[faith]

Originally Posted by KK95GT

My '95 has a 3.35 first gear.

3.55 rear gear x 3.35 trans first gear = 11.89 total gear multiplication.

Assuming your '87 only has a 2.95 first gear, 3.73 x 2.95 = 11.00 total.

What's this mean? If you do have a 2.95 first gear, you can put in 3.73s and will actually have less "total" gear, in first gear, than I do with only 3.55s! This means I actually have more torque multiplication (and will have to shift sooner too) than you will with 3.73s! So if I had a transmission with a 2.95 first, I'd probably go with the 3.73s. But.....

There is a down side to 3.73s with either transmission. (I'm pretty sure the '87 and '95 both have the same ratios in 2nd thru overdrive). The difference now comes down to how does the ratio affect 2nd, 3rd, 4th, and overdrive. In those upper gears yes with 3.73s you'll have more torque multiplication than with 3.55s. But, with 3.73s you'll be shifting sooner than with 3.55s and you'll be running a higher RPM for any given MPH.

Tire diameter affects all this too. Think of using a long 1/2" breaker bar vs a short 1/4" ratchet. The 1/2" breaker bar has a much larger turning radius. Which one takes less effort to turn a big bolt? (Which one makes for less effort on your part or gives less resistance to your force applied). Tire diameter works like this but in reverse. The larger the tire diameter, the larger the turning radius. The larger the radius, the more "resistance" to your motors torque. (So why go with a bigger tire? One reason, a bigger tire usually allows for a larger "contact patch" to the ground). So with tall tires you'll need more gear to go with them to get the same "torque" to the ground vs a smaller tire. They won't be turning as fast as a smaller tire though.
With a smaller diameter tire, you'll have less turning radius or "resistance" so you'll be able to put more torque to the ground compared to a larger diameter tire using the same final gear ratio. You'll have more "torque" to the ground, but, with a smaller diameter tire, your tires and therfore your motors RPMS will be "turning" faster at a given MPH than the taller tire. Everything has a plus and a minus to it.

Everything goes together as a "complete packge". To just say 3.55s or 3.73s are the "right gear" is too simple. Each choice is unique to a given application. You have to do some math, do your homework, and then make an educated decision.

Well, I thank you for explaining so much. I think I will take your advice on the 3.55, it seems more resonable.

[crazydude107]

Yea you did a good job explaining the difference between 3.55's and 3.73's thanks.

[90GT AOD]

I just read this whole thread , and it was worth the eye strain. From this site and every other site I've been on, it seems that a 3.73 gear in my stock 90GT AOD will work perfectly. As was mentioned in a few thread reguarding AOD's, I'm tired of the "bogging" down feeling in first gear with 2.73 set up. I garaged my GT for a few years, and I just put it back on the road, and I want some more spirt out of first gear. I don't drive it much, mostly a weekend cruiser, but I don't want to be running high RPM's on the highway when I do hit the open road.

[dwcls]

my conclusion for the automatic (and guess-timating for a manual because of the comparable 4th gear AOD versus 5th gear manual ratio):
was that if you consistently drive over 90mph on the freeways/highways then I would get the 3.55s, but if you don't like excessive speeding or don't drive on the freeways much, then 3.73s are really nice i like to cruise at 85mph with 3.73s all the time and it is just fine at around 2800 RPMS. instant power at my foot, and feels like driving a fast go cart around traffic on the freeway

Also, like jeff90lx said... by getting 3.73s or even 3.55s you will be loosing much of your top speed. But as most people rarely go over 120mph in regular driving or in the 1/4 mile I would think either gear is awesome...

I have also heard that 3.55s are better for manuals as you won't be shifting as much as 3.73s (just a little less)....

and I have also 'heard' that if you plan on making more horsepower(guessing 250-300+), then 3.55s are probably they way to go even if you have an Automatic. Though I make a little extra horsepower with a few bolt ons, and I LOVE the 3.73s with my automatic... Feels what I imagined a supercharged to feel like on a stock motor, stock gear mustang.

Anyways, I am certainly no expert.... but I love chirpin' my tires in seconds gear when my AOD is pulling hard.

and lastly, my gas mileage actually increased by about 10-20 extra miles per tank and I do about 50/50% driving city/highway
cheers.

