Looking for some Differential advice

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j par said:
Impossible??...
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Yes when all the cars and semi trucks are going 80 mph you will be a big danger in your slant 6 with 3.73’s that can’t maintain 60.

Just go out and drive it around in second gear if you want to get an idea of how it will drive.
 
72DartGuy said:
Thanks guys, I’m going to put a built 727 and a 408 Stroker in her down the road. I have all the parts. Just want to know if I’d save myself a lot of time by swapping the stock 7 1/4” rear end for my 8 3/4” 3:73 sure grip rear end?
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Will you want 3.73 gears with a 4" arm? I wouldn't.
I am taccing about 4k at 70 mph with 4.10 gears with a 3.31" stroke. It's going to suck even more when I get my 3.58" engine in the car. My car is not a highway car so it is acceptable.

With the torque of a 408, you won't need that gearing. I'd change the gearing in that 8 3/4" to something like 3.23 or 3.55 at the lowest.

If you go this route with the 3.73 gearing, consider installing a lot of DynaMat, or other sound deadener...
 
413 said:
Yes when all the cars and semi trucks are going 80 mph you will be a big danger in your slant 6 with 3.73’s that can’t maintain 60.

Just go out and drive it around in second gear if you want to get an idea of how it will drive.
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LOL you're preaching to the choir... Last May I drove my son's 76 power wagon back from Colorado to Oregon doing 60 across Wyoming LOL... Everyone in their Grandma passed me...
It can do 80 miles an hour no problem but slow and steady wins the race....
I can attest those kinds of gears aren't extremely freeway friendly and I wouldn't use them for Long haul vehicles but then again wouldn't hesitate to jump on the freeway for a little while with it on occasions. Definitely not impossible...
 
With 3.73s and 26s, 80mph maths to about 4000 at 5% slip, just saying. I sure wouldn't run my slanty far at that rpm; my stockers usually threw a rod out the side shortly after that.
I would consider that situation as close to impossible as is possible, without actually being impossible; possibly being just, nearly impossible; while quite possibly being dangerously close to a possible engine-failure.
I might possibly be wrong, but in this case I doubt that's possible; yet I admit that there is an ever so small and slight possibility.
Now, having said that, consider that it is possible that we Earthlings do not actually live on a ball, but very possibly .........
 
I guess it’s personal preference. I have no problem revving the snot out of these cars on the highway. Gas mileage? Don’t care.
 
I ran a car with 4.10s daily on the freeway in socal for years. 3700 at 70mph, 20 mile one way work commute. You guys are spoiled with your overdrive. Factory gear ratio, only ratio available.

Op, drive around with your slant in second gear for a while. Thats kinda how it will run with 3.73s in it.

Edit:,oops, I see i got treed, by 413, lol.
 
O.P. is in california. THEORETICALLY, truck speed limit is 55 mph. Practically, they do 62-64. He should be okay on the freeway in the slow lane if he can maintain that.
Agree, Sunday morning on an empty freeway, 80 in a 65 is common.
 
33IMP said:
O.P. is in california. THEORETICALLY, truck speed limit is 55 mph. Practically, they do 62-64. He should be okay on the freeway in the slow lane if he can maintain that.
Agree, Sunday morning on an empty freeway, 80 in a 65 is common.
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Even with the 13" short tires and 3.23s, Vixen clicks along at 70 Purdy good.
 
The thing is if you put in the 408 and it's transmission in there you're going to have to change the gears anyways and building the car from the back forward is the adult way to do it...
 
33IMP said:
I'd put in the 3.73s, and put the tallest 15" tires that will fit in the wheelwell, even if I had to move the rear-end back an inch. Btdt.
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She's gettin 4.11s in a Ford 9" with 215 70 14s and a World Class Ford T5 transmission.
 
RustyRatRod said:
She's gettin 4.11s in a Ford 9" with 215 70 14s and a World Class Ford T5 transmission.
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that should work VERY nicely. Good first gear in the trans, but with the 4.11s its gonna be short. The fifth overdrive will tame the 4.11s down a bunch, but not so low that you will have to downshift all the time. Like the tall 14s, too.
Loved my T5, and it wasn't even a world class.
 
So, if I’m reading this right, you guys all agree the /6 would do better with the 8 3/4 rear end, but 3:73 gears are going to be a ***** with either the /6 Or the 408? I have 2 new sets of 3:73 gears. What would the BEST gear be? 3:23 or 3:55? I’m not racing it, but I want it to scare a few Challengers!
 
MY opinion only:
I would run the 3.73s with the 408. Just know it won't be a freeway flyer.
I'm running a 440 with 3.91s and another with 4.10s, and a small block with 4.57s. All CAN be driven on the freeway, I just don't do it much.
Obviously, this will be a fun toy, not a daily driver. It should be a rocket ship with the 3.73s. That should have the same crank speed with a 4" stroke, as my 3 3/4 stroke 440, with 3.91s. For an occasional use toy, it will be fine.
Again, MY opinion only.
 
33IMP said:
MY opinion only:
I would run the 3.73s with the 408. Just know it won't be a freeway flyer.
I'm running a 440 with 3.91s and another with 4.10s, and a small block with 4.57s. All CAN be driven on the freeway, I just don't do it much.
Obviously, this will be a fun toy, not a daily driver. It should be a rocket ship with the 3.73s. That should have the same crank speed with a 4" stroke, as my 3 3/4 stroke 440, with 3.91s. For an occasional use toy, it will be fine.
Again, MY opinion only.
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So you wouldn’t put 3:73’s in a daily driver? I’ve pretty much replaced the entire interior and wiring in her. With the new motor and trans she’s practically a new car
 
33IMP said:
that should work VERY nicely. Good first gear in the trans, but with the 4.11s its gonna be short. The fifth overdrive will tame the 4.11s down a bunch, but not so low that you will have to downshift all the time. Like the tall 14s, too.
Loved my T5, and it wasn't even a world class.
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I got fortunate with this one. It was given to me along with a Ford 2.3 and a bunch of other Ford stuff. It sat on the outside shelf three years covered up until I got to thinking about a T5 swap in Vixen, then I got it out and got some numbers off of it showing it is a world class V8 transmission. It's even the Tremec version....for whatever that's worth. lol
 
72DartGuy said:
So you wouldn’t put 3:73’s in a daily driver? I’ve pretty much replaced the entire interior and wiring in her. With the new motor and trans she’s practically a new car
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I would not without over drive.
 
Thanks guys. I’d rather change the gear before I put it in. I’ve wound up spending money twice a few times. Now to find a set of 3:23’s!
 
72DartGuy said:
Thanks guys. I’d rather change the gear before I put it in. I’ve wound up spending money twice a few times. Now to find a set of 3:23’s!
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I'm sorry, blame me for side tracking.....my bad, but what do you need 3.23s for? A 7 1/4 or 8 3/4?
 
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