3.09 gear set with 3.23's

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skep419

skep419

5.9 Magnum 4 speed afficionado
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1969 Dart 360, ede heads, air gap, h116 speed pros, scat i beams, stock crank, 60403 voodoo cam, holley 750dp, 273 adj iron rockers, d453's, msd 6al, accel 59301 dizzy.

I had made the swap to a 4 speed a few years ago and swapped back to an automatic due to a demonized oil leak.

With the 2.66 first gear and the 727 3.23's were a pooch out of the hole. 3.91 are just barely tolerable with 28" tires, yet perfect out of the hole.

So I know I want to run 3.23 gears. I don't want to go overdrive because I have an awful vibration in high gear above 4000 rpm's (I'd imagine it would be worse with an overdrive)

Will the 3.09 gear set let me have cake and eat it to? (only thing I'm missing is the dust cover and a tailshaft housing)

Is there a magic torque converter that will fix the sluggishness?

Don't think I can go smaller cam because the compression is already awesome.
 
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skep419 said:
1969 Dart 360, ede heads, air gap, h116 speed pros, scat i beams, stock crank, 60403 voodoo cam, holley 750dp, 273 adj iron rockers, d453's, msd 6al, accel 59301 dizzy.

I had made the swap to a 4 speed a few years ago and swapped back to an automatic due to a demonized oil leak.

With the 2.66 first gear and the 727 3.23's were a pooch out of the hole. 3.91 are just barely tolerable with 28" tires, yet perfect out of the hole.

So I know I want to run 3.23 gears. I don't want to go overdrive because I have an awful vibration in high gear above 4000 rpm's (I'd imagine it would be worse with an overdrive)

Will the 3.09 gear set let me have cake and eat it to? (only thing I'm missing is the dust cover and a tailshaft housing)

Is there a magic torque converter that will fix the sluggishness?

Don't think I can go smaller cam because the compression is already awesome.
Click to expand...
Difference between 2.66 and 3.09 low gear is roughly 14%. So the 3.23 will feel like a 3.68 axle with the 3.09 low gear.
 
You’ll need to play with some math.
First gear ratio of the current trans (2.66) times the rear axle ratio (3.23) equals 8.5918.
The current trans first gear ratio with the 2.66 starter gear and 3.91’s equals 10.4000
Now figure the feel good out of the hole ratio of 10.4000 divided by the 3.09 first gear to get 3.36 as a gear ratio. Since that’s in between normal Chrysler ratios, move up to the next nearest one.

Since Dan already stated 3.23’s will feel like 3.68’s, the 3.23 is to numerically low, step up to 3.55’s. 3.55 X 3.09 = 10.960 Very close. 10.960 - 10.400 = .056 difference. You can add the difference to the 3.91 to get the feel of the first gear ratio on take off.
3.91 + .056 = 3.966 Close to the 3.68.

If you liked the cruise rpm with the 3.23’s, it will only be a few hundred rpm higher with the 3.55’s. This is only a few miles an hour. Something you can ether slow down the car when driving to meet the old cruise rpm or step on the pedal for a few more rpm to meet the mph when driving down the road.

Ive made this exact rear gear swap between 3.23 & 3.55. It is a nice improvement but yet a very mello and minor one.
 
OH! I forgot, you can get a custom torque converter or have the OE one opened up and rest Alex a few hundred rpm’s higher. The costs are almost the same. I went with these guys that did a great job. Though any good converter shop should be able to do this, if they do custom work.

http://protorque.com/
 
I think I could live with the 9.98 starter gear (3.23 with 3.09 first gear) but the 1-2 shift might be an issue.

Not sure there is a magical torque converter that can make a 8.20 starter gear (2.54 727 with 3.23 gears) snappy out of the hole.
 
The 1-2 shift for auto or manual is less than optimum. You would need to rpm the engine a bit more. How much more is a good question that some math could figure out for you. I don’t know exactly what trans we are working with here. So.....

