Gear ratio decision

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dukeneutron

dukeneutron

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I got a 70 duster. Going to be running 560hp small block with a 4 speed manual transmission. Not much freeway mainly cruising and city. 8 3/4 rearend. Mini tub rear to fit some good size meats back there. Not 100% on the size yet. I'm currently setting up the rear end, I'm looking at 4.10 gears. Seems to be a goos choice but i want to be certain My heads swimming trying to figure it out.
 
the height of the rear tire is going to be helpful in making a decision. The taller the tire the more gear you can run.
 
71 Duster, 525 hp Big block, 727 with 3500 actually flashes to 4000. i have an L-60/15 on the rear, 28" tall i went 3.73 gears. It destroys the tires as it is. lol and the nice thing is 60 mph is 2600 rpm.
 
I'm going to run 3.91 with my 416 CRT reverse manual 727 with a Frank Lupo 4200 stall convertor. 275x60x15 Nitto Drag Radials. Hope to have it on the road in 30 days.
 
I'm a long way from being on the road for sure. Thanks guys I wanna do it right the first time.
 
A good starter gear for a SBM streeter is between 10 and 11 to 1.
A 2.66 low gear times 4.10 gets you a 10.91.
If your engine has a lot of torque down low, you could probably go 1 or 2 sizes smaller.(3.73 minimum)
If your engine has a pretty big cam, then 4.10s are probably right on.
And 3.55s and the 2.66 low gear (9.44 starter) almost suck with big cams.
But 3.55s are awesome with the 3.09 low; equaling 10.97 And the bonus here is under 2800 cruise rpm at 65mph with 28s. So now you get to cruise to car shows in other states.

The bad I gotta warn you 4.10s will be through first gear in a really big hurry.
The good tho is; 4.10s and second gear will get you 65mph @ 6140 with 28s;and that's a pretty nice place to be.
And the ugly with 4.10s is cruising at 32mph will be 3023 in second, or 2204 in third:neither of which is particularly good for anything :(
3.73s might be better, giving you 33mph @2800. You got torque at 2800?
3.91s would be [email protected]
 
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I had a 68 dart with 325/50/15 & 4:30 gears. Cruising around town is was awesome but any thing over 55 it was screaming. O & it was a small block.
 
Yeah I had 4.30s to for a while But I had double-O/D, turning them into 4.30x.71x.78 = 2.38s for the hiway. I found the starter gear of 4.30x 3.09 = 13.29 hopelessly silly around town. In fact I was starting in 1st-over most of the time which was 10.36. So it wasn't long and I swapped trannys and gears in favor of my current combo; see my Avatar.

With the right cam, the A-833 o/d box can be made to work behind a stout 360. But that would have to be an unusual combo. The splits in that box are very wide, so a high-rpm cam will suck, and that means the hp number will look weak.
But if a guy was gonna build the engine for the tranny and for street, I think it could be a real fun pkg.
I can visualize a couple of combos........lol
I ran it behind a hi-comp 360 with small 223*@050 cam, and found it a little bit fun, but I think a bit more stroke coulda made it even more fun. The take off was more than adequate, but the small cam was a bit weak on the top. I think more cubes woulda added some welcome pull from 85 mph and beyond. The combo still went 106mph, without any tune, so it wasn't THAT weak.
 
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I run a 28 inch tire (325 50 15)
A833 4 speed
With a very healthy 418 sb and w2 heads
I run the 3.55 gear ratio and it lights the tires up freely

When I was deciding on camshaft they wanted me to step up to at least 4.10 but I only do back road cruising and some city streets.
I have no complaints with my gear ratio that I chose. I get the best of all world's.

If I ever save enough cash to get the passon overdrive I would swap the gears in the rear
 
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