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View Full Version : The benefits of overdrive



67440Dodge
01-26-2013, 09:30 PM
With 3.91 gears and 3spd auto
587

3.55 gears and 6-spd auto
588

ws27
01-26-2013, 10:32 PM
You forgot to mention the computer controlled engine management which will allow higher load/torque at lower RPM. I don't think we can do that with our old engines they'll knock themselves apart.

Besides, they won't sound as awsome.

67r/t4speeder
02-17-2015, 03:25 PM
I am still planning some sort of OD in Max. I think the kits are still $2,000 for a OD 4th

85mph 2100 rpm wow Mike I likey

markz
02-17-2015, 03:30 PM
Oh yeah baby! My new GTX build is getting a Gear Vendor's OD! It will drop the 4.56 gears to an equivalent 3.55.............

67r/t4speeder
02-17-2015, 03:35 PM
This going to be the drive it to the track race it drive it home car Mark?

markz
02-17-2015, 04:07 PM
This going to be the drive it to the track race it drive it home car Mark?

That is the plan! I tow the race car daughter drives the GTX.

honcho
02-17-2015, 09:17 PM
Yea overdrive is so awesome

thebankerstoy
02-18-2015, 09:17 AM
I know very little about these new OD units, so please excuse what might seem like a stupid question by those who have researched these units, but I'm a bit confused about one thing concerning these OD units for our older muscle cars. I run a 3.91 gear ration in my 66 Coronet and Mark says that he will be running a stout 4.56 gear ratio, so won't there be a fair amount of heat build up on our older rear differentials with lower gear ratios even with an OD unit in place when running at highway speeds on longer trips? The engine will be running at a lower rpm range, but those healthy rear gears will still be spinning at their usual rate per rear tire revolution, so how will the extra heat be dissipated?

Richard

markz
02-18-2015, 01:45 PM
I know very little about these new OD units, so please excuse what might seem like a stupid question by those who have researched these units, but I'm a bit confused about one thing concerning these OD units for our older muscle cars. I run a 3.91 gear ration in my 66 Coronet and Mark says that he will be running a stout 4.56 gear ratio, so won't there be a fair amount of heat build up on our older rear differentials with lower gear ratios even with an OD unit in place when running at highway speeds on longer trips? The engine will be running at a lower rpm range, but those healthy rear gears will still be spinning at their usual rate per rear tire revolution, so how will the extra heat be dissipated?

Richard

Very good point but I will be running very close to the same highway speed just the engine rpm will be lower. I will be running 4:56 gear because the tires that showed up today are 30 inches tall. Without the OD I would be turning around 3350 RPM at 65 mph. With the OD it will be around 2600 rpm.

So I don't believe additional heating will be factor.

thebankerstoy
02-18-2015, 02:57 PM
I'd be a bit worried with that 4.56 gear ratio driving longer distance trips myself Mark, but I will be very interested in hearing how this set-up works out for you. I hope that you will update us after it's all in place and will let us know how you like it.

Richard

65rbdodge
02-19-2015, 06:30 AM
I have an 833od in my desoto with 323 gears I think it should have a very friendly rpm on the highway. I pulled an 89 a500 trans for any future project I might need it for.

67r/t4speeder
02-19-2015, 09:50 AM
I have an 833od in my desoto with 323 gears I think it should have a very friendly rpm on the highway. I pulled an 89 a500 trans for any future project I might need it for.

That should drop the Desoto down to near idle on freeway LOL

Joe mama
02-19-2015, 12:10 PM
I love the 5 speed tremec in my challenger. 2,700RPM @ 80 MPH with a 3:54 dana.

markz
02-22-2015, 10:51 PM
I'd be a bit worried with that 4.56 gear ratio driving longer distance trips myself Mark, but I will be very interested in hearing how this set-up works out for you. I hope that you will update us after it's all in place and will let us know how you like it.

Richard

Richard - you got me thinking so I did some research.

If I did my math right, some of the dually pickups have an equivalent of a 4.60 gear (equating tire size and my 4.56 gears) and I believe they use a Dana 60. If that is the case, then running a 4.56 with 30 inch tires should not be a reliability problem.

I will continue to try and figure out some of the dynamics going on in a hypoid rear and how the increased rpm affects heat and reliability. My good buddy is a good lubrication and gear expert - he will have comments I am sure. Will see him in a few weeks.

thebankerstoy
02-23-2015, 12:16 AM
Hello Mark,

The taller 30 inch rear tire diameter will help to reduce the rear tire revolutions per tire rotation for your 4.56 gear ratio set up.

What front tire diameter will you be running? If you're planning on running a 25 or 26 inch front diameter, that will give your car a nose down rake, which will give you some additional issues, such as a somewhat increased load on your front brakes on the street and it will affect your front to rear weight transfer during your launches at the starting line at the drag strip.

It will interesting to see what you find out with your additional research.

Richard

markz
02-24-2015, 07:34 PM
Hello Mark,

The taller 30 inch rear tire diameter will help to reduce the rear tire revolutions per tire rotation for your 4.56 gear ratio set up.

What front tire diameter will you be running? If you're planning on running a 25 or 26 inch front diameter, that will give your car a nose down rake, which will give you some additional issues, such as a somewhat increased load on your front brakes on the street and it will affect your front to rear weight transfer during your launches at the starting line at the drag strip.

It will interesting to see what you find out with your additional research.

Richard

Yup - right again. I am very concerned about the rake. I bought neutral Caltrac leaf springs and am seriously questioning why I didn't go -1". I was concerned about the tire hitting the top of the wheel house but we are modifying that and it appears that the wheel house is plenty tall enough - at least I think so.

Right now looking at a P225/70-R15 tire which is 27.4 inches tall. It will have rake but hopefully not too much................

thebankerstoy
02-25-2015, 10:25 AM
Very good Mark, please post pictures after all of the new parts are installed!

Richard

markz
02-25-2015, 08:34 PM
Car is almost done! rofl

They installed the gas tank mount today. I made the mount and they installed it. Looks like I got lucky on the design and it came out real good!


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