Speedo / Tach / Gauges: Standard rpm range?

[62james]

I recently installed a tachometer in my 62 lark 259 v8, and am I am not to sure if its accurate because I have no reference to the normal rpm rang of a 259 v8 engine. How should I go about figuring it out, I'd love some help in the matter since I am a 19 year old that wants to learn more about his car!

[JohnM15]

Know anyone with a test set that has a tach function?

[52-fan]

A cheap dwell/tachometer would allow you to compare the readings. As far as the range for a 259 goes, the reading at any given speed for an engine will depend on the gear ratio in the rear end.

[PackardV8]

If you're wanting to use the tachometer for performance shift points, there's not much to be gained by revving a stock Stude past 4500 RPM. The torque peak is 2800, so for best on the street performance, keep the engine pulling right around the torque peak; rev to 3200 and shift. The revs drop back to 2500, pull up to 3200 and shift again.

jack vines

[JoeHall]

As others have said, a timing light with tach function gives good cross calibration opportunity. If not available, it may help to know the RPM your motor should be spinning at road speeds, and you could use a GPS to insure accurate speeds. First crawl under the car and determine the rear end ratio. Hopefully the tags are still there. If you have an automatic just drive in high gear, if an OD, lock the OD out and drive in high gear. ASSuming you have tires around 27" tall, with a 3.73 rear end, your should be spinning 2500 RPM at 55 MPH; with a 3.54, at 2500 should be 57-58; with a 3.31, at 2500 should be 60, and with a 3.07, at 2500 should be 65 MPH. That should get you in the ball park in determining how accurate the tach is. If it is an original tach, and the needle lags/sticks at any point, accuracy is highly suspect.

[Jeffry Cassel]

I concur. I show about 2400rpm at 60mph with a 3.31. Just hook up dwell-tach and see if they read the same: if they do not then you'll have to decide which one is in error!

[62james]

As others have said, a timing light with tach function gives good cross calibration opportunity. If not available, it may help to know the RPM your motor should be spinning at road speeds, and you could use a GPS to insure accurate speeds. First crawl under the car and determine the rear end ratio. Hopefully the tags are still there. If you have an automatic just drive in high gear, if an OD, lock the OD out and drive in high gear. ASSuming you have tires around 27" tall, with a 3.73 rear end, your should be spinning 2500 RPM at 55 MPH; with a 3.54, at 2500 should be 57-58; with a 3.31, at 2500 should be 60, and with a 3.07, at 2500 should be 65 MPH. That should get you in the ball park in determining how accurate the tach is. If it is an original tach, and the needle lags/sticks at any point, accuracy is highly suspect.

Alright will do! I'll check it out!

[62james]

I concur. I show about 2400rpm at 60mph with a 3.31. Just hook up dwell-tach and see if they read the same: if they do not then you'll have to decide which one is in error!

Thanks jeffry I'll definitely check it out