Is this right? I would think at 70 mph my rpm's would run more than 1500. Shouldnt it be a little higher than this. The motor idles at 800 and around 600 when put in gear. There is no differance in HP and the idle is smooth.



forgot: 305 TBI is what I have

 

Go here.

If you have the stock size tires on the car you should be turning ~1700 RPM at 70mph.

If the tires are a little bigger, you're going to turn less RPMs at any given speed.

Go here to find the stock tire size for your car.

If your tires aren't stock sizes, enter the numbers from the sidewall here.

It'll tell you the proper radius to use for the calculator above.

 

You can calculate the "RPM at 70" but you'll need a little more info.

Like tire diameter, rear gear ratio. transmission ratio.

RPM @70MPH = 70 x 336 / rear tire diameter x rear gear ratio x trans ratio

Generally "D"(auto) and or 4th gear(man) is 1:1

"OD"(auto) or 5th(man) is usually right about .70:1 (30% overdrive)

 

The tach in these cars (or any stock tach for that matter) is not an "instrument", it's a "trim package". They are not dependable for accurate reality. It's also possible that your speedo is inaccurate. That's easy to verify; first drive down a stretch of road like an expressway with measured mile markers, and see if the odometer agrees (that will tell you if you have the right speedo gears); then drive at exactly 60 mph on the speedo and see how long it takes to go one mile, should be exactly one minute, if it's not, your speedo is off.

Idle speed and smoothness, or lack of it, won't make the tach read differently or the engine turn at a different RPM while driving down the road.