Slant Six Forum :: Rear End Ratio with an 833OD

Quote:

So it seems that with the 65 non-OD 833 a 3.23 or maybe a 2.94 rear end would be fine. If I ended up using the 833OD, the rear end ratio ought to be stepped up to at least a 3.55 or preferably 3.91 or 4.10 for all around in town and highway driving. Do I have this correct?

Consider the following approach to your problem...... think about starting from a dead stop on a hill:
1) I've been running a 2.94 rear in my 65 Dart with slant & 833 OD & seen gas mileage in hilly New England between 26 & 31 mpg depending on season & highway. At 70 mph the rpm is at 2100 ....slightly below the sweet spot for peak slant torque. At 75 it feels particuliarly strong. I never have to downshift from OD into 3rd if above 55 mph on any hill. I've run this combination just under 15000 miles......Consequently I think you need to consider starting up in first rather than cruising in 4th as the controlling decision maker. People running heavier Darts, Aspens, or Trucks may not get these results.

2) The factory provided the light weight 65 Dart's with slants with 3.55 rears (optionally with 3.23) when equipted with 4 speed manuals...1st gear in those manuals was 3.09. Consequently, assuming the factory knew something about getting the car underway on a hill from a dead stop then the 3.23 gear ratio was OK for those bent on good gas mileage & 3.55 was good for those wanting more pep starting up. With the emphasis in the 60's on performance the 3.55 was the stock rearend but the 3.23 was offered to improve the gas mileage.

3) The 833 OD also has a first gear ratio of 3.09 consequently it's possible that the 3.23 & 3.55 rear axle ratios would give the same pep for starting up but when put into 4th it's possible to get better gas mileage at a cruise.

Based on my experience I think you would be happy with the 3.23 if you live in a particuliarly hilly area but could go up or down from there depending on your position on pep versus gas mileage for your type driving. I can't imagine the need for a combined 833 OD & rear ratio higher than 3.55.

Author:	sandy in BC [ Thu May 03, 2012 5:59 pm ]
Post subject:
Nope....its a 4 speed with OD 3rd gear

Author:	SlantSixDan [ Thu May 03, 2012 6:42 pm ]
Post subject:
Nopeâ€¦it's a 5-speed with overdrive Reverse.

Author:	65 dartman [ Sat May 26, 2012 5:23 pm ]
Post subject:
So it seems that with the 65 non-OD 833 a 3.23 or maybe a 2.94 rear end would be fine. If I ended up using the 833OD, the rear end ratio ought to be stepped up to at least a 3.55 or preferably 3.91 or 4.10 for all around in town and highway driving. Do I have this correct?

Author:	DusterIdiot [ Sat May 26, 2012 6:26 pm ]
Post subject:	On the money...
Quote: Do I have this correct? Yes...

Author:	sandy in BC [ Sat May 26, 2012 7:15 pm ]
Post subject:
2800lb car ....26" tires ..... .70 OD ........3.55 gears works for me.

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Rear End Ratio with an 833OD https://slantsix.org/forum/viewtopic.php?t=48682	Page 2 of 2

Author:	DonPal [ Sat May 26, 2012 7:48 pm ]
Post subject:
Quote: So it seems that with the 65 non-OD 833 a 3.23 or maybe a 2.94 rear end would be fine. If I ended up using the 833OD, the rear end ratio ought to be stepped up to at least a 3.55 or preferably 3.91 or 4.10 for all around in town and highway driving. Do I have this correct? Consider the following approach to your problem...... think about starting from a dead stop on a hill: 1) I've been running a 2.94 rear in my 65 Dart with slant & 833 OD & seen gas mileage in hilly New England between 26 & 31 mpg depending on season & highway. At 70 mph the rpm is at 2100 ....slightly below the sweet spot for peak slant torque. At 75 it feels particuliarly strong. I never have to downshift from OD into 3rd if above 55 mph on any hill. I've run this combination just under 15000 miles......Consequently I think you need to consider starting up in first rather than cruising in 4th as the controlling decision maker. People running heavier Darts, Aspens, or Trucks may not get these results. 2) The factory provided the light weight 65 Dart's with slants with 3.55 rears (optionally with 3.23) when equipted with 4 speed manuals...1st gear in those manuals was 3.09. Consequently, assuming the factory knew something about getting the car underway on a hill from a dead stop then the 3.23 gear ratio was OK for those bent on good gas mileage & 3.55 was good for those wanting more pep starting up. With the emphasis in the 60's on performance the 3.55 was the stock rearend but the 3.23 was offered to improve the gas mileage. 3) The 833 OD also has a first gear ratio of 3.09 consequently it's possible that the 3.23 & 3.55 rear axle ratios would give the same pep for starting up but when put into 4th it's possible to get better gas mileage at a cruise. Based on my experience I think you would be happy with the 3.23 if you live in a particuliarly hilly area but could go up or down from there depending on your position on pep versus gas mileage for your type driving. I can't imagine the need for a combined 833 OD & rear ratio higher than 3.55.

Author:	Rug_Trucker [ Sun May 27, 2012 8:32 am ]
Post subject:
My OD came from a 74 Duster with a 225 and 2.74's. Never drove it as it was all out of the car. Must of had lots of top end!

