Which trans is the better one? Does one have an advantage over the other when comparing the ratios of the the gears? The earlier '67-'69 4 speeds had the 2.66 low first ( what I have in my car ) and the later had a 2.44 first with closer gear ratios. What are the advantages and disadvantages of each? I have driven a couple Darts with the 2.66 low gear but have never driven one with the close ratio trans. Can you tell the difference is normal driving? I am just curious is all.
2.66 low gear vs close ratio
- Thread starter duster360
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acpat
Well-Known Member
later trans will have wide ratio synchro's less prone to cracking and easier to shift. close ratio has interlock side cover (junk) and steel shift forks (good). I have ran both and really don't have a preference between the two. They are both good pieces. I do junk the interlock side cover and cut the tits off the steel forks. I then run the standard non interlock side cover and steel forks on later close ratio trans.
j par
Well-hung Member
When I think close ratio, I think a higher ratio first? Thus the gear ratios are closer? No?
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Ok, so this is something I have first hand knowledge, since I have run all three, er, all four,er all5 ratios.Yes there are at least 5 ratios in the Mopar 1x23 sbm box; and I've run them all.
Here's the key; the ratio to run needs to match the intended useage and the engine powerband needs to match the chosen ratio.This will give the best results.
Here are the ratios,from memory;
2.66-1.92-1.40-1.00 This set can be had with a 3.09 low
2.47-1.77-1.34-1.00 the close ratio box
And then there are two O/D boxes
3.09-1.67-1.00-.71od This box can be found with a .73od
The shorter/lower the operating range of the engine, the wider the ratios can be.
The higher the rpm of the power band, the narrower or closer the ratios need to be.
If you are racing with a very narrow powerband, the tighter the ratios HAVE to be.Or the powerband needs to be adjusted for the limitations in the ratios.
for a streeter, the wide ratio 2.66 box works just fine. A streeter usually runs a 240* or less cam, and is limited to 60 or 80 mph, and just two or maybe three gears.If a streeter is running a smaller cam than that, and wants to cruise in comfort, then the 3.09Low box can be put to good use, with 3.23 or less rear gears. In this case a 10.xx/1 starter gear can be married to a sub-2400 cruising rpm.
The 2.47 box is usually reserved for road-race applications, that do not spend a lot of time at zero mph, and is really a terrible ratio for quarter mileing, except in certain circumstances.
For Quarter-mileing;Heres how the 2.47/2.66 box plays out;
Say you have a SBM with a 250* cam. That baby is gonna want to rev to make power. The power peak may arrive around 5800/6000, so you might shift it at 6700. Well the 2.66 box has splits of about 71.4% , so when shifting at 6700, the Rs will drop to 6700 x .714 =4786; and the power band will need to be from 4786 to 6700 =1914 . As can be seen the cams LDA will need to be selected to fill that requirement, for best results.
Now let's try it with the close ratio box;
The 2.47 box has splits of about 74.6%. So when shifting at 6700, the Rs will drop to 6700 x .746 = 5000, and the powerband needs to be 6700 - 5000 = 1700. As can be seen, that's 200 rpm better.
Unfortunately, the starting line advantage goes to the 2.66 box with it's approximate 8.5 % more starter gear, requiring one size less rear gear or 8.5% more torque lay-down at the line.
For Eighth mileing, it's a different story
For streeters another story
I got's to toddle off to work now so I'll continue later.
Here's the key; the ratio to run needs to match the intended useage and the engine powerband needs to match the chosen ratio.This will give the best results.
Here are the ratios,from memory;
2.66-1.92-1.40-1.00 This set can be had with a 3.09 low
2.47-1.77-1.34-1.00 the close ratio box
And then there are two O/D boxes
3.09-1.67-1.00-.71od This box can be found with a .73od
The shorter/lower the operating range of the engine, the wider the ratios can be.
The higher the rpm of the power band, the narrower or closer the ratios need to be.
