A-833 2.47 1st gear change to 3.09

[JDMopar]

Here's a question that might be relevant to the gear cluster swapping discussion. Do all of the ball & trunnion output A body 833's have the 3.09 first gear? If so, is it possible to swap those gears in and still retain a 30 spline slip yoke output? I've never had an 833 apart, but not afraid to try. I have a 65 Barracuda that has a warmed up 273, and I am swapping to a 4 speed. I have a fresh 833 OD, but....well, you know!

 

[DionR]

Here's a question that might be relevant to the gear cluster swapping discussion. Do all of the ball & trunnion output A body 833's have the 3.09 first gear? If so, is it possible to swap those gears in and still retain a 30 spline slip yoke output? I've never had an 833 apart, but not afraid to try. I have a 65 Barracuda that has a warmed up 273, and I am swapping to a 4 speed. I have a fresh 833 OD, but....well, you know!

Based on Passon's chart posted earlier, I would guess that yes, all A-Body ball and trunnion A833's have the 3.09 gearset.

I think you could swap the tail housing and output shaft from a non-OD slip yoke trans and get rid of the ball and trunnion output. Don't necessarily have to swap the gears into a different case.

I know the OD mainshaft is different, the area under 3rd is smaller on those. Not sure if the tailhousing is different between a 30 spline output OD and standard.

 

[DC 340]

Here's a question that might be relevant to the gear cluster swapping discussion. Do all of the ball & trunnion output A body 833's have the 3.09 first gear? If so, is it possible to swap those gears in and still retain a 30 spline slip yoke output? I've never had an 833 apart, but not afraid to try. I have a 65 Barracuda that has a warmed up 273, and I am swapping to a 4 speed. I have a fresh 833 OD, but....well, you know!

I took my original A 833 ball and trunnion 3.09 1st gear transmission and converted it to slip yoke using (what I believe was) a '66 trans main shaft and tail housing. It worked. But I will say, when on the track, I hated the 3.09 1st gear. Probably cause I was also running a 4.56 rear end gear. Seemed like a blink after launch I had to shift. At that point I had not even mentally recovered from the launch. FWIW.

 

[jpl572103]

I took my original A 833 ball and trunnion 3.09 1st gear transmission and converted it to slip yoke using (what I believe was) a '66 trans main shaft and tail housing. It worked. But I will say, when on the track, I hated the 3.09 1st gear. Probably cause I was also running a 4.56 rear end gear. Seemed like a blink after launch I had to shift. At that point I had not even mentally recovered from the launch. FWIW.

I have the same 3.09 1st gear a833 od with a 3.55 in the rear and hate it too because of the "blink" after launching due to my engine tach's out to 4grand and I have to shift. That 340 would do well with the 3.09 , as it probably can go another 1500 rpms and has a lot more balls than my slant. I say "go-fish" should get a trans with the gearing that you want. That way you have 2 a833's. All kinds of advice on this channel.

 

[JDMopar]

Yeah, if I did the 3.09 first, I would be trying to set up just like what @go-fish is wanting to achieve. I have a 2.76 Sure Grip chunk and a 2.94 that I would rebuild into a Sure Grip. My plan is to try the 833OD with either 3.23's or 3.55's first and see how hard it zings it up running 70-ish on the interstate.

 

[jpl572103]

