Tach (1 Viewer)

[TexYoung]

I just installed a tachometer in my 73 FJ40 with stock F motor and drive train. 2 questions:

1. Is the stock rearend 4:11 gears? That is what I was told.

2. I am taching at 3500 RPM at 70 MPH. It sounds to me more like it is wound to about 5000 RPM but the tach is showing 3500. Does that sound correct?

Thanks!

 

[TexYoung]

I just installed a tachometer in my 73 FJ40 with stock F motor and drive train. 2 questions:

1. Is the stock rearend 4:11 gears? That is what I was told.

2. I am taching at 3500 RPM at 70 MPH. It sounds to me more like it is wound to about 5000 RPM but the tach is showing 3500. Does that sound correct?

Thanks!

Forgot to mention that I have 31 inch tires

 

[Jerry D.]

Go here: Simple RPM Calculator | RANDYS Worldwide

Gives lots of info...

Jerry D.

 

[John Smith]

You could easily be turning 3500 RPM at 70, and your F engine is not happy, as you can hear. At 5000 RPM, your engine will not be long for this world. Either slow down, buy larger tires, or regear.

 

[TexYoung]

Thanks

Go here: Simple RPM Calculator | RANDYS Worldwide

Gives lots of info...

Jerry D.

Jerry, I guess that is pretty close.

 

[Bodean]

As mentioned you will have to either slow down or get bigger tires. Is the speedo saying you are doing 70? If so it's wrong. That truck didn't come with 31's so you are actually going a little faster. GPS it.

 

[TexYoung]

As mentioned you will have to either slow down or get bigger tires. Is the speedo saying you are doing 70? If so it's wrong. That truck didn't come with 31's so you are actually going a little faster. GPS it.

Speedo says zero. It doesn't work. I use GPS on my phone for a speedo. The tach may be off a bit. The RPM calculators I looked at for 4.11 gears says I should be doing about 3200 RPM at 70 so its not too far off. I assume they are 4.11 gears.

 

[Irish11]

Speedo says zero. It doesn't work. I use GPS on my phone for a speedo. The tach may be off a bit. The RPM calculators I looked at for 4.11 gears says I should be doing about 3200 RPM at 70 so its not too far off. I assume they are 4.11 gears.

I am doing about 3200 RPMs (with a 2f) at 65-70 with 33's and 4:11's. The engine sounds MUCH louder though.

 

[honk]

Forgot to mention that I have 31 inch tires

A measured 31" or a marked 31"?

Most tires don't quite come up to their marked diameter and some. I'm not sure that a one inch difference between marked and actual would account for your 300 rpm but it might.

 

[tls3601]

honk is right on; my brothers "31's" are actually slightly larger than that

 

[TexYoung]

Thanks guys as always you guide me down the right path. Love this website!