Question about non OD 833 and rpm range

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ozmoparjoe

ozmoparjoe

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Hi guys, a while ago i swapped out my OD a833 for a non OD one, i believe it's a 1967 year and noticed a huge difference in 4th gear rpm at 60 mph. With the OD gearbox at 60 the rpm was at 2200, where as now it's at 3000 rpm. Diff gears are 3.45, tires are 26.6 inch, engine is 360 for what it's worth.
Just want to ask you guys if in your experience, you think this is normal?
Thanks.
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thats the way it works /4 th gear overdrive /gas savings /
 
ozmoparjoe said:
Hi guys, a while ago i swapped out my OD a833 for a non OD one, i believe it's a 1967 year and noticed a huge difference in 4th gear rpm at 60 mph. With the OD gearbox at 60 the rpm was at 2200, where as now it's at 3000 rpm. Diff gears are 3.45, tires are 26.6 inch, engine is 360 for what it's worth.
Just want to ask you guys if in your experience, you think this is normal?
Thanks.View attachment 1715895308 View attachment 1715895309 View attachment 1715895310
Click to expand...
Use the RPM calculator here: Calculate GEAR, RPM, MPH, TIRE DIAMETER
 
ozmoparjoe said:
yes i have done several of those and comes back as me having 3.9 diff gears or rpm should be around 2700, so im a little confused
Click to expand...
You probably have 3.91's and not 3.55's like you said. You can jack it up and turn the wheel while watching the driveshaft to confirm the ratio. Both wheels will turn the same direction with a Sure Grip.
 
toolmanmike said:
You probably have 3.91's and not 3.55's like you said. You can jack it up and turn the wheel while watching the driveshaft to confirm the ratio. Both wheels will turn the same direction with a Sure Grip.
Click to expand...
I will check tomorrow, diff is supposed to have 3.45 out of an Australian early 90's ford falcon
 
Sounds right to me. 440 4spd 354 dana 275/60 x15 tires 3000@60mph. In my area on country roads i4 spds are perfect. OD transmissions eliminate 3rd. which is needed on our roads. They actually go 1st-2nd-4th-OD. OD for economy, 4spd for performance. Passion 4spd with OD for both in one trans.
 
It’s all in the math.

4.10 X a 1-1 final trans ratio is still 4.10.
4.10 X a .71 OD trans ratio is a 2.91 final drive ratio.

Now proceed to a rpm calculator with your tire size for an approximate rpm at a given speed.

While I like the OD ratio of the MoPar trans, the gear splits IMO are a bit wacky for performance usage. The deep first gear makes any normal use performance ratio rear gear about useless and the rpm drop going into 2nd gear is a big drop.

For basic driving around town, it’s not so bad. A minor annoyance when you first get the new trans & ratios. But you really have to rev it up high to make the second gear shift work for you in any seriously hard acceleration attempt.

Having had this set up before, the move back to the standard 4spd and it’s gear set is a little bit of a bummer when you have that feeling of not having that OD gear to drop rpm’s.

My E body Cuda has 4.10’s on 28 inch tires and will cruise on the Hwy approximately at 3400 in the slow lane. This is somewhere around 65 mph. It’s been a while.

The hardest thing about the old cars is the final drive ratio of 1-1, the gear set and to a smaller degree, the tire size. It can be limiting.
 
Mathematically the difference is equal to the ratio difference .
So since the overdrive ratio is .73; and the standard is 1.00;
going from 2200 is;
2200/(.73/1.00) =3014rpm; right on target; speed remaining the same..

the ratios are ;
3.09--------1.67------1.00-- .73od versus
- -2.66--1.92--1.40--1.00 ; unless you got a close ratio, then
-- 2.47--1.77--1.33--1.00


the tires on that yellow Dart appear to me to be quite a bit taller than 26.6.
According to the math; for 60=3012 with 3.45s; those tires are 22.9 tall. Obviously; either 1)you don't have 3.45s. or 2) your speed-O is out.
If in fact those tires are 26.5; then the math points to about 4.00 gears.
But to me, those tires look to be more than 28 tall. If that was true, then the rear gear would have to be closer to 4.30s

Here is the Formula so you can figure it out for yourself;

Mph= (rpm x TR)/( 1056 x R1 X R2 x R3)
where;
Mph is Miles per hour
TR is Tire Rollout ( ~diameter times pi which is 3.1416)
R1 is the rear gear
R2 is the trans gear
R3 is any other multiplier you may have installed
1056 is a constant that spits out a usable number for Mph

Here is an example;
Mph= (rpm x TR)/( 1056 x R1 X R2 x R3)
For TR =26.5 x 3.1416 =83.252
and 3.45s
Mph=(3012observed x 83.252)/(1056 x 3.45 x 1.00) = 68.8 mph..
This would point to an error of 68.8/60=14.67%.. Could be the Speed-O, or could be the rear gears, and could possibly be complicated by an error in the TR. Or even in the tachometer.
 
