For those of you that switched from 3.55 to 3.73 -- Was it worth it?


Aug 7, 2008
Sorry for another gear thread, but I'm really struggling. I have a 95 GT 5 speed with some engine mods (HCI) probably around 275 RWHP or better.

I originally installled a set of 3.55 gears in the car thinking that because it was a highway cruiser, they would be better suited. Now with all the hoopla about 3.73 gears, it had me thinking that maybe I made a mistake?

Currently the car revs around 2000 @ 60 MPH, about 2200 @ 70 MPH and around 2400-2500 @ 75 MPH with the 3.55s. I keep hearing that 3.73 will only equate to 150-200 RPMS more in cruising RPM but a heck of a lot more accelleration over the 3.55's. (I am skeptical of that claim)

For those that switched from 3.55's to 3.73's, was the change worth it in regards to the money it will take to do the swap.....or is worth the expense to change?

I really don't want to make anther mistake wishing I had the 3.55s back!!
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I really can't tell you if it would be that noticable or not because I only have 3.55's and have never switched to 3.73's.

...But, the best way to try it to see if it works better for your car would be to find someone selling a whole rear end with 3.73's already in it and swap them out. If you like it then sell your 3.55 rear end and recoupe some money back. Doing it this way you could probably end up only spending ~$100 or less.
There will be some what of a diffrence but not much if your going to switch id go with 3.90s they are right between 3.73s and 4.10s so you wont be pushing extreme rpms but you will feel a bigger diffrence.
Last5.0 has a good point try to find a another complete rear end so that way if you dont like them you can just swap them out. My buddy runs 3.90s and loves them and is running about 290hp.
I went back and forth on 373s... I swapped 355s for the same thing you speak of... Then I wanted to crack 13s..I did 373s to get there and blam....13s were had.

I go back and forth over swapping back...I dont like the real short 1st gear with the 373s... I do love the mid/upper range hit as its really sweet. Power wise I'm right around you and the 373s do work well... I do my own gears swaps so some day I'll prolly go back to 355s...just me, but the 1st gear thing really pisses me off as the gear is gone instantly. I have a 331 I'm doing here shortly and the 355s may go back in with the swap as I felt they were best for the way I drive.

I just did a 410 swap for a member and those are really sweet...i could take off in 2nd but the power band was really sweet... depends on your driving style and what you wanna do with the car.

Decisions, decisions is all I can say.... Its one of those things you have to try to see if it fits your driving style... 355s are a real nice happy medium to me...I really did like them.

Not sure if this help or not...but I know the frustration of which way to go.
This probably isn't much help but here it goes. I went from 3.73 to 4.10 and OMG what a change. With the 3.73 it was a low 14 second car and dropped to a mid 13 second car with the 4.10's. Town driving was a pain due to constant shifting and at 70 MPH it turns about 3k on the tach.

I then built the combo in my sig and the 4.10's are worthless. I hit 4th gear in the 1/8th mile and 5th in the 1/4.

So I guess what I'm saying is if you plan to do any other mods to the car, wait until it's done.

I'm working on turboing it now and expect to go to 3.27 or 3.55's when it's done.
final5-0;8209046Do the math for yourself :nice: Use this and it will make it a bit more easy :D I don't know how anybody could tell you there will be a heck of a lot more power :crazy: Grady[/QUOTE said:
Yes, I've used this calculator and the RPM differences are minimal.

With a 275/40/17 tires (25.7")

This is what is plays out to be in 5th gear:

60 mph 1893 RPM (3.55) 1989 RPM (3.73) - differnce of 96 RPM
70 mph 2209 RPM 2321 RPM - difference of 112 RPM
80 mph 2524 RPM 2652 RPM - difference of 128 RPM

4th Gear 1:1 :

60 mph 2784 RPM (3.55) 2925 RPM (3.73) - differnce of 141 RPM
70 mph 3248 RPM 3413 RPM - difference of 165 RPM
80 mph 3712 RPM 3901 RPM - difference of 189 RPM
90 mph 4177 RPM 4388 RPM - differnce of 211 RPM
100 mph 4641 RPM 4867 RPM - difference of 235 RPM

Basically, the rpms differences are neglible. The RPMs do appear to be correct as per my tach and the tire size with the 3.55's that I currently run, so I am convinced that the RPM estimates should be close with the 3.73 is reality as well.

It's really hard to judge is this the little RPM change is worth it. Judging from this.....not really worth it. However, just further reiterates that 3.73 may be the better choice if you haven't chosen gears yet?

I'm trying to gain more accelleration. Will the 3.73 be miles ahead of the 3.55s, I'm just not so sure......

