Automatic to 4 speed Conversion in '65 Formula S

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Bob Jasinski

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My first post here, but long time lurker, I'm also on the EVBC list. So...I have a '65 Barracuda Formula S, California car, no rust, owned it since 2003. I took it apart in 2009 and am now starting back in on the restoration. I've decided to convert the automatic to a 4 speed. I like original cars, so the conversion will embody the look of a factory F/S 4 speed car, including the R1234 shift bezel, shifter hump, and Hurst shifter. The original 273 4 bbl engine and 3.23, 7-1/4" axle will be retained. I do, however, want to use a later 833 overdrive trans. Since I have none of the conversion parts yet, I'm looking for advice on flywheel, clutch, pressure plate and bell housing. I know the OD 4 speed has a larger input bearing retainer, and the stock 4 speed bell housing hole either has to be enlarged or I need a different bell housing. I also know the stock clutch was a 9-1/2" unit. Instead of finding a stock bell housing and paying for machining, would I be better off with a different bell housing? I also know the 9-1/2" clutch parts are limited and I have not found a new stock flywheel, so going with a larger diameter setup is probably the best way to go. I also want to stay with stock pedals, and am concerned about firewall flex, so a pressure plate that requires a lot of force is not desired (although I could reinforce it). I also know I will need a new driveshaft to replace the ball and trunion. So recommendations on what bell housing, flywheel, clutch and pressure plate that will bolt in nicely behind the stock 273 and fit the 833 OD trans. is what I'm after. I'd like to stick with stock parts if possible. Going to the Cupertino CA Mopar Rally swap tomorrow. What should I look for?
 
Did a conversion years ago on a 66 cuda. I went with a later (10.5 inch) setup
from a 340 donor car flywheel, bell ,linkage etc. Used a centerforce clutch and
pressure plate this 10.5 has more/better options that the 9.5 inch. I installed
a strut brace( threaded rod) between the fender and firewall that hooks the inner
fender and captures the firewall with washers and nuts on each side of the firewall,
NO firewall flex. Reinforce the Z bar setup if you have a welder. Works outstanding!
 
The 4 speeds had a 10 in clutch stock from the factory as did taxis and some fleet vehicles.Even my 6 cyl 65 Barracuda 4 speed had a 10 in clutch.It bolts up to the same flywheel that the 9 1/4 does . I have taken out the small ones and put in the 10 on all my 65 and 66 standards even the 3 speeds . As for what trans to use I think I'd go with a 66 unit with the 2.66 1st gear and 1 to 1 4th. That overdrive unit with the 309 1st gear really runs out quick .It's good in a 6 but with something that makes power it works against you.
 
There is a Commando 4-speed AND converted to slipyoke driveshaft for sale on FABO right now; check the want-ads.The commando has the 3.09 low, which with 3.23s will be a fabulous starter gear.
If your 273 is a low-rpm engine, then the od box could be a good option, otherwise I wouldn't recommend it, as the splits are quite far apart.
With a low-rpm engine(hi-torque), this ain't so bad. But when your cylinder pressure falls into the sub-130 range, AND you're hitting 4500-plus rpm, then pulling from 2400, with 3.23s being 33mph, acceleration is often measured with a sundial. The 2-3 is better, but 4500 in second is 63mph, so it ain't often that you get to use the 2-3 shift.
So yes you could change the rear-end out for say a 4.30 but that just moves the problem to a new roadspeed, and the starter gear becomes too large. So now your second gear is from 25 mph to 47mph, not particularly exciting as 95% of your city driving could be in that gear....... but ya-know; 4500 at 47mph is not a gear you want to be staying in very long. So at the shift, the Rs fall to 2670, and there you are back in the basement.
So I can't recommend that box for most guys; it sorta requires a hi-compression, hi-torque engine and or a light car.
 
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My first post here, but long time lurker, I'm also on the EVBC list. So...I have a '65 Barracuda Formula S, California car, no rust, owned it since 2003. I took it apart in 2009 and am now starting back in on the restoration. I've decided to convert the automatic to a 4 speed. I like original cars, so the conversion will embody the look of a factory F/S 4 speed car, including the R1234 shift bezel, shifter hump, and Hurst shifter. The original 273 4 bbl engine and 3.23, 7-1/4" axle will be retained. I do, however, want to use a later 833 overdrive trans. Since I have none of the conversion parts yet, I'm looking for advice on flywheel, clutch, pressure plate and bell housing. I know the OD 4 speed has a larger input bearing retainer, and the stock 4 speed bell housing hole either has to be enlarged or I need a different bell housing. I also know the stock clutch was a 9-1/2" unit. Instead of finding a stock bell housing and paying for machining, would I be better off with a different bell housing? I also know the 9-1/2" clutch parts are limited and I have not found a new stock flywheel, so going with a larger diameter setup is probably the best way to go. I also want to stay with stock pedals, and am concerned about firewall flex, so a pressure plate that requires a lot of force is not desired (although I could reinforce it). I also know I will need a new driveshaft to replace the ball and trunion. So recommendations on what bell housing, flywheel, clutch and pressure plate that will bolt in nicely behind the stock 273 and fit the 833 OD trans. is what I'm after. I'd like to stick with stock parts if possible. Going to the Cupertino CA Mopar Rally swap tomorrow. What should I look for?
Brewers has everything you need. I own a automatic car and a 66 Dart with a 4 speed. In my opinion all the work and expense for a 4 speed isn't worth it. Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists
 
