T5s have a deep 1st gear, so I wouldn’t go too deep on the rear gear.
Your car probably has a 2.80:1 in it now?
Id run it and see how it does.

 

I have a T5z and run a 3:50. If I wanted to improve the "hole"shot, I'd go to a 3:89. The 3:50 nets me approx. 2K Rs at 70 MPH with 25.6 tires. I'm goos with it.

 

If you bought a new '93 Mustang 5.0HO with a T-5 you got a 2.73:1 rear gear. If you had an AOD you got 3.08's. The reason for the tall rear gear for the manual transmission cars was the steep first gear (3.35) in the T-5. If you have a 3.35 1st gear T-5 I wouldn't go any lower than a 3.25 gear. If you have the 2.95 1st gear T-5 I wouldn't go any lower than 3.40's. Anything lower and you're making 1st gear more or less useless so you might as well have used a TopLoader and a 2.79 gear.

 

I can get up to 40MPH in first with a T5 (3.35 first) and 3.50 rear end. I would hardly consider that useless. I find the OD to be more of an issue, sub 2000 RPM's at 70 MPH.

 

Depends on which T5, but with a WC ‘85 GT T5, I love my 3.73’s. Under 2,200 RPM @ 70mph. Really glad I didn’t go with 3.55’s.

 

This is a tough call to balance 1st and 5th.
I used a t5z 2.95 1st gear and changed the od gear to .80 ($80 at 5speeds.com).
i used a 3.25 rear gear.
I think i have a perfect balance. 2050 rpm at 60 mph
If i could have bought the .72 od from modern driveline ($300) i would have gone 3.40 but i would have had to buy those also and i already had the 3.25.


ken

 

I have 3.73 with mine and love it, the only other choice that i would go with is 3.55.

 

You can change the od gears it is not hard


ken

 

I currently have a t5z with a 2.80 gear and the best way I can describe it is it feels like a four speed, I’ve tried putting it in 5th going 50 and it was like at 1k rpm
3.25-3.80 range is my recommendation

 

It depends on which T5 transmission you have, as not all of them are the same, as well as a few other things like the height of your tires and finally your style of driving and the terrain that you'll mostly be driving on. Most of the T5 transmissions out of the 1980's 5.0 mustangs had a 3.35 first gear ratio as well as a .68 5th gear ratio, which will effect the rpm differently than a Toploader 4spd will with a 1:1 ratio. Linked below is a transmission ratio rpm calculator that you can play around with to figure out what you'd like, but I'd say anything at or above a 3.50 numerically would be my choice, and again depending on your tire height and so on.

For example, a car with a 3.50 rear gear ratio, a 28" tire height, .68 transmission gear ratio at 2,000rpm will only get you to 70mph. In my opinion that's kind of on the border in terms of the rpm and you'll likely experience some lagging or it's going to feel sluggish. Especially if you're going up a hill or incline and because of that, you'll likely have to downshift into 4th gear to get some more speed/momentum. Now if all of the values above are the same except that you switch out the rear end ratio to a 3.73 rear gear ratio, you'll get up to about 2,150rpm at 70mph. If you went up to a 3.93 rear gear ratio then you'll hit 70mph at 2,250rpm and lastly, if you did a 4.11 rear gear ratio you'll be spinning 2,350rpm at 70mph.

The issue is that the higher you go up in number for the rear gear ratio, aka going from a 3.50 up to a 4.11, that means the quicker you're going to have to shift out of 1st gear and into 2nd gear. Which is why I'm a proponent of getting a T5 and swapping out 1st gear to a 2.95 gear ratio and 5th gear to either a .73 or .80. That way if you go with a numerically larger rear gear ratio, you could stay in 1st gear longer and also not feel like your motor is bogging down on the freeway while in 5th gear, especially if going up a bit of an incline. Most people don't swap out gears though because it starts to get pretty expensive and they'll either live with it or go with a T5z or some other aftermarket T5 that has a lower 1st gear ratio as well as a larger 5th gear ratio. I again don't know what your tire height is, but if you live in an area with a good deal of hills or inclines then I'd maybe get something in the 3.50 - 3.73 range to where you can still use both 1st and 5th gear. If you have really steep hills, maybe something higher like a 3.93 or change up the 5th gear.

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.

spicerparts.com

 

I have a T5z, and a 3.55 first gear works just fine with the 2.95 first gear in the transmission. I have tried a standard T5 with 3.35 first gear and found first gear to rev to quickly for my liking. If using a standard T5, I would probably go 3.25.

