7.5 or 8.8, which is better for 5.0
 

obviously the 8.8 is stronger, I come from a world where 8.8s are weak (Ford Broncos 351w and 35'' tires:) Its verrry hard for me to even consider the 7.5 because the problems we have with breaking 8.8s. obviously its not a problem here with the miata being less than half the weight of a bronco) I have read over and over that the 7.5 is fine and people are running mid 10s with them... Anyway

I have a stock 88 5.0 and ill probobly do a cam with roller rockers and slightly higher compression. Maybe just maybe a set of Gt40p heads down the road. But at the most id be making 280-300hp for now. I have sourced 3 rear diffs out of t-birds in my area:

One is an 88 t-bird with the 7.5 open, one is a 95 with the 8.8 3.27 limited slip and a 94 that the size/gears/limited slip are unknown till he calls me back. Im leaning toward the 95 8.8 with locker I can get tomorrow or monday morning guy is asking 125.00.

I have also read that there is more room for exhaust with the 7.5...

Which one would everyone go with?? Does anyone have a break down of which rear diffs were in what year t-birds? Someone said somewhere that the early to late 90s were all 8.8s and the earlier were mixed depending on engine size.

I'd go with the 7.5.

Just talked to the guy he said its a 7.5 with 4:10 limited slip for 175.00. Axle code f5

Get a 7.5 with 3.27 gearing. Install new bearings & seals. Install a NEW limited-slip unit from Ford & be done with it. That 4.10 gear will be way too low for a Miata because of tire size.

Of the three you mention, the 95 8.8 is your only choice. The 88 isn't IRS, the 7.5 with 4.10 is way too low, the 8.8 3.27 limited slip is just right. Don't be too concerned about the space for the exhaust, just make sure that when you install the rear, you get it as high up as you can.

This site has a ton of info, you just have to sort thru it: http://www.sccoa.com/articles/scspecs.php

Mike

If you are using a kit you have to use the one the kit was designed around. The Monster Miata kit uses the 7.5, the Boss Frog kit uses the 8.8 and the V8R kit uses a GM unit.

I'd recommend the 7.5 as its pretty cheap and can be found with a factory limited slip. The best ratio is 3.27. Look for a T-bird with a "E" axle code stamped on the door pillar. The tag on the differential itself should read "3L27". "3_27" is an open rear. If you have a choice of a few possible candidates in the yard pick the one with the least free play (1/4 inch is normal). If you need to retain ABS make sure you get one with the mounting points cast into it.

-Jason