Author:	65 dartman [ Mon May 28, 2012 11:23 am ]
Post subject:
Quote: Quote: So it seems that with the 65 non-OD 833 a 3.23 or maybe a 2.94 rear end would be fine. If I ended up using the 833OD, the rear end ratio ought to be stepped up to at least a 3.55 or preferably 3.91 or 4.10 for all around in town and highway driving. Do I have this correct? Consider the following approach to your problem...... think about starting from a dead stop on a hill: 1) I've been running a 2.94 rear in my 65 Dart with slant & 833 OD & seen gas mileage in hilly New England between 26 & 31 mpg depending on season & highway. At 70 mph the rpm is at 2100 ....slightly below the sweet spot for peak slant torque. At 75 it feels particuliarly strong. I never have to downshift from OD into 3rd if above 55 mph on any hill. I've run this combination just under 15000 miles......Consequently I think you need to consider starting up in first rather than cruising in 4th as the controlling decision maker. People running heavier Darts, Aspens, or Trucks may not get these results. 2) The factory provided the light weight 65 Dart's with slants with 3.55 rears (optionally with 3.23) when equipted with 4 speed manuals...1st gear in those manuals was 3.09. Consequently, assuming the factory knew something about getting the car underway on a hill from a dead stop then the 3.23 gear ratio was OK for those bent on good gas mileage & 3.55 was good for those wanting more pep starting up. With the emphasis in the 60's on performance the 3.55 was the stock rearend but the 3.23 was offered to improve the gas mileage. 3) The 833 OD also has a first gear ratio of 3.09 consequently it's possible that the 3.23 & 3.55 rear axle ratios would give the same pep for starting up but when put into 4th it's possible to get better gas mileage at a cruise. Based on my experience I think you would be happy with the 3.23 if you live in a particuliarly hilly area but could go up or down from there depending on your position on pep versus gas mileage for your type driving. I can't imagine the need for a combined 833 OD & rear ratio higher than 3.55. Interesting write-up and observations. Prior to my pulling the 65 slant/833 combo from a 65 Signet I bought, I drove it quite a bit. IIRC it had a 3.23 non-SG and was quite peppy off the line. On the highway it seems the revs were up there at 70MPH but not objectionable. Other than what I have read, I've never had any experiences with the OD version. There's not a lot of hills in my area so that should not be a factor. It's too bad that the non-OD uses the B & T. It would be interesting to be able to swap to the OD for comparison. I would estimate my driving would be about 30 to 40% in town and the remainder highway. Just a cruiser with no drag strip time.

Author:	rlklaus [ Mon May 28, 2012 1:48 pm ]
Post subject:
Just a follow up observation here. This is a bit of apples and oranges but. I have a 3/4 ton Maxi-Van with the 833 O/D trans, behind a lean burn 318, with a 3.21 rear. The power of the lean burn V-8 probably puts the power in the range of a well tuned slant six. I mentioned earlier that if you do the math, a very steep rear end (3.90 or 4.10 would give you close to the non overdrive freeway gearing. That being said. Since the Van tips the scales at close to 5,000 pounds, I don't see any reason to not go with 3.23s, and take advantage of the highway mileage that the 3.23s an 833 O/D would probably give you. On my 66 Valiant, I was going to jump through all the hoops to install one of the T-5s, and might yet go that way, but the ease of putting an 833 in there does have its appeal. Just for reference the van gets about 13 mpg around town, but can get very close to 20 mpg between cities. I would think a Dart or Valiant, being almost a ton lighter, would give some great highway mileage.

Author:	DonPal [ Mon May 28, 2012 6:09 pm ]
Post subject:
Quote: There's not a lot of hills in my area so that should not be a factor. It's too bad that the non-OD uses the B & T. It would be interesting to be able to swap to the OD for comparison. I would estimate my driving would be about 30 to 40% in town and the remainder highway. Just a cruiser with no drag strip time You would then be very happy with a 3.23 in the pep dept since your without hills a great deal of the time. Your "in town" driving would be mostly in 3rd if below 45 mph....although I'm in OD at 35 mph on a flat "in town" highway that doesn't need much acceleration with my 2.94....you'd be better. Finally when it comes to your highway driving you'd be in OD most of the time with a very quiet motor compared to one without OD. Wear & tear would be also less since you'd be down around 2000 rpm around 65 mph depending on tire diameter. Without the hills you would virtually avoid a downshift under any circumstance other than exiting off the highway. And you could pull off a decent improvement in gas mileage....throw in HEI, electric fan, etc. & you could be getting up close to my results...if not better because your driving conditions on the highway would be better. If you go with the 3.23 I'm thinking somewhere down the road you might consider the 2.94 for even better results...after you have enough time evaluating the 3.23 ratio against your expectations.

Author:	nuttyprof [ Mon May 28, 2012 7:01 pm ]
Post subject:
One thing to consider, the first gear in both od and non od trannys are the same so if first gear acceleration is ok with a non od it will be the same with od! However the shifts are bigger steps so you might want to bring the rpm up a little more when shifting. JMO.

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