Just so you know;
the stock 5.9 has more than enough grunt to run any A833 4-speed, with any rear gear, in any A-body; and there are 4 SBM ratios to chose from. ......
and they fit like a glove ......
and on the street, they scoff at 450 ftlbs.....
--------------------------------------------------------------------------
As for the ratios;
3.09-1.92-1.40-1.00
2.66-1.91-1.39-1.00
2.47-1.77-1.34-1.00
3.09-1.67-1.00-.73od
As for cruising;
65mph, with 27"tires, by the math;
2.94s=2380; while 3.23s= 2615; and 3.55s =2873
As for taking off;
With a stock flywheel, and a starter gear of 11/1, taking off is a dump-it-and-go deal. By 9/1 or less, there is quite a bit of slipping the clutch going on.
Therefore, the sweet-spot is about 10/1. This would be;
2.47x 4.10, or 2.66x 3.73, or 3.09x 3.23
As for my favorite;
That would be the Commando with 3.55s, but only because she hits 60/65mph at the top of second. She's fine down to 2.94s, the lowest I have tried.
Of note;
1) any ratio can be fit into the A/F-body, alloy box and tail, making it almost as light as the AX. My alloy box survived 4 years of thrashing on the street as a DD, and was still fine when I replaced it with a Passon box..... Over 20 years ago now.
2) if you have bucket-seats, and are replacing the floor anyway, then I highly recommend moving the shifter back, and to the left, and raise it up; then use a short straight shifter. You'll love it. I used a B-body tail and mainshaft, with a home-made(custom-fabricated/lol) shifter mounting-plate.
3) I'll go out on a limb and say this, if your cylinder pressure is;
a paltry 140psi, you'll want a starter gear of ~11.8/1
by 160psi , you'd be fine at 10.4/1
by 180psi, I like 9.2/1
by 195, 8.5/1 is doable
These are the minimums recommended. This is based on my experience over 50 years of driving A-bodies with A833s

I made up this formula ;
1660/cylinder pressure= minimum recommended starter gear.
example;
1660/155psi= 10.7 starter, and
10.7/3.09 trans gear= 3.46 gears;
If you have a 2.66 box then 10.7/2.66=4.02s;
round up or down as may be required.
4) thus it can be seen, the more cylinder pressure your engine cranks, the less it needs for a starter gear.
And the less starter gear it needs, the less cruise gear it can getaway with.
5) to run the overdrive box; the more cylinder pressure your engine develops, the easier it will pull those wide ratios. But the good news is that; with that .73od, you can run almost any rear gear you want to.
And so, I like a final drive of 2.76 ,for 65= 2240(with 27s). This is because, any less rpm will not be able to develop optimum ignition timing.
Thus working the formula backwards, I need 2.76/.73= 3.73 rear gears.
The starter gear is thus 3.73 x3.09= 11.52
If I have a starter of 11.52, then My cylinder pressure can be as low as
1660/11.52= 144psi, about like a stock 318. But, the lo-pressure 318, for performance, will have a hard time with a Second Roadgear of 1.67 x 3.73=6.23 Whereas the 5.9 will find it nearly ideal..... because 65 in Second gear will get you 5040rpm (with 27" tires), which, with the stock cam peaking at around 4400, is just about right.

I found this info from AJ/Form S, thought it might interest this chat.

 

[go-fish]

I found this info from AJ/Form S, thought it might interest this chat.

I believe so read that before and became more interested in this endeavor.

 

[Newbomb Turk]

I’ve been running 3.09 boxes since the mid 1980’s.

There is no reason to not use one. The 1-2 split can be aggravating but unless you want to power shift at 7k plus it won’t be an issue.

I cringe when I see guys running a 9:1 first gear (overall). It’s not a power glide or TF.

It’s damn near impossible to get too much first gear other than the splits get too wide.

I remember when Pro Stock went to 5 speeds. Bob Glidden was doing some testing with the 5 speed but he wasn’t using 5th gear.

All the rail birds said at best the car wouldn’t be any faster with 5 gears than it was with 4.

Of course they are faster with 5 gears. You can run a lower first gear and keep the splits reasonable.

So don’t buy the close ratio is best stuff. I mean you could have 8 gears and technically go faster.

The extra gears allow the builder to narrow up the power curve. It’s easier to make power over a narrower power curve than a wider power curve.

To that end, my race car was a 3.09 box with a 5.57 rear gear. I could have used more first gear and more rear gear if I had the balls to run it to 9k on a regular basis.

I’ve used them with 3.23 gears, 3.73 gears, 4.56 and now 4.88 gears in my street/strip car.

 

[AJ/FormS]

1973 340 Duster, low compression 340, A-833, 3.21 (8.25). Numbers matching car so believed to be the stock gearing of 2.47, 1.77, 1.34, 1. The engine is a standard bore, stock piston, LD340, with a SFT 224/224 @.050, .470 lift, manifolds soon to be TTi steps.

