Some quick rear end gearing advice please.

[MxRacer855]

I just ordered a Dana 60 rear end from Strange Engineering for my '68. It will take them about a month to build (so I have a small window to change a few options if I decide). I thought everything out and I am pretty much satisfied with my order. The only thing in question is gearing...

My 8-3/4" stock rear end was trashed. The gears were beyond worn as well. The guy I sold the housing to said it had 2.7??? gears in it, which is all highway! I'm building a street car that's going to put out around 700-50 hp. I want a street car that has a lot of torque, but a good mixture of top end as well. I went with 3.73's and am wondering if I should have them put in 4.11's...

Opinions please.

Jeff

[Charger4404spd]

If your going to be doing some highway driving I wouldnt go with the 4.11. Personally Id go with 3.54 or there abouts.

[68X426]

3.54 and 3.73 are practical and will deliver in most driving conditions. Anything higher will take the practicality out of a street car.

Dana 60 with 4.10s and a Gear Vendor overdrive is a perfect combo, but 4.10 alone is no fun. 

[Ghoste]

Oh I don't know.  I've had plenty of fun with my 4:10's on the street. 

[Cooter]

With that much power, the TORQUE should be on up there as well and you don't need deep gears when you have enough motor.
No motor, and you have to gear the hell outta it.
3.54:1 will have massive traction problems with 650-700 ft. Lbs of torque.

[XH29N0G]

With that much power, the TORQUE should be on up there as well and you don't need deep gears when you have enough motor.
No motor, and you have to gear the hell outta it.
3.54:1 will have massive traction problems with 650-700 ft. Lbs of torque.

[MxRacer855]

Thanks guys. It's going to be a stock 440 for another year (which I will be driving with), but all of the plans are based off the main goal (give or take 700hp). I am going to be running a built 3 speed 727 in it with a shift kit. I should have included that before... without any overdrive or additional gears, I was worried that anything higher that a 3.73 wouldn't go above 80mph, haha.

So the big question is, if I stick with the 3.73's, and run them with my currently stock 440, is there going to be a very noticeable difference coming from the 2.7?'s???

Jeff

[XH29N0G]

I think you will notice a difference.  What you are doing in a real sense is like changing the ratio on all gears by a factor of 3.73/2.76 =1.37) which will make 1st feel different, and will make 2nd and third feel like 1st and second do now.  Your 1st gear is something like 2.45:1 (the change in rear is like changing that to 3.35:1), Second is something like 1.45:1 and this will be like changing it to 1.98:1 (in between your present 1st and second).  Third will be like changing to 1.37:1 (in between 2nd and third.  Your transmission will shift sooner, but the lower gears will transmit more torque to your drive wheels.  You are talking about a factor about about 1.37 (which is quite a bit).  

[MxRacer855]

Being as specific as that was, it actually really put the answer to my question in perspective! I'm really looking forward to the rear end now. I cannot wit to feel the difference. I'm hoping that first gear just slams me back into the seat, and second and third pull really hard but still have a decent top end on fast, highway type settings.

Thanks a lot! I'm definitely going to stick with the 3.73's. The rear end that I bought Is a Dana 60 from Strange Engineering (like I said), so S-60 being built to stock 8-3/4" specs. I wanted the same setup, just much more durable and with different gearing. Really I wanted to just start fresh vs. rebuilding my old Mopar one. It's obviously coming with 35 spline axles, and Wilwood calipers and rotors (solid) on both sides. They're powder coating it black as well. I ordered it on Monday, and they estimated the finished product around the 5th of Jan. Once I get that in, I'll give them the dimensions they need to build me the driveshaft. I cannot wait!  ;

Jeff

[ws23rt]

With that much power, the TORQUE should be on up there as well and you don't need deep gears when you have enough motor.
No motor, and you have to gear the hell outta it.
3.54:1 will have massive traction problems with 650-700 ft. Lbs of torque.

Again you are here with a reality check.

[MxRacer855]

Any idea how much top speed I'm going to lose? Not that I have even gotten above 110 with it (in which it was still pulling hard, just began to "sway"). Just out of curiosity.

Jeff

[RallyeMike]

Given same tire size and rpm, a helluva lot slower:

2.76 x 110mph / 3.73 = 81.4mph

Of course, if you keep the same speedo gear and it was correct for 2.76 gears, your speedometer will say 148.6mph ! Whoo-hoo   

[metallicareload99]

Any idea how much top speed I'm going to lose? Not that I have even gotten above 110 with it (in which it was still pulling hard, just began to "sway"). Just out of curiosity.

Jeff

Probably more than you'd like.  Especially with an automatic tranny?

I went from 2.94's to 3.54 and I miss them to some degree.  That being said I probably wouldn't go back.
I try to keep the engine below 3000 rpm, and with that gearing it seems a little too slow.  I'm looking forward to bigger tires

http://users.erols.com/dmapes/GEARCLC.HTM

[Dino]

I went from 3.55 to 2.96 and will not go back until that T-56 is in the car!  I love those gears and yes the tires still spin at will.

[MxRacer855]

So it sounds like bigger tires will be the common ground. how big can I go without "tubbing" out or modifying my wheel wells? I plan on running Centerline Pro Convo's...

Rear: 15"x10"
Front: 15"x8"

Can I big enough tires (that don't make my car look like a dragster) on those rims to make up most of the top speed I'm going to be losing, keeping the torque of the 3.73's still?