[BossHoss82GT]

My car used to be an SROD 4speed with a 3.07 first gear and 3.08s in the rear end ... It now has a late 90s WC T5 with the 3.35 first gear and the slightly lower 2nd and 3rd ratios ... This setup with my low profile 50 series tires (24" dia) works out to the equivalent of 3.36 rear gears ... This also lets me cruise at 70mph in 5th overdrive at about 2000 rpm without any surge problems...This only works because of the low profile 225-50s...Might not be the best setup for everyone,but sure corners like it's glued to the road.

[tazo]

I HAVE .355 IN MY 89 AND THEY ARE PERFECT FOR MY DRIVING 50-50 STREET & HWY,50 MILES A DAY ,WITH THE STOCK TRANNY THE SPEEDO WAS OK,JUST PUT IN A 92 T-5 TRANS AND THE SPEEDO IS 15MPH TOO FAST.GOING TO HAVE TO MIX THE CABLE DRIVE UP TO GET IT RIGHT .HAVE A GREEN AND BLACK,BLACK ON RIGHT NOW WITH 245-50-16 TIRES.HOW BOUT IT FAITH ANY IDEAS FOR A FORMULA YOU HAVE IT RIGHT ON THE MONEY.THX TAZO.

[Sliepnir16]

whats all this crap about bad gas mileage with 3.73s? I have them and a tremec and get over 20 most of the time, and I can definately go faster than 125 too.

[1985mustang]

well i do belieave that the difference between the two is that the 3.55s are suited for automatics, when the 3.73s are best for manuals.

[Canadian302]

After reading this quite interesting thread, i do believe that some people here didnt take the time to complete their gears installation with the appropriate speedometer gear. This little gear is absolutely essential if you wish to have an appropriate speed reading and therefore an accurate gas mileage. This gear is quite cheap regarding the overall price and takes a big 5 minutes to install on the tranny. So now i would like to have reviews of people who went for the 3.73 and the speedometer gear and tell me if your gas mileage went up or down. Thanks, i am just about to install myself a 3.73 and i really want to know what will happen to gas mileage.

[5.0 Liter]

From everything I've read I think it all depends on how much you stomp on the pedal. The only difference with 3.73's compared to 2.73's is that it is now easier to accelerate. If you drive the same as you did with 2.73's and keep the RPM low I dont think there will be any difference. On the other hand, if you have the power you will most likely use it therefore decreasing gas mileage. but any way you look at it the point is to go faster. You might as well do it right the first time and get 3.73's.

[JessBowers86]

The problem with car I have driven with 3.73's is that they don't have enough power to keep pushing when above 4,000rpms. 320hp. is not that much if you have 3.73 gears

I don't mean to be rude but my lx pulls way beyond 4,000 and there is no drop off

You mean fourth gear right? Even then, you should be able to hit 120-125 in fourth gear at 6000 rpm with a stock height tire.

Im running the stock tire size and everything on my lx but at about 6,000 im only taching about 90-95 mph...my speedometer is off a slight bit about 10 mph so its around there...as for not having power to pull with 3:73's, i owned an 89gt for my first car and fell in love with the gears. the weight difference between the cars vary alot, so for a gt i'd say 4:10 if its an 87-93...my car is almost stock and when i shift to 5th i can burry the speedometer till it hits the peg...and it has the 140 on the speedo. I walked all over a prelude one night till i bounced the speedo off the peg and got scared...as soon as i backed off i was toast.

there is alot of weight difference between the cars...and the shape of your motor could all vary to everyone elses...I personally find 3.55's a waste of time, cause 3:73's are perfect for terrorizing people on the street, helps get the speed up quick...powershifting don't hurt either when you're playing catch up to them damn vettes

[jimgt]

I,m running a auto 94 gt, I,m about to install 4:10,s and I won't regret it at all,also our GT is a pleasure[weekends] cruiser,so it won't matter to me.

[jimgt]

Imagine that,,,owning a GT. and fearfull of gas mileage?????

[five-0]

With the 2.95 first gear ford racing t-5 the overdrive is .63 vs .68 with the stock t-5. So 3.73 will have less first and less fifth than 3.55. .63*3.73 is less than
.68*3.55. I have the 2.95 tranny and read this whole post debating on 3.55 vs. 3.73. I drive 20 miles to work daily. I thought 3.55 was right and went ahead with 3.73. for only headers, pulleys and gears, it is pretty damn fast. Its a rocket in 1st and 2nd.

[jimgt]

HI everybody,,I just had 4:10's installed weds. in our 94 gt w/aode tranny,,love it,,it really woke up our gt.