Gears?

B-Rode

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I'm looking to get the rear end in my '70 Sport Fury 383 re-geared, any recommendations? 4:10? 4:86? Something aggressive but drivable to compliment the Edelbrock AVS2 650 going on it soon. If you also know of a good website or place to purchase them from please share.

Thanks!
 
We can’t make any recommendation before you tell us how you drive the car. Is the engine modified? Compression ratio? Camshaft size? Headers or exhaust manifolds, aluminum intake or iron? Rear tire size? converter? Etc.

Any Freeway trips? What speed do you want to cruise?
Local cruising in town?
Stop light drags?
1/4 mile or 1/8 mile drag racing?

4.10 gears and a 650 don’t go together very good, carbs too small. 4.86?
 
Maybe 3.73. The 4.10 and higher numerical ratios will really make it rev at highway speeds
 
I'm looking to get the rear end in my '70 Sport Fury 383 re-geared, any recommendations? 4:10? 4:86? Something aggressive but drivable to compliment the Edelbrock AVS2 650 going on it soon. If you also know of a good website or place to purchase them from please share.

Thanks!

If you are going with an automatic, 4:10,4:56, 4:86 will much too low (these are 4 Speed drag gears). 3:55 for mostly urban driving with the occasional heavy foot, 3.73 if heavy foot is all you do, crappy fuel mileage. If you have installed a loping cam, you might be better served with a higher stall speed on the convertor as well.

Dave
 
Engine is pretty much stock as of now, soon to do the carb as mentioned and probably different headers. I know it's a little best of both worlds but as far as use goes it's a highway cruiser and a stoplight dragster lol. What ratio is stock on one of these anyway? I just need something a bit more aggressive that doesn't have too much highway drone. 3:73 a good balance?
 
Engine is pretty much stock as of now, soon to do the carb as mentioned and probably different headers. I know it's a little best of both worlds but as far as use goes it's a highway cruiser and a stoplight dragster lol. What ratio is stock on one of these anyway? I just need something a bit more aggressive that doesn't have too much highway drone. 3:73 a good balance?
@413 I generally cruise around 70 on the highway. Around town it's pretty sluggish, carb will help but I'm hoping gears will wake it up.
 
It could be 2.76/2.94/ or 3.23 now. Probably a 2.76

Is this a 2 bbl or 4 bbl engine from the factory? What gears you got now? If you have 2.76 then 3.23 will be a change you can notice and still cruise on the freeway. 3.73 ain’t gonna work cruising at 70MPH.

I have 3.23 with 27” tall tires and a 440 HP. I think it’s a good all around combo. Still some bottom end and can drive all day at 70MPH.

Any gear ratio up or down will compromise some aspect of the way the car drives.
 
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It could be 2.76/2.94/ or 3.23 now. Probably a 2.76

Is this a 2 bbl or 4 bbl engine from the factory? What gears you got now? If you have 2.76 then 3.23 will be a change you can notice and still cruise on the freeway. 3.73 ain’t gonna work cruising at 70MPH.

I have 3.23 with 27” tall tires and a 440 HP. I think it’s a good all around combo. Still some bottom end and can drive all day at 70MPH.

Any gear ratio up or down will compromise some aspect of the way the car drives.
Factory 2bbl car, no idea which gears are in it now but I agree it's probably 2.76, in which case I'll go for 3.23 so it can still keep some top end
 
It could be 2.76/2.94/ or 3.23 now. Probably a 2.76

Is this a 2 bbl or 4 bbl engine from the factory? What gears you got now? If you have 2.76 then 3.23 will be a change you can notice and still cruise on the freeway. 3.73 ain’t gonna work cruising at 70MPH.

I have 3.23 with 27” tall tires and a 440 HP. I think it’s a good all around combo. Still some bottom end and can drive all day at 70MPH.

Any gear ratio up or down will compromise some aspect of the way the car drives.
How well does 3.55 do cruising highway speeds?
 
3.55 start to possibly compromise your ability to want to cruise at 70 for hours. Exhaust noise and reduced gas mileage.

You have to decide if it’s worth it to you and your driving needs, it’s a big heavy car so jackrabbit starts isn’t your strong suit anyway.

What size rear tires do you have?
 
3.55 start to possibly compromise your ability to want to cruise at 70 for hours. Exhaust noise and reduced gas mileage.

You have to decide if it’s worth it to you and your driving needs, it’s a big heavy car so jackrabbit starts isn’t your strong suit anyway.

What size rear tires do you have?
Rear tires are 275/60
 
With tires of the same diameter as P225/75R-15s, a 3.23 will make about 25mph/1000rpm on the highway, with the normal 3-speed TF. That puts the engine at about 2800rpm at 70mph, which is on the bump of the torque curve for most B/RB engines, with stock-type cams and such.

