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Discussion Starter #1
I was thinking of getting my 8" third-member rebuilt with new gears and a posi.  But If I do install a 351 as I plan to do will the extra torque be too much for the 8"? Maybe I should just hold out and find a versailles 9" rear.

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65 Fastback 289 4spd in storage :-(
91 CRX Si... A.K.A. my go-kart with AC!
 

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With your toploader, it could get dicey depending on the build of the engine and whether you plan to race the car...

Bolt on slicks and I'd say you're probably heading for trouble, usually in the form of a rear pinion support failure...

If you do choose to retain the 8", I'd suggest a driveshaft safety loop to keep from damaging your car in the event of a pinion support failure...

A 9" is stronger but still vulnerable in the same area....

If you can discuss your prospective drivetrain combo and use in more detail, I might be able to assist further...

Pat
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You'll get many differing opinions on this issue, so I only have two things to say about it. If you are going to drag race with slicks and a manual trans, you may want to opt for the 9". It's not the torque of your engine that will necessarily make the 8" fail, but the torque you can actually put to the ground. If you want your car to handle, consider an upgraded 8". This is because a 9" weighs 75-100 lbs more than an 8", and all that unsprung weight has an adverse affect on handling.

The poster formerly known as JAV65

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Discussion Starter #4
I'm planning on using the car just for weekend fun. No serious drag racing, but I would like to make a pass occasionally. I am concerned with handling and the added unsprung weight of the 9" would be a concern. I'm looking to build my 351 (or a 347 stroker) for about 385hp. I was inspired by the Car Craft $2500 400hp windsor article several months back. I want to tone down the cam a bit so it wouldn't be as brutal though, so I'm willing to accept a bit of power loss for more driveability. I really want a car that I can take to the local burger joint and keep the brand X dogs a bay on street. I'd also like to hit the solo 2 autox once and a while just for kicks.

http://216.71.48.244/archive/mikecar.jpg



65 Fastback 289 4spd in storage :-(
91 CRX Si... A.K.A. my go-kart with AC!
 

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Mike: This has been a hotly-debated topic here for a long time. Ford says absoulutely do not use an 8 behind a Windsor in their hot rodding manuals. However, a properly-built 4-spider 8 should hold up OK if you don't let the car get seriously hooked up. Jim Vogle is right about the advantages of an 8's lower weight. I think his 8-inch has given him good service and he runs his 289 car pretty hard. Since my 351 puts out about 360hp, I went ahead and had a serious 9-incher built for about $1,000. It may be overkill in my case. I'm just not sure. 385 is big-block horsepower - so you may want to bite the bullet and do a 9.

Glenn Morgan 66 GT Fastback 351w+toploader
 

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I would go 9” You can find them at the salvage yards under granadas fairly easily. The gearing will be low but it fits perfectly. I think Mustang and Fords did an article about this swap recently. I will have to check when I get back home. This is the route I went and had a 3.5:1 w/tracloc built for the housing. It works great. Also, w/ the granada unit, the back spacing is the same. Good luck.

Don
1965 Convertible, 351W, Tremmec, 9", continuous "improvements"
1996 Explorer XLT - daily driver
2000 Taurus - wife's driver
2001 Giant OCR3 - my 2 wheel road warrior for getting in shape
 
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i would go with the 9"
but just a note though...my 73 ragtop started life as a 6cyl. car with an auto and 8" rear...a couple of years later i installed a mild 351c and top loader,i left the 8" in for a while...
the engine was putting out 350-375 horse and NEVER did the rearend fail...i did however DESTROY numerous u-joints and left side engine mounts!!!!
since then i build the motor some more(600 horse) and i immediately tossed in a 9" !!!!! just to be safe :)

SEAN
 

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Mike - Like I said, this topic always gets lots of varying opinions. For all the reasons that Jim V has stated, I really wanted a 4-spider 8 in my car. The differential guy I went to to have one built (along with my machinist) talked me out of it and into a 9-inch. Jim is a pretty serious open track guy and has first hand experience, so I'd give alot of weight to what he says. I may well have more differential than I'll ever need because, like you, I expect an occasional Sunday at the drags, but I'll never be doing regular 5-grand launches with slicks - I leave that sort of thing to guys like Pat *G*.

Glenn Morgan 66 GT Fastback 351w+toploader
 

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Discussion Starter #10
Thanks for your input guys. I think I'm just going to bit the bullet and step up to the 9 inch. I know with the 9 inch and my toploader (after a rebuild) I'll have a bullet-proof drivetrain that I can abuse a bit. The unsprung weight is an issue, but I don't plan on going to to full race suspension so how much can a few extra pounds hurt the suspension of 35 year old mustang?

http://216.71.48.244/archive/mikecar.jpg



65 Fastback 289 4spd in storage :-(
91 CRX Si... A.K.A. my go-kart with AC!
 
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