The car is slow to get off the line and can't crawl. Its starting gear is 7.9 (2.47x3.21). I had mistakenly been thinking mine was a 2.66 1st gear with a 8.5 starter gear. I thought a jump to 3.09 x 3.21 = 9.9 starter gear would be pretty good. Now I know my '73 has a 2.47 1st the difference kinda makes it all that much more, almost, mandatory. 7.9 to a 9.9!

My cam is great. I love it and I'm not blaming the sluggishness on the cam. I believe this change will allow the cam to serve me in it's peak performance. I currently have a 3.21 SG 8.25 rear which is factory equipment BUT I do have a 8.75 housing coming together with a 2.94 Eaton True Trac diff and a core 3rd member for a 3.23

First off, lemmee say that I get where yur coming from. And I don't want talk about the engine, but in your case, I sortof have to, but maybe not for the reasons you might think.
The thing is this; it's all about footpounds from idle to about 2500 rpm. Your cam is a great choice, but you really need to know how much cylinder pressure your 340 is making, before you start throwing gears at it.
Your engine is 50 years old and is still at stock bore. It was an advertised 8.5 engine. Even when new, with the 268/276/114 factory cam, that engine barely cranked 130 psi at sea level. which , in todays terms is atrocious, and makes for a really really soft take of, from idle to around 3000 rpm.
Even if I fudge your cam numbers to 264/264/108 advertised@ zero lash, the Ica is gonna come in at around 56*. And Eastern OK, appears to be around 1000ft elevation.
These two combine to predict a cylinder pressure of 137psi, which is mediocre at best.
What this means is that to get performance out of that engine, it's gonna take a lotta gear Multiplication, and once she starts bucking a wind, with 318 type hiway-gears, in top gear, it's gonna feel like a 318.
I hate to tell you this, but gears will not cure this.
That cam has the potential to make great torque, and great fuel economy, but not at 137psi.

Having said that, lets talk about what you are thinking of doing. Lets try to forget about the engine.
Lets recap;
> you said; The car is slow to get off the line and can't crawl.
> you said; My cam is great. I love it and I'm not blaming the sluggishness on the cam
> and you have a 2.47 gearbox with, 3.21s in the back.

Ok My ears hear, that cam should have a power-peak around 5000rpm. Which translates to a torque-peak around 3500. But with low cylinder pressure , the torque peak may be less and come early, whereas the power-peak may come later and be quite a bit less. Plus with log manifolds the Overlap period does not work. Therefore, your cam will run about on par with a standard 360 2bbl cam (256/262/112, Ica of 52*, except with less pressure, and a lil more power. Oh wait, I promised to try to not talk about the engine.
Ok so, now,
you think your only options are
More torque multiplication.
and that will work, to an extent. But you are, IMO attacking this from the wrong end.
Firstly; First gear is only used to get to Second gear, which for a manual trans car is the gear in which everything happens. If you gear your car right, it will be revved out at ~60 mph, which with your cam should be about 5000>5300.
Letspick 5300.
This will take about 3.91s for 61.5= 5300, with 27" tires, and the current trans. and so half that speed will be half that rpm, 30.75=2650.
Ok so sure you can rev First to 5300 and get 44mph. That's not the point. The point is that if you run less than 3.91s you will not get to use ALL of Second gear, in the run from zero to 60 mph, and your car will be slower than if you had run the 3.91s.
So, here you are trying to run 3.21s; and 5300= 54 in First/75 in Second, and of course it is sluggish, cuz the engine is way down on footpounds in Second gear. OOps. doing just 4250 rpm@60mph, with a dead overlap cycle.
Ok so lets replace that T/A box, and get a Commando.
The ratios are 3.09-1.91-1.39-1.00 With the 3.21s your shift rpm speeds are now 43 and 69, so yur still 15% too high in Second, to overcome sluggishness off the line, she now needs 3.73s for 60=5323rpm.
So no matter how you cut it, yur gonna need BOTH a new gearbox AND rear gears, to overcome the low-pressure handicap, off the line.

If I was in your position, I'd have that engine out in a heartbeat, and build some cylinder pressure into it, which will take about 90% of the sluggishness out of it. And no, notta chance would I reuse those 50 year old bores. Ima thinking 10/1 is/or might be the place to start, it depends on your elevation and ICA. Sadly According to WIKI, 54801 has quite the changes in elevation from one side of the state to the other, so that might be a limiting factor.

