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65 vert, 4 speed 289 4 bbl completely rebuilt pushing around 300 hp


I currently have 2.79 open rear end and want to upgrade to either a 3.40 or 3.55 "locker" style 8 inch rear
I live 2 miles from work. There's not a highway that allows over 55 mph for 30 miles and then its only 65 mph for another 25 miles...
I drive the car weekly, mostly around town and to neighboring cities so all in around 60-100 miles a week.
I do plan on driving it to the mountains at some point which would obviously be interstate driving for a few hours but this would be maybe once a year.


I know this has been talked about a lot and I've read a lot.... just trying to reach a decision before I drop $1000
 

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I put 3.55's in mine somewhere around 1986-7 and have driven the car all over, including a drive from Michigan to California. At 1:1 (4th gear) you should be around 3,500 rpm at 70 mph. I would do it again in a heartbeat.

I got lucky and found a 3.55 T-loc in a Pinto wagon. Without a doubt my best junk yard find ever. :)
 

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I put 3.55's in mine somewhere around 1986-7 and have driven the car all over, including a drive from Michigan to California. At 1:1 (4th gear) you should be around 3,500 rpm at 70 mph. I would do it again in a heartbeat.

I got lucky and found a 3.55 T-loc in a Pinto wagon. Without a doubt my best junk yard find ever. :)
Did you run the 3.55 with the 4 speed?
 

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I also run a 3.55 rear with a 4 speed Toploader. Like 66coupe289, I also spin close to 3500 rpm at 70 mph, and my 65 just seems to really like it. I can get anywhere from 19 - 21 mpg if I manage to go a long ways at 70 mph.
 

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Stock 65 A code w/ T-10 4speed. Running a trac-loc and standard/stock 3.00 gears. Satisfied with the get-up and gone performance street and freeway. Brian
 
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Add another to the 4-speed toploader with 3.55 gears, in my case a truetrac.

I upgraded my original 8 inch 2.79 one-wheel-peel a few years ago during my engine upgrade work and bought it directly through here:

https://www.ford8and9inchrears.com/

At the time, TJ Rebert was the owner but unfortunately passed away last December. His employee, Alan Von Ahnen, is now the owner and continuing TJ's exceptional work. If you do a search on VMF, you will probably find numerous recommendations for TJ/Alan.

John
 

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toploader with 3.70 here, came out of an old pickup truck. and I wouldn't go any higher, had 4.11, too much for me
 

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Did you run the 3.55 with the 4 speed?
No, I ran them with a C-4, also 1:1 in drive and now with a T-5, 1:1 in 4th. Also, my tires are small(ish) at 225/60r-14.
 

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seems like quite a few satisfied 3.55 / 4 speed ppl out there
65-66 Shelbys had 3.89 gears with a 4 speed. Somehow I would be satisfied with that too. ;)
 

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I have a similar setup to yours except with a 3 speed manual. I went with a 3.25 trac-loc. I run 205/70/14 tires. If I had to do it again I would go 3.55 and still might after I get my T5 in.
 

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65-66 Shelbys had 3.89 gears with a 4 speed. Somehow I would be satisfied with that too. ;)
When gasoline was going for 24 cents a gallon! :) That's the cheapest I remember ever paying for a gallon of gas...for the lawnmower.
 

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for some reason I thought the 65/66 shelbys had 3.55.... now I know differently

"65/'66 Shelbys had a 9" rear. I have never seen nor heard of 3.55 gears for a 9".


When gasoline was going for 24 cents a gallon! :) That's the cheapest I remember ever paying for a gallon of gas...for the lawnmower.

When I started driving in 1970 gas was 21.9 cents per gallon and sometimes the stations would have a gas war and drop the price to 19.9 cents. As good as that may sound it is my understanding that based on inflation gas at the present time is actually cheaper.
 

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Live the experience

Rear-end gearing selection is a messy process. IMO and from my perspective, this is mostly due to personal preferences, not the science and mechanics of it all. That part is relatively simple. To wit, there are many urban legends about it, and most are indeed false or misapplied. For example, a deeper (numerically higher) gear does not automatically mean it will have lower fuel economy. Depending on the engine's build, a deeper gearset may often provide better economy. Besides, even if it is a bit less, did you spend this much money on it to cheap-out on the driving experience?