If you are racing with a very narrow powerband, the tighter the ratios HAVE to be.Or the powerband needs to be adjusted for the limitations in the ratios.
for a streeter, the wide ratio 2.66 box works just fine. A streeter usually runs a 240* or less cam, and is limited to 60 or 80 mph, and just two or maybe three gears.If a streeter is running a smaller cam than that, and wants to cruise in comfort, then the 3.09Low box can be put to good use, with 3.23 or less rear gears. In this case a 10.xx/1 starter gear can be married to a sub-2400 cruising rpm.
The 2.47 box is usually reserved for road-race applications, that do not spend a lot of time at zero mph, and is really a terrible ratio for quarter mileing, except in certain circumstances.
For Quarter-mileing;Heres how the 2.47/2.66 box plays out;
Say you have a SBM with a 250* cam. That baby is gonna want to rev to make power. The power peak may arrive around 5800/6000, so you might shift it at 6700. Well the 2.66 box has splits of about 71.4% , so when shifting at 6700, the Rs will drop to 6700 x .714 =4786; and the power band will need to be from 4786 to 6700 =1914 . As can be seen the cams LDA will need to be selected to fill that requirement, for best results.
Now let's try it with the close ratio box;
The 2.47 box has splits of about 74.6%. So when shifting at 6700, the Rs will drop to 6700 x .746 = 5000, and the powerband needs to be 6700 - 5000 = 1700. As can be seen, that's 200 rpm better.
Unfortunately, the starting line advantage goes to the 2.66 box with it's approximate 8.5 % more starter gear, requiring one size less rear gear or 8.5% more torque lay-down at the line.
For Eighth mileing, it's a different story
For streeters another story
I got's to toddle off to work now so I'll continue later.
That is some good indepth info. Thanks..
goldduster318
Overzealous Car Modifier
I thought that almost all A-body A-833's other than the OD's and some early ones were 2.66:1 first. I'm running a 2.66:1 first trans with a 340 with a 227/231 Hydraulic roller and 3.23's. 25.6" tall tires. Maybe I could use a slightly deeper first gear to be totally optimized for launching, but otherwise it's fabulous.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Well I'm back, so let's play with applications,starting with the O/D boxes.
The ratios are 3.09-1.67-1.0-(.71/.73) and the splits are .54-.60-.71/.73 hereafter .71
-Say you have a slanty that rarely sees 4000rpm.If you put this box behind it, and want to cruise at 2000/60mph, then you will need 3.73 gear.This will get you a nice 11.53 starter gear, and a 2.68FD (Final Drive).So that's a double win so far.Next let's work the splits; Let's use .575 as an average % drop. Shifting into 2nd from 4000/1st, the Rs will drop TO 57.5% of 4000, so to 2300. the powerband will thus need to be from 2300 to 4000 equals 1700rpm. This is very doable in this application
-Now let's put this same stuff behind a stockish teener.This baby might want to be shifted at 5000. So the rpm drops to 5000 x .575 = 2875; and the power band is thus from 2875 to 5000 =2125rpm, still doable.
-Next, let's put this behind a 360 that want's to be shifted at 6000. the rpm will drop to 6000 x .575 = 3450;and the powerband will need to be from 3450 to 6000 = 2550. This is getting tougher. This combo will need a cam that provides a long power curve, which usually means some sacrifice in specific output. So now begins the compromising. It will still work on the street cuz it has 360cubes and 3.73s out back. But it will lose it's fun factor with each gear-change. And it will not do well at the track.
-Finally let's put it behind a hot 360 that want's to be shifted at 7000. the Rpm drop will be 7000 x .575 = to 4025. And the power band will need to be from 4025 to 7000 = about 3000Rpm. This is unrealistic for performance. Of course you can still drive it on the street, for the same reasons as the last combo, but it will be kindof a slug compared to what it could be with a tighter tranny gearset. And forget about racing it; The cam is impossibly large for these ratios.
-So you see what I did here; starting with a low rpm engine and working up in 1000rpm steps, and showing how this tranny works with different engines and applications, all the while keeping the starter gear constant at 11.53. This is an excellent all-round starter gear for all Sbms and the slanty does ok with it as well.It is the same starter gear as 11.53/2.66 = 4.30s with the standard 2.66low box
Typically 4.30s are the go-to gear for running from 115 to 125mph with a SBMs. However,with this box you have to get there with just 3 gears,so you better have some serious power.