Did a conversion years ago on a 66 cuda. I went with a later (10.5 inch) setup
from a 340 donor car flywheel, bell ,linkage etc. Used a centerforce clutch and
pressure plate this 10.5 has more/better options that the 9.5 inch. I installed
a strut brace( threaded rod) between the fender and firewall that hooks the inner
fender and captures the firewall with washers and nuts on each side of the firewall,
NO firewall flex. Reinforce the Z bar setup if you have a welder. Works outstanding!
Thanks for the tips, I do have a welder, thanks!
 
I have changed over several. I like shifting gears an worth the work and expense. Not everyone lives out in the sticks like me. Yes Brewers I a great source, for all but especially the small stuff just in case you score the big parts local, lot cheaper.
I agree with the 10inch clutch.
I say keep it oem and forget the friggin hydraulic clutch. also changing it to a 4 speed ever the OD unit, makes it worth the costs f the parts.
 
The 4 speeds had a 10 in clutch stock from the factory as did taxis and some fleet vehicles.Even my 6 cyl 65 Barracuda 4 speed had a 10 in clutch.It bolts up to the same flywheel that the 9 1/4 does . I have taken out the small ones and put in the 10 on all my 65 and 66 standards even the 3 speeds . As for what trans to use I think I'd go with a 66 unit with the 2.66 1st gear and 1 to 1 4th. That overdrive unit with the 309 1st gear really runs out quick .It's good in a 6 but with something that makes power it works against you.
Thanks Valiant wagon guy, that's really good information on the 10" fitting the small flywheel. I looked on Rock Auto for a clutch kit listing just now ('65 Barracuda 273) and they don't even show a 9-1/2", just 10" and even a 10-1/2" that surprises me. Learned something new, thanks.
 
Thanks Valiant wagon guy, that's really good information on the 10" fitting the small flywheel. I looked on Rock Auto for a clutch kit listing just now ('65 Barracuda 273) and they don't even show a 9-1/2", just 10" and even a 10-1/2" that surprises me. Learned something new, thanks.
10 1/2" is wrong for a early A Body. You would have to change the flywheel, bellhousing and some of the linkage.
 
Brewers has everything you need. I own a automatic car and a 66 Dart with a 4 speed. In my opinion all the work and expense for a 4 speed isn't worth it. Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists
Toolmanmike, I have spoken with Brewer's and am certain I will use them for some of my needs, but all the various parts start to add up quickly so it can't hurt to see what's out there. I also like to get different opinions on the conversion. As far as doing away with the torqueflite, its not that I dislike them, they're a fantastic transmission. But, I've decided I won't go through the expense of the restoration with an automatic, they're just too common and the value is not there when its finished. Besides, I just plain want a 4 speed with overdrive in the car. It would be great on the freeway going to shows, and for touring. I think the 4 speed offers more of the sportiness the Formula S was meant to convey.
 
I have changed over several. I like shifting gears an worth the work and expense. Not everyone lives out in the sticks like me. Yes Brewers I a great source, for all but especially the small stuff just in case you score the big parts local, lot cheaper.
I agree with the 10inch clutch.
I say keep it oem and forget the friggin hydraulic clutch. also changing it to a 4 speed ever the OD unit, makes it worth the costs f the parts.
Thanks Barbee, I agree, no hydraulic clutch for me either. There's so many heavily modified '65 Barracudas out there, the world doesn't need another one. OK, to be fully honest, I will be running later SBP Mopar rallye wheels, and dual circuit brakes (Kelsey Hayes discs in the front, they were a dealer option). Original gold with black factory stripe is going back on too.
 
here is a 10 inch clutch kit from Rock Auto More Information for PERFECTION CLUTCH MU15251

the Borg Warner kit # is 90308 .I have ont in my 65 valiant station ( 10 in ) behind my 170 and in front of an A833 1965 4 speed. Also had one in my 65 Barracuda with a 318 ,4 speed,and 323 sure grip.Had no problems with either.The kit runs about 100 bucks
 
Toolmanmike, I have spoken with Brewer's and am certain I will use them for some of my needs, but all the various parts start to add up quickly so it can't hurt to see what's out there. I also like to get different opinions on the conversion. As far as doing away with the torqueflite, its not that I dislike them, they're a fantastic transmission. But, I've decided I won't go through the expense of the restoration with an automatic, they're just too common and the value is not there when its finished. Besides, I just plain want a 4 speed with overdrive in the car. It would be great on the freeway going to shows, and for touring. I think the 4 speed offers more of the sportiness the Formula S was meant to convey.
Study up on the use of overdrives here on FABO. Many don't like them behind a V8. @AJ/FormS can give you some numbers about gear ratios and what works.
 
here is a 10 inch clutch kit from Rock Auto More Information for PERFECTION CLUTCH MU15251

the Borg Warner kit # is 90308 .I have ont in my 65 valiant station ( 10 in ) behind my 170 and in front of an A833 1965 4 speed. Also had one in my 65 Barracuda with a 318 ,4 speed,and 323 sure grip.Had no problems with either.The kit runs about 100 bucks
So these fit the slant 9 1/2 flywheel?
 
