3.55 gears..

[tx65coupe]

I would not go more than 3.20 gears with out an overdrive transmission. I would probably go with 3.00 gears if you drive it a lot.

[09Frank65]

I have 3.55 with C4 transmission. You will NOT be limited to 55 on the highway. With 235/60 rear tires I turn 3200 RPM at 70MPH. I have driven it for 10 hours straight with the only downside being frequent visitation to the gas station along the way. I wouldn't want to do it daily as the higher engine speed will lead to earlier wear on the engine. But for a cruiser it's just fine.

Just to give you an idea:

With 3.40's 70MPH would be 3046 RPM (on my tires)
With 3.25's 70 MPH would be 2930 RPM

It's a trade-off. The lower the gear is (higher numerically) the bigger the torque multiplication will be (more oomph off the line) but it will raise your RPMs and lower your top speed accordingly.

As a few others have mentioned, with an open differential you will be spinning one tire furiously, especially if you are running stock size tires.

I would personally wait until I could get a track-lock center section and make the gear swap at that time.

[Mustang_zulu]

If your going to do alot of highway driving or want that option ava, 3.55 will not be what you want. with my 255/60/15's on the rear i was doing 27-2800 rpms at 60 mph on the highway. with my 235/60/15's i was running just about 3k rpms doing 60. im in the process of finding a "daily driver" one i can drive anywhere and i will stick with 3.00 gears for sure... unhless i go with an AOD, then 3.55's at least.... think about the type of driving your going to do... if you want to go on long trips (4 hours +) stick with the higher 3.00 gears... when my 3.55's drive to work and back (30 miles round trip) im buring a 1/8 tank easy cuz of the high rpms on the highway...

[ToneMT]

Here use these calculators to see what changes you'll see. I do a good deal of Highway time - so went with the 3.25 on a fresh C4.

ENGINE RMP/Speed
Tire Calculator

[64.25]

I agree you should change to some kind of lsd at the same time because you'll have to pay someone to set those gears up properly and then pay again sometime in the future. You could consider buying a complete re-built center section or get the components and do it yourself if you feel capable- the difference is about $200 labor. I bought a used center section with 3.55 and detriot tru-trac from a trusted member here who was switching to a nine inch rear. Be aware that these don't come up to often so have your cash ready. Which gear set you go with depends on your amount of highway driving 3.4 and 3.55 are not that different and I would focus on the difference between those and 3.25 which is about 240rpm at 60 mph. Oh and since you have to pull both axles when doing the job you'll have to buy axle seals as well (and check the axle bearings). John

[Trinks54]

Ford Eight inch Rear End Mustang or Street Rod 8 " Trac Loc Posi 550HP 9 | eBay

I would do something like above with the 3.55s. I had the 3.55s in my 65 for a long time with a 4 speed. Yah the RPMs were a little high on the highway but it was a lot more fun to drive stop light to stop light. Plus I believe you had an earlier thread about wanting to run 13s. You can always put a little taller tire on too. I would highly recommend the trac-loc rear too, otherwise you will be spinning that tire. I understand the budget thing though. I did the gears first and then a few years later bought the item below
8" Ford Traction Lock Posi Unit 28 Spline Trac Lock New Made in USA | eBay

If you have questions Brayden from Quick Performance (the 2nd EBAY link) was awesome with answering questions and selling me the right parts at a good price. Good Luck

[horsehead]

Originally Posted by Josuizzle16

Alright so my last question.. I've heard to get 3.55, 3.40, and 3.25.. So considering everything that I have what would be the best option for me..
Stock auto 3 speed tranny, 289 with headers, exhaust, intake, and 600 CFM carburetor and I think thats it.. So what do you guys think my best option is? Thanks!

Depends on how you use the car---If you do a ''lot'' of interstate driving--3.00's---don't change at all, thats' probably what you have. If your going to mix it up and do some interstate and mostly local driving 3.40's. If your car will hardly ever see the interstate 3.55's. Heck--I run 4.11's in the car below for 2 years, all local driving though with no problem. I like the 3.40's i have in my 70 right now and i have run all three of the gears you mentioned---And like said, do it once, get a tract-lock when you do. Good luck--

[jdub]

I got 3.55s. Rarely drive on the highway. Wish I went lower.

[horsehead]

Originally Posted by jdub

I got 3.55s. Rarely drive on the highway. Wish I went lower.

Heck yeah---. The 4.11's I had made my car made it feel like it had tons of torque for a little 302. I had a 2800 stall in it. Was a blast to drive. Don't remember ever driving it on the interstate, and probably wouldn't want to-- for long. But made the local roads, none over 55 MPH around here, and to town fun to cruise on. I am running a tall 275/60/15 BFG's on the rear though.

[Markh]

Originally Posted by bartl

I've got 3.00's behind a top loader (same final drive ratio in 4th as a C4 in drive), and I'm dead on 3,000rpm at 70mph on 215/65R15's. I like driving on the highway and I don't think I'd want to go much lower than this.

X2 on this IMO. I had a 8"/3.50 gear in my old '67 fb (289/C4) and it would turn close to 3000 @ 60. While others don't mind turning 3000+ on the highway, I much prefer a 2400-2600 cruise. (The 3.50 was a great red-light/city gear, though.)

Like bartl, I currently have a 3.00 gear in the '67 vert (289/C4), and it's not too bad off-the-line and nice on the highway. Personally, the most gear I would consider without over-drive would be 3.25s.

Also - you may want to consider/research a higher stall torque-converter. A decent converter and 3.25s would give you a much improved hole-shot (over your stock converter and 2.79? or 3.00? gear.) Good luck!

[beechkid]

Originally Posted by bartl

Just be prepared.....with 3.55's and a peg leg rear, you'll be spinning that inside tire like a commercial washing machine.

I haven't heard that in years!! So very true & i am laughing my butt off right now!

[Josuizzle16]

Damn thanks for all the answers. This really helped a lot..!I think I might buy those parts with the links. Seems like a good deal!

[sdmustangrider]

Trust me!! you put the trac loc and 3.40 gears, just step on it on 2nd gear and you'll feel the power hahaha Even first gear gives a great launch.

[Huskinhano]

Originally Posted by bartl

I've got 3.00's behind a top loader (same final drive ratio in 4th as a C4 in drive), and I'm dead on 3,000rpm at 70mph on 215/65R15's. I like driving on the highway and I don't think I'd want to go much lower than this.

Ditto. I still have the 2.8's in from when my car was auto. I had a 3:1 carrier that was in good shape when removed from a parts car I was going to install when I put my wide ratio toploader in. But it got rusted pretty badly when stored. I thought the 2.8's were going to be horrible but as bart said, great on the hiway. I'd like to try the 3:1's though.

I've driven T5 5.0 Mustangs with 2.73, 3.08 and 3.27's. I really like the WR Toploader vs the T5. The WR Toploaders 4 gears are much closer together then any of the gears in the T5. You either lug in 5th with tall gears or loose 1st with low gears. Out of the 4 useful gears, you get a big gap between 2 gears no matter what.

[vetshelby]

I have the 3.40 posi in mine.i was running a 351w solid lifter cam with a 4 speed tl .i put a 302 roller motor in with the 5 speed.l can say I like the lower revs on the highway but I miss the power of the 351.pinto wagons used to come with 3.40 gear option fits right in a 65 66 8 inch