Long story short is this; this ratio loses it's appeal with engines that need to really wind up.It works best with low rpm engines like slantys and stockish teeners.
So let's move on.
The ratios are 3.09-1.67-1.0-(.71/.73) and the splits are .54-.60-.71/.73 hereafter .71
-Say you have a slanty that rarely sees 4000rpm.If you put this box behind it, and want to cruise at 2000/60mph, then you will need 3.73 gear.This will get you a nice 11.53 starter gear, and a 2.68FD (Final Drive).So that's a double win so far.Next let's work the splits; Let's use .575 as an average % drop. Shifting into 2nd from 4000/1st, the Rs will drop TO 57.5% of 4000, so to 2300. the powerband will thus need to be from 2300 to 4000 equals 1700rpm. This is very doable in this application
-Now let's put this same stuff behind a stockish teener.This baby might want to be shifted at 5000. So the rpm drops to 5000 x .575 = 2875; and the power band is thus from 2875 to 5000 =2125rpm, still doable.
-Next, let's put this behind a 360 that want's to be shifted at 6000. the rpm will drop to 6000 x .575 = 3450;and the powerband will need to be from 3450 to 6000 = 2550. This is getting tougher. This combo will need a cam that provides a long power curve, which usually means some sacrifice in specific output. So now begins the compromising. It will still work on the street cuz it has 360cubes and 3.73s out back. But it will lose it's fun factor with each gear-change. And it will not do well at the track.
-Finally let's put it behind a hot 360 that want's to be shifted at 7000. the Rpm drop will be 7000 x .575 = to 4025. And the power band will need to be from 4025 to 7000 = about 3000Rpm. This is unrealistic for performance. Of course you can still drive it on the street, for the same reasons as the last combo, but it will be kindof a slug compared to what it could be with a tighter tranny gearset. And forget about racing it; The cam is impossibly large for these ratios.
-So you see what I did here; starting with a low rpm engine and working up in 1000rpm steps, and showing how this tranny works with different engines and applications, all the while keeping the starter gear constant at 11.53. This is an excellent all-round starter gear for all Sbms and the slanty does ok with it as well.It is the same starter gear as 11.53/2.66 = 4.30s with the standard 2.66low box
Typically 4.30s are the go-to gear for running from 115 to 125mph with a SBMs. However,with this box you have to get there with just 3 gears,so you better have some serious power.
Long story short is this; this ratio loses it's appeal with engines that need to really wind up.It works best with low rpm engines like slantys and stockish teeners.
So let's move on.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Now let's consider the 2.47 box.
the ratios are; 2.47-1.77-1.34-1.00 and the splits are 71.6-75.7-74.6 let's use 75%
I'll give you the short version first;
This box is for roadracing,
And for weekend bombers, and only if you can tune your engine to work with it, and not let it detonate itself to death. A lot of time and skill will be required.
Now the AJ version;
To get a cruise rpm of 2000@60 you will need 2.73s. Ok, we're in trouble already, cuz 2.73 x 2.47 = a 6.74 starter gear. So let's start over; to get a nice starter gear close to 11.5 we need 4.66 gears. Oops, you see where this is going right. Ok so let's compromise. #1 this box is out for cruising and out for DDs. That leaves racing and weekend bombers.For racing, and the go-to 4.30s you are left with 4.3 x 2.47 = a 10.62 starter gear. This will need a lot of clutch and a lot of launch rpm. Not the best idea, so that leaves just the bomber. Let's make it work.
We are gonna use the 4.30s. The starter gear is 10.62 and the cruise rpm will be about [email protected] earplugs.
Now the splits; Since it's a bomber we can put some cam into it, so let's say it power peaks at 5500and it wants to be shifted at 6300. Let's work it out;6300 x .75 = 4725 the drop-in rpm,so the powerband will need to be from 4725 to 6300 =1575 Boy-O-boy we're on to something!
