Hello all! I am new and I just want to say thanks for having me. Anyway, I have a 73 duster that is currently an A 230 3 speed with low first gear and a mild 360, 2.02 heads, 9:1 compression, flat tops, and a comp HE268 cam. Was wanting to go to an overdrive manual. I began thinking... why not go to a four speed and then pick a smaller rear gear of 2.76. (Of course in a 8 1/4, no 7 1/4 rear ends here) I was thinking that the low first would make up for the 2.76 gear and the 1:1 4th would be a nice overdrive type gear. Or is there another gear between 2.76 and 3.23. I'll be running a 27 inch tire. I just want 70 mph rpm to be about 2500 or 2700 and liveable. 3200 rpm just is too high for me. I live near the interstate so Alot of my trips Into the city are interstate,30 miles one way. Any thoughts or experience? Or am I trying to have my cake and eat it too.?
rear gearing with a four speed A833.
- Thread starter alpha13
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The 4 speed OD gear was generally a 3.55.
Mrmopartech
Well-Known Member
If you had a 3.23 gear-275-60-15 tires and in O/D,at 70MPH you would turn the 2200rpm.You can play with this calculator for fun,mrmopartech
http://vexer.com/automotive-tools/speed-rpm-calculator
http://vexer.com/automotive-tools/speed-rpm-calculator
I've done a lot of calculator conversions and whatnot already. I considered the A833 4 speed because of its strength. I read somewhere that the OD unit was just as strong but wore out faster. I don't remember where I read that. But like I said the 1:1 gear just isn't going to cut it. I don't have a weak engine so I don't need the incredibly low first gear for a good launch. The four speed was designed for strength and for small engines to multiply torque faster. Un less I used a smaller rear end gear. Then I could use the low first as a good launch gear and then have the nice small gears for 70 mph cruising. I suppose I was more or less asking if my thinking behind this was on the right track, and if anyone has done it already.
goldduster318
Overzealous Car Modifier
There is a 2.94:1 gearset as well.
I run 3.23's, a 1:1 A-833, and 25.6" tall tires and I run 3000 at 70.
A 2.76:1 rearend would have about the same amount of gear at take off with the 3.09 first of the A-833OD as I do with the 2.66:1 first and the 3.23's IF your tires were the same height. With 27" tall you need at least a 2.94 if not the 3.23. I wouldn't consider any gear that's taller than that because taking off would involve more clutch riding than it really should.
I run 3.23's, a 1:1 A-833, and 25.6" tall tires and I run 3000 at 70.
A 2.76:1 rearend would have about the same amount of gear at take off with the 3.09 first of the A-833OD as I do with the 2.66:1 first and the 3.23's IF your tires were the same height. With 27" tall you need at least a 2.94 if not the 3.23. I wouldn't consider any gear that's taller than that because taking off would involve more clutch riding than it really should.
Well I suppose I could go with the 25.6 inch tire. Those are cheaper anyway. I have a pair laying around I could slap on. At 70 with the 2.76 and the 25.6 inch tire will get me just over 2500rpm. Would you say you have a good launch with your current set up?
I'm not trying to turn this into a pissin match, but this statement is incorrect. Automatics were actually designed as torque multipliers. Torque converters are THE torque multipliers. The OD 4 speeds almost always had a 3.55 gear. That's about the best gear for them.
A 2.76 gear with an OD will be either just at the beginning or out of your engine's power band. Either way will result in a combination that lugs along in high gear at cruise speed. That's not good for the engine or economy.
If you look at 4 speed applications through history, they almost always had lower (numerically higher) gears than automatics. This is because they do not have a torque multiplier (converter) they have to rely on better leverage.
Believe it or not, even with a 2.76 gear, that 3.09 first gear will have a much harder time getting the car moving than if it had a 3.55, which is designed to go with the ratios in the OD transmission. Lots of people even go to 3.91s or 4.10s and are happy.