 

I have a 2.95 T5 with 3.70 gears. I’ve only done a test drive around the block and down the street up to about 55, but 1st absolutely felt usable to me and I have no regrets. Additionally, I would push back on any idea that you can’t cruise with your 289 at less than 2,000 rpm. Just to see how it drove, I put mine in 5th at lower speeds and it did totally fine cruising at 1,600ish rpm - no lugging and it drove wonderfully. Sure, I downshifted for more power when I needed it, but don’t be afraid of overdrive.

 

Agree 100%. My car can cruise just fine at 1,500 rpm and my cam is a bit more aggressive than a Hipo cam.

This whole concept of "you cannot pass without downshifting..." is a bunk argument. MOST cars cannot pass without downshifting. That's why they put kickdown mechanisms on automatics. To drive at cruising speed at the perfect RPM band for passing is a huge waste of fuel and unnecessary wear on the engine.

 

I had a T5 in a 66 coupe with 289. Started with 4.11s and went to 3.50 gears after a few years. To me 3.50 is the sweet spot, especially is you're doing any freeway cruising.

 

i run 3.80;s with my t5z and 235-60-14's, about 2100 at 70. the z has a 2.95 first instead of the 3.35 on the non z

edit in no way, shape, or form does a 3.80 and a 2.95 first gear make first gear useless.

 

Just incase the OP is looking for additional feedback. The T-5 has a low first gear compared to the t-5z. If you go with too low of a gear "3.70-4.11" you won't be able to clear an intersection before you have to shift into second. The T5 came on cars with highway gears as posted above so it has a low first gear so you need to strike balance somehow. I wouldn't go higher than 3.50 myself. I had a 3.40 on my 8" and I was happy with it. You don't need a 9" rear end for anything less than 450hp, the upgraded 8" is more than enough. I like this guy for the center section. 8 AND 9 INCH FORD REARS TJ1141 | eBay Stores

 

As the others say, depends on what model T5. The problem with them is guys just look at that tall 5th which allows you to run a 4.10 on the highway. It works out to like 2.66:1. However you need to calculate the final drive ratio of all 5 gears and not just 5th. What happens with the 4.10’s is now 1st gear is all but useless. You end up with 4 gears that work. You’re starting off in 2nd gear.

The T5 factory gear ratio set with 3.35 is all about economy. It’s designed to start off very easily with 2.73 gears and absolute maximum fuel economy on the highway. With the 3.35, there’s a very narrow range of axle ratios that work. I’ve driven 2.73, 3.08, 3.27 and 3.40. Even the 2.73’s were no problems. I think my favorite were the 3.27’s . You should have no issues with the 2.80 gears.

I have a wide ratio Toploader 4 speed. First gear is 2.78. I ran 2.80’s because my 66 was automatic. The Toploader worked great. I never had any issues starting off and I live in a very hilly area, The Endless Mountains of PA. I currently have 3.55’s but will be going back to 3.00. The 2.80’s were worn and howling. Again 5th gear on the production 3.35 T5 is designed for nothing else but absolute fuel economy. It is not designed as the next progression in gear ratio like 1-2 or 2-3 and so on. The ZT5 is the best one with more sensible gear ratios but even that I wouldn’t go lower then 3.55.

This may sound totally wrong and not make sense but when you do, you’re in for a shock. If you take the 3.35 T5 with 4.10’s, outside of 1st gear which is useless, 2-5 compare just about exactly as a Wide Ratio Toploader with 2.80 gears. Calculate the final drive ratios of each gear and see.

 

In my 95 GT: It came with 2.73 rear gears. Much too tall. When I was drag racing (stock engine) I ran 3.73 gears. If I got a really good launch (5000 rpm launch) my 60' would be worse because I was shifting before I got to the lights. But that put me through the traps around 5k rpm in 4th. Even with 70 mph speed limits it wasn't bad. Eventually I quit drag racing and did some open track events (road racing) and put in 3.55 gears as I'd run out of 4th gear at some tracks. All this with the stock 0.68 OD and 3.35 1st gear.

I also have a TurboCoupe, which has the closer OD (0.86?). It was a bit of a mutt as it was an auto that I converted to T5. With the 3.73 rear gears it was at 3k rpm at just over 70 mph, which was a problem as they go open loop and rich at 3k which makes the fuel economy fall off a cliff.

Was it the SN95 that manual was 2.73, auto was 3.08 and 3.27 was the option?

 

Before any talk of axle ratios is had, how much power you have to begin with matters more. If you have a stock 225hp car you will find a different ratio is better suited than if you have a 400 hp car.