So we can put a real tight LDA on that cam, and get some pretty good specific power out of it, and this combo will rock the quarter! Finally some good news.
Or is it?
The thing about this combo in a streeter is compression. An engine built like this, with the tight LDA will tend to build a lot of Dcr, with just a small Scr. So, detonation will be an ever-present possibility. It will always need the best gas, and a very well controlled timing curve.
The 4.30s will get old in a hurry. In city driving the constant shifting will soon wear thin, and you will wonder what you were thinking! But you are into it now for thousands of dollars and dozens of hours and you will not want to spend even more money on it.Before long it will be parked in the garage, and just occasionally raced...with high octane,high-dollar, race-gas. Cuz really that's all this combo is good for.
IMHO, I would not want this combo. I sold my 2.47 box a very long time ago.
the ratios are; 2.47-1.77-1.34-1.00 and the splits are 71.6-75.7-74.6 let's use 75%
I'll give you the short version first;
This box is for roadracing,
And for weekend bombers, and only if you can tune your engine to work with it, and not let it detonate itself to death. A lot of time and skill will be required.
Now the AJ version;
To get a cruise rpm of 2000@60 you will need 2.73s. Ok, we're in trouble already, cuz 2.73 x 2.47 = a 6.74 starter gear. So let's start over; to get a nice starter gear close to 11.5 we need 4.66 gears. Oops, you see where this is going right. Ok so let's compromise. #1 this box is out for cruising and out for DDs. That leaves racing and weekend bombers.For racing, and the go-to 4.30s you are left with 4.3 x 2.47 = a 10.62 starter gear. This will need a lot of clutch and a lot of launch rpm. Not the best idea, so that leaves just the bomber. Let's make it work.
We are gonna use the 4.30s. The starter gear is 10.62 and the cruise rpm will be about [email protected] earplugs.
Now the splits; Since it's a bomber we can put some cam into it, so let's say it power peaks at 5500and it wants to be shifted at 6300. Let's work it out;6300 x .75 = 4725 the drop-in rpm,so the powerband will need to be from 4725 to 6300 =1575 Boy-O-boy we're on to something!
So we can put a real tight LDA on that cam, and get some pretty good specific power out of it, and this combo will rock the quarter! Finally some good news.
Or is it?
The thing about this combo in a streeter is compression. An engine built like this, with the tight LDA will tend to build a lot of Dcr, with just a small Scr. So, detonation will be an ever-present possibility. It will always need the best gas, and a very well controlled timing curve.
The 4.30s will get old in a hurry. In city driving the constant shifting will soon wear thin, and you will wonder what you were thinking! But you are into it now for thousands of dollars and dozens of hours and you will not want to spend even more money on it.Before long it will be parked in the garage, and just occasionally raced...with high octane,high-dollar, race-gas. Cuz really that's all this combo is good for.
IMHO, I would not want this combo. I sold my 2.47 box a very long time ago.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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And finally the standard 2.66 box.
The ratios are 2.66-1.92-1.40-1.00 and the splits are 62-72.7-71.7 let's say 72%
This box is middle of the road and can be adapted to most applications and engines. I guess that's why it exists.Now that you know how to work the % splits and the powerbands, I will leave you to bench-build a motor for your application.......
Naw, I can't do it! Here we go...
Let's say you want a nice 360 street-rod with plenty of bottom end and want a reasonable cruise rpm.
I have what I think is an awesome combo, so I'll pass it along. It has a 230/237/110 cam, that power peaks around 5600. I have the 3.09low version of this box and can use 3.23 gears. So the starter gear is 3.09 x 3.23 = 9.98 nice enough. (This is equivalent to 3.73s with the 2.66low.) cruise is 2400@60mph. So far,so good. Now the splits; This combo wants to be shifted at 6500, to drop in at 6500 x .72 =4680, and the powerband will need to be from 4680 to 6500 =1820rpm . This is Bang-On easy.I use a 110LDA cam, cuz it was off the shelf. But this cam makes a power-curve as wide and flat as Saskatchewan and is not the best match for the track.As a streeter tho, it is incredibly fun to drive cuz there is never any waiting for the power hit. Just hammer down and hang on.