You would have to physically see where the shift leaves you when you shift. Notice the rpm. Adjust shift point higher or lower to get it where you want it to be when you land in second gear.

skep419 said:
I think I could live with the 9.98 starter gear (3.23 with 3.09 first gear) but the 1-2 shift might be an issue.
Click to expand...
9.98?
3.23 x 3.09 = 10.197
3.55 X 3.09 = 10.960

Not sure there is a magical torque converter that can make a 8.20 starter gear (2.54 727 with 3.23 gears) snappy out of the hole.
Click to expand...
This is where a pro comes in.
I doubt it as well simply because your sticking with the 3.23 gear set. I’m sure a good diverged man/company can do something really cool and trick, but in the end, the 3.23’s hurt off the line performance vs 3.55’s. It’s minor change that helps a lot. I suggest you reconsider and think about it on the over all scheme of things. This ball is in your court.
 
skep419 said:
1969 Dart 360, ede heads, air gap, h116 speed pros, scat i beams, stock crank, 60403 voodoo cam, holley 750dp, 273 adj iron rockers, d453's, msd 6al, accel 59301 dizzy.
Click to expand...
What is your actual cranking cylinder pressure ,
and elevation.

It's really hard to beat a properly working Torque convertor for off-the-line jump.
Every TC has a an internal torque-multiplying feature that at stall may be as high a 1.8 to 1. And this automatically diminishes to in the neighborhood of 1.1 with speed and rpm.
So on the starting line,in first gear at zero mph,and at WOT, the 3.23s could behave like 5.81s. A few feet out the ratio is automatically reducing towards say 1.5 at peak torque and maybe 1.3 at shift rpm. It's like having an automatic planetary super low gear.
Below is a snapshot of what your engine's power curve MIGHT look like. That build sorta mirrors mine, except I have OOTB Eddie heads and ~180 psi pressure.
Ok so with 3.23s and a 2.45 low gear, out of the gate, it will feel like
3.23 x 2.45 x 1.8=14.25... whereas the 2.33 4-speed will feel like
3.23 x 2.33 =7.53
Ok so say you have a 3000 stall; look on the graph and find the power at 3000, I get 210hp; which is 367 ftlbs torque. Multiplying that by 14.25, you get 5237 available ftlbs on the start line
To get that from the 4-gear, you would need
5237/7.53= 695 ftlbs which is impossible for this engine to generate.
Lets move to the torque peak, I'll go with 4800rpm.
So if your TC ratio is 1.5 then
437 x 1.5 x 2.45 x 3.23=5190 ftlbs available, and the 2.66 still can't touch it. This is why the factory almost always gave the 340 4-gear cars more rear gear. Let's try 3.55s
437 x 2.66 x 3.55=4127 still no contest. Lets try the 3.09 low
437 x 3.09 x 3.55=4794 getting there.
Let go to peak power, say 5700rpm and 437hp =400 ftlbs.
with the automatic;
400 x 1.30 x 2.45 x 3.23= 4115 ftlbs available. and the 4-gear is
400 x 2.66 x 3.23= 3437, while the 3.09 is
400 x 3.09 x 3.23= 3992, closing the gap. And with 3.55s
400 x 3.09 x 3.55= 4388 badaboom!
Like I said, in first gear, combo for combo, it's really hard to out accelerate an automatic. The auto will be way out in front, even with the 3.09 x 3.55, until after the torquepeak has flown by.
I have an engine combo similar to yours, and I do have the 3.09 x 3.55 combo. I don't really need the 3.55s, but they work well with my GVod. If I didn't already have it, I would put the 3.23s back in.

So that leads to the final question; What's wrong with either; your combo, your stall, or your TC itself.


land_dyno.jpg
 
rumblefish360 said:
You’ll need to play with some math.
First gear ratio of the current trans (2.66) times the rear axle ratio (3.23) equals 8.5918.
The current trans first gear ratio with the 2.66 starter gear and 3.91’s equals 10.4000
Now figure the feel good out of the hole ratio of 10.4000 divided by the 3.09 first gear to get 3.36 as a gear ratio. Since that’s in between normal Chrysler ratios, move up to the next nearest one.

Since Dan already stated 3.23’s will feel like 3.68’s, the 3.23 is to numerically low, step up to 3.55’s. 3.55 X 3.09 = 10.960 Very close. 10.960 - 10.400 = .056 difference. You can add the difference to the 3.91 to get the feel of the first gear ratio on take off.
3.91 + .056 = 3.966 Close to the 3.68.

If you liked the cruise rpm with the 3.23’s, it will only be a few hundred rpm higher with the 3.55’s. This is only a few miles an hour. Something you can ether slow down the car when driving to meet the old cruise rpm or step on the pedal for a few more rpm to meet the mph when driving down the road.