I know you don't want to hear it and already gave two guys an earful, but com'on man, there's an elephant in the room and you can't say that nobody told you, I'm just numberr 3 or 4.
What's a replacement gearbox and different gears gonna cost you installed? I bet more than new pistons and a rebore.

BTW-1
If yur having trouble getting that 340 to pull itself at 500 rpm, that there is proof that the tune is off and maybe the engine needs more cylinder pressure. Yeah I get that 500 rpm in your current combo is 5mph and that ain't exactly crawling, but, the 3.09 low will only get you 4mph still not low enough to parade with. Yur gonna need 3.73s to get down to 500= 3.5, or 3.91s to get 550=3.66mph. But if your oilpump can't keep the engine happy down there, then there's no sense in talking about it. So yur gonna have to install a hi-volume pump anyway and a hi-capacity oilpan. I mean pistons are then, only a few more bolts. OOps sorry, lol.
AFTER you have installed the hi-volume pump, I'll give you a recipe to idle at 500 rpm. Oh heck, just retard the stinking timing to 5*, and away it will go. Oh wait, maybe not at 137psi CCP.
By now, you should have figured out that, with a manual trans, EVERYTHING is tied to everything else, and it all has to be working together.
BTW-2
Your Best bet, if keeping the cylinder pressure low, is to get an overdrive five speed, and run the biggest starter gear you dare. Or, in your case if running the 3.21s, then a deep-low 5-speed.
BTW-3
If I was gonna rebuild a 340, I would install flat-tops at near zero deck height, and Alloy closed-chamber heads, for a tight Quench between 030 and 040, and run the cylinder pressure up close to or just over 195 psi. Now yur talking.
Now you can run any box any gears.
BTW-4
notta chance would I try to put the Commando gears into the TA box. Instead, I would put the Commando gears into a A/F alloy box, with the alloy tail, and the alloy cover, and the matching alloy BH. Oh wait, I already did that. Great combo. lol
Oh and notta chance would I run an aluminum flywheel on the street with your combo, so hopefully you got that pig-heavy factory flywheel.
BTW-5
Remember my funky formula of 1600/ starter gear = suggested cylinder pressure?
Well 1600/ 7.9 your current combo = 202 suggested psi
Whereas with the 3.09 low, it is 1600/9.9= 162psi,
Whereas with just 137psi it works out to 1600/137= 11.68.
To get that with a 3.09 low is 11.68/3.09= 3.78 rear gears, rounds down to 3.73s, and 65= 3020 with 27"tires.
I have used this formula with all my personal combos and it works great.
BTW-6
I get what yur trying to do, and your ideas are good, but IMO, just not radical enough for a low-pressure engine.
On another note; if the engine gets jumpy at low rpm, take a bunch of timing out. Bring it down to about 5*, reset the Transfer slot exposure if you need to. Trust me, even my 292/292/108 cam idled at 5*, sometimes even less. If yours doesn't, with adequate valve lash; something is not right.

OTHER
>Your results may vary, and for sure things will change once the headers are on. The H-pipe will add quite a bit of Low-rpm torque, so I wouldn't to anything until after they are on and a new tune is in the engine.
>Listen, my deepest apologies for dragging your engine into the conversation. But I had to. Hopefully you now understand why.
Pressure makes heat. Heat makes torque. Torque is Power. Power is performance.
In the absence of Pressure, you gotta throw Torque-multiplication at it, but when that builds to a head, in top gear, it's back to just motor.

Happy HotRodding.

 

[go-fish]

Thanks @AJ/FormS . My 340 is low comp wimp compared to what it could/should be.
I believe the engine runs better than in 1973 but it’s still hot factory slugs in it.

To be honest I am planning an engine build but was going to do that after I built the 8.75 and figured out trans gearing.

I was planning on using the same cam and wanted to find a forged crank to switch to if at all possible. I’m fine with the factory crank but if I’m going to have it apart and can find a forged crank I’ll darn sure scoop it up.

I have a set of highly ported X heads I may use. I want to keep the originality of iron heads.

I have a roadrace Milodon pan on my 416 engine, below, I can rob or just buy a new one.It really needs a rear sump anyway.