Other legends are also prevalent, such as revving the engine too high on the highway. Not possible unless you are exceeding redline. Ask yourself how those thousands of Ford U-Haul trucks ran for a zillion miles with the pedal floored and riding the 4400 rpm speed-limiter, across the country and back, over and over again? Or, how you don't have an issue with driving your Ford-powered boat all day, tank after tank, at 75% to wide-open throttle and full load? It's OK. They're OK.

There are many urban legends about gearing, and it mostly gets messy with squeamish drivers or those wanting something other than what the car is. They are worried that their classic doesn't sound like their new Honda and they're not used to it, or they'll hurt it, or they want their classic to ride and drive like a modern luxury car. If that's what you want, then get one of those. Don't castrate your stallion. Do you buy a Harley because it rides and drives like a Gold Wing or BMW? I hope not. You get it for the experience. The sound, the rattles, the noise, the looks. Classic cars have all of those, and the experience is real. It's real. Don't be afraid to gear your classic down, just because your Lexus purrs on the highway. It's not a Lexus. This is what they were built to do. Give it what it can use best for the job and live the experience.

David
 

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I have a Tremec TKO 600 (5 speed) tranny with a .82 ratio in 5th gear. With my 3.0 rear end and 26.7" diameter tires, I'm turning about 2300 rpm @ 72 mph. I prefer the lower revs on the highway, quieter and won't wear my engine out as fast.
 
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Rear-end gearing selection is a messy process. IMO and from my perspective, this is mostly due to personal preferences, not the science and mechanics of it all. That part is relatively simple. To wit, there are many urban legends about it, and most are indeed false or misapplied. For example, a deeper (numerically higher) gear does not automatically mean it will have lower fuel economy. Depending on the engine's build, a deeper gearset may often provide better economy. Besides, even if it is a bit less, did you spend this much money on it to cheap-out on the driving experience?

Other legends are also prevalent, such as revving the engine too high on the highway. Not possible unless you are exceeding redline. Ask yourself how those thousands of Ford U-Haul trucks ran for a zillion miles with the pedal floored and riding the 4400 rpm speed-limiter, across the country and back, over and over again? Or, how you don't have an issue with driving your Ford-powered boat all day, tank after tank, at 75% to wide-open throttle and full load? It's OK. They're OK.

There are many urban legends about gearing, and it mostly gets messy with squeamish drivers or those wanting something other than what the car is. They are worried that their classic doesn't sound like their new Honda and they're not used to it, or they'll hurt it, or they want their classic to ride and drive like a modern luxury car. If that's what you want, then get one of those. Don't castrate your stallion. Do you buy a Harley because it rides and drives like a Gold Wing or BMW? I hope not. You get it for the experience. The sound, the rattles, the noise, the looks. Classic cars have all of those, and the experience is real. It's real. Don't be afraid to gear your classic down, just because your Lexus purrs on the highway. It's not a Lexus. This is what they were built to do. Give it what it can use best for the job and live the experience.

David
Potentially better highway economy with a 3.40 vs 2.79 with a small block Ford (which is at issue here)? Exactly how would someone build such an engine? Dropping my final drive ratio (via overdrive transmission) from 3.55 to ~2.23 netted me about 6 more mpg on the freeway. No myth, real world experience.

For a vintage Mustang engine with the same maintenance intervals, an engine needing to spin 3,000 rpm to travel the same distance as an engine spinning 2,000 rpm will experience more wear. Both rpms are well below red line and well within the operating torque range of a small block Ford. As such, wear becomes more a function of the distance traveled by the piston rings on the cylinders and the distance of a spot on the crank and cam vs bearings and lifters. The internals of an engine spinning 3,000 rpm will travel (be rubbing) 50% more than the engine that only needs to spin 2,000 rpm to propel the car the same number of miles. Secondly, each cylinder will be subject to 50% more combustion cycles per oil change interval which means more contamination.

If people were to leave vintage Mustangs as the cars they were designed, most would not be driving a "stallion" but rather an ill handling secretary car. I offer up my car that started life as a Tahoe Turquoise, T code automatic as a prime example. The OP actually wants to switch from a 2.79 to 3.40/3.55 so I don't see where anything is being castrated.
 
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