3.73s worth it?

[Sky Render]

Counterpoint: 3.73s are better for road racing.

Yes, I am THAT guy.

 

[Norm Peterson]

My 07 gt came with 3.55s from the factory and I think its a great overall gear. I dont want to have to shift too soon and lose top speed (although its not like I top it out) and would like a bit more acceleration. Im thinking 4.10s would be too much for what Im after but 3.73s are too close to 3.55s to feel much of a difference. Thoughts?

3.73's from 3.55's with OE-height tires?

You will feel some difference. Not as much as the drag-racing crowd prefers, but is there. You will lose some top speed in 4th, being only able to hit 127 @ 6000 rpm vs 133 @ 6000 with the 3.55's. That mostly matters out on a road course, where having to shift to 5th if you've got some straight left is still too big of a jump. The 3650 could really use one more gear midway between its 4th and 5th.

4.10's will drop the speed in 4th @ 6000 rpm to about 116.

Engine rpms in normal driving with 3.73's vs 3.55's aren't enough different to matter.


I'm running 25.9" tall tires with 3.55's, which is very close to 27"-ish OE tires with 3.73's, and those are my observations over the past four years.


As to the peer pressure that seems to always crop up in axle gear discussions (that "don't fear the gear" thing) . . . you need to decide what is going to be right for you from your point of view rather than somebody else's. Think about exactly what you want (and maybe don't want) and do a little math using the tire revs per mile data that's readily available at Tire Rack and other online sources (all of the online speeds in gears calculators that work from tire size I've ever seen calculate speeds that are about 3% higher than actual).


Norm

 

[Pentalab]

A 27.2" tall tire and 4:10 gears will top out at 120 mph @ 6 krpm. Which is probably good enough for a dd / street / hwy application... on a NA 2007 car.

3.55 / 3.73 = .9517

Multiply all your current max speeds in each gear (say at 6 k rpm) by .9517 to find out what your new (slightly reduced speed) will be. aprx a 5% redux.

3.55 / 4.10 = .8659 Same deal...but this time its aprx a 13.5% redux.

If you have a blower on the 05-10 car, and a manual, a 3.73 is ideal. If it's a 05-10 automatic, with blower, a 3.31 is ample.
2nd gear on the auto is 14% lower than 2nd gear on the manual. 3rd gear on the auto is 16.5% lower than 3rd gear on the manual. In 4th gear they are both 1:1 ratio.

IMO, installing a 3.73 in your case is a wasted effort. A 4:10 would show the improvement you want... albeit you are maxed out at 120 mph with an oem 27.2 " tall tire.

 

[Ryan Moore]

And the thing is, if you buy either gear and you're not happy, it's a royal pain to take them all out and start over. I used to have a Camaro that came with 3.42's since it was a 6 speed. About $200 for a 4:10 gear. It was $200 well spent. Out of the hole, I could pull on even more powerful cars until I hit the top of 2nd gear. But at least you'd have the out of the hole launch advantage. You just have to make sure you have somebody who knows what they are doing. They either have prior experience putting a lot of these in, or they have the equipment to dial it in. If it's off a bit, you can end up having gear whine. If you get gear whine, then you have to go take it all apart and start over again.

 

[Pentalab]

If paying somebody to install the new gear, get it with a ...'no whine guarantee'.

 

[702GT]

If paying somebody to install the new gear, get it with a ...'no whine guarantee'.

I offer a tail light warranty.

 

[JBert]

spoken like one who's not had 4.10s in a 3V S197

12 years of history show 4.10s are a perfect choice for these cars either N/A or centri blower - twin screw is a different discussion.


" shift a lot quicker" also a farce in my view, the difference (with stock height tire) from 3.55s to 4.10s in MPH at 3000 rpm is 3 mph, so you shift 1-2 at 17 mph instead of 20 mph... really, that's "a lot quicker"???

4.10s make the car a lot more responsive off the line and while in gear

I guess I need to stop by more often; this site is more active than some of the others that have all but died.

True I have never had a Mustang with 4.10's and I am quite sure I would not want one for my use. Might be good for a drag car, but not what I would want for a street car.

Here's the picture: you have a Mustang with fairly loud exhaust and 4.10 gears, manual transmission of course. You are commuting to work, not looking to call a lot of attention to yourself at 6:30 AM in commuter traffic. Stopped at a red light next to a Prius. Light turns green, and you have to either tach out each gear and make a lot of noise, or short shift up to third by the time you are through the intersection, just to keep up with the Prius. Definitely not what I want. With my old 3.31's I could use the torque in the low end of the powerband and easily stay ahead of the Prius without a lot of fuss or fancy quick shifting.

For road track, "it depends" on the track. For one of the tracks I go to, which is a bit tighter, 3.73's are just about right because they put me in the meat of the powerband in 3rd for most of the track. At another track which is more open and a bit faster, taller gearing would be better because there are parts of the track where I am hitting the rev limiter in 3rd, but not a good spot to shift to 4th.

There is no "perfect gear" ; they are all a compromise and it depends on what you are doing with the car.