Besides,
I just plain want a 4 speed with overdrive in the car.
It would be great on the freeway going to shows, and for touring.
I think the 4 speed offers more of the sportiness the Formula S was meant to convey.
Nobody can argue with that!
Here are the A833od ratios
3.09-1.67-1.00-.73od, and here are the road gears with a 3.23 rear
9.98-5.39-3.23-2.36 , and the splits
.54-.60-.73 , meaning that at whatever rpm you chose to shift at, the rpm will fall to those percents.
So let's say your engine sounds good at 2800, like mine ,lol, and so you shift out of first at 2800/22mph. And so in second your rpm will be 2800 x.54=~1500rpm.
I see two problems right away; 1) does your 273 have enough torque at 1500 to to continue accelerating in this 5.39 roadgear?, and 2) will it pull hard enough to satisfy you?
Let's say your 273 makes 140ftlbs at 1500, and so 140 x 5.39 x24/25.5=710ftlbs to the road. This is torque below mediocre. In other words you can cruise at 1500 but don't expect much in terms of acceleration. And that leads to having to hold first gear to a higher rpm.
So where does the hi-compression 273 start to make torque. Lets say it torque-peaks at 3200rpm, and say at 2800 it had 80% of that . This is why she sounds good at 2800, cuz she's loafing at high efficiency. So, for reasonable acceleration she will want to come in at 2800, and that means the 1-2 shift will need to be at 2800/.54=5185rpm/40 mph. You see the problem with that? Me too. Nobody drives like that ALL the time.
And that means at normal throttle openings, on the primaries only, your acceleration will always be mediocre in second gear.
So what is the problem here? Two things; 1) the 5.39 roadgear, and 2) the very wide 1-2 split. How do you overcome that? Well you can re-gear the back and get second gear to work for you at a better rpm, but you cannot do anything about the wide split.
What I like to do is to put the second gear rpm in the fat part of the torque curve at the roadspeed I do most of my driving. So for you that might be 32mph and 2800rpm. This will take 3.91s in the back, for 32mph=~2700 (4.10 would be 2900). So now you have second gear working from say 2500 to say 5000 with a 4bbl cam, which is 28 mph to 56mph.... Do you see the problem with that? Me to; this is a really long pull, in 3.91x1.67=5.39 road gear.
And we're still in second gear. When you hit third at 56mph your Rs will drop to 60% or 3000, and your little 273 is all done; even tho it now has 3.91s. And lastly; 65~ 2400 still with the3.91s.
Ok one more; with 3.91s your starter gear is 3.91x3.09=12.08; kindof a race-track starter. This works great for acceleration when you are in a hurry, but not so much when just cruising.... unless you rev first gear high enough to get into second with enough torque to continue accelerating to what ever speed you had in mind between 28 and 56 mph, at the rate of acceleration that makes you happy.
Ok so what's the conclusion?
The A833od trans will be fine in second gear if geared right, at the back.
With a low-torque engine,read small cubic inch, this compromises all other gears.

I tell you the truth; I had a 367 hi-torque engine putting out over 180psi cylinder pressure; and I had nearly every rear gear in my stable from 2.76 to 4.30, and I could find no love for that transmission, until I installed a GVOD and began splitting those very wide gears. oh and one more thing; That overdrive gear is IMO incredibly weak. I blew up a couple of them just by forgetting that trans was not a 4-speed but rather a 3 plus 1.With my 367,and 4.30s, shifting into that gear took a lotta concentration.

Ok so now, I know you may not want to hear this, but I think I should at least mention it;
The A999 TF with a hi-stall, operates like a wide-ratio five-speed with a short 5th. And your 3.23s are perfect for it. The ratios are 2.74-1.54-1.00 And the TC might have an internal torque-multiplier ratio of up to 2.0 to 1. Say with your 273 it works out to 1.8, and say it couples at 1.05 at WOT. And it has a lock-up feature.
When you couple this with a 3.23rear, the road gears might look like
15.93 decaying to 9.29-5.22-3.39-3.23locked up. 4.5 gears
From 15.93 to 9.29 is about 2 gear ratios, and it's all automatic, operating like a CVT (Constant Velocity Transmission). If you split that space in half you will see that the splits would be .76 or a pretty close ratio. And the in-between gear might be 12.10, so now if you rearrange those ratios and splits it looks like
15.93 decaying to 12.10 decaying to 9.29-5.22-3.39-3.23locked-up, with splits of
.77-.76-.56-.65-.95 Of course the 12.10 is an imaginary gear but kindof shows you what is happening inside the TC. So I call that a 5.5gear trans with a very short final shift.
So what does that mean to your 273?
Well put a 2800TC in there and find out. Going back to the original torque curve, lets say at 3200 she puts out 290 ftlbs, and at 2800 say 260 which is ~140 hp.
So now you nail it and the engine spools up to 2800, and instantly she is putting down
260 x 2.74x3.23x24/25.5=2166 ftlbs to the road, and the result of that is tirespin. So now the TC is ramping down through an infinite amount of graduations to 9.29 ratio as the car is moving and accelerating. So let's say 40 feet out, she hits 9.29 and now the rpm has climbed to (I'm Guessing) 4000, and the torque has fallen to 90% or 260ftlbs, but the hp has climbed to 198hp, on its way to say 235@4800. So I'm guessing the tirespin is coming to an end at about 30 mph, and now you are really accelerating, towards the manual 1-2 shift at say 5200/44mph . So now, still at WOT, the Rs drop to 56% or to 2800...... again, and now the roadgear is only 5.22 so your race is over. You can fix this with more rear gear, but that will subtract from your 65=2700. You could do this with an
A998loc-up (2.45 low) and 3.55s and get about the same first gear, but would tighten up all the splits, with a higher cruise rpm. The roadgears would be
15.66 decaying to 9.13-5.40-3.73-3.55 ,and splits of
.60-.59-.69-.93 This makes second gear 3.4% better. But 65=2970cruise

