Engine RPM on highway?

[Fastmax32168]

I am in the process of doing the rear for the 80 Monza I am putting a 3500 in and weighing the performance/mileage trade off associated with gear ratio selection. I have several sets of gears I can use sitting around.
The lowest of these is a 3:42 which using my tire diameter and trans is going to calculate out to about 2600 RPM on the highway at 75 MPH and 2500 RPM at 70.
I also have a 3:23 available which will knock about 150 RPM off either of those figures.
The mileage is important to me in this car as that is one of the reasons I am building it.
Are both these ratios too low for good fuel mileage? What type of RPM does GM set these motors up at?
I have a 2:73 as well, but I think that would turn the car into a slug off the line.
I was hoping to get 30 on the road, is that acheivable with either one of the first two ratios? Input welcomed.
Thanks
Roy

[2.8-350TBI]

What kind of transmission are you using with this?

[Fastmax32168]

Using a 700R4
Roy

[2.8-350TBI]

Id say go for the 3.42.

Ive driven several cars with the 700r4 and 3.42 gearz and they have all had a decent balance with cruise rpms, mileage, and acceleration.

The blazer in my sig has a 3.73, and sometimes I wish it was a little lower, since its a 5 speed manual. Too much shifting. With an auto it would be cool, but lacks the 5th gear. Well, was, I sold it

[hoosierloser]

the 3.42 will probably not hurt fuel mileage enough to want to use the 2.73's. My 3.1L cavalier turns 2600rpms at 70mph and usually returns 28-29mpg. Its a 3.69 final drive with a .74 overdrive ratio I believe. With your newer more efficient engine you could expect to get about the same or better. I would say more but you will probably have higher drivetrain losses associated with an automatic/rwd configuration.

When I owned a 3400 grand am with an auto trans with a 2.7X or so final drive, it would shift into 2nd at nearly 50 mph. Not ideal for spirited driving. If its a fun car, then keep it fun and quick.

[geoffinbc]

I have a .72 fifth with 3.42's and 26" tires and my RPM is right around 2000RPM which is perfect. I get very good highway mileage. My Trooper has a .809 fifth with 4.56 gears in the rear ans 33" tires and I am around 2500 to 2700 RPM on the freeway. Not as nice as the S-10 but the Trooper is heavier and so are the tires.