Street trim Cuda with 528" Hemi, 500ft/lb at rear tire at 2k rpm, Tremic 5 sp with 2.87 1st, .64 5th, 27" tall tire, 8.75 rear with 489 case. Street car.
I'm thinking 3.91 or 4.10. On the RPM calculators I have found, I can't plug in trans ratio, only tire, rpm and rear gear.
Also, would you go with the Sure Grip or the Easton True Track?
Thanks!

4.10 with a Tru Track...You still may not use 5th gear a lot with a .64 ratio...

4.10 is too deep for that car. The 2.87 first gear would be incredibly short with that rear.

You'll be fine with 3.73 gears.

We put a Tremec in a car with 3.54s and it liked 70 mph more than 60 mph in 5th gear.

i would run 4.10 if you don't have short tires.

28" tire at 70mph with 4.10 gives you 2200rpm in fifth...

The 4.10 is great in 5th but makes 1st useless.

I have 3.23's in it now. There is plenty of torque to pull that gear but thought a steeper gear would optimize the package.

So you have a 2.87 First gear. For years I have used an overall ratio of 10:1 for the First gear, as a calculation goal. 10 / 2.87 = 3.48. In a Dana 60 I'd use a 3.54 gearset. Ford 9" I would use a 3.50. 8 3/4 I'd use a 3.55.

That's just a rule of thumb but it has worked for me.

R.

On your deal I would opt for the 3.91
I ran from 3.73 to 4.30 in my old pump gas Duster, it ran almost the same ET(10.30s) and MPH(127.) in the 1/4 mile at Woodburn. It seemed like it spent more time in high gear with the 3.73 but it ran almost the same
The stick tranny with the O.D. should still hook and book with the proper starting line RPM at the drags It won't be easy to get it correct on the first pass but it is doable with some testing You can spin or bog on the starting line, your right foot will control that
BTW, Yukon makes a 3.73 gear set for the 741 center section Those are the ones I used in my car

I run a 3.55, 28" tire, 2.66 1st (or whatever 1st is in an 18 spline) in a warm 440.

In your car I would run either a 3.55 or maybe a 3.73 (if I could find one) with a clutch type sure grip and a solid spacer in that 489.

You have a LOT of bottom end, a low first gear and a medium height tire. I think with even a 3.91 you'll find 1st gear to be almost unnecessary.

You also risk ending up with noisier gears with a 3.91 than a 3.55.

Course nobody has asked you about how/where you drive, terrain ect. If your in the flats then definitely a lower numbered gear. if in the mountains then higher.

Pacific Northwest, like you!

I don't know if going to a 3.55 from a 3.23 is worth the time and effort. Thoughts?

Nope. Stick with what you have. You could always test something later.

Dr Dave, as you can see the recommended gear ratios are all over the place. Why don't you decide for yourself? You can make the RPM calculator work for you like this:

1. Pick a rear end gear ratio to calculate on, say 4.10 for example.

2. Multiply that number by your overdrive ratio to get an "effective rear end gear ratio". In this case, 4.10 x 0.64 = 2.624

3. Use the standard RPM calculator to see what your rpm's would be with your tire diameter.

FYI - You can do the same sort of thing to get a feel for what your "shift point" would be in each gear at a reasonable rpm too. For example, with the same 4.10 gears and a 2.87 1st trans. gear you'd calculate like this:

a) 4.10 x 2.87 = 11.767 "effective gear ratio in 1st gear with 4.10's"

b) using your tire size, you can calculate a mph at a given rpm, say a 3000 rpm target shift point for daily driving, and see how many mph's you'd be going before you had to shift.

c) repeat the above with your other trans. gear ratios with a "target shift rpm" (like I just used 3000rpm) for the other gears to see how fast you'd be going in the other gears too.

Hope This Helps!

Really helpful, thanks!

I've done it twice, it's noticeable, but yea, you could argue not worth the trouble.

This is good advice. Multiply the trans ratio and the rear ratio. Take the tire height into consideratio and make a choice.

Too low of a 1st gear is like having a truck with bull low.

I'D DO 4.30'S if it were mine. That thing would be a beast with them.

With a big HEMI you are going to murder 27" tires on the street with any gear ratio. A gear set numerically higher than what you currently have will most likely make driving the car exponentially more exciting.

What kind of tire is on the car?

It seems like quite a few people have been surprised by similar ET's when they went up or down in rear end ratio either way.

For a street car that's not after every last tenth of ET, I like higher gear sets. I also don't mind a short smoke show 1st gear. Right foot input will control that on the street anyway. Stop and go traffic? That short gear will be happier on the clutch.

I had a TKO with .64 OD. I hated having RPM so low that 5th gear was useless below 65 mph. I went 4.56 and loved it. Tire frying through 3rd if I wanted to, yet cruise the highway at 70 mph at 2400 RPM.

I'm surprised nobody has mentioned that all factory 426 Hemi cars used the Dana when the 4 speed was used. You are now using an engine 102 cubes bigger with a smaller axle than stock?

I am a little surprised at that, too. But, then I suppose he will be using a Radial T/A type tire that is more for show than grip and that should keep the 8.75" OK for now.

I think this sums it up very well. The car will not be any faster or et any better with a gear change. First gear will be crisper, but other than that, the only difference is what gear you choose to be in.

I did notice that you used the word "optimize", probably not by accident. So if you don't like the engine rpm when you are cruising down the freeway (i.e. it is too low) then a numerically higher gear ratio make good sense.

To determine your final OD engine rpm simply put your information into your favorite online calculator, then multiply the rpm by the OD ratio, i.e. 0.64.

To me much depends on how much street and or race you plan to use it. And as many said with that big Hemi you dont need as much gear as it should have the torque to pull about the same et with lower number gears. Of course if you plan to race it and put sticky tires on it then I would go with a Dana or Ford 9" with the manual trans. I also agree it will work better with a taller tire. I run a 30" tall tire on my 63 with a 440/493 wedge that I am sure makes alot les power then your Hemi and the 30" tires work nice for me at the track and on the street. If you plan to race alot I would go with about a 30" tire and run 3.91's with your combo. Good luck what ever you decide on. Ron

Just say no to a phord 9" in a Mopar.

Danas are super cool and tough and if the OP is gonna beat on the thing hard with sticky tires, it is the ultimate rear. But his 8 3/4 will handle most duties. I have had an 8 3/4 in my Cuda with a 500" Wedge for more than a decade. And now have a 540 Hemi in front of it.

I have hurt a couple of gear sets over the years but that still doesn't amount to the cost of a Dana.

We run 3.91s. Mostly because they are a good compromise between fun and hiway cruising. If we ran more hiway, we would have higher gears. If we raced more, we would have lower gears. But 3.91s are a good match for the way we run our cars.

I also run an 8-3/4 but behind a Hemi with a manual trans if I was going to race it with stickies I would definetly upgrade the 8-3/4 as I think it may break in time behind that combo in a manual trans. I believe the Dana's are actually cheaper then the Ford 9" but I do like a Jackpot rear when it comes to working on them as I like that you can take the jackpot out and work on it on the bench. I want to upgrade to a Dana myself one day if I ever get the money. Ron

I have that tranny in my Dart.

Smallblock stroker,28 inch tire,253/255 @.050
solid cam,RPM Intake.

Started out with 3.91 then swapped to 4.30

My motor is happier at highway cruise with
the 4.30's

Mike

My 2 cents...... 3.91 gear ratio.... And the next time you buy tires go with a 28" or 29"... That should put that 528" motor in the sweet spot...