Rear gear questions

[Zachary]

I have a 347 with a TK0500 in my 1979 Fairmont wagon. I am rebuilding the rear end now. I am currently running a 8.8 with 3.27 gears. I am replacing the gears along with clutches and bearings. My problem is- I cant decide what gear ratio to use. I have Bullit wheels on it with 245/45/17 tires (25.68'' tall). The first gear in TKO500 transmissions is 3.27. I have a brand new set of FRPP 3.73 gears but I am afraid first gear will be useless coupled with the 3.27 gear in the transmission. Any suggestions? Thanks!

[n2omaverick]

3.73s will be great. I run 3.89s in mine with a 2.95 first gear and wish i would have gone with a 411 or 430.

[Zachary]

What size tire are you running?

[306gt]

Depends on what you use it for street/strip or street only. It also depends on how high you want to rev the motor and where it peaks at. I run 4.33's with a Tremec 3550 with the 3.27 first gear. and a 26" tire. For me it is a street/strip car and runs well either way. First gear is real short but not useless.

[DeraldRice]

If this is a street car, Keep the 3.27's.

I have 3 cars with a 2.95 first with 3.55's and it is OK, but sometimes I wish I had the 3.27. I also run the same diameter tire as you have.

[Zachary]

It is a street car and I usally on rev it 6500. I do run it at the track some too.

[xctasy]

Your better off with 10.5:1 over all first if your on 28" rears as opposed to 24". Those bigger tire sizes can add 17%, then thats 3.73 to 3.8's rather than 3.27's.

Overall first gear on a light 5 liter can go down to 9:1 with 24 inch tall tires, but 2.75*3.27 can be rough on take offs in urban settings.

Before CAFE/EPA and traffic jams, Ford always used to run 2.78's on 302's and sometimes 2.46/2.42/2.32's on the bigger 351/390/BB's if they had the power to weight. 3.25's were ideal ratios for combination drag and circuit racing, with 3.91:1's the common drag racing gear. Most of the early Fords were in at 25" for tires, so you can go right down to 7:1 if you have to. Modern American conditions equate to traffic jams, so its not even a little 260 1966 Sunbeam Tiger with a 2.32 first and 2.87 diff. 7:1 is too tall with 24" tires.

3.27 1st is a great street 1st gear ratio with a 3.27 and 25.68" tires. How much traffic duty you gonna see? 3.73*3.27=12.2:1. A cammed up 5 liter might like that in traffic.

[86bluecobra]

I have a T-5 with the same ratio and I have 3.73's in my car. I love the combo. You do shift out of 1st quickly but I don't really notice it as an issue at all.

[horsepowerjunkie]

I have the 3.35 ratio first gear T5 with 4.10's in my 82 Capri & I love it. Still easy to drive on the street, runs aprox 2400 @ 70 in 5th and pulls awsome 60 ft's at the track!

[Zachary]

Thanks! This real world advice is what I need. I do see alot of traffic since I live in the metro Atlanta area. I actually think I would like 3.73 rear gear better for that situation for the easier "take off" to pull up one car length an d stop again. I want to be able to cruise at 70 mph as well. If I shift at 6000-6500 RPM would I still be in first through the 60' line at the track? How do I figure that out?

[86bluecobra]

I have the 3.35 ratio first gear T5 with 4.10's in my 82 Capri & I love it. Still easy to drive on the street, runs aprox 2400 @ 70 in 5th and pulls awsome 60 ft's at the track!

Yep that the first gear ratio in my T-5.

My brother inlaw went for a ride in my car. His words about how the car pulls in 5th was, "Most cars don't pull this well in third this is awesome."

The 351w has to take some of the credit for that quote.