But if I was to track it, or make a weekend bomber out of it, I would tighten up the LDA to 106 or maybe 104, and add a little duration and a tad more gear. I would be targeting 114mph, cuz I'm not mph-greedy or into spending big-money. I would be trapping in 3rd gear@ about 6800, so 3.55s it would be. I already know it won't ET well with this combo, and I would be ok with that. Then it would be just a matter of getting the weight down to make the speed.
So there you have it; the almost complete guide to the A833.
The ratios are 2.66-1.92-1.40-1.00 and the splits are 62-72.7-71.7 let's say 72%
This box is middle of the road and can be adapted to most applications and engines. I guess that's why it exists.Now that you know how to work the % splits and the powerbands, I will leave you to bench-build a motor for your application.......
Naw, I can't do it! Here we go...
Let's say you want a nice 360 street-rod with plenty of bottom end and want a reasonable cruise rpm.
I have what I think is an awesome combo, so I'll pass it along. It has a 230/237/110 cam, that power peaks around 5600. I have the 3.09low version of this box and can use 3.23 gears. So the starter gear is 3.09 x 3.23 = 9.98 nice enough. (This is equivalent to 3.73s with the 2.66low.) cruise is 2400@60mph. So far,so good. Now the splits; This combo wants to be shifted at 6500, to drop in at 6500 x .72 =4680, and the powerband will need to be from 4680 to 6500 =1820rpm . This is Bang-On easy.I use a 110LDA cam, cuz it was off the shelf. But this cam makes a power-curve as wide and flat as Saskatchewan and is not the best match for the track.As a streeter tho, it is incredibly fun to drive cuz there is never any waiting for the power hit. Just hammer down and hang on.
But if I was to track it, or make a weekend bomber out of it, I would tighten up the LDA to 106 or maybe 104, and add a little duration and a tad more gear. I would be targeting 114mph, cuz I'm not mph-greedy or into spending big-money. I would be trapping in 3rd gear@ about 6800, so 3.55s it would be. I already know it won't ET well with this combo, and I would be ok with that. Then it would be just a matter of getting the weight down to make the speed.
So there you have it; the almost complete guide to the A833.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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And now a short rant.
With just 4 gears, there's a lot of compromising going on to make the A833 work the way you want it to, or need it to. It would be just so much easier with one more gear. And I see they are coming.
I would like to see a tranny something like this;
The ratios; 2.95-1.76-1.24-1.00-.68 and the splits; .60-.70-.80-.68
If you run 4.30s with this, you will have a starter gear of 12.68, and a cruise rpm of 2180 at 60mph.Third will get you 95@6100. and Direct 4th will get you 118@6300
But remember this one thing; you will be outshifting 3rd at 102mph@6500, so 4th only needs to pull from 102 to 118, and from about 5500 to 6300. Did you see that? An 800rpm pull right through the heart of the power peak ! And did you also see 3rd gear? Almost the perfect tranny; A really nice starter gear(if a little high for a streeter),excellent cruise gear,a pretty good trans for both 1/8th and 1/4 mileing.Oh and a really really nice 1-2.Think zero to 60mph.60mph will be 5650 in 2nd. Pretty sweet.
This might not be the perfect tranny, but IMHO it would be a great street tranny that could track pretty good too, certainly far better than any A-833.
A quick comparo with 4.30s; the FD will look like this;
the 5spd, 12.68-7.57-5.33-4.30-2.92, and the splits; .60-.70-.80-.68
the 4spd, 11.44-8.26-6.02-4.30-none, and the splits; .72-.73-.71 this is the 2.66low
Ok, drive thru
With just 4 gears, there's a lot of compromising going on to make the A833 work the way you want it to, or need it to. It would be just so much easier with one more gear. And I see they are coming.
