looking at a gear change...

Odds are you have 273s....they suck....cars a complete mutt with em...5th is something you never use as the cars doggy enuf, never mind slipping it into 5th..

I swapped 355s with 5spd for 2 seasons....no complaints...mpg was better, much more fun to drive, more sack and I actually could use 5th for a change....mid range hit was way better, 70 mph was a sweet spot and passing cars is a hoot as it will actually move some....speedo needed a gear swap and was pretty much right on....all goodness...

In the never ending quest for more hit I stepped up to 373s....mpg took a slight dump as I romp on it more often...stay out of it and the mpg is just fine.....first gear can be real short...from there on out its all goodness...midrange and upper pull is even better....you always have 5th and youll find yourself using it more often...
speedo gear remained the same and is off by maybe 3-4 mph...

choose your weapon...both are nice....373's and the 5spd seem to go hand in hand...for me I would not opt for anything higher than the 373s....depends somewhat on your goals...street car or a 1/4 mile terror...

How much would my speedo be off if i went to 3.73's from stock?

with 3.73s, when my speedo says 70, i am really doing about 65

i'll be yanking the 3.73s and going 3.27s in the spring, so my 3.73s will be for sale after i get them out

if you had 2.73 and put in 3.73 then your car will read 100mph and you are really going about 73 mph if you put in the 3.73 and do not correct for the gears.

Now if you put in the 3.73 and change out the drive gear to compensate for these it will be off about 5mph on the highway since the only gear out there is really for the 3.55 gears if I remember correctly.

Where can I get one of these speedo gears?

n/m they are all over e-bay
And they have ones made for 3.73's and 4.10's

What gear are you runnin now John?

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Right now 3.08's but all of my estimatations tell me 3.55 will be the best gear for me but I'm determined to develope a numerical conclusion with confidence. Right now I'm just thinking 3.55 with the assumption that I finish the 1/4 mile in 3rd gear @ ~105mph. If I went 4.10's, it would cost me one shift near the end and I wouldn't get through the whole gear so I don't see it being optimal.

The Green GT said:

How much would my speedo be off if i went to 3.73's from stock?

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I was scared you caught the bird flu from one of those penquins.....lol

I'd go with 3.73's. 4.10s will make it tach pretty high at higher speeds, like on the interstate...

3.73 is generally known by most people as the "best all-around gear."

Although we have 3.55's in our Cobra, and I'm quite happy with them. But of course, it has other work done to it too...so who knows how much of it is really the gear!

I think you can pick up the little plastic gears from the Ford dealerships for around $8.

Zero Signal said:

Right now 3.08's but all of my estimatations tell me 3.55 will be the best gear for me but I'm determined to develope a numerical conclusion with confidence. Right now I'm just thinking 3.55 with the assumption that I finish the 1/4 mile in 3rd gear @ ~105mph. If I went 4.10's, it would cost me one shift near the end and I wouldn't get through the whole gear so I don't see it being optimal.

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Hey John

1) Math is the best way to get an idea about rpm's crusing down the highway but you know that.

2) There are formulas to help determine rpm at the end of the 1/4 mile and again, I'd bet you know that too.

What I wanted to tell you has nothing to do with 1 or 2

Over the years I have had quite a few different cars and bikes and changed their rear end ratios.

IMHO, you can use this general rule of thumb to get an idea of the difference in how it feels to be running around on the street when you change the ratio.

1/4 of a turn will be very slight. You can't hardly tell you have made a change at all.

1/2 of a turn will let you know something has happened but the difference is not all that much greater than 1/4 of a turn.

3/4 or a turn will be noticable for sure and most noticable in the higher gears. IMHO, if one is stock, this is not too bad of a place to start for performance & the rpm's don't climb too high at highway cruise. Remember if you were a 2.73 kinda guy, you will only be woking with 355's here

Speaking about the high gears. You get a combo that makes good low end torque, power under the curve, or whatever you wanna call it and fourth gear absolutely rocks.

I was at 308's when stock and the first mod I did was move to the 373's.
These days, I kinda wish I had 410's but when I was stock, I think the 410's would have been a bit much and speaking about that ...

One last thought and I'm done here John.

Be careful who you listen to about gears. Here are two extremes for an example.

Stock Stang
H/C/I Stang

The stock Stang will start to peter out before 5K.
The stock Stang will build power quicker or at a lower rpm

The h/c/i Stang will have a higher range of rpm and will build power a bit later in the rpm band which means a steeper ratio will seem more tame with this kind of combo.

373's or 410's in each example will not act the same

That is one reason you see some say 410's are just great
AND
You see others say 373's are just too much

btw, the above info is stick trans related.

Sorry, but I needed to say one last quick thing.

You know how some peeps talk about 373's making first gear too short.

Mine is great ... then again I'm a h/c/i kinda guy

Grady

Yeah with my powerband now, it pulls hard past 6k so a steeper gear is going to be a good thing. I may just go 3.73 when the time comes. I'm ordering up a TFS Track Heat intake which may hurt alittle more low end so the steeper gear may help it out a bunch. Iguess if I can ever afford a KB I may go back to a low ratio so I can take advantage of the crazy low end.

Zero Signal said:

Yeah with my powerband now, it pulls hard past 6k so a steeper gear is going to be a good thing. I may just go 3.73 when the time comes. I'm ordering up a TFS Track Heat intake which may hurt alittle more low end so the steeper gear may help it out a bunch. Iguess if I can ever afford a KB I may go back to a low ratio so I can take advantage of the crazy low end.

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That is just the kind of thoughts I was trying to get across but was not sure I knew how to explain it.

Grady

Final5pt0 said:

i spoke to a local mechanic of mine that works on performance cars and when i spoke to him bout the gear change i just simply asked if the price included speedometer gear for the car he asid yes...but a couple of posts before someone said that the gearing makits it a few mph off even with a gear? is this true, or if i put 3.73's and got the correct gear would the speedo be right?

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Don't know if you be a stick or auto kinda guy

but

With my t5, 373's, 26" tires, and a 23 tooth driven gear, I'm off a couple mph cruising around town. At 80 mhp the error grows to about 4 mph.

You can go in the tail shaft of the tranny and replace the drive gear for more accurate speedo readings.

You can also get a magic box of some kind with dip switches for around 100 bux to correct the speedo. Speed Cal is it's name IIRC

Grady

Final5pt0 said:

my car has the stock 16in 5 star rims and its a 5 speed

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http://www.allfordmustangs.com/Detailed/608.shtml

Grady