Ive made this exact rear gear swap between 3.23 & 3.55. It is a nice improvement but yet a very mello and minor one.
Click to expand...

Yes , what he said ! Good grief ! I’m mathematically challenged, to say the least !
 
rumblefish360 said:
The 1-2 shift for auto or manual is less than optimum. You would need to rpm the engine a bit more. How much more is a good question that some math could figure out for you. I don’t know exactly what trans we are working with here. So.....

You would have to physically see where the shift leaves you when you shift. Notice the rpm. Adjust shift point higher or lower to get it where you want it to be when you land in second gear.


9.98?
3.23 x 3.09 = 10.197
3.55 X 3.09 = 10.960


This is where a pro comes in.
I doubt it as well simply because your sticking with the 3.23 gear set. I’m sure a good diverged man/company can do something really cool and trick, but in the end, the 3.23’s hurt off the line performance vs 3.55’s. It’s minor change that helps a lot. I suggest you reconsider and think about it on the over all scheme of things. This ball is in your court.
Click to expand...

I’m still coming up with 9.98?

I’ve got 2 742 suregrips. 3.23 and a 3.91. Currently running the 3.91’s. I’d rather not go with 3.55’s.
 
Hey! I’d rather 3.91’s or better but the vibration issue will happen earlier with the higher gear set... a complaint of not liking the rev’s generated by the 3.91’s..
It kind of bottles me in on a recommendation. Era on the side of caution is what I did.
 
AJ/FormS said:
So that leads to the final question; What's wrong with either; your combo, your stall, or your TC itself.
Click to expand...

skep419 said:
1200
Click to expand...

Whoa! 200psi@1200' ; so those ain't the problem,lol
That sorta leaves just the convertor.
_______________________
I gotta say that I love my 3.09/3.55s/ at 177 to 180psi. When I installed the Hughes HE3037AL That 367 of mine lost a bunch of take-off torque, compared to the HE2430AL. The only way to get it back was with 4.30s or the 3.09 low. I ran the 2.66/4.30 for one summer, for a starter gear of 11.44 just to prove I was gonna like it, then pulled the trigger on the 3.09 x3.55=10.97. Which has been in there ever since.
Second maths to hit 60@5140 perhaps a lil low. But using the GV as a splitter, she maths to 60 @ 6450, on the way to 7000@65mph..... with only the one full-power electric-shift. So basically, when I stomp it, she goes to the rev-limiter and stays there to 65 mph. So for me, the 3.55s are the right gear.



Peak torque comes in the speed-range of about 40 to 50mph in second, and the lil 367/750DP breaks the 295s loose with just a footstomp, and they sometimes keep spinning into third gear at over 80. It's a good thing those BFGs are quiet.
 
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skep419 said:
I’m still coming up with 9.98?
Click to expand...
yes 3.09 x 3.23, I get 9.98 as well, and
9.98/2.66=3.75 so
the 3.09 combo takes off about like a regular 2.66 does with 3.73s
The thing is, lower number gears, keep your engine in each trans gear a lil longer, unless the tires are spinning. The 3.09 low is great in first gear, but when she hits second, the 3.23s take a longer time to hit shift-rpm versus a bigger number rear gear, unless of course the tires are spinning.
Whereas a bigger number rear gear will blast thru the gears quicker, putting down more average horsepower per unit of time, usually leading to a lower ET over a given distance....... unless the tires spin,lol.
On the street you can't get traction unless you spend big coin on the back end, so it hardly matters what rear gears you run. It doesn't really start to make a difference until you start pushing wind at say 85mph or higher.

If I had to guess, I'd say your vibration is caused by driveshaft run-out. The driveshaft machines I have seen, do not spin your shaft to 6000, but maybe to 2000 . It may be in pretty good balance there, but if the driveshaft has a bend in it, it just gets worse and worse with driveshaft-rpm. I had to get mine done 3 times, and on the third time I replaced the tube, and now it's fine. Like you, I spent a lotta hours looking for that hi-speed vibration.
Jus saying.
 
