I m currently converting my 65 289/C4 coupe to a tremec T5. Im just curious about what other people are running for gears out back. I was thinking about 3.55's or maybe 3.73's. Im running 17 inch wheels. Whats everyone's opinion? Thanks

 

most of them on here say 3.55 is a great highway gear.

 

I have 3.55 gears and yes it is great on the highway. The other thing to consider is the usefulness of first gear. If you go to 3.73 or 4.11 gears you have to shift out of first gear very fast unless you're winding the engine to very high rpm.

 

J.M.H.O., but I have a 302, (was a 289), that does have a useable RPM range to 6500, so that lets me use that first gear of the T-5. I love the 4.11's. When I'm not pushing it hard, I start in second gear and the car is very comfortable with that. It doesn't bog down or chatter, it moves... like it's supposed to. I frequently drive it like a three-speed when the family is with me. Nice and easy 2-4-5 pattern is very smooth. But when my neighbor wants to horse around, and I don't want to lose to his little mercedes, I use every one of those gears and I love each one. I've yet to be annoyed by the warning I got here, that is, that I'd be, "shifting into second before I got through an intersection". I've come to appreciate the 4.11's. And with the fifth gear, I still cruise at 70 mph at about 2100 rpm with an awesome passing capability even at highway speeds. No regrets, but I must admit that I haven't driven a thousand sporty cars, just a couple dozen or so. (My neighbor is a used car dealer and comes home with all sorts of toys.) I just don't think I'd want to trade my push off the line for a faster top speed or better gas mileage. The way I drive it, the mileage is going to suck no matter what gears I have back there.

 

It depends on a number of things.

Mechanically, it's your tire size and usable engine rpm. Other things involve your own approach to driving.

I'm guessing 245/45-17 and ~6000 rpm, so 4.1's or so should work fine at the dragstrip until you're crowding 110 mph at the finish.

The same rpm and 3.73's will give you just under 60 mph in 2nd. 3.55's will go a couple of mph above 60. Unless you're involved in some sort of competition involving sprints between 30 or so and 62 (where you need to avoid shifting at 60), you may not feel any difference (though at those same speeds in 3rd or 4th you might).

Perhaps the question you need to ask yourself is whether you are (or expect to become) naturally inclined to downshift or simply step a little deeper into the throttle. It may help if you have any motorcycle experience.

If it's a bigger slice of fuel economy that you're after, choose gears that are slightly taller than 3.55, maybe in the 3.2x range. I got better highway mpg with 3.27's and a Tremec 3550 than I do with the 3.73's that I replaced them with. Around townwas close to the same mpg as long as I took advantage of the shorter gears and short-shifted it (this is even harder to do consistently than it sounds, BTW). Car was a 3450# Malibu with a mild/moderate 350, which as far as this discussion is concerned should behave inreasonably similar fashion to a 289/302 in a 2900 lb Mustang.

Note that the taller gear (3.27) will be happier with 1st gear tranny ratios that are around 3.3, and that the deeper gears will better deal with the taller 1st gear ratios that are in the upper "two's". What ratios are in the model that you're considering?

Norm

 

Keep in mind that there are different gear sets in the transmissions so you'll want to take that into account. Do you have a 2.95 or 3.35 first gear? Is your OD 0.63, 0.68 or 0.80?

 

I have 370's in the rear with a 335 first get and a .68 OD. I wish I had either 3.50's in the rear or the 2.95first gear cuz first is almost useless to me right now. I'm also running a 408 stroker that makes gobs of low end torque and doesn't like to rev as much as ya'lls 289's and stuff.

 

I had 4.11's and it wasnt very good on the highway, around my 25 mph development, i cruised in 3rd. I put in 3.73's and like them a lot better, cruises good on the highway at 70~ and is smooth with not high rpm. and around town it does feel faster than the 4.11's. Also its not as loud, not having to wind out the engine like it did with the 4.11's. -Jon