[War wagon]

Being as specific as that was, it actually really put the answer to my question in perspective! I'm really looking forward to the rear end now. I cannot wit to feel the difference. I'm hoping that first gear just slams me back into the seat, and second and third pull really hard but still have a decent top end on fast, highway type settings.

Thanks a lot! I'm definitely going to stick with the 3.73's. The rear end that I bought Is a Dana 60 from Strange Engineering (like I said), so S-60 being built to stock 8-3/4" specs. I wanted the same setup, just much more durable and with different gearing. Really I wanted to just start fresh vs. rebuilding my old Mopar one. It's obviously coming with 35 spline axles, and Wilwood calipers and rotors (solid) on both sides. They're powder coating it black as well. I ordered it on Monday, and they estimated the finished product around the 5th of Jan. Once I get that in, I'll give them the dimensions they need to build me the driveshaft. I cannot wait!  ;

Jeff

I think you'll really like those gears and setup  
This past summer I had a similar setup built by bears performance. Used a S60 housing , 35 spline axles, Detroit locker, 3:73 gears.
Car cruises at 70mph at 3200rpm , with 275 rear tires.
Oh and I went with the slotted and drilled rear rotors from wilwood on the rear

[MxRacer855]

Sounds like a great setup War Wagon. Can I ask what trans your running? Also rear rim size?
Thanks

Jeff

[War wagon]

Sounds like a great setup War Wagon. Can I ask what trans your running? Also rear rim size?
Thanks

Jeff

I have a "built" 727 running full line pressure, reverse valve body, 4200 rpm stall speed converter from frank lupo.
My father has a belvedere running same rear with spool 4:10's and 5500 rpm stall , I decided to keep mine a little more street friendly LOL
Sorry rear rims are 15"

[MxRacer855]

Good deal! Thanks War wagon! Now I just have to be able to pick the right tire size that will work with my rear end (when I get my 15"x10" rear rims that is).

[MxRacer855]

Currently on my car, I have American Racing (Dukes of Hazzard) 15"x8" rims on all 4 tires with B.F. Goodrich Radial T/A's (P225/70R15) on all four of those rims.
In the latest issue of Mopar Muscle Magazine (Jan '12), there's an article called "Inspired Justice" featuring Robert Frost's '69 Charger SE R/T. He's running Center Line "Convo Pro" wheels (15"x6" in the front and 15"x10" in the rear). In the rear he's running Hoosier 295/50R15's. Do you think I can run that setup on my '68 with a stock setup? And will that make a big difference?

I apologize if I'm talking in circles a little bit..
Jeff

[Dino]

Currently on my car, I have American Racing (Dukes of Hazzard) 15"x8" rims on all 4 tires with B.F. Goodrich Radial T/A's (P225/70R15) on all four of those rims.
In the latest issue of Mopar Muscle Magazine (Jan '12), there's an article called "Inspired Justice" featuring Robert Frost's '69 Charger SE R/T. He's running Center Line "Convo Pro" wheels (15"x6" in the front and 15"x10" in the rear). In the rear he's running Hoosier 295/50R15's. Do you think I can run that setup on my '68 with a stock setup? And will that make a big difference?

I apologize if I'm talking in circles a little bit..
Jeff

The 295's will fit but the tire height is almost an inch less than what you are running now.  I stuck 275/45/17's under mine and raised the rear tires from 26 to 29". 

[MxRacer855]

I must be extremely confused on tire sizing. If I wanted to go an inch or so bigger... I would want the middle number to increase? So 70 to..80 or 90?

[Dino]

I must be extremely confused on tire sizing. If I wanted to go an inch or so bigger... I would want the middle number to increase? So 70 to..80 or 90?

The first number is the tires' width in millimeters.  This is roughly though.  Put two different brand 295's side by side and you'd be shocked at the different actual sizes.

The second number is the height of the sidewall calculated by ratio of the first number.  So a 295/50 is 295 mm wide with a sidewall of 147.5 mm.

Google tire height chart to find a bunch of them, listing all common tire sizes with their total height.  

[MxRacer855]

Thanks Dino. I guess since I have bigger rims and tires on my car as it is, I shouldn't have to worry about losing AS MUCH top speed in each gear as I could have. When the time comes to purchase rims and tires, I'm sure I'll inquire about it again. I just would like to find tires the same size or an inch or two taller to go on those 15"x10" rims I'm going to get. Hopefully they fit!

Jeff

[Dino]

Thanks Dino. I guess since I have bigger rims and tires on my car as it is, I shouldn't have to worry about losing AS MUCH top speed in each gear as I could have. When the time comes to purchase rims and tires, I'm sure I'll inquire about it again. I just would like to find tires the same size or an inch or two taller to go on those 15"x10" rims I'm going to get. Hopefully they fit!

Jeff

If backspacing is 5 - 5.5", they will fit.  I wanted a 2" difference in height front to back, which is why I got the tires I did.  There are several tire combos I like but I prefer a rake.  Others like the same size everywhere like a 245 or 255 all around.  If I would install 15" rims they would have 235/60 on the front and 275/60 on the back to get the rake I like.  A 245/60 on the front looks real nice as well and is still almost 1.5" shorter than the 275/60. 

My best advice is to look at Chargers until you see the size combo you like.  Then all you have to do is hope he will tell you what sizes he's running.