AJ/FormS said:
yes 3.09 x 3.23, I get 9.98 as well, and
9.98/2.66=3.75 so
the 3.09 combo takes off about like a regular 2.66 does with 3.73s
The thing is, lower number gears, keep your engine in each trans gear a lil longer, unless the tires are spinning. The 3.09 low is great in first gear, but when she hits second, the 3.23s take a longer time to hit shift-rpm versus a bigger number rear gear, unless of course the tires are spinning.
Whereas a bigger number rear gear will blast thru the gears quicker, putting down more average horsepower per unit of time, usually leading to a lower ET over a given distance....... unless the tires spin,lol.
On the street you can't get traction unless you spend big coin on the back end, so it hardly matters what rear gears you run. It doesn't really start to make a difference until you start pushing wind at say 85mph or higher.

If I had to guess, I'd say your vibration is caused by driveshaft run-out. The driveshaft machines I have seen, do not spin your shaft to 6000, but maybe to 2000 . It may be in pretty good balance there, but if the driveshaft has a bend in it, it just gets worse and worse with driveshaft-rpm. I had to get mine done 3 times, and on the third time I replaced the tube, and now it's fine. Like you, I spent a lotta hours looking for that hi-speed vibration.
Jus saying.
Click to expand...

didn't change with 2 different shafts/yokes.
currently using a DR Diff 1350 style shaft.
 
skep419 said:
I’ve tried. (Pinion angles, driveshafts, wheels/tires, 3rd members, 904, a833, etc)

3.23’s puts the vibration above 100mph.
Click to expand...
Axle bearings? Bent axles? That vibration would be the first thing I’d fix. Not much fun having a nice engine in a chassis that can’t use it. I wouldn’t spend much more time trying to “gear” around the vibration, it ain’t gonna get any better.
 
I'd like to mention that, in years gone by I worked at a tireshop as a alignment tech. I have watched those guys balance troublesome tires, to perfection yet they would shake the car. I have seen; out of round tires, and tires with cord problems; in perfect dynamic balance on the machine produce a vibration on the car. And sometimes, we could not find any problems with the tires at all yet they Shook.
Sometimes just making the tires run in the opposite direction, solved the problem.
But if not, a new tire always cured it.
I couldn't believe it the first time my boss asked me to put the tire on the other side of the car. I thought to myself, what a dope. Boy was I glad I kept my usually energetic trap shut! Sure enough the problem , in this case, was resolved; and many others cases besides.
Jus saying, tires can be wicked sob's
 
TT5.9mag said:
Axle bearings? Bent axles? That vibration would be the first thing I’d fix. Not much fun having a nice engine in a chassis that can’t use it. I wouldn’t spend much more time trying to “gear” around the vibration, it ain’t gonna get any better.
Click to expand...
AJ/FormS said:
I'd like to mention that, in years gone by I worked at a tireshop as a alignment tech. I have watched those guys balance troublesome tires, to perfection yet they would shake the car. I have seen; out of round tires, and tires with cord problems; in perfect dynamic balance on the machine produce a vibration on the car. And sometimes, we could not find any problems with the tires at all yet they Shook.
Sometimes just making the tires run in the opposite direction, solved the problem.
But if not, a new tire always cured it.
I couldn't believe it the first time my boss asked me to put the tire on the other side of the car. I thought to myself, what a dope. Boy was I glad I kept my usually energetic trap shut! Sure enough the problem , in this case, was resolved; and many others cases besides.
Jus saying, tires can be wicked sob's
Click to expand...

I have 3 sets of wheels and tires and been through multiple sets of tires on each. I sell tires for a living.

Also I think if it was a tire it would do it at the same speed and wouldn’t change with gearing.

i have a 7 1/4 in my other car I could slap in there to rule out the rear end.


It was awhile ago but I’m pretty sure it did it on jack stands with the axles removed.


I’ve tried 3 different 3rd members also.
 
Try and figure out why it's vibrating.

Driveline? wrong balancer or torque converter weighting?

The rpm drop from 3.08 1st to 2nd's 1.90's is the noticable torque affector. It will loose some 'charge'...might bug you after a while.

Jmo
 
MOPAROFFICIAL said:
Try and figure out why it's vibrating.

Driveline? wrong balancer or torque converter weighting?

The rpm drop from 3.08 1st to 2nd's 1.90's is the noticable torque affector. It will loose some 'charge'...might bug you after a while.

Jmo
Click to expand...

1st and 2nd gear there is Zero vibration all the way to 6500.

vibration happens in 3rd above say 3600-4000.

3.23 gears 100+ mph. Fixed

if you’ve got a driveshaft you want to send me that doesn’t vibrate I’ll gladly try it.
 
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