Tachometer or Vacuum Gauge?
 

I am trying to decide between getting a Vacuum Gauge or a Tachometer as my car has neither. I have a 1981 Honda Civic Wagon so a Scan Gauge II is out of the question.

Which would give me better feedback for the purpose of improving FE?
Which would have the most impact?

Knowing your gear ratios, tire diameter and differential ratio would allow you to calculate RPM in gear.

I would go with the vacuum guage, since knowing the vacuum reading is probably the single most important piece of information for getting best mileage as well as diagnosing any issues you may have mechanically.

I keep thinking about putting one in my 94 VX so I can keep it at the 6 inches lean burn threshold, but after 29,000 miles I can feel the transition fairly well, and I doubt if I would improve my mileage beyond it's current level since most of my driving is 50-65 MPH average speeds in the VX.

regards
Mech

+1 on the vacuum gauge.

...did any version of that model Honda come with a tach? if yes, consider finding a replacement at a junkyard...wiring is (usually) already there, just not connected to anything.

That's exactly what I did. It was as simple as getting the instrument cluster (with gauges and tach, I was replacing dummy lights and a HUGE gas gauge), pulling out the old one, and plugging the same connectors into the back. I had to calibrate the tach, though, because it came from a V6 and I have an I4.

Who says you can't have both?

...my 1984 Honda DX didn't have a tachometer, so I simply got a dash from an '84 model that did, and installed it into my car -- everyting worked fine!