Still more confused than ever.....
Let me give you the benefit of what I've found when dealing with gear ratios on bicycles, motorcycles, and cars :D

If you change the ratio by 1/4 of a turn ... It Will Be Subtle :eek:

As a matter of fact ... you can hardly notice it :scratch:

Rule of thumb I have always gone with is :)

You gotta go 1/2 of a turn before the effort is worth it ;)

I think you just lost me with that analogy. If you are meaning the ratio split between them is only .18 of a turn difference....or basically a 1/4 rotation of the rear tire, then I understand.

With that being said, I shouldn't bother now that I already have the 3.55's in there. If I was still stock, I'd have been better off with the 3.73's.

Is 1st gear really that much shorter with 3.73? The differences seem so minimal on paper. Real world is where it counts.

I had one guy tell me that the RPM difference from 3.55 to 3.73 was going to be around 300 RPM on the highway!!!

That just can't be right...
Is 1st gear really that short? At 20 mph, you'd be shifting out of 1st @ 3100 RPM with 3.55s....with 3.73, you are shifting 3250 at the same speed. 150 RPM is hard to even notice on the tach?

I guess if your car revs up very quickly, then yes, 1st gear will seem really short and deeper gears will accentuate that.

I find my 1st gear reasonable right now with the 3.55s....
I guess if your car revs up very quickly, then yes, 1st gear will seem really short and deeper gears will accentuate that.

When talking about NA application :)

There is a real difference between the powerband of a stock Stang
or one that has just done bolt-ons and one who has h/c/i :Word:

The reason being is the h/c/i Stang has a powerband that has been
shifted up and it has been extended

Those two things make a real difference in how the first gear acts
between the two example Stangs we talk about here :D

Its all about when the torque and hp start to come on in the
powerband and with a little stocker ... it comes on sooner and
it peters out much sooner ;)

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All I can say is base it around your final outcome.

Info based on basically full weight sn95 w/ 5spd with 1/4 mile in-mind. 1/8th only go BIGGER!!

I was stock with 2:73s - obviously sucked lol
I was h/c/i @ 300rwhp with 2:73s - still sucked, way too little gear for the power
I was h/c/i @ 300rwhp with 4:10s - VERY fun around town, sucked on highway, 1-2 was too short...good n/a gear if you are 1/4 only and shift it VERY high
I was h/c/i @ 300rwhp with 3:73s - excellent balance for the power, very fun, very usable 6200 shifts
I was h/c/i+vortech @ 420rwhp with 3:73s - Tad too much gear; not terrible but at my shift point at 6200 in 4th gear I would and could have really used that 4-600 rpm difference on the bigend hwy pulls as 5th is unusable for racing.

In conclusion; if you are 300-350rwhp I would suggest a 3:73 for a streetcar/ 4:10 for a track car
If you are 400-500rwhp I would suggest 3:55s for a streetcar and 3:73/3:90 for a track car, go bigger if you run a centrifugal and a 28" tire, turbo go lower. Only choose 4:10s or better if your trans is setup to pull through 5th imo
If you are 500+rwhp you are going to base your gear off your power adder; your tire size, and transmission and there are way too many variables.


Driving to work this morning, my tach showed:

60 MPH - 2000 RPM on the nose
75 MPH - 2250 RPM
80 MPH - 2500 RPM on the nose.

This is with 3.55s and a 25.7" tall tire (275/40/17). The car seems very comfortable cruising at 70-75 MPH around 2200-2300 RPM.

What were your RPM on the highway - real world driving?
Driving to work this morning, my tach showed:

60 MPH - 2000 RPM on the nose
75 MPH - 2250 RPM
80 MPH - 2500 RPM on the nose.

This is with 3.55s and a 25.7" tall tire (275/40/17). The car seems very comfortable cruising at 70-75 MPH around 2200-2300 RPM.

What were your RPM on the highway - real world driving?

If I was in your shoes I'd leave the gears well alone. The 3.55 is fine for your use.
Now I've had a recommendation to go to 4.10s instead of 3.73s!

Cripes, I'm so confused at this point. I like the 3.55s for the freeway....very comfortable...but do seem on the mild side for the street. Car still has great accelleration, but a guy is always searching for more.

I was convinced to go to 3.73s, then someone mentioned the 3.90s and 4.10s. I can't help but think the 1-2 shift with either of those ratios would be absolutely pointless and hard to control wheel spin. Not to mention, 4.10s would probably suck on the highway (I had them in a Camaro and it was not a highway car - but rocked between lights ;0)

I still leaning towards going ahead with the 3.73 when money permits.....still debating. Any more advice is appreciated..