Limited Slip/Posi and Gear Ratios ... HELP

[69stang 11]

So I officially decided I want to swap the gears in my 8" rear.

 

I have a 302, AFR 165's, spreadbore carb, offenhauser dual port intake, long tube hooker headers and 2 1/2 inch dual exhaust. The trans is a T-5 with .63 OD.

 

The car is a daily driver with gas mileage being a concern.

 

It currently has 2.79 gears, which with the .63 OD really seems to HATE doing 60-65 mph (the speed limit) because the rpm's are so low. I also would like more "seat in the pants" launching strength.

 

I don't know a lot about either topic, but what are the positives and negatives of a posi/limited slip type rear (and what is needed to do the change?).

 

How would I determine if 3.55's or 3.80 would be a better fit?

 

My tire size I believe is 225/65/15 but I will be confirming that.

[69stang 11]

Just a follow up, I also would like first gear to be usable .. I don't know how to determine this, but it seems like higher gears can all but deem 1st gear as worthless

[mikem 13]

I'll share my experience. I started with a 302 2 v, C4 auto, and 3:00 open rear end. I swapped out the original stuff for a performer intake, 268H comp cam, headers and changed the 3rd member to a 3:55 traction loc. The engine would rev fairly high between 60 - 70 mph but the launch from a stop was much improved. About 3 weeks ago, i swapped out the C4 for an AOD for that 4th gear. Ahhhhhh. So nice. It seems like it is lugging a bit at 60-65 buy maybe i'm just not used to all that quiet yet. I honestly would like to have a set of 3:73's in the rear. I think that would be perfect. I think someone will be able to tell you the formula for the 1st gear usefulness as compared to what rear ratio you decide on. Math hurts my brain. The thing i noticed about a posi is that the rear can come around really quickly on damp pavement or hard acceleration in a corner. I need to practice somewhere so i know what to expect and how to control it.

 

Now, would you mind sharing? Did you go from the 302 stock heads to the AFR 165's or did you get the car that way? I am VERY interested in the AFR's so wondered all that is involved in the swap such as did the headers for the stock heads fit the AFR, did you go with hardened push rods and what size were they. What about head bolt size or kit used to bolt them on and did you go with roller rockers with screw in studs? The big question, what was the difference in hp and torque from stock heads? Thanks and good luck with your swap. Mike

[Moteaux 10]

I think you may be looking for something like this start line ratio. http://www.5speedtransmissions.com/startlineratio.html

http://www.5speedtransmissions.com/calculators.html

http://www.5speedtransmissions.com/gear_calculator.html

 

Just remember, as the web page says, to take in to account your tire diameter to figure in with the overall equation. The gear calculator link uses your tire size, gear ratios and such and also aids in predicting your SLR (start line ratio)

 

If you look around at the rest of the calculators for gears and transmissions there, you can find some good useful info.

Edited March 25, 2010 by Moteaux

[69stang 11]

What is a name of a good STREET limited slip rear?

 

Also what parts are necessary to do the swap/install (spell out as much as you can).

 

Thank you guys for the help!

[maxum96 32]

Either gear ratio is going to do what you want. They're not that far apart. With that T5 it's not going to matter much on performance and driveability. I run 4.11 gears with a Tremec TKO 5 speed. With a 28" tall tire I turn around 2,000 rpm at 60mph. If mileage is a big concern, then run the 3.55 gears.