kn7671

3.73 vs 3.08: Better gearing choice??

So I got to kicking around the idea of changing the rear gear ratio to a higher gear so that 1st gear could become more usable than with 3.73's (max 40mph at 7000 rpm), and 2nd gear more than 60mph, and being able to run the 1/4 mile trap w/o running out of gear.

3.73 @ 7000 rpms
1 = 41 mph
2 = 62 mph
3 = 89 mph
4 = 114 mph
5 = 150 mph
6 @ 80mph = 2425 rpm

3.08 @ 7000 rpms
1 = 50 mph
2 = 75 mph
3 = 108 mph
4 = 138 mph
5 = 182 mph
6 @ 80mph = 2000 rpm

Now compare a Mustang 5.0 MT-82 to the Base C6 Corvette 6-speed manual:

3.42 @ 6600 rpms
1 = 50 mph
2 = 71 mph
3 = 104 mph
4 = 148 mph
5 = 209 mph
6 @ 80mph = 1950 rpm

or 2010+ Camaro SS

3.45 @ 6600 rpms
1 = 52 mph
2 = 76 mph
3 = 110 mph
4 = 158 mph
5 = 188 mph
6 @ 80mph = 1850 rpm

I'm really torn on how to think a 3.08 couldn't be a better overall gear than the 3.73. With 1st gear being close to useless, the increase to a 3.08 would split the speed capability between 1st and 2nd with 3.73's, and 2nd is good for over 60mph. Since I use 2nd almost exclusively for my starting gear now, maybe going to 3.08's be best.

Does anyone know of any challenges of putting 3.08's in the 2011+ 5.0, and do you think better mileage is possible with 3.08's?

Ltngdrvr

Why not go even further than the 3.08 and snag some 2.73 gears from someone with a V6 that swapped out to another gear. Bet you could get them for next to nothing and with 2.73's you wouldn't even get out of 3rd at the drag strip since it would be good to 123 mph. 1st gear at 57, 2nd at 86!

LagunaBeach

The ONLY thing 3.08 would be good for is fuel mileage on a flat highway. In order to achieve the best mileage you want to get into the highest gear as soon as possible. With a 3.08 the engine has to work harder to get up to speed. Any time you want to accelerate you will be pushing the gas pedal farther down to achieve the same results which in turn is just dumping fuel into the engine.

As for being better in the 1/4 mile I think again you will be disappointed. You want to go through the traps as close to the HP peak as possible, which is 6500 in the 5.0. A 3.73 gear gets you there just perfectly at the top of 4th, a 3.08 would be running about 5700 in 3rd. Hardly ideal for all out performance.

If there was any benefit to a 3.08 don't you think Ford would offer it in the 5.0? Especially with all the attention on fuel economy these days.

Bottom line, I think you would be very disappointed with a 3.08. It will seem like the car lost 100HP. Seriously.

Ronin38

Why go all the way from a 3.73 to a 3.08? How about the 3.55?

Just a thought.

Five Oh Brian

Gears are a torque multiplier by definition. The GM V8's are much bigger engines that make more torque than our 5.0L, so they can get away with less gearing without hurting acceleration. The high-revving 5.0L Ford needs gearing to make up for the lack of torque.

That said, the 3.08's will make the car feel like a turd, 1/4 mile times will suffer drastically, and fuel economy on the highway will barely improve, while fuel economy around town will suffer as you'll need more throttle to get the car moving.

kn7671

I think you guys are missing something I'm seeing. This would be very close to putting 4:10's in your car, but skipping 1st all together. Don't know about most of you guys with 3.73's, but I barely use first unless I'm at the drag strip or am moving the car around at slow speeds. Compare each gear below, between 4:10, 3:08, and 3.73:

4.10 @ 7000 rpms
1 = 37 mph
2 = 56 mph
3 = 81 mph
4 = 104 mph
5 = 137 mph
6 @ 80mph = 2675 rpm

3.08 @ 7000 rpms
1 = 50 mph
2 = 75 mph
3 = 108 mph
4 = 138 mph
5 = 182 mph
6 @ 80mph = 2000 rpm

3.73 @ 7000 rpms
1 = 41 mph
2 = 62 mph
3 = 89 mph
4 = 114 mph
5 = 150 mph
6 @ 80mph = 2425 rpm

As for needing to use more throttle to get the car moving, remember I use 2nd as my 1st gear for the most part today. The new 5.0 motor makes plenty of torque at low rpm's with the VVT, almost dead-on to the torque curve of the Camaro 6.2L SS. I think that being able to use 1st again under normal conditions would improve efficiency a little compared to using 2nd all the time as the starter gear.

As for the 1/4 mile, with 3.08's you would be running through the traps at about 5800 rpm @ 116mph in 4th, instead of running out of gear with the motor at it's maximum rpm on the verge of needing an upshift to 5th.

LagunaBeach

Why do you skip 1st gear? It's not like it's just ridiculously low that you can only go 5MPH with it. I have driven many Mustangs with 3.73's and never once thought about not using 1st gear. You do realized that you are putting more wear on your clutch by starting in 2nd, right?

If there was any benefit, fuel economy or performance, to using a 3.08 gear Ford would offer it from the factory. Personally I think that the stock 3.31 is way too low for the 5.0.

I guess there is only one way to find out how it will work.