I have a 650 hp 408, below, in a 5-speed 70 ‘cuda and the 550hp 416 waiting for another project.

I just really like this Duster with 3.23 gears. I like that it idles well, drives well, gets good mileage, and doesn’t need attention all the time. Good stock engine. The most I want to go to it is add some compression and get it to pre-low compression era performance.

So, @AJ/FormS , thanks for the pointers. I do have a rotating assembly replacement. I just wanted to do gearing changes first. The car isn’t undriveable. Like I said, it’s a great street car but my main complaint is when you let off onto first it wants to go 10 mph right away. To go slower is a lot of clutch play. EVERYTHING else is pretty good. All it is is just the low comp 340 and 1st gear.
So, yes, the engine will get rebuilt in the next year. I’m not going numerically higher than 3.23 for now. I’ll just do some rearranging and do the engine before regearing the trans.

PS. I love how this topic went straight to , “Your engine is old tired and worn out .” It’s just a low compression 1973 340 put back to stock spec except for a lil extra duration and lift! It’s not old tired OR worn out. It has fresh rings, bearings, and a cam 4,000 miles ago by previous owner. I had no control over that but Arthur (PO) wanted this car to be super duper all original. The engine was assembled when O got the project. He’s dead now but I’ll respect his wishes to a point, and that puts alloy heads and mini-tubs out. Engine will be rebuilt but trying to narrow down gearing.

 

[go-fish]

 

[moparlvr166]

Clean stock looking ride.

 

[DionR]

First off, lemmee say that I get where yur coming from. And I don't want talk about the engine, but in your case, I sortof have to, but maybe not for the reasons you might think.
The thing is this; it's all about footpounds from idle to about 2500 rpm. Your cam is a great choice, but you really need to know how much cylinder pressure your 340 is making, before you start throwing gears at it.
Your engine is 50 years old and is still at stock bore. It was an advertised 8.5 engine. Even when new, with the 268/276/114 factory cam, that engine barely cranked 130 psi at sea level. which , in todays terms is atrocious, and makes for a really really soft take of, from idle to around 3000 rpm.
Even if I fudge your cam numbers to 264/264/108 advertised@ zero lash, the Ica is gonna come in at around 56*. And Eastern OK, appears to be around 1000ft elevation.
These two combine to predict a cylinder pressure of 137psi, which is mediocre at best.
What this means is that to get performance out of that engine, it's gonna take a lotta gear Multiplication, and once she starts bucking a wind, with 318 type hiway-gears, in top gear, it's gonna feel like a 318.
I hate to tell you this, but gears will not cure this.
That cam has the potential to make great torque, and great fuel economy, but not at 137psi.

Having said that, lets talk about what you are thinking of doing. Lets try to forget about the engine.
Lets recap;
> you said; The car is slow to get off the line and can't crawl.
> you said; My cam is great. I love it and I'm not blaming the sluggishness on the cam
> and you have a 2.47 gearbox with, 3.21s in the back.

Ok My ears hear, that cam should have a power-peak around 5000rpm. Which translates to a torque-peak around 3500. But with low cylinder pressure , the torque peak may be less and come early, whereas the power-peak may come later and be quite a bit less. Plus with log manifolds the Overlap period does not work. Therefore, your cam will run about on par with a standard 360 2bbl cam (256/262/112, Ica of 52*, except with less pressure, and a lil more power. Oh wait, I promised to try to not talk about the engine.
Ok so, now,
you think your only options are
More torque multiplication.
and that will work, to an extent. But you are, IMO attacking this from the wrong end.
Firstly; First gear is only used to get to Second gear, which for a manual trans car is the gear in which everything happens. If you gear your car right, it will be revved out at ~60 mph, which with your cam should be about 5000>5300.
Letspick 5300.
This will take about 3.91s for 61.5= 5300, with 27" tires, and the current trans. and so half that speed will be half that rpm, 30.75=2650.
Ok so sure you can rev First to 5300 and get 44mph. That's not the point. The point is that if you run less than 3.91s you will not get to use ALL of Second gear, in the run from zero to 60 mph, and your car will be slower than if you had run the 3.91s.
So, here you are trying to run 3.21s; and 5300= 54 in First/75 in Second, and of course it is sluggish, cuz the engine is way down on footpounds in Second gear. OOps. doing just 4250 rpm@60mph, with a dead overlap cycle.
Ok so lets replace that T/A box, and get a Commando.
The ratios are 3.09-1.91-1.39-1.00 With the 3.21s your shift rpm speeds are now 43 and 69, so yur still 15% too high in Second, to overcome sluggishness off the line, she now needs 3.73s for 60=5323rpm.
So no matter how you cut it, yur gonna need BOTH a new gearbox AND rear gears, to overcome the low-pressure handicap, off the line.

