Gear ratio

[Juice It 10]

What is the best gear ratio for a stock 351W with I believe its called an FMX 3 speed auto trans to have great low end power and be able to cruise on the highway with no issue. I think I have a 275 rear and it has absolutely zero low end torque.

 

 

 

Thanks,

 

Jeff

[chillininnh 21]

Mine came with a 3.00 open rear and FMX tranny. I ran it for years with that ratio. The car wasn't a beast out of the hole, but boy did it have legs on the highway. When the rear let go 5 years ago I installed an Auburn Gear limited slip with a 3.70. This really woke the car up from light to light, but on the highway it was revving the engine up too much for my liking. I f you do a lot of highway driving I would stick with either a 3.0 or a 3.25. If you like to race from light to light, try a 3.50. Good luck!!

[coz 108]

No overdrive - 3.50 or 3.55s. Seems most stick with that ratio as a happy medium.

[Juice It 10]

Can I cruise on the highway at 75ish with a 350 rear or will it rev too high. I am craving some low end power but need that balance. Is a 350 the most ideal?

[6T9Mach1 12]

If you want to run at 75 mph down the highway then 3.25's will be better suited to your needs. With 3.50's and 26 inch tires you will be turning almost 3400 rpms at 75 mph. With 3.25's it will be 3150 rpms.

[coz 108]

6T9 brings up an interesting issue - tire size. It will affect overall gear ratio. A 28" tire would give you 3150rpm at 75mph w/ 3.50 gears.

 

I tend to be heavy on the gear and would "grin and bear" 3.50 gears at 75mph. However, if you truly want a 75mph cruiser 3.25 gears may be better suited for you needs. Everything is a trade off.

 

here's every calculation you would ever want and them some....

 

http://www.csgnetwork.com/automotiveconverters.html

 

Where in MD are you Juice It?

[Boogerschnot 12]

I'm in the same boat man.. Running the 2.75's and bogged down off the line. But it is pretty decent for the highway. I really want a 5 speed with some 3.70 somethings in the rear.. That could make me happy..

[bnickel 10,004]

my favorite all around gear for a non overdrive trans is the 3.25, i've been running it in my 69 gt for about 20 years now and it's the perfect blend of city/highway gear IMO. i run a 26" tire

[ultrastang 10]

http://www.ultrastang.com/Page.asp?PageID=8

 

http://www.ultrastang.com/Page.asp?PageID=9

[d.reese 13]

I tried 3:50's with no tack and sounded pretty wound up at 65, but a guess about 2800 rpm at 60 - 65 mph! We do 50 -50 in town and the freeway and no racing! I like the 2:75 s it came with for all round and gas milage!

[Juice It 10]

I tried 3:50's with no tack and sounded pretty wound up at 65, but a guess about 2800 rpm at 60 - 65 mph! We do 50 -50 in town and the freeway and no racing! I like the 2:75 s it came with for all round and gas milage!

 

Do you have any low end power with the 2.75? Mine has zero. I don't have a tach either so I don't know what rpm is good @around 70-75mph.

[d.reese 13]

Yea, it takes off great. I can do 70 -75 and I believe it to be around 2200 to 2400 at that speed. Put a little advance timing in the distributor or check the vaccum advance / weights in the top of the distributor.They been none to rust and get stuck or even have broke springs. Should not be ZERO!

 

The reason I went 3:50 was to include the possi. These cars are so light, I would not drive on damp or slick roads with a possi.

[Justafordguy 10]

I'm running a 3.27 gear right now but it's not good on the highway. It turns over 3K at 65 mph. I just purchased a set of 2.73 gears and will put them in this weekend. I think they will be much better for the highway. I'm running a 315-35r17 tire so they are less that 25" tall. This is the main reason the 3.27 gear is too low. I'll let you know how the 2.73 work.

[ForceFed70 14]

I went with 3.73's when I had my FMX... was great around town, but highway driving sucked.

 

If I was going to do it again, I'd probably go with something closer to 3.50's

[Boogerschnot 12]

How much of a difference will a 5 speed make if I were to go from 275's to 350's does the 5th gear make up for any of the over revving? Or is it going to be about the same? I guess I need a tach to see exactly what my engine is doing on the highway, im still just guessing.

[d.reese 13]

I believe its 1 to 1 like all trans. Same if the tranny is a 3, 4 or 5 speed unless the 5th is an overdrive. Then I believe your on to something that will make a difference.

[Justafordguy 10]

I took the coupe for a long ride today after the 2.73 gear swap and it's way better on the highway now. Not as good out of the hole but 2500RPM at 70 is nice. It's very quiet at cruzing speed now. I can even hear the stereo.

[Grabber70Mach 107]

See if this might be of some help to you.

 

http://www.ultrastang.com/Page.asp?PageID=8

[Juice It 10]

Since I don't have a tach, what RPM is normal at 60 mph with say a 26 inch tire and what rpm does it start to rev too high for normal highway cruising?

 

Thanks,

 

Jeff

[d.reese 13]

The chart tells the story! Great tool for figuring where you are, the overdrive is the way to go if you want to do street / strip.

[Boogerschnot 12]

Same thing I was thinking.. 3.70 something in the rear and a .68 to 1 5 speed would be nice!

[djs69stang 10]

I have a 302, c-4 3-spd, 3.55's, posi, 235-60/15's, and at 65 mph I am 3100 rpm's. No problem with temp.

I had 2.75's with limited slip and it cruised great but that was just too slow off the line. A Cougar friend has the same engine and tranny but has 3.75's and his gas gauge moves almost as much as his speedo.

It comes down to what you want to do when it is time to go.

[bnickel 10,004]

if you do a lot of city driving sometimes it works out better to have the lower (higher numerically) gears instead of highway gears. that's one of the reasons i really like my 3.25's, great all around compromise and when i swap in a wide ratio AOD it will be like having 3.50 or 3.70 gears in 1st and 2nd and more like 2.40 gears in overdrive while keeping the same 3.25 gear out back.