So lets stack 'em;... rear gear..........second..... top... cruise.. 1-2 split
First the A833od with 3.23s....... 9.98-5.39-3.23-2.36; 1975 ..54%
next the A833od with 3.91s;.... 12.08-6.53-3.91-2.85; 2385 ..54%
next the A999 and 3.23s; 15.93>9.29-5.22-3.39-3.23; 2700 ..56%
then the A998 and 3.55s; 15.66>9.13-5.40-3.73-3.55; 2970 ..59%
The T/A box, and with 3.73s; ..... 9.21-6.60-5.00-3.73; 3120 ..72% the ripper
Commando 4spd w/3.23s;...... 9.98-6.20-4.52-3.23; 2700 ..62%
This Commando box shows you why I recommended this box earlier. It gives you tighter splits at every shift (EDIT: except for the T/A box). Check this out;
Commando with 3.55s; ....... 10.96-6.82-4.97-3.55; 2970@65; splits of 62-72-71% This is the best 4-speed for your 273 as regards rapid acceleration; just gear it to put second gear where you want it.
The A998/3.55 will be better off the line with about a 2800TC; 15.66 is a hard act to follow;

15.66x 260ftlbs@2800=4072 ftlbs, decaying automatically to 2374 ... versus
10.96x 290ftlbs@3200 =3178, the best the Commando can do with 3.55s.. if the 273 cannot spin this, or bogs, (shouldn't) then the A998 is the hands down winner.
Traction control and a SureGrip will be mandatory.
So that was at WOT
What about just normal driving? If you like the 4-speed, you gotta have the Commando box. You can run it with the 3.23s and probably will enjoy that combo for a long time. The 6.20 second gear will make 32 mph to be 2555rpm, a bit low to whack it open from, but the downshift gets you 4100, so then yur gone. Also, that 6.20 gear will get you 60= 4800, about right on the power-peak. And 65=5200 about shift-rpm. Then into third at 3750 Badaboom! we are moving right along! And passing from 55 will get you 3200 in third, right on the torquepeak, or 4400 in second at about 90% of peak horsepower if yur in a real hurry.
This is about as Sporty as it gets and still having some cruisability, namely 65=2700 with 3.23s.

I love that Commando box with my 3.55s. Because I have a bigger engine (and a bit more weight;3650), I am sure she would be happy with 3.23s... but I need the 3.55s to hit 93@6150 with, in the Eighth, by gearsplitting; so they are staying.
There are other boxes that can be adapted to the 273, Five-speeds with overdrives , but generally the 1-2 splits are too wide.
 
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Nobody can argue with that!
Here are the A833od ratios
3.09-1.67-1.00-.73od, and here are the road gears with a 3.23 rear
9.98-5.39-3.23-2.36 , and the splits
.54-.60-.73 , meaning that at whatever rpm you chose to shift at, the rpm will fall to those percents.
So let's say your engine sounds good at 2800, like mine ,lol, and so you shift out of first at 2800/22mph. And so in second your rpm will be 2800 x.54=~1500rpm.
I see two problems right away; 1) does your 273 have enough torque at 1500 to to continue accelerating in this 5.39 roadgear?, and 2) will it pull hard enough to satisfy you?
Let's say your 273 makes 140ftlbs at 1500, and so 140 x 5.39 x24/25.5=710ftlbs to the road. This is torque below mediocre. In other words you can cruise at 1500 but don't expect much in terms of acceleration. And that leads to having to hold first gear to a higher rpm.
So where does the hi-compression 273 start to make torque. Lets say it torque-peaks at 3200rpm, and say at 2800 it had 80% of that . This is why she sounds good at 2800, cuz she's loafing at high efficiency. So, for reasonable acceleration she will want to come in at 2800, and that means the 1-2 shift will need to be at 2800/.54=5185rpm/40 mph. You see the problem with that? Me too. Nobody drives like that ALL the time.
And that means at normal throttle openings, on the primaries only, your acceleration will always be mediocre in second gear.
So what is the problem here? Two things; 1) the 5.39 roadgear, and 2) the very wide 1-2 split. How do you overcome that? Well you can re-gear the back and get second gear to work for you at a better rpm, but you cannot do anything about the wide split.
What I like to do is to put the second gear rpm in the fat part of the torque curve at the roadspeed I do most of my driving. So for you that might be 32mph and 2800rpm. This will take 3.91s in the back, for 32mph=~2700 (4.10 would be 2900). So now you have second gear working from say 2500 to say 5000 with a 4bbl cam, which is 28 mph to 56mph.... Do you see the problem with that? Me to; this is a really long pull, in 3.91x1.67=5.39 road gear.
And we're still in second gear. When you hit third at 56mph your Rs will drop to 60% or 3000, and your little 273 is all done; even tho it now has 3.91s. And lastly; 65~ 2400 still with the3.91s.
Ok one more; with 3.91s your starter gear is 3.91x3.09=12.08; kindof a race-track starter. This works great for acceleration when you are in a hurry, but not so much when just cruising.... unless you rev first gear high enough to get into second with enough torque to continue accelerating to what ever speed you had in mind between 28 and 56 mph, at the rate of acceleration that makes you happy.
Ok so what's the conclusion?
The A833od trans will be fine in second gear if geared right, at the back.
With a low-torque engine,read small cubic inch, this compromises all other gears.

