355s vs. 373s

apex827 · Dec 17, 2008

Hey guys, I'm new to the forum. I have a white 93 5.0 Notch that is for the majority of it stock. I want to switch gears in the rear end and was wondering what the difference between 355s and 373s are?

7upstang91 · Dec 17, 2008

They are both good gears. Depends what you're looking for? 3.73s will really liven the car up. Personally i was going to get 3.55s then i was talked out of them at the shop i was going to have them put into. A guy was there telling about all the mustangs he has owned and how the 3.73 were one of the best gears. The 3.55s don't really do that much over the stock gears.

NIKwoaC · Dec 17, 2008

For most people, it comes down to personal preference, especially for a street car. The gears really only have about a 5% difference between the two sets. Consider that to be 100-150 rpm difference in cruise RPM.

I'd suggest 3.73s, I enjoy mine, and will give you that much more acceleration ability over the 3.55s. I wouldn't go any higher than 3.73s (4.10s for example), a street car with a mild motor and stock T5 gearing can't really take full advantage of them, though again, that's partly personal opinion.

apex827 · Dec 17, 2008

Thanks guys. I think Im definatley leaning towards the 373s. Ive heard from a few people that the gear change makes a major difference in take off. Right now I think the car could def use it. The stock gears make it really sluggish, especially with the AOD thats in it. Im hoping that 373s and a manual tranny swap will make a difference.

Sicarius428 · Dec 17, 2008

If you have an auto, I would go no less than a 3.73... 3.55 would be just at home in a manual.
Kevin

85_SS_302_Coupe · Dec 17, 2008

Don't fear the gear...go with 3.73s (hell IMO, go with 4.10s )

wythors · Dec 17, 2008

I put 3.73's in my car when it was still an AOD and it made a huge difference in accelleration. That said, I'm really glad that I didn't go 4.10. I wouldn't enjoy driving it on long trips if it was wound any tighter at high speeds. Now that the car has a T5, it's damned near perfect, gearwise.

Brian@PAR · Dec 17, 2008

I've run 273, 327,355,373,410. I'm now going to 430. For a street car the 373s were my favorite. Couple that with a T5 and you'll have a world of difference. Heck the T5 alone frees up a bunch of power over an AOD. Those transmissions are power hogs. If you do a standard WCT5 your first gear will be pretty short so expect that.

moostangvert · Dec 17, 2008

NikwoaC said:
For most people, it comes down to personal preference, especially for a street car. The gears really only have about a 5% difference between the two sets. Consider that to be 100-150 rpm difference in cruise RPM.

I'd suggest 3.73s, I enjoy mine, and will give you that much more acceleration ability over the 3.55s. I wouldn't go any higher than 3.73s (4.10s for example), a street car with a mild motor and stock T5 gearing can't really take full advantage of them, though again, that's partly personal opinion.

i really couldnt have said it better myself

Boostedpimp · Dec 18, 2008

With an AOD i'd suggest 3.73's but I did favor my 3.55's over my 3.73s in my last fox (manual) only because I did allot of highway driving and at the top of the quarter I could keep it in fourth which helped et allot

jrichker · Dec 18, 2008

With 3.73's and a 3.35 first gear in a T5, first gear will be of little use racing except to make smoke. It is too short to get any speed out of it before you need to shift to second. If you want 3.73 gears, you will be best off with a T5 with a 2.95 first gear or a Treme TKO 600 with a 2.87 first gear.

The 3.55's will top out in fourth gear (about 5200-5500 RPM) just as you cross over the quarter mile mark in most Mustangs with stock height tires. That keeps you from needing to shift to 5th and a big RPM and power drop.

Here's the math, so use it rather than someone's opinion. Opinions are like noses, everyone has at least one...

This chart assumes stock height tires (25.6")

Stevejr · Dec 18, 2008

That chart was great I just ordered a 3:55 and was hoping i made the right choice. According to this chart i did I put several hundred miles a week on my car at 75+ anymore would have been to much.

Fast63 · Dec 18, 2008

7upstang91 said:
They are both good gears. Depends what you're looking for? 3.73s will really liven the car up. Personally i was going to get 3.55s then i was talked out of them at the shop i was going to have them put into. A guy was there telling about all the mustangs he has owned and how the 3.73 were one of the best gears. The 3.55s don't really do that much over the stock gears.

3.55's do a lot over the stock gears. 3.73's are only a little bit different than 3.55's.

Basic math.

2.73 to 3.55 = approx 30% change
2.73 to 3.73 = approx 36% change
3.55 to 3.73 = approx 5% change

In my opinion, with how stock your car is, I would use 3.55's. If you plan on upgrades in the future, go with the 3.73's.

I have 3.45's and I have aftermarket heads, exhaust, intake, roller rockers... I like my gears. I have a T-5

Foxfan88 · Dec 18, 2008

3.55s

Beasty306GT · Dec 18, 2008

my rearend is in the shop gettin 373 put in....go with 373

NIKwoaC · Dec 19, 2008

jrichker said:
With 3.73's and a 3.35 first gear in a T5, first gear will be of little use racing except to make smoke. It is too short to get any speed out of it before you need to shift to second. If you want 3.73 gears, you will be best off with a T5 with a 2.95 first gear or a Treme TKO 600 with a 2.87 first gear.

The 3.55's will top out in fourth gear (about 5200-5500 RPM) just as you cross over the quarter mile mark in most Mustangs with stock height tires. That keeps you from needing to shift to 5th and a big RPM and power drop.

Here's the math, so use it rather than someone's opinion. Opinions are like noses, everyone has at least one...

This chart assumes stock height tires (25.6")

According to that chart, if you are at 5500 rpm in 4th gear with 3.55s as you cross the 1/4 mile mark, you're doing about 123 mph. I think that is more than what most mildly built Fox cars can expect their trap speed to be.

At 5500 rpm in 4th with 3.73 gears, the car is doing 117.5 mph. Again, a little much for even a pretty hot 302 car. If you use one of those basic "HP from trap speed and vehicle weight" calculations, you're looking at about 365+ HP at the rear wheels in a 3300 lb car (with driver). Of course those numbers aren't terribly accurate, but its usually ballpark. For most, that's getting into stroker or turbo/supercharger territory.

Edit: I guess what I'm trying to say is you don't need to worry about "running out of gear" in 4th with either 3.73s or 3.55s until you're making large surpluses of horsepower. Now with 4.10s, you get closer to that limit. Just my .02$.

Vinnietbird · Dec 19, 2008

I like the 3.55's.I started with 2.73's in a 7.5,so the 8.8 with 3.55's was wuite a step up.The car is quick,and as stated above,first gear is really short.

Cougar5.O · Dec 20, 2008

I had 3.73's until the differential blew up and damaged the gears as well. I was running out of gear at the track so I switched to 3.55's with the new differential. The difference is subtle at best, though I have noticed that 1st gear is somewhat more useful than before. I don't lack for torque with the KB though

apex827 · Dec 21, 2008

Cougar5.O said:
I had 3.73's until the differential blew up and damaged the gears as well. I was running out of gear at the track so I switched to 3.55's with the new differential. The difference is subtle at best, though I have noticed that 1st gear is somewhat more useful than before. I don't lack for torque with the KB though

A KB Cougar, nice...Ive never seen one of those before.

Cougar5.O · Dec 21, 2008

apex827 said:
A KB Cougar, nice...Ive never seen one of those before.

It's "different" on top of "different" - I love it!

355s vs. 373s

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