I would like to see a tranny something like this;
The ratios; 2.95-1.76-1.24-1.00-.68 and the splits; .60-.70-.80-.68
If you run 4.30s with this, you will have a starter gear of 12.68, and a cruise rpm of 2180 at 60mph.Third will get you 95@6100. and Direct 4th will get you 118@6300
But remember this one thing; you will be outshifting 3rd at 102mph@6500, so 4th only needs to pull from 102 to 118, and from about 5500 to 6300. Did you see that? An 800rpm pull right through the heart of the power peak ! And did you also see 3rd gear? Almost the perfect tranny; A really nice starter gear(if a little high for a streeter),excellent cruise gear,a pretty good trans for both 1/8th and 1/4 mileing.Oh and a really really nice 1-2.Think zero to 60mph.60mph will be 5650 in 2nd. Pretty sweet.
This might not be the perfect tranny, but IMHO it would be a great street tranny that could track pretty good too, certainly far better than any A-833.
A quick comparo with 4.30s; the FD will look like this;
the 5spd, 12.68-7.57-5.33-4.30-2.92, and the splits; .60-.70-.80-.68
the 4spd, 11.44-8.26-6.02-4.30-none, and the splits; .72-.73-.71 this is the 2.66low
Ok, drive thru
joeboy
Well-Known Member
Wow. That is all.
Joe
Joe
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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You are feeling it, aren't you?
2.66 x 3.23 =8.59. This is a pretty tall startergear. It works for you because of the mild roller-cam.if you were to go up two cam sizes or so to 240*, you might be begging for more rear gear; perhaps 3.73s or better. If you had a flat tappet cam, you would probably be looking for 3.55s. If you had a 360, it would be a non-issue with that cam.
In 64 or 65 Mopar put a 3.09 low in that box, behind 273s. None of the gears swap around.
In 1970 IIRC the T/A set came out with the 2.47 low set.I think it was E-bodies only.IDK
weedburner
Well-Known Member
Here's something that can throw a kink in gear calculations when it comes to predicting rpm drops at the track. Here is a graph from a NMRA factory stock racer using one of my ClutchTamers to control clutch slip.
...the dark blue line is the actual trace from the run.
...the added lite blue line represents calculated rpm drops based on the ratios in the transmission.
As you can see, straight gear calculations do not account for clutch slip. On the above 1/2 gearchange, actual rpm drop was a little over 1000rpm less than the calculation predicted. On the 2/3 shift, the difference was around 650rpm, 3/4 shift was around 375 less rpm drop than predicted. Of course if the clutch would have locked up quickly the drops would have been closer to the predictions, but it would have taken longer for the car to complete the run as the engine would have had to work it's way back up from a lower rpm after the shifts.
Quicker clutch lockup would not only result in a slower run, but the quick engagement would also pass along more abuse to your transmission/drivetrain.
...the dark blue line is the actual trace from the run.
...the added lite blue line represents calculated rpm drops based on the ratios in the transmission.
As you can see, straight gear calculations do not account for clutch slip. On the above 1/2 gearchange, actual rpm drop was a little over 1000rpm less than the calculation predicted. On the 2/3 shift, the difference was around 650rpm, 3/4 shift was around 375 less rpm drop than predicted. Of course if the clutch would have locked up quickly the drops would have been closer to the predictions, but it would have taken longer for the car to complete the run as the engine would have had to work it's way back up from a lower rpm after the shifts.
Quicker clutch lockup would not only result in a slower run, but the quick engagement would also pass along more abuse to your transmission/drivetrain.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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I was hoping you would show up!
j par
Well-hung Member
I knew we could count on AJ/FormS for the short version... LOL :burnout:
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Thx J
I thought I did a pretty good job of editing and condensing and revising and organizing, and breaking it up into sections and not including all the rabbit-trails, nor confusing it with multiple pumpkins,.....e....t.....c
I thought I did a pretty good job of editing and condensing and revising and organizing, and breaking it up into sections and not including all the rabbit-trails, nor confusing it with multiple pumpkins,.....e....t.....c
j par
Well-hung Member
AJ thank you for taking my comments in their intended light.
rmchrgr
Skate And Destroy
I was just talking about gear splits on Moparts the other day in regards to my D100. I would like to have a closer ratio trans in the truck, it's an NP435 behind an over-cammed, stock long-block 400 with 3.23 rear gears. It's about the worst combo you could come up with (I didn't)
In regards to the trans, there is a 50% ratio drop between each gear. The cam starts working at higher rpms so there is very little torque down low. It can be tricky to keep the truck in the power band in traffic when you have to shift. You're either revving the piss out of it or it falls flat on it's face in the next gear. Drives me nuts.