If I was in your position, I'd have that engine out in a heartbeat, and build some cylinder pressure into it, which will take about 90% of the sluggishness out of it. And no, notta chance would I reuse those 50 year old bores. Ima thinking 10/1 is/or might be the place to start, it depends on your elevation and ICA. Sadly According to WIKI, 54801 has quite the changes in elevation from one side of the state to the other, so that might be a limiting factor.

I know you don't want to hear it and already gave two guys an earful, but com'on man, there's an elephant in the room and you can't say that nobody told you, I'm just numberr 3 or 4.
What's a replacement gearbox and different gears gonna cost you installed? I bet more than new pistons and a rebore.

BTW-1
If yur having trouble getting that 340 to pull itself at 500 rpm, that there is proof that the tune is off and maybe the engine needs more cylinder pressure. Yeah I get that 500 rpm in your current combo is 5mph and that ain't exactly crawling, but, the 3.09 low will only get you 4mph still not low enough to parade with. Yur gonna need 3.73s to get down to 500= 3.5, or 3.91s to get 550=3.66mph. But if your oilpump can't keep the engine happy down there, then there's no sense in talking about it. So yur gonna have to install a hi-volume pump anyway and a hi-capacity oilpan. I mean pistons are then, only a few more bolts. OOps sorry, lol.
AFTER you have installed the hi-volume pump, I'll give you a recipe to idle at 500 rpm. Oh heck, just retard the stinking timing to 5*, and away it will go. Oh wait, maybe not at 137psi CCP.
By now, you should have figured out that, with a manual trans, EVERYTHING is tied to everything else, and it all has to be working together.
BTW-2
Your Best bet, if keeping the cylinder pressure low, is to get an overdrive five speed, and run the biggest starter gear you dare. Or, in your case if running the 3.21s, then a deep-low 5-speed.
BTW-3
If I was gonna rebuild a 340, I would install flat-tops at near zero deck height, and Alloy closed-chamber heads, for a tight Quench between 030 and 040, and run the cylinder pressure up close to or just over 195 psi. Now yur talking.
Now you can run any box any gears.
BTW-4
notta chance would I try to put the Commando gears into the TA box. Instead, I would put the Commando gears into a A/F alloy box, with the alloy tail, and the alloy cover, and the matching alloy BH. Oh wait, I already did that. Great combo. lol
Oh and notta chance would I run an aluminum flywheel on the street with your combo, so hopefully you got that pig-heavy factory flywheel.
BTW-5
Remember my funky formula of 1600/ starter gear = suggested cylinder pressure?
Well 1600/ 7.9 your current combo = 202 suggested psi
Whereas with the 3.09 low, it is 1600/9.9= 162psi,
Whereas with just 137psi it works out to 1600/137= 11.68.
To get that with a 3.09 low is 11.68/3.09= 3.78 rear gears, rounds down to 3.73s, and 65= 3020 with 27"tires.
I have used this formula with all my personal combos and it works great.
BTW-6
I get what yur trying to do, and your ideas are good, but IMO, just not radical enough for a low-pressure engine.
On another note; if the engine gets jumpy at low rpm, take a bunch of timing out. Bring it down to about 5*, reset the Transfer slot exposure if you need to. Trust me, even my 292/292/108 cam idled at 5*, sometimes even less. If yours doesn't, with adequate valve lash; something is not right.

OTHER
>Your results may vary, and for sure things will change once the headers are on. The H-pipe will add quite a bit of Low-rpm torque, so I wouldn't to anything until after they are on and a new tune is in the engine.
>Listen, my deepest apologies for dragging your engine into the conversation. But I had to. Hopefully you now understand why.
Pressure makes heat. Heat makes torque. Torque is Power. Power is performance.
In the absence of Pressure, you gotta throw Torque-multiplication at it, but when that builds to a head, in top gear, it's back to just motor.

