3.55's or 3.73s?

Are you more worried about acceleration/ drag times/ highway cruise speeds etc...

I have 3.73's now...
at the strip I wish I had 4.10's ...
on the highway I wish I had 3.27's...

I would honestly say I would not want to step down to 3.55's at this point, I can still go on long road trips & knock down 280ish to a tank of gas & the rev's are still modest. Plus at the track it works out pretty well.

There isn't that much of a difference in either. I have had both. Now, the 3.73's are more popular. A few years back, I seem to remember more people using 3.55's. The only thing I don't like about 3.55's is you seem to be in the drone RPM's on the highway. With 3.73's at about 70, you are not. The only way it would matter would be if you were running a high horsepower car at the track and would run out of gear with the 3.73's. If that is not your trouble, then I would go for 3.73's.

What criteria are you going by to come up with "better?"

If your Mustang is stock, Ford designed it to run the quarter in third with 3.08:1 gears. If that is what you are interested in doing, leave it alone. If it isn't stock, and that is what you are interested in, then where does peak power occur? How wide is the power band (how far does it continue to pull after peak power)? How much does the car way with driver and gas (full race weight)? What is your actual tire height? These all go into the equation for figuring out the correct gearing.

If what you want is snappier response, but don't mind losing ultimate quarter mile times, the 3.55:1s are what Ford recommends for snappier street driving with stock sized tires as 3.73:1s cause too much torque multiplication making it difficult to plant the stock sized tires. If you've got more tire (width or height) you can go with 3.73:1s and have even snappier response while still planting them. Both should'nt show much of a degradation in longevity of engine or gas mileage with freeway driving. But be aware, changing the gear will change the way the computer deals with the engine. There is a parameter in the computer that is dictated for a specific gear multiplication value, and changing the gear will screw up the computer's ability to deal with controlling cylinder burn so you may feel a hollow feeling during acceleration. That can be remedied by having a chip burned to change that value or utilizing a computer that will allow you to tune that value yourself.

If you want both snappier response and the ability to quarter correctly with a stock engine, the ideal gear set is 4.10:1. You should have wider, stickier tires and possibly some traction help or a T5Z transmission with the 2.95:1 first gear.

quiksilver9531 said:

I wanna get gears and it seems like everyone likes 3.73's better but this guy i work with swears that 3.55's are better and that I should get them instead of 3.73's..so the question is which one should i get?

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quiksilver9531 said:

I wanna get gears and it seems like everyone likes 3.73's better but this guy i work with swears that 3.55's are better and that I should get them instead of 3.73's..so the question is which one should i get?

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It really depends on the car and your plans for it. There's no right answer, although most people will just spit out "3.73's for 5spd 4.10's for aod". If you do a regular highway driving and don't plan to hit the track too often, 3.55's may be in your best interest. If you want to have a n/a street-track car that you also drive on the highway occasionally, 3.73's would probably be your gear... if you're building a track-only n/a combo then look at 4.10's+, etc. Everyone's experiences are varied so you'll get a lot of different opinions. I'm happy with my 3.55's in my (summer) daily driver. I do a lot of highway cruising and the car will hardly see any track time. I can hit 60mph in second gear, and highway cruising speeds are at a reasonable rpm. I've driven cars with 3.73's and in my situation I'm glad I went with the 55's instead.

Let me try to put it simple:
The more power you have, the less gear you want (numerically lower).
The less the power you have, the more gear you want (numerically higher)

If you want good gas mileage, go with a numerically lower gear.
If you could care less, go as numerically high as you want.

If you do a lot of racing and little highway driving, numerically higher of a gear is to your advantage.
If you do a lot or almost all highway driving, then you better keep the gear ratio high (again - numerically lower).

Automatics are going to want a lower gear (numerically high) due to drivetrain loss of the torque converter.
Manuals are going to want around 1 step down in gearing (numerically lower) than automatics due to the fact they have 100% torque/power transfer from the engine.

Now with that aside, there are plenty of variables. It's all preference really. Both are popular because they have their places and are nice compromises. I myself went with 3.55's because for 1) My stang see about 90% highway, and 2) My new 327 5.0 engine buildup is something i'm setting up for the 300-350 rwhp range with the capability of a power adder. With that said as well, haveing 3.73 gears are a little much for my setup and 4.10's are completely out of the question.

Nothing can make you decide this, it's something you need to pick and go with it. Both are very similar and you will notice a marginal difference between the two. With regards to the above basic guidlines, you should be happy with either one.

FWIW - 26" tire in 4th gear crossing the traps at 6000rpm with....

4.30 = 109mph (this mph is good for 12's)
4.10 = 114mph (this mph is good for 11's)
3.73 = 125mph (this mph is good for 10's)
3.55 = 132mph (this mph is good for 9's)

please remember that all this is based on the above info, change your finish line rpm/ tires size /transmission ratio then all this info will be off.

With that being said...also take into consideration it's main use... IE weekend car/ street car/ commuter etc.

quiksilver9531 said:

thanks guys this all good information..well the reason im asking is because this guy i work with had a mustang and he said 3.73's actually made him run a slower time in the quater mile and that 3.55's made him faster...i mean he knows alot more than me..this is one of the mechanics i work with...

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There are circumstances where that could be true. Depends on where his car is making power, his shift points, traction, track condition/weather, and mostly on his driving. I definately wouldn't say that 3.55's will give you a faster et than 3.73's in most cases.

There's so little difference between the two that it makes little difference which you pick - especially if you're trading up from 2.73's. Toss a coin - there's only 5% engine speed difference between the gears. Most speedos and tachs aren't accurate enough for you to tell the difference between the two. And the performance difference is negligible.

I have 3:55s and man I really wish I had 3:73s

Ford_Racing said:

I have 3:55s and man I really wish I had 3:73s

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If it bugs you that much, go to a 1/2" shorter tire.

Ford_Racing said:

I have 3:55s and man I really wish I had 3:73s

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Why? (not trying to sound like a prick).. I think you'd be awful dissapointed spending the money to go from 3.55's to 3.73's on a street car. As stated above there's not much difference and any SOTP gain is minimal (I've driven the same car with both, hardly noticable if at all). Heck you could just go with a shorter tire and get the same results. If you want more gear you might want to check out some 4.10's or higher...

Well there is also a limit that is reached with the tire sizes available & too short of a tire will, not to be smart..., just look stupid.

So there is something to be said of using the correct combination of Gear ratio & tire height/ width. This is not just an ascetics thing either... handling/traction issues play into this.

Takes a 1" shorter tire to turn 3.55's into 3.69's actually. 1/2" shorter only turns 3.55's into 3.62's.

If you have 3.55's and want 3.73's - next time you need tires, switch from 225/55/16's to 225/50/16's. That goes from the stock 25.7" tire height to 24.85" tall - turns 3.55's into 3.67's.

edit - but I should add - you'll never know the difference. With 3.55's, it'll take 3.90's or 4.10's to notice much difference.