you can cruise at 30 mph with the 16'' rim right at 1500 rpm and about 1900 at freeway speed.