I tell you the truth; I had a 367 hi-torque engine putting out over 180psi cylinder pressure; and I had nearly every rear gear in my stable from 2.76 to 4.30, and I could find no love for that transmission, until I installed a GVOD and began splitting those very wide gears. oh and one more thing; That overdrive gear is IMO incredibly weak. I blew up a couple of them just by forgetting that trans was not a 4-speed but rather a 3 plus 1.With my 367,and 4.30s, shifting into that gear took a lotta concentration.

Ok so now, I know you may not want to hear this, but I think I should at least mention it;
The A999 TF with a hi-stall, operates like a wide-ratio five-speed with a short 5th. And your 3.23s are perfect for it. The ratios are 2.74-1.54-1.00 And the TC might have an internal torque-multiplier ratio of up to 2.0 to 1. Say with your 273 it works out to 1.8, and say it couples at 1.05 at WOT. And it has a lock-up feature.
When you couple this with a 3.23rear, the road gears might look like
15.93 decaying to 9.29-5.22-3.39-3.23locked up. 4.5 gears
From 15.93 to 9.29 is about 2 gear ratios, and it's all automatic, operating like a CVT (Constant Velocity Transmission). If you split that space in half you will see that the splits would be .76 or a pretty close ratio. And the in-between gear might be 12.10, so now if you rearrange those ratios and splits it looks like
15.93 decaying to 12.10 decaying to 9.29-5.22-3.39-3.23locked-up, with splits of
.77-.76-.56-.65-.95 Of course the 12.10 is an imaginary gear but kindof shows you what is happening inside the TC. So I call that a 5.5gear trans with a very short final shift.
So what does that mean to your 273?
Well put a 2800TC in there and find out. Going back to the original torque curve, lets say at 3200 she puts out 290 ftlbs, and at 2800 say 260 which is ~140 hp.
So now you nail it and the engine spools up to 2800, and instantly she is putting down
260 x 2.74x3.23x24/25.5=2166 ftlbs to the road, and the result of that is tirespin. So now the TC is ramping down through an infinite amount of graduations to 9.29 ratio as the car is moving and accelerating. So let's say 40 feet out, she hits 9.29 and now the rpm has climbed to (I'm Guessing) 4000, and the torque has fallen to 90% or 260ftlbs, but the hp has climbed to 198hp, on its way to say 235@4800. So I'm guessing the tirespin is coming to an end at about 30 mph, and now you are really accelerating, towards the manual 1-2 shift at say 5200/44mph . So now, still at WOT, the Rs drop to 56% or to 2800...... again, and now the roadgear is only 5.22 so your race is over. You can fix this with more rear gear, but that will subtract from your 65=2700. You could do this with an
A998loc-up (2.45 low) and 3.55s and get about the same first gear, but would tighten up all the splits, with a higher cruise rpm. The roadgears would be
15.66 decaying to 9.13-5.40-3.73-3.55 ,and splits of
.60-.59-.69-.93 This makes second gear 3.4% better. But 65=2970cruise

