Help with rear differential size

[LAC99]

Hi all. I´m working on a 84 levin that originaly had a 3.90 rear differential with no LSD and drum brakes, so as you can imagine I need to change my entire rear axle. I have two options right now but I have some doubts that I hope you can help me with.

7.5 inch rear diff with LSD and 4.37 final ratio with disc brakes (i think is from a nissan pickup, already modified to fit in the ae86).

6.7 inch rear diff with LSD and 4.11 final ratio with drum discs (from a 82 or so corolla). Of course I would have to fit in disc brakes later if I choose this one

My biggest concern is about the size of the differential, I don´t want to lose power if I choose the 7.5 inch diff. Have any of you adapted a big differential like this one? did you lose any power?

by the way, my engine is a 20 valve 4ag (silver top)

thanks!

[Ivan141]

You might loose a bit on power, but you gain reliability.. you can do a lot to that 7.5" rearend without it even breaking a sweat..partwise the toyota rear axle is a lot more expensive to maintain too (compared to puckup truck rear axles).

[LAC99]

Thanks, I totally agree with the reliability part, but would I feel that "little bit" of power loss? I mean if its 3 hp I don´t care but I don´t want to have 10 or 15 less hp because of that differential

[Ivan141]

Cant help you there..no experience with it. I dont see why it would rob that much power.. the frictional losses cant be that much bigger than on the 6.7, so it's probablythe weight that's going to count.

[LAC99]

ok, thanks a lot anyway!

Does anyone have an idea of how much % would the power loss be? With the 7.5" differential?

[jamiemirror]

The power loss is no concern here, don't worry about difference between 6.7 and 7.5. Get 7.5 IMHO.

[LAC99]

7.5 it is then
thanks a lot for your help!