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Old 11-08-2008, 01:46 PM
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Limits of the Ford 8" rear

I need to decide whether or not to get a new gear for my 8", or switch to a 9". I'm looking to go to a 4.30, possibly a 4.56 gear. As of now, I have 3.80's in the 8". I raced it this summer with zero problems with a 350hp or so SBF.

This winter I'm stepping it up a bit in the engine department, so there will be considerably more power. I have been told that the 8" will hold up well under quite a bit of power as long as it's built right, and the gears don't get much higher than 3.80 or 4.11. Anything over that the pinion is really small and won't last long.

So should I get a 9", go to the work of narrowing it, and put in the gears I want? Or press my luck with the 8" and hope for the best?

The car is real light (2550lbs) if that makes a difference.

Mr. Pinto
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Old 11-08-2008, 03:26 PM
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I dont think you can get anything past a 4:11 in a 8" rear so you would have to go 9"...Am I right on this guys??
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Old 11-08-2008, 03:39 PM
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8"s have very limited gearing options.

Make a poor-man's 9". Get the center bowl and carrier from a small 9" and put your 8" tubes on it. That's how Shelby did it for the first mustangs, and it will save you big bucks over buying a complete 9"
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Old 11-08-2008, 10:19 PM
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Plenty of ratio's available:

You might consider selling the 8' while it's in good shape,I see them selling on Ebay for pretty good money, I bet you can get enough money to at least get core 9' housing and get the housing work done with a little left over. I would worry about the 28 spline axles in the 8' if your gonna keep making more power.

Last edited by prostreet6t9; 11-08-2008 at 10:41 PM.
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Old 11-09-2008, 07:05 AM
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Originally Posted by mr.Pinto

The car is real light (2550lbs) if that makes a difference.
Weight is a BIG factor in the fact that your 8 inch Ford has lasted as long as it has. My wife says I over do most everything ... But I believe I would go ahead and move up to a 9 inch Ford with 31 spline axles. Most sanctioning bodies want a good axle shaft in a car if you are going reasonably quick. Just go ahead and get the good rear end with good aftermarket axles and be done with it. Peace of mind ... and safety are the benefits
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