3.55 compared to 3.73, differences?

[tp8728]

k, ive been looking into swaping gears and from what ive read so far i think i need to do a 3.55, the 3.73 will give me more torque and accelerate quicker from stop, but i do travel on the interstate to work everyday so how do these compare, how does this affect the speedo, im not looking for alot of power but do want a little more accelleration capabilities. lemme know what ya think, and where i could gettem at a good price.
also will this work for our cars
ebay item # 7938606729
gonna put one of those on to when i swap the gear
thanks

[p71towny]

with those wheels, Id go 3:73, you'll need all the help you can get.

[Lincolnmania]

yes go with 3.73's with those wheels and tires........how tall are the tires? theres a tire height /gear calculator out there somewhere

[mrltd]

3.73's....They will be about the same as running a 3.27 with that diameter tire.

[DuceAnAHalf]

id bet that with 3.73s and your tires you speedo would be pretty close.

[tp8728]

the tires are are 275/45/20, i was hoping that it would even out my speedo a bit, its way off at highway speeds, wheres the best place to get some?

[gabegt90]

yeah I would go with the 3.73

[89GrandMarquis]

Based on your tire size, which I calculated to have a 29.74" diameter, a 3.90 would work best for you (assuming that a 3.55-equivalent is your goal).

With a stock size tire, an increase from:

3.08 to 3.55 yields a 15.26% increase in RPMs.
3.08 to 3.73 yields a 21.1% increase in RPMs.

With your tire size, after considering the tire size difference, an increase from:

3.08 to 3.73 yields a 9.9% increase in RPMs (compared to a 27" stock size tire). This is due to your tire diameter. If you have 3.08's now, you have a rear axle equivalent gear of 2.80 (as compared to a stock size tire).

So, with a 3.73, your not going to get the same result as a stock size tires that would equal a 3.55 change.

A 4.10 seems too much:

3.08 to 4.10 yields a 20.8% increase in RPMs (compared to a 27" stock size tire).

Although no offered by FRPP, a 3.90 looks best for you.

3.08 to 3.90 yields a 14.92% increase in RPMs (compared to a 27" stock size tire).

With this combo, you should be able to get a speedometer gear that is with 2 or 3 percent of exact (less than 2 MPH off).

[tp8728]

wow, thanks for that info 89merc, 3.73 it is

[Mercracer]

A 4.10 seems too much:

3.08 to 4.10 yields a 20.8% increase in RPMs (compared to a 27" stock size tire).

4.10's are perfect for that tire size if you subscribe to the drivetrain harmonics paranoia crowd. You are turning 1% less RPMs than you would with a stock 27" tire and 3.73 gears. At 65MPH, you are only turning 2017RPMs. At 150MPH, you would only be turning 4655 in OD.

[89GrandMarquis]

My point is: what was your goal?

If you are looking to get gearing that is close to our cars (with a 3.55), then use a 3.90.

I agree that if you are looking to get gearing that is close to our cars (with a 3.73), then get the 4.10.

It's up to you.

The crowd seems to be mixed - 3.55, 3.73 seem to be the most recommended for our cars (with "normal" tires), but certainly there are some that believe that 4.10s are the only way to go. Having just put in 3.55's, I'm liking them, and I now think that 3.73's would have been OK, too. No mileage numbers yet, so that will tell the tale, since my car is a daily driver, and I wanted some improvement without too big a hit on gas mileage, so I chose the 3.55's. Actually, saying that I "chose" them is not quite right. The 3.55's were left-overs from my E150 van upgrade to 4.10's. Free parts can really sway a decision sometimes.

Again, it's up to you and what is your goal.

[Mercracer]

One more thing......cost.
For mileage and investment, 3.73s are the best bargain.
The 3.90 gear is aftermarket only. The 3.90 gear is $100 more expensive new than a set of 4.10's and $85 more expensive than a 3.73 set. Used, 3.73 and 4.10's can be $150 or more cheaper.
With a stock engine, and if there were no price difference, the 3.90 gears would make sense.
The whole "speed costs money" thing definitely comes into play with 3.90 or 4.10 gears.

[tp8728]

im not looking for speed, deffinatly not worried about top end, just trying to get some better accerleration due to added weight, i dont get good gas milage now, it was a daily driver but now i drive it 3-4 days a week so mostly better acceleration because i can feel it struggling when im pulling from a light. replacing the gear wont affect the idle rpm's will it?

[Tiggie]

I'd go with at least a 3.73. As mrltd said, it's equal to a 3.27 with P215/70-R15 stock tires.

The 4.10's would be equal to 3.73's with a stock tire.

They won't mess with your idle.

[turbo2256b]

You need to measure the loaded radius of rear tire to be the most accurate in figuring gear ratio and speeds at RPMs.