Find a 8.8 it will be cheaper in the long run but the rule or thumb is 3.55 for 5 speed 3.73 for auto and 3.27s if you want a little gas mileage with a little more performance. remember the higher the gear you go the smaller the pinion gear and the less metal meaning less strength. Go 8.8 with a Auburn HD diff and you will be cool down into the 11's with dependability. The 7.5 is just not up to the power it is a time bomb waiting to break at the worst time. But the ratios are the same if you decide to keep the 7.5. As far a auto manual and the 3.27 if they even have a good selection of ratios.
What gears to go with depends on what you're doing. If it's just a daily driver you want to have fun with, then go with 3.55s or 3.73s at the most to keep your fuel mileage reasonable (3.55s would be the better choice if you do mostly highway driving, my '87 GT 5.0 got 29mpg highway with it's factory 2.73s, and only dropped to 27.5mpg highway with 3.55s, my in town mileage jumped from 8mpg city to 13mpg city so I was thrilled with the trade-off, but my in-town mileage would've probably been better with 3.73s (heck, my '75 Chevy pickup with it's built-up 400 and TH350 gets 14-16mpg in town with a 4.56 rear end, but about 4mpg highway (no joke)).
If it's just a drag car? 3.73s on up depending on where you want your RPM range to be there are guys out there running 4.56 and 5.14 gear sets in their Mustangs (though the lowest I've seen in a 7.5 is 4.11, I've not seen a 4.56 or lower (the higher the number, the lower the gear is) for a 7.5 rear-end yet) but if it's a drag car I'd be right there with coolwaterblvd in recommending you junk the 7.5 in favor of at least an 8.8, even a stock 2.3L N/A engine has enough torque to wreak havoc on a stock 7.5, though there are a few upgrades available for the 7.5 including girdled covers and aftermarket gear sets that are stronger than stock.
If you're road-racing or circle-track racing with the car, then the gear set is going to have to be a good compromise between acceleration and top speed to fit the track/class your racing and your engine's RPM range. There are tracks where a 2.73 is great due to really long straight stretches that let you really wind it up, and other tracks where you'll never get going too fast, but need enough acceleration to pass the other guy coming off the corner where only a 4.11 or lower will give you a chance.
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1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4 tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)
it is just gonna be a daily driver that i have fun with from time to time im going to put a turbo four cyl from a 86 mustang svo in as soon as i get the motor finished
im still driving my car daily its gonna need a new clutch SOON but untill it goes out im still drivin it (it slips like crazy) and i have a new clutch waitin to go in
i would like to get a little more get up and go action out of he car before the turbo motor goes in
I doubt you'll hurt that 7.5" axle even with a turbo 4. You can find 7.5 Trac-Locs on Ebay quite often for under $100.00. Rebuild kits are still available and you may as well throw one in when you have everything apart.
Factory gears were 3.45 for 5-speeds and 3.73 for automatics.
My car was a factory auto car. After the 5-speed swap, I left the 3.73s in the car and I'm perfectly happy with them. I run a 25.5" tall tire and highway speeds put the motor in the 2800-3200rpm range cruising in 5th.
so if i take the 3.45s out and stick in some 3.73s what kinda change will i have before i put the turbo motor in
looks like im gonna have to drive the factory motor for a bit longer having some problems with the turbo motor and a friend just gave me some 3.73s and i kinda want to put them in now hehehe just wanted to know how the factory motor will handle with 3.73 put in
well i dont have a 5 speed in my 1980 2.3l n/a...it came with a 4 speed...what kinda gear ratio would i want to go with to beat these lil rice rockets that run around or should i stick a t-5 in it?? ...granted when i find a 2.3l turbo i'll beat them anyways...but i would like more get up and go...and not hurt the gas milage alot.
I had an 88 Ranger with a 2.3L, 26psi boost, Engle Cam and some other work back in the early 90's.
Broke a 4.10 and a 4.56 gear in the 7.5"' rear. Stripped the pinion teeth clean off leaving at 5,000. This was with 26x8.5 slicks with ladder bars. The Mazda 5spd never let me down though.
They made the 4.56 gear for a while for lifted Rangers with big tires.
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2006 Legend Lime GT: Samco, Metco, LPW, Brembo 6 pot brakes with floating rotors, Magnacharger with 8-Rib, LubeLocker, Royal Purple, FR500S front end, APR Performance Carbon Fiber Rear Wing, Roll bar, 10 qt upgraded oil system...Thank you Capaldi Racing for all your help! 2007 Mustang GT/CS : Wife's Car, Magnacharged too. 1966 Mustang GT-K Code Coupe: Restored
well of course u broke a 7.5 with 26pounds of boost and slicks.. thats jus obvious.. u wont break it with 20pounds and street tires tho
I was only 21 at the time (17 years ago), and didn't put the fore thought into the end result with the driveline. I knew the engine part of it and it lived for 3 years until one rod got tired (the other 3 were bent a little shorter than when new). Wish I had it to do over again with the money and knowledge I have now. Back then I had $1000 into the whole engine project.
Sure was fun spanking 5.0L Rangers though.
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2006 Legend Lime GT: Samco, Metco, LPW, Brembo 6 pot brakes with floating rotors, Magnacharger with 8-Rib, LubeLocker, Royal Purple, FR500S front end, APR Performance Carbon Fiber Rear Wing, Roll bar, 10 qt upgraded oil system...Thank you Capaldi Racing for all your help! 2007 Mustang GT/CS : Wife's Car, Magnacharged too. 1966 Mustang GT-K Code Coupe: Restored
well of course u broke a 7.5 with 26pounds of boost and slicks.. thats jus obvious.. u wont break it with 20pounds and street tires tho
+ 5000RPM?!?!?
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Woe to him who builds his palace by unrighteousness,his upper rooms by injustice,making his countrymen work for nothing...Does it make you a king to have more and more cedar?Did not your father have food and drink?He did what was right and just,so all went well with him. He defended the cause of the poor and needy,and so all went well...But your eyes and your heart are set only on dishonest gain,on shedding innocent blood and on oppression and extortion. Jer 22:13, 15-17
Leave at 5k, shift at 7800. Carried the Left Front tire for about 40ft. Made the Super Shops video long time ago when they were in business.
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2006 Legend Lime GT: Samco, Metco, LPW, Brembo 6 pot brakes with floating rotors, Magnacharger with 8-Rib, LubeLocker, Royal Purple, FR500S front end, APR Performance Carbon Fiber Rear Wing, Roll bar, 10 qt upgraded oil system...Thank you Capaldi Racing for all your help! 2007 Mustang GT/CS : Wife's Car, Magnacharged too. 1966 Mustang GT-K Code Coupe: Restored
What gears work best for a 7.5" rearend in a Mustang? 
