Gears: 3:55 or 3:10 ?

[moparfanUSA]

I'm sure thr rear has 3:91's in it, so where I go down the road the engine seems a little to much RPM's, so I want to change the gearing..I was thinking 3:55 as a nice all around gear.....any thoughts? It is not a Dana rear. The bolts are in the front.

 

[moparfanUSA]

sorry, I meant 3:54

 

[68GTX4SPEED]

Dont be sorry:sad: when its right, 3.54 is Dana 3.55 is 8-3/4, myself will try 3.23 this summer.

 

[Al K]

Moparfan;what is the diameter of the tires you're running? It's another factor to consider. I plan to run 3.91's but with a tall(29") tire. I might find that a 3.73 or 3.55 might work better. We'll see...

 

[midnightrider1818]

i think it depends where you do alot of your driving. interstate, highway, city driving etc. interstate driving id prob go with the 3.23 or w/e. lower the gear the higher and therefor lesser rpm at rated speeds.

 

[moparfanUSA]

gears

The tires that are on there are P225 70 R14's I do notice that the speedo is telling me I am going a little faster that I am. I want to change the gears because I plan on doing some sunday driving on some highways. When it says I'm doing 60mph the tach is around 2500rpm. I do not know if I have an 8 3/4...I know alot about cars from my many days taking my 69 RR's apart, but that was a long time ago, and have heard of it, but i'm not up to speed on rear ends...(at least the car kind). I was going to take a picture of it, but the wife took the camera. I just want a nice all around gear. Best place to get them?

 

[65-440]

When it says I'm doing 60mph the tach is around 2500rpm.

****, i would kill for that. im at 3300RPM @45mph. was thinking about new center section w/3.55 for the street. a very good all around gear

 

[moparfanUSA]

gears

Well, I found out real quick...I have a 489 stamping on the rear end and so far 3:55 is the best I can find...but I will keep trying.

 

[Crunchy_Frog]

According to my calculator, at 2500rpm, with 225/70 R14ires, you should be around 62mph. You said your speedo is saying 60, do you know your actual speed? I put a 3.91 suregrip in mine years ago, and when i would do ... ahem... acceleration trials, the back end would hop everytime. 3.23 is in it now. If your actual speed is 50ish, you have a 3.91 if it's 55ish, you have a 3.55. Both cases, wrong speedo drive gear.

here's a neat little java based calculator. Mine's just a simple spreadsheet.
http://vexer.com/automotive-tools/speed-rpm-calculator

 

[moparfanUSA]

gears

Yes, I do have 3:91's in it now...looks like I'm going to put 3:55's in it...just waiting for a friend that owns an auto parts store to find them a give me a price.

 

[Super Stock HEMI]

I Have A Couple Buds In NJ That May Be Able to Help You Out..PM Me And I Will Give You His E-Mail Addy.

He Also Organizes A Cruise In And Car Club..


SSH

 

[Ghosty]

Here's a neat little java based calculator. Mine's just a simple spreadsheet.
http://vexer.com/automotive-tools/speed-rpm-calculator

Badass! Thanks for the link, that is hella useful. (yeah I know it's an old bump, but still useful for people who missed it, or newcomers.)

 

[67440chrg]

I have 275/60r15s and 355:1 gears and at 70mph im at 3000 rpm. my tires are 28" tall. The 355:1 work good for me.

 

[Ghosty]

I have 275/60/R15's and 3.55:1 gears. At 70mph I'm at 3000 rpm. My tires are 28" tall. The 3.55:1 work good for me.

Good to know. Did you plug your numbers into that calculator and see if it also shows close to 3k rpm's in final gear?

What did you put for converter efficiency (if auto)? I'm just putting in a 10% driveline loss if testing an auto.

 

[Jasoncoronet]

I have 3.55 in my car and think it is a little to much gear for the street. I wish i had 3.23 that would be perfect. I also run a 275/60/15 and i am always looking for another gear. Power is good however but if you have a good motor meaning descent hp and tourque a 3.23 will be a better choice.

 

[Dennis H]

Off topic but I found the sweet spot for mine when I put the 295/50 15 Coopers on an 8" Ralley on the rear of the Coronet. 2150 rpm @ 70 mph. 3:54 Dana. Tremec TKO 5.

 

[Budnicks]

Badass! Thanks for the link, that is hella useful. (yeah I know it's an old bump, but still useful for people who missed it, or newcomers.)

Also Try over @ www.wallaceracing.com/Calculators.htm tons of automotive related different Calc.s/Formulas

- - - Updated - - -

Off topic but I found the sweet spot for mine when I put the 295/50 15 Coopers on an 8" Ralley on the rear of the Coronet. 2150 rpm @ 70 mph. 3:54 Dana. Tremec TKO 5.

Nice to have a O/D trans, drop cruising RPM's on Hwy speeds, then especially a man. trans with a low 1st gear {to get near your final 10:1 ratio for performance = 1st gear ratio X final drive ratio}, like having the best of both worlds, performance & drive-ability...