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My comments are based on assumptions of 140-150whp Duratec 2.0, a 7000-7200 rpm redline, M5OD-R1, Ford 8.8, and a 25" OD tire.
yup basicly the same set up the D25 is 175 hp @ 6000 and 175 tq @ 2700 withe the 2.3L M5ODR1 , 3.73 8.8 and a 25.7" tire
ill have to admit I was a little depressed seeing the numbers with the 3.73 it gave me a top speed of around 98 mph..
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Ultimately, my plan would be to run it with the stock ratio for a while at first, to really get comfortable with the car and get a better feel for exactly how much of a rear end ratio change I really want when theory meets reality.
3.07/3.08: This is what comes stock in my diff.
right now Im thinking on running my 3.73 lsd for a while also to see if i like it as well ... we'll have to compare notes after logging a few miles ...however I dont think my car will see much track use or auto x ( maybe 10%) ? mostly DD in the spring summer and fall as long as I can get away with it..
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I think the most important thing is too decide what your car is going to be. My car is a Sunbeam Alpine, built for long distance cruising. I'd guess the typical road weight would be about 2750 pounds. Tranny is the stock Ranger M5, axle ratio 3.80, tires 24". This gives me 3000 rpms @ 70 and I love it, as I'm at the bottom of the power curve at cruise and we can go up from there until I run out of bravery. I might add the big four with balance shafts seems to be perfectly content at those speeds. For a while I had a 3.55 rear, but it seemed the engine was always playing catchup and I did not like it. It gave me 60 mph in second, which I liked, but I don't spend very much time at 60 in second. I spend hours on the road at 70 in 5th. Highway mileage, low 30's. In a lighter car, I think I would be pretty happy with a 3.55. I would really hesitate to go lower.
That was one of my concerns with the 3.73 is having the 70mph cursing speed to far up the RPM range.. but it sounds like you've found a sweet spot at the 3k mark for 70 MPH
Ill have to play with my numbers some more ..