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Hi I'm putting together a 68 cougar going to be installing a mild 302 that's around 300-350hp I was wondering how long the stock rearend will hold up thinking around a 3.55 gear too.
 

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Discussion Starter #3
Maybe new leafs but new bushings new shocks and new slightly bigger street tires. I got the car in boxes and starting to see what I need to keep an eye out for. Everything I find on this rear end just say go to the 9 inch but I don't have that kinda money right now
 

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I know everyone wants a nine inch, but I personally have never heard of anyone killing an 8 inch rear end. If you are only building a street motor, The 8 will probably be fine. Slicks, nitrous and turbo, a beefier 9 will be required.
300 HP at the flywheel, an 8 inch will be good enough. It may however be more expensive, than finding a 9 inch!
 

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I built my 9" for pretty cheap. Bought one off craigslist for $50 with 31 spline axles and a 3.50 gears. It was from a 70's Bronco. I had a hot rod shop narrow it to my liking for $100 and got custom axles from moser for $420. I rebuilt the center section myself with a rebuild kit for $45. Overall, it taught me a lot and I got a custom built rear-end for about $600 which is pretty good compared to buying one from strange or currie. Oh and I bought another rear end that had disc brake setup so my car will have 4 disc. Overkill? Yeah probably but that's ok.
 

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Discussion Starter #6
OK thanks guys and overkill is never a bad thing. I can pick up a 9' from a truck for around $100 by me but wasnt sure how much of a pain that would be to make work
 

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You can easily beef up the 8 to meet your requirements.... No point spending a ton.... Btw I think somebody listed a 9 on here from a cat just a few days ago.... If you really are set on it
 

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Discussion Starter #8
Not really looking at spending the money on one just don't want to rebuild an axle that will blow up after a year. What can you do to beef them up?
 

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Currie makes axles, there a few choices for for diffs ( trutracs, lockers etc). Usually much more expensive than a 9 inch. And I don't believe anyone makes an aftermarket carrier so really you can only do so much. But like was said before, I've never seen one broken...
At the lower power levels it's really a smarter choice imho. Less weight, less rotating mass, better mileage potential and performance...
 

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Hi I'm putting together a 68 cougar going to be installing a mild 302 that's around 300-350hp I was wondering how long the stock rearend will hold up thinking around a 3.55 gear too.
I have tried to kill an 8 inch and have not succeeded. In 40 years and dozens of Mustangs and other 8 inch equipped fords I never toasted one. The last one I punished was in a 65 Shelby clone that I autocrossed and I flogged it pretty hard with a posi and sticky tires and it never gave up. BUT for those few cars where I built a rather stout motor with serious intentions, I went 9 inch. My current build I sought out a 9 inch.
 

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The 8 inch diff's are tough as nails the trouble is the weak 28 spline axles. A 28 spline 9 inch have the same weak axles. A 31 spline 9 inch is the only way to go if you are going to have serious power and the traction to put it to the ground. That being said a buddy of mine had a 525 ci KB Hemi powered altered rail dragster with a fiberglass model A Ford truck body on it. It had M&H grow tires on it and he never broke an axle in the 8 inch he used. It had a 4 speed stick of some kind. He never had the engine dyno'd but it had to have 700+ HP. Car was light compared to a cat so I would guess somewhat less stress on the rear diff and axles. It had everything needed to be street legal not counting the tires, I'd guess 2500 lbs? He drove it on the street almost every weekend for years. I got a ride in it when it was first built back in the early 80's. He freakin scarred the crap out of me which is not easy to do. I made him pull over and I walked back. Cold M&H grow tires with 7 psi in them made for a death ride. Sideways in every gear going across the original Smith Av High bridge in St. Paul will do it to me every time. The only pictures I could find of the old bridge should give you an idea of how freakin scared I was. http://www.loc.gov/pictures/search/?q=Photograph:%20mn0076&fi=number&op=PHRASE&va=exact&co=hh&st=gallery&sg=true

Bill
 

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Hi I'm putting together a 68 cougar going to be installing a mild 302 that's around 300-350hp I was wondering how long the stock rearend will hold up thinking around a 3.55 gear too.
I have the same set-up. Warmed over 302 with 8" and 3.55 gearing. No issues what so ever. You might want to go with an AOD if you don't have a standard. A lot of my hot-rod building buddies use the 8" as well. I know of a '39 chevy with blown 350 using 8" for 20 years now without an issue. They're pretty tough.
 

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the main reason i built the 9" though is because I want it to last and later on down the road I want to race it in the autocross division. so, on that note the 8" would be fine if you are just keeping the mild motor setup, but knowing me and a lot of my friends we are always looking for more power so I just decided to build a reliable 9" for now and upgrade the center section later on when I get into racing.
 

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Discussion Starter #14
ok thanks for all the input guys i think im going to stick with the 8 for now. i want to either do an aftermarket 5speed or the 4r70w swap.
 
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