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Discussion Starter #1
I'm considering pulling the trigger on a long considered purchase: the rear end of the car is howling pretty loud and spring is coming. I have a 289 with a C4 and a 8" 2.79 open rear. No plans to do anything drastic like an AOD. I want more seat of the pants giddyup - should I go with a 3.0 or a 3.25 posi rear? More of a weekend cruiser type car that becomes a driver when the wife's Jetta is in the shop. Some interstate, some city. Thoughts?
 

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I think you would notice more difference with a 3.25 rear and not scrafice too much on the highway. My 3.00 rear is a dog from a stop.
 

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3.55s are pretty tough with a C4. I ran my fastback with a C4 and 3.25s for many years, and thought it was a great combo.

Regards,
MrFreeze
 

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Assuming you have a stock block and tire diameter, I think 3.55 is going to result in the 70mph engine rpm being a little on the high side.

I would go with 3.25 max.

There are calculators that can tell you the exact rpm for a given tire diameter and road speed. This is the best way to know exactly what you will end up with.
 

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If you know your rpm for a given speed, your new rpm at that speed is simply your (old rpm/old ratio)*new ratio. My 289 with C-4 ran 60 at about 2400 with 3.00 gears. So, 3.55 would put it at 2840 rpm at 60 mph, (neglecting slip). Since dividing by my old gears normalizes it, this result should be close to what you should expect. 3.25=2600 rpm at 60mph.
 

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I have a 3.00 equilok in my 68 vert and am changing to a 3.25. I wanted a little more seat of the pants feel when taking off but didn't want to suffer with turning the engine too much at highway speeds (3.55) I can let you know in about a month how it feels, I am way deep in the garage right now and don't have time to swap it out.
 

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Discussion Starter #8
I think I've heard enough folks say 3.25 to clinch it for me. Thanks to everyone - you folks are great!
 

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where do you find different gear sets? i am currently running 3.00's and want to go to 3.25's. i have a posi rear.

sorry don't mean to chime in on your post, but thought it might be a relative question.
 

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Discussion Starter #11
I need a whole new pumpkin, so that's what I'm after. You can buy new gear sets with different ratios at any of the parts houses.
 

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Don't bother with a 3.00 - not enough difference to justify the cost. I would go with the 3.25.
 

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you'll be much happier with the 3.25's. and I seem to remember someone on here that sells rebuilt 8" 3rd members :winkgrin:
 

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I can sell you a new set(motive) shipped for $175
 

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e-mail me direct and we'll discuss it.
 

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On my 68 GT coupe I had many years ago I ran 3.50 with a C-4 I liked the nice pull from a stop, it made the Stang pull well from a stop.
 
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