All I really need is a certain RPM in a certain gear and what speed it is. I have 12A with 12A tranny and 3.909 rear. Stock 12A drivetrain. I want to say that 3K in 5th gear was right at 60, 4K in 5th gear was right on 80, and so on. I want to say that every 250 RPM was 5 MPH. Is this right?

Thanks in advance.

-IanS

 

Just find a flat stretch of interstate...have your girlfriend run the stopwatch. Time how long it takes to go 5 miles (according to the highway mile markers...not your odometer) at exactly 60 mph (according to your speedometer). From there you can do some math to find out your actual speed and make the correction.

Rich

 

Or you could just get a GPS, that will tell. Thats what we did on my buddys truck, when we got done liftin it.

 

Using a stop watch is how we calibrated the speedometer on the engines when I worked on the railroad, works quite well. Many of the interstates now have those white posts every 1/10 th of a mile now. At 60 mph, you pass a post every 6 seconds.

 

lol, first thing i thought when i saw this thread was "hes not wearing his speedo and now he needs some "help" I think i am the man for the job!" LOL

 

That's somewhat disturbing

Rich

 

kinda brokeback, lol...... thats the stock ratio. why do you guess that your speedometer is off? do you think you may be missing a tooth on your drive gear or that perhaps someone had replace the speedometer drive gear?

 

Hey Ian, and also, do you have stock size wheels/tires? otherwise the speedo would be affected as well.

 

in my stock 12a, 3k in fifth is 60mph and 4k in fifth is 80mpph. ~7k in third is 80mph, as well.

 

candyassmiler - Thank you, this is the info I needed.

Yes Carlos, my wheels and tires are stock size. Thanks, I forgot to mention that before.

Rich, this is what I was talking about when you gave me a ride in your car. That is why I asked if you had a 13B tranny in yours since the tach was considerably different than mine.

Mazdaverx713b - I previosuly changed tachs to one that I thought was better and didnt realize that I put the needle on wrong. I then thought that the speedo was off until I had my girlfriend following me while I was doing "80" which in reality was 93. SO, this is why I changed back to my other tach and need to fix my speedo but wanted to make sure what was what. BTW, it is really hard to get the needle of the speedo to rest at zero. The only way I have found (which isnt safe) is to have it reading a speed and then place the needle on the pin.