Lastly, the "jump" from one gear to the next in that OD 4 speed with a 2.76 gear ain't gonna be fun either. You're gonna have to twist first gear up pretty good to keep the momentum going shifting into second. You're talking about going from 3.09 to 1.67. LOL That's a huge jump, but good luck with that.
dodge71demon
Well-Known Member
Let's see here I'm using the 833 OD behind a bone stock 318 with 2 something gears I have no problems getting the car moving without twisting first gear up or crusing down the road in fact I often start moving in second gear but I should say this car was built with no performance just a really good driver
That's good. But that's not how the factory engineers designed it and that's not optimal gearing for economy and performance.
dodge71demon
Well-Known Member
I should have stated that's what i had so that's what it got untill some future date
Along a slight different note (but along the same idea), is that generally the case with the slant 6? Reason I ask is I have both a regular 833 (a 65 model that came behind a slant and set-up for a B & T - no big deal) and a an A/F Body 833OD I can use in my wagon. The rear end that was in the 65 with the 833 had 3.23 gears.
All I have ever seen in any original OD vehicle was the 3.55 and ONE 3.91. The 3.91 was in a slant truck. I think most everything with the OD got the 3.55. Using the final .71 of the OD, the 3.55 becomes a 2.52 final drive.
With a 2.76 rear gear the final drive is 1.96 final drive. That's really kinda stupid.
Like I said, I am not trying to make this a pissin match. Put it together like you want. It's your car and your money.
With a 2.76 rear gear the final drive is 1.96 final drive. That's really kinda stupid.
Like I said, I am not trying to make this a pissin match. Put it together like you want. It's your car and your money.
goldduster318
Overzealous Car Modifier
The launch on mine is okay, but I would probably like it better with a 3.55.
Pulling it in 4th gear shouldn't be a problem even with 2.76 at freeway speeds.
I've been in a lot of T56 or ZF 6-speed equipped GM cars (they are FI, which helps somewhat) that have 3.08:1 gears and a 0.5:1 OD. 1.535 final drive ratio. Those things get fantastic gas mileage (easily high 20's) on the highway. Lugging right along.
Pulling it in 4th gear shouldn't be a problem even with 2.76 at freeway speeds.
I've been in a lot of T56 or ZF 6-speed equipped GM cars (they are FI, which helps somewhat) that have 3.08:1 gears and a 0.5:1 OD. 1.535 final drive ratio. Those things get fantastic gas mileage (easily high 20's) on the highway. Lugging right along.
Well Rusty, my original plan was the OD. But now I'm not even talking about OD. If I had an OD transmission in the car I wouldn't even be talking about rear gears. Hence the reason I started this thread. When the enginerest put out the four speed with the 3.55 they were selling them as hot street cars that would go fast on the weekends. Gas mileage wasn't really an issue. But this day and age people are used to lower rpm and better gas mileage. That's why they invented Overdrive. Leverage, torque multiplying. You get the point. The low gear was for a good launch with smaller engines so they didn't have to mash the pedal from a dead stop. Also it's a great launch gear for more powerful engines as well. But anyway. I was running an A230 with the low 3.10 first with 3.55 gears with the 25.6 inch tire before I took the wheels off for a new paint job. My engine just feels wrapped out way too fast with the 3.55 gear. I feel like I lose so much momentum going into second. The car has been down for a few weeks so I've been pondering about a four speed and 2.76s I'm not trying to start anything. But it seems like some people can't follow a conversation. Thank you Goldduster318, you have been very helpful. I think I may dig up a 7 1/4 rear for testing purposes In the spring.
If I remember correct didn't the F body volare come out with the 2.76 gear with the A833 OD? Also the feather duster? Atleast that's what I was always led to believe.
You said in your original post "I was thinking that the low first would make up for the 2.76 gear and the 1:1 4th would be a nice OVERDRIVE type gear.
I followed just fine. YOU brought up overdrive. Not me. I just went with what YOU brought up. Forgive me for wasting time trying to help.
I don't know, but I owned a 76 Feather Duster. Slant, 4 speed OD and 3.55 gears. Whether 2.76 was an option, I don't know. I guess it could have been for the auto equipped cars.
http://www.slantsix.org/forum/viewtopic.php?t=26227&sid=77b412fbaa99e7128f293cc49e754b70
Well I didn't say overdrive gear, I said overdrive TYPE of gear. I suppose you could probably get any gear option at the factory with the feather duster. But this is what I turned up.
