Differential Recomendation

[daveh]

Hi Guys,

I'm considering switching my differential during the rebuild from my current 3.23 set up.  I'm running a mildly modified 340 with a Keisler 5 speed, TKO 600 and 255-60-15's in the rear.  What do you think, 3.55's or 3.91's?  Will I notice that much of a difference going from 3.23 to 3.55 if I go that route?  This will be purely street driven.  Whatever information you can give me is always appreciated.  Thanks

Dave

[msbaugh]

With the over drive 5 speed I would go for the 3.93s!! There's a 3.73 ratio too just harder to find. It'll make a pretty big difference and it'll be hell of a lot of fun street driving stop light to stoplight. Do you have an 8 3/4? Go with dr diff!! I got his third member with a Detroit true trac sure grip. I freaking love it!

[ToxicWolf]

Hi Guys,

I'm considering switching my differential during the rebuild from my current 3.23 set up.  I'm running a mildly modified 340 with a Keisler 5 speed, TKO 600 and 255-60-15's in the rear.  What do you think, 3.55's or 3.91's?  Will I notice that much of a difference going from 3.23 to 3.55 if I go that route?  This will be purely street driven.  Whatever information you can give me is always appreciated.  Thanks

Dave

I'm thinking the same thing. I don't know how to do the math, but I'm afraid that with the 3.23 I'll be going 70 or 80 at 1000 rpm with the 5th gear.

[daveh]

I had 3.73's in my 69 Z/28 and thought they were perfect.  I think the 3.55's just won't show that much of a difference over the 3.23's.  So if I can get 3.73's I'm going with those if not it's going to be the 3.91's.

[ToxicWolf]

I had 3.73's in my 69 Z/28 and thought they were perfect.  I think the 3.55's just won't show that much of a difference over the 3.23's.  So if I can get 3.73's I'm going with those if not it's going to be the 3.91's.

If you find the 3.73 let me know where I can get some too. 

[msbaugh]

One of those eBay guys had a couple I think last time I checked... They might add a hundred bucks or something since they're harder to get ahold of

[70CUDA4SPEED]

Give Scott a call, I have bought alot of stuff from him.
http://marketplaceadvisor.channeladvisor.com/storefrontprofiles/DeluxeSFItemDetail.aspx?sid=1&sfid=92390&c=0&i=236709383
http://marketplaceadvisor.channeladvisor.com/storefrontprofiles/DeluxeSFItemDetail.aspx?sid=1&sfid=92390&c=0&i=247875658

[daveh]

Thanks

[Chryco Psycho]

What is the ratio in 1st gear ?? you may find it low enough without swapping the rear gearing

[ToxicWolf]

What is the ratio in 1st gear ?? you may find it low enough without swapping the rear gearing

Rear is 3.23

First is 3.27

Second is 1.98

Third is 1.34

Fourth is 1.00

Fith is 0.68

FROM THE KEISLER SPECKS

I was just wondering what the rpm would be when we are at 65 mph in 5th gear. We have the same setup. I am concerned that the rpm in 5th gear may be too low at 60 to run in 5th without changing the rear end.

[brads70]

What is the ratio in 1st gear ?? you may find it low enough without swapping the rear gearing

Standard  1st gear is 3.27 road race and close ratio is 2.87
Depending on what tire your using your hwy rpms at 65 mph will be around 1800 rpm's which might be a little low depending on what your cam likes? ( it might " lug" at 1800 rpms)  mine does with the 4 speed auto OD engine is "happy" at 2400 and up, problem is that's about 75 mph for me and most guys in blue frown on that! 

I'd go with 3.91 as that will rev at about 2200 at 65 mph. If we were closer I'd lend you my 3.91 gear pot to try out first.

[brads70]

Try this to figure out rpms...
http://keislerauto.com/speed_analyzers.php?sa=mopar_5

[ToxicWolf]

Try this to figure out rpms...
http://keislerauto.com/speed_analyzers.php?sa=mopar_5

Thanks Brad, I'll go check that out. 

[ToxicWolf]

Try this to figure out rpms...
http://keislerauto.com/speed_analyzers.php?sa=mopar_5

Yes, the calculator said the same thing. At 1800 rpms we would be going 65 mph. If we wanted to be really legal and go 55 mph we would be turning about 1600 rpm. I don't think she would like that at all. 

[brads70]

Yes, the calculator said the same thing. At 1800 rpms we would be going 65 mph. If we wanted to be really legal and go 55 mph we would be turning about 1600 rpm. I don't think she would like that at all. 

I wish I had picked 3.73 gear ratio when I bought the new Dana, with my combo to get the rpms up a little at hwy speeds. The thing that makes it ok/bearable is that with the auto I can simply select with the tranny controller when ( at what rpm) the convertor locks up. Driving 55 is painful for me.... the car just wants to go. Around town and slower speeds I don't put it in OD.