3.55 or 3.80 gears

I'm getting ready to order some new gearing for the maverick. I want to still drive it on the highway to shows and stuff, so I was hopping someone here with these gear ratios can tell me what RPM there running on the highway? right now i'm running 2750rpm at 70 mph. I'm not sure what the stock ratio is for a 75 I6 w/auto trans.

In it now is a 312ci about 400hp with a C4, the C4 is being rebuilt and beefed up as we speak.

 

The factory rear end would either be 2.79:1 or 3.00:1.

Do you plan on taking this car to the strip?

 

I've always hear great things about 3:55 that's what I am going to run.

My plans are, Street strip tour

 

Good choice. That is what I'm going to run paired with a 347 and a C4. I also run the same ratio in my Mustang II with a 302 4 speed.

 

I run 3.55:1, and average 1800 RPM at highway speeds, but I have a AOD.

 

Yes but only to see what it can run, not goint to make a habit of it

 

Go with the 3.55s'...If you had an overdrive trans I would say 3.80:1
The 3.55s' will make for a good all around gear set for your car considering its usage.

 

3:55s in both my Mach I and Bronco. Had them in my 1969 Chevelle SS, too.

I actually purchased 3:08s for the Mach I to use on the German Autobahn, but never installed them.

 

C-4 is the killer...could be turning 3-3200 RPMs @ 70 with the 3:55/C-4...

I'm at 2200 RPMs at 80 MPH w/3:55 and OD.

...

 

You could use the 3.80 w/ a really tall tire,but w/ out OD you`ll rev higher than you want & it will kill you`re fuel mileage.

 

Yup my '69 Fairlane with 428CJ turns same, in a almost 4" stroke motor, things are real busy at 3200 RPMs... All this was acceptable in the olden days, but now days anything over 2500 RPM seems extreme...

If I can't live with the 3:00 in my Comet, it will get a AOD & 3:80 gear swap...

 

I am running 3.80 with 255/60r15 rear tires. Around 3000 rpms at 65. Still pulls 20 mpgs, and accelerates like a banshee. If I feel the need to pass someone, especially if I downshift, it will leave them like they are standing still. Without downshifting it will still get up and go pretty quickly.

 

Have 3.55's and it's 3200 rpm at 70mph with the 302 & C4. I think 3.40's would have been a better choice. I'm fine with the 3.55 but certainly would not want anything higher.

 

I'm fine with the 3.80, and sometimes wish I had a 4.11! But that would definitely be screaming on the highway!

 

In that case I would go 3.55:1.