Last edited:
AJ/FormS said:
Mathematically the difference is equal to the ratio difference .
So since the overdrive ratio is .73; and the standard is 1.00;
going from 2200 is;
2200/(.73/1.00) =3014rpm; right on target; speed remaining the same..

the ratios are ;
3.09--------1.67------1.00-- .73od versus
- -2.66--1.92--1.40--1.00 ; unless you got a close ratio, then
-- 2.47--1.77--1.33--1.00


the tires on that yellow Dart appear to me to be quite a bit taller than 26.6.
According to the math; for 60=3012 with 3.45s; those tires are 22.9 tall. Obviously; either 1)you don't have 3.45s. or 2) your speed-O is out.
If in fact those tires are 26.5; then the math points to about 4.00 gears.
But to me, those tires look to be more than 28 tall. If that was true, then the rear gear would have to be closer to 4.30s

Here is the Formula so you can figure it out for yourself;

Mph= (rpm x TR)/( 1056 x R1 X R2 x R3)
where;
Mph is Miles per hour
TR is Tire Rollout ( ~diameter times pi which is 3.1416)
R1 is the rear gear
R2 is the trans gear
R3 is any other multiplier you may have installed
1056 is a constant that spits out a usable number for Mph

Here is an example;
Mph= (rpm x TR)/( 1056 x R1 X R2 x R3)
For TR =26.5 x 3.1416 =83.252
and 3.45s
Mph=(3012observed x 83.252)/(1056 x 3.45 x 1.00) = 68.8 mph..
This would point to an error of 68.8/60=14.67%.. Could be the Speed-O, or could be the rear gears, and could possibly be complicated by an error in the TR. Or even in the tachometer.
Click to expand...
Impressive!
 
Oldmanmopar said:
Impressive!
Click to expand...
LMAO!


Not…. But I’ll be honest, it’s a PIA to do the math never mind remembering the way it gets done BUT the sites are out there and the information is in books currently available.

A thanks to AJ for the helping hand with the math.
 
rumblefish360 said:
It’s all in the math.

4.10 X a 1-1 final trans ratio is still 4.10.
4.10 X a .71 OD trans ratio is a 2.91 final drive ratio.

Now proceed to a rpm calculator with your tire size for an approximate rpm at a given speed.

While I like the OD ratio of the MoPar trans, the gear splits IMO are a bit wacky for performance usage. The deep first gear makes any normal use performance ratio rear gear about useless and the rpm drop going into 2nd gear is a big drop.

For basic driving around town, it’s not so bad. A minor annoyance when you first get the new trans & ratios. But you really have to rev it up high to make the second gear shift work for you in any seriously hard acceleration attempt.

Having had this set up before, the move back to the standard 4spd and it’s gear set is a little bit of a bummer when you have that feeling of not having that OD gear to drop rpm’s.

My E body Cuda has 4.10’s on 28 inch tires and will cruise on the Hwy approximately at 3400 in the slow lane. This is somewhere around 65 mph. It’s been a while.

The hardest thing about the old cars is the final drive ratio of 1-1, the gear set and to a smaller degree, the tire size. It can be limiting.
Click to expand...

To combat that I went with Passon OD gearset. Passon A833 Transmission - A Four-Speed Overdrive for Hemis

I just got it all together and hope to have it in the road soon.

Screenshot_20220325-124947.png


Screenshot_20220325-124931.png
 
Thanks for all the replies guys much appreciated.
So I checked the diff ratio and it is in fact 3.45:1.
Tyres are 245/60/15 making them a 26.6 inch tyre. So perhaps I can swap out the rear gears for 3.23 which would help with the freeway driving or I can just live with it.
Driving long distance at 3000 rpm shouldn't hurt the engine should it?
We have a huge mopar show here every year and it's about a 4 hr drive away.
I will be putting 28 inch tyres on it soon which should also help.
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Last edited:
I have never heard or seen a MP rear end stamped or offered with a 3.45 ratio. 3.55? Yes!
 
Overdrives have spoiled us.
Continued high ( to you ) rpm was normal .
A lotta these engines were used in industrial/commercial application where they powered generators, pumps, power boats, where the engines were started at start of shift, and ran @ 4000ish rpm all day, hour after hour, dock to dock.
 
inertia said:
Overdrives have spoiled us.
Continued high ( to you ) rpm was normal .
A lotta these engines were used in industrial/commercial application where they powered generators, pumps, power boats, where the engines were started at start of shift, and ran @ 4000ish rpm all day, hour after hour, dock to dock.
Click to expand...
Good point!
 
I drove mine 2 hrs one way with 456 gears and a 5500 stall. Couldn't even hear vocals on the stereo at full volume. I was constantly watching the temp and oil pressure. My wife said she would never go again and she never did. One thing that was good was I couldn't hear her either.
 
Oldmanmopar said:
I drove mine 2 hrs one way with 456 gears and a 5500 stall. Couldn't even hear vocals on the stereo at full volume. I was constantly watching the temp and oil pressure. My wife said she would never go again and she never did. One thing that was good was I couldn't hear her either.
Click to expand...
Hahaha love it...
 
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