Ethanjbeau

Hey don't be bashing the 3.31 crowd

kn7671

I can modulate the clutch and throttle well enough that I can successfully and repeated take off in 2nd gear at barely 1000-1200 rpms, so I highly doubt I'm wearing the clutch any quicker. If I need a performance take-off from a dead stop, I will use 1st gear when traction permits.

As for skipping 1st and using 2nd, I usually skip shift more than that, shifting 2-4-5-6 most of the time.

I find 1st useless most of the time due to the speed at which traffic accelerates around here. The engine makes enough torque that starting off in 2nd lets you easily maintain speed with all the automatic heavy footed drivers with ease.

Ltngdrvr

Taking off in 2nd is no biggie, a friend used to have a '76 T/A with a 468 BBC and a Doug Nash 5 speed and a 9" rear with 4.10's and he would take off in 5th a lot of the time because he had his right hand busy with his girlfriend...

mystickeith50

Don't put 3.08s in. You will be disappointed in all aspects. You won't even see that much better mpgs. And no matter how good ur doing it, starting in second every time will wear your stuff out faster. Part of my job is driving big rigs and other cdl trucks. They have torque out the ying yang where you can start out in almost any gear u want. U learn the hard way though that you wear stuff out quicker.

assasinator

ok folks i have fuel economy documented on the corral for going from 3.90's to 2.73's a few years ago with the turbo 96gt.

i went from 21 highway to 31 highway. all that pulling HILLS worse and other crap is just that.

i think 3.08's is a great choice. you'll lose only the first 40mph accleration, but the splits from there will be identical. and if you are rolling, you'll lose no acceleration.

dafreeze

I think you an a couple other guys should go to them, then...let us know how that works out for you.

For me, this gearset is perfect. But then I bought this car for what it is..new but still classic working man American muscle. And quite awesome, at that.

mustangGT90210

40mph is useless? Please explain that to me. My truck with 3.08s shifts to second gear at 35 (at 3700rpm, redlines around 4k) and the 5 speed Escape 4cyl I used to get to drive could only do 35 at 6k rpm.

And I have never once felt these gears were worthless. That little escape could push you back in your seat pretty **** good in 1st, and it got going real easy, much like my truck. I'm clearly just lost as to how maxing out at 40 is "useless"

kn7671

40mph isn't useless, it's the short gap between 1st to 2nd that's really useless w/3.73's. To be honest, it all depends on how you want to drive your car. I want to drive my Mustang like an automatic when I'm not using the car in a performance manner, and the easiest way to accomplish that is to shift as little as possible, taking advantage of the Torque instead of the HP and RPM's.

An automatic shifts quickly, keeping the revs/noise down while simultaneously keeping your car steadily pulling away from a stop light. You simply can't do that quickly enough while trying to use every gear in a manual 5.0 w/3.73's and shift at a moderate 2000-2500 rpm's, like an automatic would, and maintain the speed all the traffic around you is moving.

Where I live the speed limits on most roads is 40-55, and traffic accelerates pretty quickly around here, so unless you rev up on first pretty hard, traffic just moves on by you, and I hate being a road-block simply because I couldn't keep pace with the traffic w/o revving the engine like rice boy racer.

I think I'm going to get the 3.08's installed in a month or so. It won't be the end of the world, and if I don't like it, I can always get the original 3.73's put right back in.

Here is a 3.08 6spd-manual compared to the stock 3.15 6spd-automatic, and then both 3.7L V6's in manual and auto:

3.08 manual @ 6800 rpms
1 = 48 mph
2 = 73 mph
3 = 105 mph
4 = 134 mph
5 = 177 mph
6 @ 80mph = 2000 rpm

3.15 auto @ 6800 rpms
1 = 41 mph
2 = 74 mph
3 = 114 mph
4 = 152 mph
5 = 199 mph
6 @ 80mph = 2175 rpm

2.73 manual 3.7L V6 @ 6850 rpms
1 = 47 mph
2 = 79 mph
3 = 121mph
4 = 162 mph
5 = 201 mph
6 @ 80mph = 1900 rpm

2.73 auto 3.7L V6 @ 6850 rpms
1 = 48 mph
2 = 86 mph
3 = 132 mph
4 = 176 mph
5 = 232 mph
6 @ 80mph = 1900 rpm

You don't hear many automatic people complaining that the gearing of the stock 5.0L automatic is horrible, and their drag strip times don't reflect horrible performance either. 3.08's in a 5.0L manual car would still be shorter than a 5.0L automatic with 3.15's (exception of 1st gear), and is still even shorter gearing than the 3.7L V6 automatic or manual car with 2.73's.

FYI - the Corvette Z06 is capable of 59mph in 1st gear, and the ZR1 can do 68mph in 1st. (I know they are lighter and more powerful than the Mustang)

AlsCobra

Just go 3:55. Unless you want more fuel economy. Should trap out at top of 4th if you play with shift points.

MyStang2010GB

He obviously has his mind all ready set on the 3.08s so just do it and report back what your observation is... plain and simple.

LagunaBeach

The autos have different ratios in the trans, namely a taller 1st gear. Either way, it seems like you have your heart set on 3.08's.

Overboost

I see this ending horribly...

Joe_in_Naples

Im happy with my 355's. Good luck on the 308's.