View Full Version : Speedster RPMs

05-19-2007, 03:32 PM
Hi, My 55 Speedster is great with a standard shift overdrive setup that I think is rare. The problem is I live in a very hilly area so hardly ever use the OD. At 60 MPH it's turning over at exactly 300RPMs out of OD. What RPM are Speedsters turning at 60 with an automatic and does anyone know what the Rear end ratio is for my car?

I guess an additional question is will I be harming my 259 running at 3000RPM ?

Thanks guys

05-19-2007, 04:26 PM
Sounds like you have a 4.11 rear, AT would be a 3.31 and about 2500 RPM. 3000 RPM will cause no real harm, the 4.11. and even 4.56 were a late option for AT Avanti's and Avanti powered cars.


63 GT R2
63 Avanti R1
63 Daytona convert
63 Lark 2 door
62 Lark 2 door
60 Lark HT-60Hawk
59 3E truck
58 Starlight
52 & 53 Starliner
51 Commander

Dick Steinkamp
05-19-2007, 05:20 PM
You probably mean 3,000 RPM's. :).

If you have 205 75 15 tires or the equivalent height bias ply tire, 3,000 RPM's and 60 MPH means you have a 4.09 rear end.

You can go here to calculate with other tire sizes if you need to...


You could also look at the back of your differential cover. Under one of the bolts there should be a metal tag with two numbers on it. Divide the big number by the small number and that will give you your rear end ratio.

My 54 was originally an automatic and came stock with a 3.54 rear end ratio. With that rear end, and the above tires, 60 MPH would be at 2,600 RPM's. With a 3.31 rear end ratio and the above tires, 60 MPH would be at 2,450 RPM's.


Dick Steinkamp
05-20-2007, 09:44 PM
quote:Originally posted by hotwheels63r2
you should be able to get the car slowed enough to stop by keeping the RPM's up.