So lets stack 'em;... rear gear..........second..... top... cruise.. 1-2 split
First the A833od with 3.23s....... 9.98-5.39-3.23-2.36; 1975 ..54%
next the A833od with 3.91s;.... 12.08-6.53-3.91-2.85; 2385 ..54%
next the A999 and 3.23s; 15.93>9.29-5.22-3.39-3.23; 2700 ..56%
then the A998 and 3.55s; 15.66>9.13-5.40-3.73-3.55; 2970 ..59%
Commando 4spd w/3.23s;..... 9.98-6.20-4.52-3.23; 2700 ..62%
Bottom line shows you why I recommended this box earlier. It gives you tighter splits at every shift. Check this out;
Commando with 3.55s; ....... 10.96-6.82-4.97-3.55; 2970@65; splits of 62-72-71% This is the best 4-speed for your 273 as regards rapid acceleration; just gear it to put second gear where you want it.
The A998/3.55 will be better off the line with about a 2800TC; 15.66 is a hard act to follow;
15.66x 260@2800=4072 ftlbs, decaying automatically to 2374 ... versus
10.96x 290@3200 =3178, the best the Cammando can do with 3.55s.. if the 273 cannot spin this, or bogs, then the A998 is the hands down winner.
Traction control and a SureGrip will be mandatory.
So that was at WOT
What about just normal driving? If you like the 4-speed, you gotta have the Commando box. You can run it with the 3.23s and probably will enjoy that combo for a long time. The 6.20 second gear will make 32 mph to be 2555rpm, a bit low to whack it open from, but the downshift gets you 4100, so yur gone. Also, that 6.20 gear will get you 60= 4800, about right on the power-peak. And 65=5200 about shift-rpm. Then into third at 3750 Badaboom! we are moving right along! And passing from 55 will get you 3200 in third, right on the torquepeak, or 4400 in second at about 90% of peak horsepower if yur in a real hurry.
I love that Commando box with my 3.55s. Because I have a bigger engine (and a bit more weight;3650), I am sure she would be happy with 3.23s... but I need the 3.55s to hit 93@6150 with, in the Eighth, by gearsplitting; so they are staying .
This is about as Sporty as it gets and still having some cruisability, namely 65=2700 with 3.23s.
 
AJ,
Wow, what an in-depth assessment of the possibilities, quite eye opening to say the least. I read through it 3 times to let the math sink in to visualize whats happening between engine RPM, trans ratios and rear end reduction. So based on your assessment, what it boils down to is Chrysler engineering had it right from the start and I should go with the standard 4 speed 833 to provide the best performance match. Thanks so much for taking the time to share this, I need to do some soul searching as to the importance of the low RPM freeway cruising offered by the OD transmission.
As a side note, I just got back from the MoPar Rally swap meet in Cupertino and I scored an original cast iron '65, 4 speed bell housing, 2465523, and two correct 122 tooth flywheels (both nice, he said I had to take both), all for $100. Moving forward.
 
the standard 4 speed 833
Careful using that word standard.
IIRC the Commando box, the one you want with the 3.09 low gear in it, was a 1 or 2 year deal.
The Standard box has a 2.66 low in it.You don't want this one
and the later T/A box has a 2.47 and is even closer ratios.
The T/A box would be an even better choice .. if you don't mind sacrificing off-the-line punch, or cruising rpm. Your starter would be 2.47x3.23=7.98 which with a 273 would be somewhat lame, and it wouldn't come alive until 27 mph@2800 rpm. Now with 3.73s yur starter would be 9.21, and more importantly, your second would be 6.60, and third is 5.00 and direct is 3.73. I'll add this to post 17 above. Those numbers are really good.
 
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Nobody can argue with that!
Here are the A833od ratios
3.09-1.67-1.00-.73od, and here are the road gears with a 3.23 rear
9.98-5.39-3.23-2.36 , and the splits
.54-.60-.73 , meaning that at whatever rpm you chose to shift at, the rpm will fall to those percents.
So let's say your engine sounds good at 2800, like mine ,lol, and so you shift out of first at 2800/22mph. And so in second your rpm will be 2800 x.54=~1500rpm.
I see two problems right away; 1) does your 273 have enough torque at 1500 to to continue accelerating in this 5.39 roadgear?, and 2) will it pull hard enough to satisfy you?
Let's say your 273 makes 140ftlbs at 1500, and so 140 x 5.39 x24/25.5=710ftlbs to the road. This is torque below mediocre. In other words you can cruise at 1500 but don't expect much in terms of acceleration. And that leads to having to hold first gear to a higher rpm.
So where does the hi-compression 273 start to make torque. Lets say it torque-peaks at 3200rpm, and say at 2800 it had 80% of that . This is why she sounds good at 2800, cuz she's loafing at high efficiency. So, for reasonable acceleration she will want to come in at 2800, and that means the 1-2 shift will need to be at 2800/.54=5185rpm/40 mph. You see the problem with that? Me too. Nobody drives like that ALL the time.
And that means at normal throttle openings, on the primaries only, your acceleration will always be mediocre in second gear.
So what is the problem here? Two things; 1) the 5.39 roadgear, and 2) the very wide 1-2 split. How do you overcome that? Well you can re-gear the back and get second gear to work for you at a better rpm, but you cannot do anything about the wide split.
What I like to do is to put the second gear rpm in the fat part of the torque curve at the roadspeed I do most of my driving. So for you that might be 32mph and 2800rpm. This will take 3.91s in the back, for 32mph=~2700 (4.10 would be 2900). So now you have second gear working from say 2500 to say 5000 with a 4bbl cam, which is 28 mph to 56mph.... Do you see the problem with that? Me to; this is a really long pull, in 3.91x1.67=5.39 road gear.
And we're still in second gear. When you hit third at 56mph your Rs will drop to 60% or 3000, and your little 273 is all done; even tho it now has 3.91s. And lastly; 65~ 2400 still with the3.91s.
Ok one more; with 3.91s your starter gear is 3.91x3.09=12.08; kindof a race-track starter. This works great for acceleration when you are in a hurry, but not so much when just cruising.... unless you rev first gear high enough to get into second with enough torque to continue accelerating to what ever speed you had in mind between 28 and 56 mph, at the rate of acceleration that makes you happy.
Ok so what's the conclusion?
The A833od trans will be fine in second gear if geared right, at the back.
With a low-torque engine,read small cubic inch, this compromises all other gears.

