gears!

bkoz1990 · 06-23-2009, 01:53:17 PM

i have a 81 z28 w/ 400sb and mildly upgraded through out the car and compleatly demolished the old gears n my car and am n need of repalcing them im not all that knoledgible when it comes to the ratios and everything with that. so any help or advice as to wht gears i should replace the old one with would be greatly apprishiated.

BusDriver · 06-23-2009, 02:07:02 PM

What rear end, what trans, and what is your primary useage of the car? Street, strip, combo?

bkoz1990 · 06-23-2009, 02:16:20 PM

it has a 350 tans auto w shift kit and i believe the rear end is a 10 bolt and id say more of combo im n colege so it is a daily driver but still need some speed

BusDriver · 06-23-2009, 02:36:08 PM

Without overdrive, I'd keep the gears moderate. 3.08s, 3.23's or so.

Not horrible performance, but anything higher and RPM when just driving get's pretty high. With a healthy 400 the motor can still turn these conservative gears plenty fine.

Did you have a posi before, and is it still in good shape? If so just a new gearset and install is all you need to be up and running.

bkoz1990 · 06-23-2009, 06:31:35 PM

i have a limited slip in there right now and is still in good working condition but the gears your sugestioning im guesing are a more high end gear and cause more of a slower accel than with a gear ratio more n the low 4's??? im really not sure how it all works w the ratio #'s and significance as to higher the nubmber means better lowend or wht...

-=79z28=- · 06-23-2009, 06:39:00 PM

lowest gearing i would go on a DD is 3.42. that'll be nice for highway driving, while still getting you up to speed quick.

but as busdriver said, the torque of that 400SB can make 3.08's feel a lot lower. so in the end its up to you, but you have 2 votes for 3.23's.

mopar · 06-23-2009, 07:01:22 PM

Over the years (I'm 56), I've run everything from 4.88 to 2.56 on the street. Lately I've grown partial to 3.42 to 3.55 gear ratio for Daily Driver and cruising.

z28rod · 06-23-2009, 09:32:21 PM

bkoz1990 · 06-24-2009, 02:16:05 PM

thnks yall have been alota help really aprishiate it

BusDriver · 06-24-2009, 03:07:23 PM

Higher numbers are lower gears, you get more mechanical advantage and accelerate faster, but your RPM at any giver gear/speed is higher. thus, worse gase mileage.

Thus the trade, higher gears will give you better acceleration at the cost of higher RPM/worse mileage when cruising at speed.

The best solution, but not the cheapest, is an overdrive trans that compensates with a steeper gear in the transmission to lower RPMs when at highway speeds, while retaining performance ratios in the lower gears.