Happy HotRodding.

Maybe I missed it, but did you ever answer the original question? Can he swap the 3.09 gearset into his case?

I saw the comment that you wouldn't, but that wasn't the question.

 

[Hyper_pak]

Yes, 3.09 will go into his 2.47 case.
I would buy a set from Dan Brewer.

 

[go-fish]

3.09 gearset will swap into your cases without any other modifications. I run this gearset in my 72 Demon, with 3.23 axle and 27" tire.

Maybe I missed it, but did you ever answer the original question? Can he swap the 3.09 gearset into his case?

I saw the comment that you wouldn't, but that wasn't the question.

Dan Brewer chimed in and said it would. I’m going to trust him as a solid source. His comments have been the most helpful. A guy that is in the industry. He’s in the manual trans segment of the industry. He has a real world report on 3.09 / 3.23 A-bodies.
It’s not just bias on what I wanted to hear but it’s because it shakes out in the math (no matter what your power plant is or makes). The gearing is better for that rear gear and drivability.
This is all about driveability. I’ve talked several times about parking lot manners. 3.09 helps. I’m satisfied *enough* with the low comp 340 to do the gearing first.
So, now I have a plan. Or a multi-pronged approach. Try to acquire a case like mine (bearing size), get the Commando gearing and start getting really familiar with it. Then, when weather is crappy rebuild my case. I’ll do the ball and detent cover at the same time. I think I have to modify something so I need to learn that too.

 

[DionR]

Dan Brewer chimed in and said it would. I’m going to trust him as a solid source. His comments have been the most helpful. A guy that is in the industry. He’s in the manual trans segment of the industry. He has a real world report on 3.09 / 3.23 A-bodies.
It’s not just bias on what I wanted to hear but it’s because it shakes out in the math (no matter what your power plant is or makes). The gearing is better for that rear gear and drivability.
This is all about driveability. I’ve talked several times about parking lot manners. 3.09 helps. I’m satisfied *enough* with the low comp 340 to do the gearing first.

For what it's worth, my combo is a 3.09 first A833OD with a 3.21 gear and a low compression 360. And it works fine for me.

 

[go-fish]

Yes, 3.09 will go into his 2.47 case.
I would buy a set from Dan Brewer.

When I have the 2.94’s in it I would love to drive it down your way. No way with my 3.21’s now. Texas International Speedway is like a 4 hour trip doing 65mph @2800 rpm. 70mph @2500 with the 2.94. Doing the 2.94 swap w/o 3.09 would not be an improvement. So, I guess this is also about me wanting to cruise at a higher speed and also have that better parking lot 1st gear.

 

[go-fish]

For what it's worth, my combo is a 3.09 first A833OD with a 3.21 gear and a low compression 360. And it works fine for me.

In the cold take off video you can see when I let off the clutch and take off in first there is a “bog”. That’s a gearing issue. Does yours lug down or “bog” or whatever you want to call it?
I would like to improve that to where it lurches and “bogs” less.
Just 2 mph less in a parking lot would be huge for me. Again, driveability issue, not “performance”.

 

[DionR]

In the cold take off video you can see when I let off the clutch and take off in first there is a “bog”. That’s a gearing issue. Does yours lug down or “bog” or whatever you want to call it?
I would like to improve that to where it lurches and “bogs” less.
Just 2 mph less in a parking lot would be huge for me. Again, driveability issue, not “performance”.

Do you give it gas or just let the clutch out?

I can get a lurch like that if I don't get the clutch and gas right, more so when it is cold. But I've always figured that was just the nature of driving a stick. I guess I haven't thought about parking lots much, but as I sit here now I don't ever remember having issues getting around in a parking lot or creeping forward at a light.

 

[Slantsix64]

Do it! I have both gear boxes and the early 3.09 first gear pulls hard and launches hard, the 68 gear box pulls okay , with 3.55 gears but it could be better with 3.91s

 

[go-fish]

Do you give it gas or just let the clutch out?

On that take off I lightly feathered the throttle. If I feather more it takes off at a faster starting speed. Depends on the driving situation.