 

[stkjock]

ok, "not what I'd want for a street car" that's fine, but the question is a performance based one on a performance based site. they work very well in a street car, I had them in mine for a number of years and not once did I feel that they were a short gear, granted it wasn't a commuter car, nor very loud, but if you want a loud Mustang, well then enjoy it loud all the time.

frankly I don't see "short shifting" ever an issue

lastly, if a prius was next to me, I'd be extra loud!

to each his own for taste

 

[Norm Peterson]

OP is pretty clear about his car remaining in street duty (feels the 3.55's are a pretty good gear and specifically mentions that he doesn't want to be shifting too soon). I agree, "a bit more acceleration" isn't very definite, and certainly means different things to different people just within this thread.

He could probably go either way at this point, 3.73's or 4.10's. Maybe taking a little time to think it over will help him decide between the two, and whether he really wants to get any more serious about acceleration than Ford did back in 2008 with the Bullitt (came with 3.73's IIRC) or does today with either of the Performance Package options.


Norm

 

[stkjock]

OP is pretty clear about his car remaining in street duty (feels the 3.55's are a pretty good gear and specifically mentions that he doesn't want to be shifting too soon). I agree, "a bit more acceleration" isn't very definite, and certainly means different things to different people just within this thread.

He could probably go either way at this point, 3.73's or 4.10's. Maybe taking a little time to think it over will help him decide between the two, and whether he really wants to get any more serious about acceleration than Ford did back in 2008 with the Bullitt (came with 3.73's IIRC) or does today with either of the Performance Package options.


Norm

umm, nope, he asked a pretty open ended question

My 07 gt came with 3.55s from the factory and I think its a great overall gear. I dont want to have to shift too soon and lose top speed (although its not like I top it out) and would like a bit more acceleration. Im thinking 4.10s would be too much for what Im after but 3.73s are too close to 3.55s to feel much of a difference. Thoughts?​

​

 

[Norm Peterson]

Different things to different people.

You're dragstrip-oriented, I'm street and road course oriented.


Norm

 

[stkjock]

Different things to different people.

You're dragstrip-oriented, I'm street and road course oriented.


Norm

agreed, for strip/street 4.10s in a 3v have a long history of being a great setup

for a road course, I can't speak too, I'll leave that to you.

 

[Norm Peterson]

for a road course, I can't speak too, I'll leave that to you.

Nearly always a poor choice, as it would require upshifting 5th (where acceleration falls on it face) on too many occasions.

In street driving, it would depend quite a bit on whether you're dragstrip oriented or road course oriented. Or maybe how seriously. FWIW, I almost never launch very hard on the street. Not completely never, but it's extremely rare.


Norm

 

[stkjock]

Nearly always a poor choice, as it would require upshifting 5th (where acceleration falls on it face) on too many occasions.
Norm

wouldn't that really depend on the track one races? FWIW - a track with short straights would that issue be a non-event, like Lime Rock witch is fairly local to me, the entire track is only 1.5 miles.

 

[Pentalab]

The real issue is the various gear ratio's in the tranny itself, they are not optimized. This is where a 6+ speed tranny may fare better. Would be nice (in a perfect world) if the end user could specify exact tranny gear ratio's for each gear. IE: optimized gear ratio's for 1-5. 6th is the 1:1 gear. 7th is the OD.

A 4.10 rear gear + 27.25" tall oem rear tire.... results in a top speed of just 120 mph @ 6 krpm...in 4th gear ( with it's 1:1 tranny ratio). Want to go faster, put it into OD..watch tach drop like a rock, and car falls flat on it's face. For most applications, street or road course, or strip, 120 mph may well be plenty good enough. If not, a 3.90 is your next choice, followed by the 3.73.

Right now, with 3.31 rear gear, and my 2010 auto, and a 27" tall tire, it's aprx as follows. (6 krpm)
1- 42 mph
2- 62 mph
3- 94 mph
4 - 150 mph
5- 200 mph

As can be seen from above, there is way too big of a jump from 3rd to 4th. There is no real way to optimize the above mess. Tweak tranny gear for a higher top speed in 3rd, and then its sluggish getting there. Use a lower rear gear to compensate for the sluggish 3rd gear..then 1+2 are now too low. It needs another tranny gear, mid way between 3rd and 4th...that tops out at 122 mph.

Even better, would be shorter ratio spacing's, so it ends up more like this
1-42
2-62
3-82
4-102
5-122
6-142
7-162
8-200 (gas saving gear)

Ok, now you can always find the sweet spot.

 

[stkjock]

my 06 GT I'd shift at 6500 that's good for near 130

 

[Vallee]

I am running 3.73:1. They did make a noticeable difference or over the stock 3.55's and didn't kill the gas mileage... However I am boosted, and with the added power I think 4:10 might be a bit much for daily use.

 

[stkjock]

I am running 3.73:1. They did make a noticeable difference or over the stock 3.55's and didn't kill the gas mileage... However I am boosted, and with the added power I think 4:10 might be a bit much for daily use.

not with a Centri

 

[Pentalab]

Track folks on road courses have different issues vs a 11 sec drag race. The road course folks use a lot of high sustained rpm....for the typ 15-30 min track session. Flip side is, they usually are not using a blower. With a centri, typ the boost goes up to the square of the rpm... hence the lack of boost at low rpms. PD blower is instant boost. Toss in the tq converter, in it's many different config's, on any auto, + PD blower, and 4.10 gears.. and the car might be handful in some cases.

 

[stkjock]

yea, agreed, however 4.10s + 28" tire have shown to be a great street/drag combo on a 3V