To the OP, whatever 'pass car' trans you have with whatever 1st gear ratio is in it, stay with it and be happy you don't have a gearbox designed for a farm tractor like me. :burnout:
I went over to Wallace Racing to get a better idea of why I was hating my truck. The numbers speak for themselves. Click here for the calculator.
Gear Shift Drop Calculator
RPM: 3,000
Rear Gear Ratio: 3.23
Tire Diameter: 28"
Gears in Tranny:
1st Gear Ratio: 6.68:1
2nd Gear Ratio: 3.34:1
3rd Gear Ratio: 1.66:1
4th Gear Ratio: 1.00:1
After 1st Shift: 1,500 RPM. 50.00 % RPM Drop
After 2nd Shift: 1,491 RPM. 50.30 % RPM Drop
After 3rd Shift: 1,807 RPM. 39.76 % RPM Drop
1st Gear is 11.59 MPH at 3000 RPM
2nd Gear is 23.17 MPH at 3000 RPM
3rd Gear is 46.63 MPH at 3000 RPM
4th Gear is 77.40 MPH at 3000 RPM
In regards to the trans, there is a 50% ratio drop between each gear. The cam starts working at higher rpms so there is very little torque down low. It can be tricky to keep the truck in the power band in traffic when you have to shift. You're either revving the piss out of it or it falls flat on it's face in the next gear. Drives me nuts.
To the OP, whatever 'pass car' trans you have with whatever 1st gear ratio is in it, stay with it and be happy you don't have a gearbox designed for a farm tractor like me. :burnout:
I went over to Wallace Racing to get a better idea of why I was hating my truck. The numbers speak for themselves. Click here for the calculator.
Gear Shift Drop Calculator
RPM: 3,000
Rear Gear Ratio: 3.23
Tire Diameter: 28"
Gears in Tranny:
1st Gear Ratio: 6.68:1
2nd Gear Ratio: 3.34:1
3rd Gear Ratio: 1.66:1
4th Gear Ratio: 1.00:1
After 1st Shift: 1,500 RPM. 50.00 % RPM Drop
After 2nd Shift: 1,491 RPM. 50.30 % RPM Drop
After 3rd Shift: 1,807 RPM. 39.76 % RPM Drop
1st Gear is 11.59 MPH at 3000 RPM
2nd Gear is 23.17 MPH at 3000 RPM
3rd Gear is 46.63 MPH at 3000 RPM
4th Gear is 77.40 MPH at 3000 RPM
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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jpar
By now I know you already.I know you like me.I enjoy all your ribbing, so fire away!
By now I know you already.I know you like me.I enjoy all your ribbing, so fire away!
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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rmchgr
I feel for you. You have my sympathy.
That's a terrible street set up. IIRC there are several ratios for that 435 box as well.But they all have that granny gear, to get the loaded grain-trucks off the soft dirt fields. I used to build those in batches. They got some funky synchronizers in them.
I feel for you. You have my sympathy.
That's a terrible street set up. IIRC there are several ratios for that 435 box as well.But they all have that granny gear, to get the loaded grain-trucks off the soft dirt fields. I used to build those in batches. They got some funky synchronizers in them.
rmchrgr
Skate And Destroy
Thanks but I was the grade A mo-ron who bought the truck with that setup.
I have an 833 OD on the shelf that needs rebuilt, gonna put that in once I find the rare and expensive bell to mate it to the BB.