I tell you the truth; I had a 367 hi-torque engine putting out over 180psi cylinder pressure; and I had nearly every rear gear in my stable from 2.76 to 4.30, and I could find no love for that transmission, until I installed a GVOD and began splitting those very wide gears. oh and one more thing; That overdrive gear is IMO incredibly weak. I blew up a couple of them just by forgetting that trans was not a 4-speed but rather a 3 plus 1.With my 367,and 4.30s, shifting into that gear took a lotta concentration.

Ok so now, I know you may not want to hear this, but I think I should at least mention it;
The A999 TF with a hi-stall, operates like a wide-ratio five-speed with a short 5th. And your 3.23s are perfect for it. The ratios are 2.74-1.54-1.00 And the TC might have an internal torque-multiplier ratio of up to 2.0 to 1. Say with your 273 it works out to 1.8, and say it couples at 1.05 at WOT. And it has a lock-up feature.
When you couple this with a 3.23rear, the road gears might look like
15.93 decaying to 9.29-5.22-3.39-3.23locked up. 4.5 gears
From 15.93 to 9.29 is about 2 gear ratios, and it's all automatic, operating like a CVT (Constant Velocity Transmission). If you split that space in half you will see that the splits would be .76 or a pretty close ratio. And the in-between gear might be 12.10, so now if you rearrange those ratios and splits it looks like
15.93 decaying to 12.10 decaying to 9.29-5.22-3.39-3.23locked-up, with splits of
.77-.76-.56-.65-.95 Of course the 12.10 is an imaginary gear but kindof shows you what is happening inside the TC. So I call that a 5.5gear trans with a very short final shift.
So what does that mean to your 273?
Well put a 2800TC in there and find out. Going back to the original torque curve, lets say at 3200 she puts out 290 ftlbs, and at 2800 say 260 which is ~140 hp.
So now you nail it and the engine spools up to 2800, and instantly she is putting down
260 x 2.74x3.23x24/25.5=2166 ftlbs to the road, and the result of that is tirespin. So now the TC is ramping down through an infinite amount of graduations to 9.29 ratio as the car is moving and accelerating. So let's say 40 feet out, she hits 9.29 and now the rpm has climbed to (I'm Guessing) 4000, and the torque has fallen to 90% or 260ftlbs, but the hp has climbed to 198hp, on its way to say 235@4800. So I'm guessing the tirespin is coming to an end at about 30 mph, and now you are really accelerating, towards the manual 1-2 shift at say 5200/44mph . So now, still at WOT, the Rs drop to 56% or to 2800...... again, and now the roadgear is only 5.22 so your race is over. You can fix this with more rear gear, but that will subtract from your 65=2700. You could do this with an
A998loc-up (2.45 low) and 3.55s and get about the same first gear, but would tighten up all the splits, with a higher cruise rpm. The roadgears would be
15.66 decaying to 9.13-5.40-3.73-3.55 ,and splits of
.60-.59-.69-.93 This makes second gear 3.4% better. But 65=2970cruise

So lets stack 'em;... rear gear..........second..... top... cruise.. 1-2 split
First the A833od with 3.23s....... 9.98-5.39-3.23-2.36; 1975 ..54%
next the A833od with 3.91s;.... 12.08-6.53-3.91-2.85; 2385 ..54%
next the A999 and 3.23s; 15.93>9.29-5.22-3.39-3.23; 2700 ..56%
then the A998 and 3.55s; 15.66>9.13-5.40-3.73-3.55; 2970 ..59%
Commando 4spd w/3.23s;..... 9.98-6.20-4.52-3.23; 2700 ..62%
T/A box with 3.73s 7.98-6.60-5.00-3.73
Bottom line shows you why I recommended this box earlier. It gives you tighter splits at every shift. Check this out;
Commando with 3.55s; ....... 10.96-6.82-4.97-3.55; 2970@65; splits of 62-72-71% This is the best 4-speed for your 273 as regards rapid acceleration; just gear it to put second gear where you want it.
The A998/3.55 will be better off the line with about a 2800TC; 15.66 is a hard act to follow;
15.66x 260@2800=4072 ftlbs, decaying automatically to 2374 ... versus
10.96x 290@3200 =3178, the best the Cammando can do with 3.55s.. if the 273 cannot spin this, or bogs, then the A998 is the hands down winner.
Traction control and a SureGrip will be mandatory.
So that was at WOT
What about just normal driving? If you like the 4-speed, you gotta have the Commando box. You can run it with the 3.23s and probably will enjoy that combo for a long time. The 6.20 second gear will make 32 mph to be 2555rpm, a bit low to whack it open from, but the downshift gets you 4100, so yur gone. Also, that 6.20 gear will get you 60= 4800, about right on the power-peak. And 65=5200 about shift-rpm. Then into third at 3750 Badaboom! we are moving right along! And passing from 55 will get you 3200 in third, right on the torquepeak, or 4400 in second at about 90% of peak horsepower if yur in a real hurry.
I love that Commando box with my 3.55s. Because I have a bigger engine (and a bit more weight;3650), I am sure she would be happy with 3.23s... but I need the 3.55s to hit 93@6150 with, in the Eighth, by gearsplitting; so they are staying .
This is about as Sporty as it gets and still having some cruisability, namely 65=2700 with 3.23s.
Thanks for stopping by AJ. Your knowledge and formulas are invaluable.
 
