What would be a good gear for my car?

[keith88]

Hi, My next project this spring is to redue the rear in my car. Its an 8 1/4 rear with 2:76 i was looking at replacing it with 3:55  as well as replace all the bearing and seals, its a 318 with mild cam and a 904 transmission so i wasn't going to change to a 8 3/4 any time soon if ever.  Any opinions on this? or what other gear size would work.

[polywideblock]

my vote is for the 3:23 or 3:21 whatever is available,   seems to be the best all around gear 

[Mike DC]

               
A lot depends on you.  How much highway driving does the car get?  How badly do you want more grunt?  It's a compromise. 

3.55 is about the lowest I would consider for a street car.  That's just me. 

[c00nhunterjoe]

Go big or go home, i have 4.88s in my street car.... lol

[Ghoste]

I would leave the 3:55's in there.  A nice compromise between high end manners and around town performance.  If all you will ever do is highway then a higher ratio is fine and if quick acceleration is the main use of the car then lower is better.

[keith88]

Right now it has 2:76 in it, the highway driving i would be doing would be to get to shows and that kind of thing it is not my every day driver.  I had them in a camaro i used to have and they worked well but the motor was built more than this that was my biggest concern.

[b5blue]

I've a 3.23 in my 70 and like it over 20 years now. Given your use/build I think your spot on with the 3.55's. (I've a big block.)

[crj1968]

3.55's are a bummer on the freeway...

I had 2.94s in my last charger. Gonna run 3.23's in my new one, with some pretty tall tires. It's all a personal preference in if you wanna cruise comfortably or run light to light.

I think 3.23s are a great all around gear for a street car.

Or 3.55's with an OD.   

[six-tee-nine]

Why not upgrate to a 8 3/4 axle? If you are a bit Lucky you could pick one up for not all that much and rebuild it for almost the same cost as the one you have now.

And when midlife crisis kicks in and you want to bolt 2 turbo's onto your 318, then you got something to handle the added horses......

[Troy]

Just leave it alone! Seriously, some of my best driving cars were 318s with 2.76 rear gears. You'll look dumb trying to burnout or launch from a stoplight but you're driving a 318 so it's not going to be spectacular no matter what you do. From the sounds of it, you aren't "hot rodding" around any way. What you didn't mention was tire size. If you're driving around on tiny stock tires then stick with the stock gear. But if you bump up to a 28" (275-60R15 is what lots of people run) or 29" rear tire then you're "effective" gear ratio with a 3.23 will be something like a 3.00 which is about perfect since you get more acceleration from a stop but still great cruising RPM on the highway. A 2.76 will end up being below a 2.50 and you'll be lugging the engine all the time. That's the only reason I'd change gear ratios. Plus, it's not cheap so why spend a bunch of money on something that likely isn't going to make a huge difference? Bearings + seals + gas = win.

Oh, in recent weeks I've been poking around on Craigslist and found 3 complete B-body 8 3/4s for about $200 each. Center chunks in decent condition can usually be found the same way so you could pick a range of gear ratios. A 2.94 without a Sure Grip would probably cost you $50-75. Any of the "performance ratios will be more (3.23, 3.55, 3.90, 4.10).

Troy

[crj1968]

Probably would be easier to bolt in an 8.75.....your brakes will swap right over

[Ghoste]

Funny how different our tastes are on this.  I think a 3:55 is fine as a highway gear but someone else not so much and another guy runs a 4:88 which I would never do in a street car. 

[keith88]

 Its going to remain a small block car even if the 318 goes someday ,so im going to keep it a 8 1/4 but thanks for the 8 3/ 4 idea more than enough there to handle a small block. The reason im going though it is because i want to know that's its OK make a small noise now at a certain rpm that only at that rpm  that could be a gear I want a little more take off than what it has so i have been torn between 3:55 and 3:23 but i am leaning more to the 3:55 I will not be doing a whole bunch of highway driving so im not so worried about that. But i do like what im hearing so far. The tire size is 27 " so im taking that in account to. I'm rebuilding the rear any way so i might as well do what i want now.

[Ghoste]

What ratios can be had for the 8.25?

[polywideblock]

I've got 3:23  81/4 diff in the roadrunner and it is  a great all-around drive   with the 340   but that is with a 4 speed 

[XH29N0G]

My guess is that you will be fine with 3.55's.  I had 3.23 and liked them.  I would go through the calculation of RPM vs MPH that you will get at the speeds you drive, and then drive around at those RPM in a lower gear to see whether it is offensive to you or not.  I am now running 4.30 and think those would be a bit much at 1:1 final drive (I have an od and larger tires that brings them down to something like 3.11)

[1974dodgecharger]

ADD a blower to your car and low end problems solved with a 2.73 or whatever tall gear you can put in there...

[Dino]

I had 3.55s with 26" tall tires and felt like I was missing a 4th gear all the time, but I did drive the car daily.  I changed them to 2.96 gears and loved it until I installed 28" tires.  I now run 3.23s and I like it!

[DixieRestoParts]

A lot of these on the internet, but here's a simple calculator:

http://www.advanced-ev.com/Calculators/TireSize/

I say give the 3.55 a try. If you hate it, then change accordingly.

[c00nhunterjoe]

Funny how different our tastes are on this.  I think a 3:55 is fine as a highway gear but someone else not so much and another guy runs a 4:88 which I would never do in a street car. 

I would not venture onto the highway with my car running the 88's. However, in my area, even with my old 2.76's, i did not take the interstates. 80mph is the norm for the slow lane and i dont prefer having people weave in and out around my 69'. The 88s make the car a blast for how the car is set up, what i do with it and how i drive it.

[keith88]

Hears a little comparison.(what i have now 2.76) at 2500=72 MPH
                                                        3.23 at 2500=62 MPH
                                                        3.55 at 2500_56 MPH


According the the calculator!

[c00nhunterjoe]

Hears a little comparison.(what i have now 2.76) at 2500=72 MPH
                                                        3.23 at 2500=62 MPH
                                                        3.55 at 2500_56 MPH


According the the calculator!

4.88s 28" tire, 4 speed, 2500 is 45mph....lol. its a bit steep for most, but in my scenario, the car is still skipping off the cam pretty hard anywhere at or below 2000, it doesn really "cleanup" untill 2500 anyway. I may put 4.56s in it in the near future and swap to a 29.5" slick and see how my 60's and lights change.

[Mike DC]

         
To each his own. 


Me, I can't imagine a street car that cannot be highway cruised.  Without overdrive a 3.23 feels low. 

Modern engines get spun half as fast and they last twice as long.  It's not a coincidence. 

[keith88]

Right now i probably drive faster than i should with the 2.76, one can do 80 to 90 and it dont even feel like it because of the rpm. 2500 -3300 would be good for the highway and help keep my speed down.

[Homerr]

Here's the small tire option, for lower ET.