The Ford Barn - View Single Post - Want o go highway speeds ??? Need opinions.

Juergen · 01-29-2019, 08:44 AM

With stock tires and a 3.78 rear end, the Service Bulletins say at 60 you will be at about 2750 rpm which is a little high for prolonged flathead use. So a 3.54 will get you at about 3.54 / (3.78) x 2750 = 2575 rpm while a 3.25 gets you at about 2360 rpm. Finding a used 3.54 will probably be easier and cheaper than buying a new 3.25 and getting it set up. A bigger tire may be the cheapest. A 6.00 x 16 tire has a diameter of 28-29 inches. So one equivalent to a 3.25 (13% change) would need a diameter of about 32 inches. Of course use a turtle for a 3.25 (17 tooth I think)

01-29-2019, 08:44 AM	#11
Juergen Senior Member Join Date: May 2010 Posts: 503	Re: Want o go highway speeds ??? Need opinions. With stock tires and a 3.78 rear end, the Service Bulletins say at 60 you will be at about 2750 rpm which is a little high for prolonged flathead use. So a 3.54 will get you at about 3.54 / (3.78) x 2750 = 2575 rpm while a 3.25 gets you at about 2360 rpm. Finding a used 3.54 will probably be easier and cheaper than buying a new 3.25 and getting it set up. A bigger tire may be the cheapest. A 6.00 x 16 tire has a diameter of 28-29 inches. So one equivalent to a 3.25 (13% change) would need a diameter of about 32 inches. Of course use a turtle for a 3.25 (17 tooth I think)