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Discussion Starter #1
Hey, I've got a very restored 66 k code over in France. It's got a 4 speed. and I believe its got a detroit locker differential. The person who restored it must have used a 3:90 (or more) rear end, as in 4th I'm cruising at 4500 RPM at 80mph. The problem is that normal highway speed is 80, so I think I would need to change it for a more reasonable cruising RPM. What would be the best compromise to not lose too much low end power, yet be comfortable on the highway? (it's got the original 9" rear end).
 

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Hi there,

this site should help you out:

Randy's Ring & Pinion. RPM Calculator.

just type in your specs and it calculates your rpms for all 4 transmission types. So try typing in 3.73 gears, 3.55 gears, 3.40 gears, etc. until you get down to an rpm level you are more comfortable with at 80mph... say like 3000-3500 :bigthumbsup
 

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Discussion Starter #3
Hi there,

this site should help you out:

Randy's Ring & Pinion. RPM Calculator.

just type in your specs and it calculates your rpms for all 4 transmission types. So try typing in 3.73 gears, 3.55 gears, 3.40 gears, etc. until you get down to an rpm level you are more comfortable with at 80mph... say like 3000-3500 :bigthumbsup
very cool site, thanks
 

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Discussion Starter #4
by the way, given that my the casing, and the entire rear end is virtually new, what parts do I buy?
And whats the best differential to buy for a k code? I do like torque in low gears, but highway drivability is more important to me.
 

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by the way, given that my the casing, and the entire rear end is virtually new, what parts do I buy?
And whats the best differential to buy for a k code? I do like torque in low gears, but highway drivability is more important to me.
Hi,

Unless you are adept at setting up rears, pull the jackpot and hand it over to your mechanic. Regarding the ratio, a 3.55 is about the lowest, most reasonable ratio for the street when running a 4 speed.
At 110 Klms and depending on tire dia. you should be taching just under 3K. Not too bad.
Google "Currie rears". I purchased a complete setup, ready to bolt in. It was too easy. The strength of the Euro vs. the USD is very good for this prurchase. Do you belong to a local mustang club. If not find a few shows, join a club. See what your new gear-head friends are running.
Happy Trails!
 

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Discussion Starter #6
Hi,

Unless you are adept at setting up rears, pull the jackpot and hand it over to your mechanic. Regarding the ratio, a 3.55 is about the lowest, most reasonable ratio for the street when running a 4 speed.
At 110 Klms and depending on tire dia. you should be taching just under 3K. Not too bad.
Google "Currie rears". I purchased a complete setup, ready to bolt in. It was too easy. The strength of the Euro vs. the USD is very good for this prurchase. Do you belong to a local mustang club. If not find a few shows, join a club. See what your new gear-head friends are running.
Happy Trails!
I called mustangsunlimeted who suggested I only need a 3.25 gear and pinion set, not to change the entire differential, if I just want to change the ratio? Is this correct?
 

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I called mustangsunlimeted who suggested I only need a 3.25 gear and pinion set, not to change the entire differential, if I just want to change the ratio? Is this correct?
Hi Johney5,

Yes, the 3.25 is good, as well. The gears, are pretty much all you need, as long as, you have local access to the ancillary parts, bearings, cruscher washers, seals, etc. I ran a 3.25 when running my C4 until, I found a good deal through a local club member who was selling my current T-lok 3.55. Since there was a T5 in my future I snapped it up for $300 USD.
I've dealt with Mustang Unlimited in the past and are a good bunch. Another good source, here on the east coast, is Glazier-Nolan Mustang Barn located in Pennsylvania. They are very knowledgable, friendly, and responsive to email contact. "Google" for details.
Happy Motoring!
 
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