You want highway cruising and "stop light" capabilities? Then a 3.73 with a OD automatic will do that. A thread of two of using later-model Chrysler 5+ speed automatics, most which have a 4.50 low gear and OD on the top side. Cost of adapters and the multiple pressure switches to make things work WILL be expensive, not to mention the cost of the upgraded rear axle gears. If you open up the rear axle, then you'll want a new Sure-Grip unit, new bearings, new seals, new wheel bearings, and all of that TOO, for good measure. PLUS getting the new driveshaft made and mounts for the newer trans procured. Maybe $4K+ by the time it's all done, or more?

A 3.73 by itself will certainly "wake things up", AND you'll hear it all of the time on the highway, too. Along with the much-decreased fuel economy ALL of the time!! What you now call "highway cruising" will become louder as the engine will be on the downside of the torque curve and headed toward the horsepower peak rpm. No "loafing" in that situation.

Tune the car to work as good as it can . . . now and with the later AVS2. Just remember that the secondaries in the carb will only open above about 2500rpm AND only at WOT, for best results. Adding a 4bbl alone will probably make little difference in low speed operation and power.

With a somewhat heavier car and highway gearing, it's usually best to not use WOT at lower road speeds, unless a WOT kickdown situation happens. Otherwise, use a bit less throttle input and keep ALL of the vacuum advance working as the centrifugal mechanical advance builds with rpm. WOT at lower speed loses the vacuum advance, so less power and more fuel use, by observation, especially when moving from a stopped position. LEARN how the equipment works best and then do things as it likes them, NOT how you perceive what it should be with what you have to work with. In other words, "realistic expectations".

Just some thoughts,
CBODY67
 
Having run gears above 3:91 in street cars "back in the day"...anything over 3:55 is going to affect your highway cruising exponentially and gas mileage will be non existent. Your Zero to 80 mph tromp will be exciting but even that will grow tiring as you leap from exit to exit, and gas station to gas station.
You can bring your low end up with a "high stall" convertor and 3:21 gears, and 3:55s will work well with 275 tires. Gears lower than that will require rethinking your drive train from crank pulley to rear u joint.
 
My car has a 383 under the hood and is riding on 27" tires, with what I believe to be a 2.76 rear. Anyway, it is perfect for the highway. If I ever do change the rear gear and I'm hesitant to for that reason, I won't likely go lower than 3.23. It's an automatic, not a manual, so they tend to let the engine rev a little bit more. Not a direct comparison, I know, but I have a 3.54 rear in my F-100 2WD with a 390 under the hood. It has a manual trans with OD and seems to be the perfect city/highway combination. The highway revs are just right and it gets surprisingly decent highway mileage if I just cruise and keep my foot out of it. However, without the overdrive I would probably grow to hate it on the highway in a very short time.

I'm not suggesting the OP do this, if it's even possible with a 727, but this is something I've heard of some Chevy guys doing. In order to keep the rear gear ratio for highway, they swap out the planetaries in the automatic to get a lower 1st gear and, I would assume, a slightly lower 2nd gear. I haven't heard of any Mopar or Ford guys doing this, maybe because no planetary gears with other ratios are available. Now, I'm not a transmission expert by any means, but with all of the interest in drag racing over the years, especially among the B-body and E-body crowd, it would surprise me if no aftermarket planetaries were ever offered for this.
 
Thanks for the detailed replies everyone, I'll have to consider all those things. At the end of the day it's best on the highways so I won't go too deep on the gears.
 
I'm looking to get the rear end in my '70 Sport Fury 383 re-geared, any recommendations? 4:10? 4:86? Something aggressive but drivable to compliment the Edelbrock AVS2 650 going on it soon. If you also know of a good website or place to purchase them from please share.

Thanks!
just did a gear swap in my 1970 fury conv b
I'm looking to get the rear end in my '70 Sport Fury 383 re-geared, any recommendations? 4:10? 4:86? Something aggressive but drivable to compliment the Edelbrock AVS2 650 going on it soon. If you also know of a good website or place to purchase them from please share.

Thanks!
just went from a 2.91 gear to a 3.21 gear in my 70 fury conv wow so fun to drive now if you have a 8.75 rear go with a 3.23 gear a perfect combo.
 
just did a gear swap in my 1970 fury conv b

just went from a 2.91 gear to a 3.21 gear in my 70 fury conv wow so fun to drive now if you have a 8.75 rear go with a 3.23 gear a perfect combo.
Nice, is it noticeably better around town?
 
There is a deeper low gear planetary, factory, but for the 904 family. 2.75. It was used on some six-cylinder applications, but it's a 4-pinion planetary (as are the 727 Hemi planetaries,. A drop in situation.

When Greg at Phoenix Trans suggested it for my '80 Newport 360, I initially declined, but with the factory 2.45 rear axle ratio, the 2.75 put things back to the old 2.76 + 2.45 gear combination of old. I can tell a little difference off the line, but nothing ground-breaking. Perhaps if the stock 360 2bbl had more "guts"?

CBODY67
 
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