Keep in mind, I use the 6.25 +/-.25 second gear ratio, cuz I like it at 32.5+/- 2.5 mph with 25.5 tires, it gets me a cruiser gear of about 2600 rpm, but more importantly is the backshift into 3.09-first which is ~4180 If you don't have the cam for that, then you're gonna run out of gear and have to go back to second pdq. That's two shifts and slows you right down. With a 2.66 low gear, it drops in at 3600 which is less power, but 2.66 low will go to 45 mph versus 39 with the 3.09 low. (5000rpm and 3.23s)
It's all about the compromises.
I built my last engine to work with those Commando ratios, and my GVOD, and couldn't be happier.
But yaknow, everybody is different, and my favorites may not be the next guys favorites. So with that in mind here is the formula I use; straight out of my head;
mph= (rpm x tc x TC)/(1056 x R1 x R2)
where tc is the tire circumference; also called roll-out, or diameter x 3.1416
R1 is the rear-gear, and R2 is the trans gear, R3 would be for a third reducer like the GVOD.
TC is correction for the convertor slip and is; 1/TM , where TM (Torque Multiplication) can be between 1.05 to as high as 2.0 I arbitrarily use 1.05 for small engines and 1.08 for street-SBMs. Except at zero mph I might use 1.5 to 1.8 depending on how much power I imagine the engine is gonna make, at stall.
Here is an example;
Mph = (5000rpm x 85 x 1/1.08)/(1056x 2.45 x 3.55); solve for mph
393518/9184.56 =42.8 mph. If the TC only slips 5%b then mph will be 44mph

At zero mph with a 360, the TC might put out a TM of 1.8 so then the starter gear could be treated as 1 x 2.45x3.55x1.8= 15.66 times the engines torque at stallspeed. With a 2800stall and say 300 ftlbs, this would work out to 15.66 x 300=~4700 footpounds into the rear axles, and instant tire annihilation..
The same TC behind a slanty might only have a TM of 1.6, and 120 ftlbs at 2800 so then
120x2.45x3.55x1.6=1670 ftlbs into the rear axles. So that's about a chirp plus. But as soon as the tires slip, that 1.6TM will begin to ramp down to something like 1.2 in first gear. So if she spins, as the rpm goes up more ftlbs is going into the TC, but it is being multiplied less. So say at 3500 the slanty is up to 140 ftlbs, then;
140 x 2.45x3.55x1.2=1461, not enough to sustain the tirespin
But if it doesn't spin then the TC will ramp down more slowly as the Rs go up, and the car begins to move out. In any event this large TM ramps down fairly rapidly. I'd be guessing but I think by one or maybe two car-lengths out it it has decayed to the minimum for that gear. Every successive gear will have less TM in the TC because as the road speed goes up the turbine and impeller are approaching synchronization. At WOT,there will always be some slip between them, and so always some TM. Typically I use 5 to 10% as an average for a streeter. For me it's all guesswork, based on common sense, and as long as I compare apples to apples, nobody is the wiser,lol. Yeah it hurts to say that I don't know everything.
Happy computing
BTW, with a manual trans, there is no TM so the factory usually gave the manual cars the next bigger rear gear, with an across the board increase in TM of about 10%. The penalty of course was a higher cruising speed.
And of course, with the same rear gears, autos are usually or at least often, a lil quicker out of the gate.
 
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The trans you want is the A833 with the ball & trunion flange on the back end.That is what was used in all 63 _65 A bodies including the S in 65. The 2.66 first gear trans has a splined back end and takes a slip yoke drive shaft .It was used in 66 and some later years .I have a few of the 65 transmissions but I'm in NY and shipping this stuff is way too expensive but the good news is that they are out there and pretty easy to find and also somewhat less expensive ( not by much). I'm running one in my Valiant station wagon right now behind a 170 slant 6 and love it.I had one in my 65 barracuda that I had a 318 in and it was real sweet too .Got about 18 MPG . So you burn some gas,who cares,you aren't going to use this car as a daily driver
 
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I will say, my HP273 in my 66 isn't much more than stock. I did advance the valve timing a couple degrees for a bit more bottom end and I could use some 901 Comp valve springs instead of the short, shimmed, up E bay springs I have in there now. The engine wouldn't run out of steam at 4500 rpm if I would make some changes. I have the original 833 in there as well as the original 3:23's. I shot myself in the foot by installing a a pair of 225-70/15's on the rear. (for looks) I am not a clutch side stepper but once I get her under way she pulls you back in the seat pretty good. First is a fairly short gear but second is my power gear. I need to pay closer attention to the rpm and mph of my shifts. 3rd is surprisingly powerful as well and by that time I am at 75 or so and time to shift into high gear. I am real happy with the 1966 833 and the 3:23 gear. I would need to degree the cam and get some better valve springs in her to be able to take advantage of another 1000 rpm or a 355 or better rear gear.
 
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