Well I didn't say overdrive gear, I said overdrive TYPE of gear. I suppose you could probably get any gear option at the factory with the feather duster. But this is what I turned up.
Yes. I quoted you so I read what you wrote. I am also not a mind reader, so Since you brought up OD, that's what I ran with.
All I know is what the car had. Slant, OD 4 speed and 3.55 gears. It was a Feather Duster. Had all the aluminum and lightened stuff. You could bend the front fenders very easily. It was freaky. I ended up selling it and a Gold Duster I had as a pair.
I'll try to tune the crystal ball in a little better on some of your other threads......or maybe I'll just leave it to you. You seem to be your own best expert anyway. Don't know why you're even asking questions.
Look I'm not gonna go back and forth over this. I kinda laughed when I read the part about the crystal ball, but sometimes I try to explain things and people don't get it. Then I continue to explain and they still don't get it. I'm throwing in the towel on this one. No amount of bickering is going to make you Understand what I wrote. Besides, I've read plenty of your other posts to know sometimes your advice isn't sought after. Atleast by anyone who has a clue. I dont know all things, but I have enough ideas and general understanding to produce reasonable theories and open up to new ideas.
So for a decent cruise rpm, it's the tall 2.76, with the 1:1 four speed which should be just over 2500 rpm at 70. And with the 2.94 gear it will be just at 2700 rpm. Liveable? I think so! =) I think I'm going to try the 2.94 gear first and see how I like it.testing will be done with a A833 four speed with the low3.08 first and the 1:1 fourth. I will Post results in the spring! Stay tuned.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Alpha
In my 68 S-clone, I have had, at different times, just about every rear chunk and for sure every Mopar 4 speed combo.If you sift through Rustys posts, you will find some good nuggets there.I can give you my opinions on any combo you like, but you will have to focus your questions in such a way that you and I dont also get into a pissing match.If youre up for that, fire away.
And no theres nothing wrong with your thinking.I went down that road 10 years ago.
In my 68 S-clone, I have had, at different times, just about every rear chunk and for sure every Mopar 4 speed combo.If you sift through Rustys posts, you will find some good nuggets there.I can give you my opinions on any combo you like, but you will have to focus your questions in such a way that you and I dont also get into a pissing match.If youre up for that, fire away.
And no theres nothing wrong with your thinking.I went down that road 10 years ago.
Hay, I was tying to help. It won't happen again.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Yeah, I would like to respond to Mr Demon re post #8.
If your teener can pull away with 2 somethings and 2nd gear, Thats quite the torque monster. The math says........ 1.67(2nd) x 2.76 (the typical A rear) = 4.61 overall. Well if you had a regular 4spd with the 2.66 low, that would be the equivalent of 3rd gear and a 3.29 rear, or 4th gear and 4.61s. While not impossible to do, it would sure be hard on parts, and the 0 to 60 typically would be measured as Dead Slow. If I were behind you, I think Id be wanting to just run over you. If in fact, your teener pulls it briskly, keep that girl. Shes a prize. Put it in a truck.
-My 360, is a real sweet engine.With that od-box, it wasnt happy with anything less than 3.23s and FIRST gear. Sure I could baby it out in 2nd. But I couldnt (in 2nd)give it any decent throttle til well past 30 mph(2000rpm).
-Like I said, Thats a tractor motor, a keeper for sure.
If your teener can pull away with 2 somethings and 2nd gear, Thats quite the torque monster. The math says........ 1.67(2nd) x 2.76 (the typical A rear) = 4.61 overall. Well if you had a regular 4spd with the 2.66 low, that would be the equivalent of 3rd gear and a 3.29 rear, or 4th gear and 4.61s. While not impossible to do, it would sure be hard on parts, and the 0 to 60 typically would be measured as Dead Slow. If I were behind you, I think Id be wanting to just run over you. If in fact, your teener pulls it briskly, keep that girl. Shes a prize. Put it in a truck.
-My 360, is a real sweet engine.With that od-box, it wasnt happy with anything less than 3.23s and FIRST gear. Sure I could baby it out in 2nd. But I couldnt (in 2nd)give it any decent throttle til well past 30 mph(2000rpm).
-Like I said, Thats a tractor motor, a keeper for sure.
Woods74
Broke Senior
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