It really is a poor choice for a street machine. Some people say the granny low is good for getting a load going but I can't see how it's useful for towing on a regular road surface. I won't be pulling a trailer out of the mud, just my driveway.
1st gear is not synchronzed, presumably because it was limited for use in situations where you would need the grunt but no road speed. It's almost like an add-on gear, like it's there if you need it. I take off in second.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Careful now
your current ratios are 3.34-1.66-1.00 (granny not included).
The 833 O/D ratios are 3.09-1.67-1.00 (od not included)
You might be trading one big pos for a little pos.
your current ratios are 3.34-1.66-1.00 (granny not included).
The 833 O/D ratios are 3.09-1.67-1.00 (od not included)
You might be trading one big pos for a little pos.
rmchrgr
Skate And Destroy
Huh, interesting. Did not realize they were so similar!
But... even though the ratios are almost the same, the NP435 and 833 OD are totally different in terms of character. The 833 has a usable 1st gear and the OD allows a steeper rear gear (mitigated for highway driving with the OD) which would obviously help with torque multiplication in gears 1-3. I do a lot of highway driving with my truck but I need the steeper gear too because it's a heavy vehicle that tows sometimes. Only real option for anything like that with a 435 is to put a Gear Vendors behind it but you are still saddled with that giant, unwieldy shifter.
I could see how I'd potentially wind up in the same situation with the 833OD where I'm at the practical rpm limit for a given gear and have to shift into a higher gear where it falls flat. Again though, a steeper rear gear would help keep it closer to where the rpm needs to be so the drop may not be as noticeable.
vntned
Well-Known Member
I personally hate my A833 OD, except when on the interstate cruising at 70mph. My combo isn't optimal however. I've got the OD behind a stock 170cuin slant six, 3.55 rear gear and 24" tires. First gear isn't bad, the jump to second is a bit much, going to 3rd feels like you missed a gear, and going to 4th is useless if less than 55mph.
I'm sure it would be better if I had the torquier 225, or a steeper rear gear.
I'm sure it would be better if I had the torquier 225, or a steeper rear gear.
rmchrgr
Skate And Destroy
I agree, your combo is not optimal. Only way to solve it is to put a cam in it that generates more torque at a lower rpm to compensate for the large drop in rpm between shifts or switch to a steeper rear gear to help with torque multiplication. Or ditch the Slant altogether and build a small-block stroker...
Honestly, I never fully understood what 'torque down low' meant until I experienced it first hand at cruising speed in my truck. When a car falls on it's face after a gear change it's because of lack of torque, plain and simple.
My Duster suffered from a lack of torque but in a different manner which was off the line. It's a manual valve body automatic and it had a low gear set in it; 2.74 1st, 1.54 2nd. Motor was a high-winding 340 which did not generate big torque 'down low'. Once you were past 2,500 rpm (which was like instantly), you were off and it pulled hard to 7,200 and the torque didn't matter so much.
But, it definitely needed a steep rear gear to get it out of the hole. My 60ft times at the track suffered some when I took out the 4.30 gear and put a 4.10 in it, even though it was only a 5% change. I drove the car 80 miles one way to the track through NYC traffic so a 4.30 gear was not practical. 4.10 was about the absolute limit but the trade off hurt the overall combo.
Just to add a note here. Sometimes we fight an uphill battle with parts that were designed 40 years ago for every day driving. Factory engineering in passenger cars is and has always been a compromise and/or trade off between a certain amount of performance, comfort, drivabilty and economy. Performance does not generally come without some degree of noise, vibration and harshness. These things are a big factor to car makers, people hate N/V/H. I was a dealership tech for several years, most of the complaints that came in had to do with one of these conditions. We had several classes training us about NVH.
So to decrease complaints and unnecessary service, car makers design stuff so people literally don't notice the car when they are driving it. You definitely notice when a car is built without compromise - lumpy cams, loud exhaust, gear noise, neck-snapping shifts at speed, stiffer suspensions and way more mechanical noise. It's a totally different driving experience which requires more attention than your average driver is willing to devote to their car. Performance always suffers because of this because you wind up with a compromised combination of parts.
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