 

[DionR]

On that take off I lightly feathered the throttle. If I feather more it takes off at a faster starting speed. Depends on the driving situation.

My gut feeling is that when mine is cold it acts like yours did there. I have to be more careful about the right clutch engagement (slip) and giving it enough throttle or I get a lurch like that. When it warms up I don't think about it much and just drive it.

 

[halfafish]

@go-fish, I've been down the same logic path you are on. If you haven't played with this calculator yet, you might want to do so.

Speed/Tire/RPM calculator

I've fiddled with it a lot to see what balance I can get for good street manners, decent acceleration and gear splits, and some kind of cruising mileage. As info, if you want to put in a gear or rear end ratio that's not listed, you can enter whatever you like into that field and the calculator still works.

 

[65 Cuda 340]

My 65 Barracuda originally had a 3.09 low gear and 3.23 rear gears. With an almost stock 340 in it, it was fast off the line just letting out the clutch and giving it gas. No hi-rpm clutch dumps, just go. Well at 150,000 miles or so, the main shaft got a groove worn in it, under the needle bearings. I was told that replacement shafts weren't available (this was mid-seventies), so I switched to a late sixties four speed. Bolted right in, just needed to get a driveshaft.

That's when I found out my original trans had the 3.09 low gear. Later trans had a 2.66. The difference was unbelievable. You could still take off reasonably quick if you revved it up and dumped the clutch (it was still two tenths slower in the quarter), but it was a dog off the line with normal driving. I hated it. Later found out that the original 3.09 gearset that I had saved out of the original trans would fit in the newer case with the newer main shaft (no ball and trunnion). So I swapped. Have never regretted it.

With 3.23 gears, the overall low gear ratio with the 3.09 trans is 9.98. With 2.66 low gear, you only have an overall low gear ratio of 8.59. To get a 9.98 overall low gear ratio with a 2.66 low gear, you would need 3.73 rear gear.

The 2.47 low gear is even worse. Its overall low gear ratio with 3.23 rear gears is 7.98. To get a 9.98 overall low gear ratio with this trans, you'd need a 4.04 rear gear.

Now you could of course change the rear gears instead of the trans. 3.91s would work. But the OP is complaining about how many rpms he's turning at 70 mph with the 3.23 gears he has now. It would turn 20% higher rpms with 3.91 gears. Top speed would be 20% lower (if that's a consideration).

To those who suggest that if it's kinda sluggish of the line with 2.47 gears the OP just needs to tune his motor up, I say BS. Maybe a stroker crank. More cubes can handle taller gears. A 340 needs gears. Either at the trans or in the rear end, take your pick.

And don't give my any crap about how well an automatic works with 3.23 gears. Automatics have torque converters to multiply torque. Manual trannies only have gears.

Strictly for drag racing, or road racing, the close ratio trans would work better. For the former, choose the rear gear you need, and the close ratio trans would keep the motor in the power band better. For road racing, same deal except you don't worry about standing start acceleration.

FOR THE STREET, with streetable, relatively tall rear gears, and only 340 cubes, the 3.09 gearset is absolutely the way to go. Its not even a close question.

 

[sireland67]

Dan Brewer chimed in and said it would. I’m going to trust him as a solid source. His comments have been the most helpful. A guy that is in the industry. He’s in the manual trans segment of the industry. He has a real world report on 3.09 / 3.23 A-bodies.
It’s not just bias on what I wanted to hear but it’s because it shakes out in the math (no matter what your power plant is or makes). The gearing is better for that rear gear and drivability.
This is all about driveability. I’ve talked several times about parking lot manners. 3.09 helps. I’m satisfied *enough* with the low comp 340 to do the gearing first.
So, now I have a plan. Or a multi-pronged approach. Try to acquire a case like mine (bearing size), get the Commando gearing and start getting really familiar with it. Then, when weather is crappy rebuild my case. I’ll do the ball and detent cover at the same time. I think I have to modify something so I need to learn that too.

Now you have the gears clicking in my head, I have an A-body commando box, that I could swap the gears in my Duster.
I think that I have another project now....

Also on a separate note, I have an extra ball-n-trunion B body trans, would that also have the 3.09 first gear?