Cruising RPM

D

dcnner

Member
I am nearing completion on my 6 year project, a widened 27 roadster on a 32 frame and I am still pondering the gearing. I have a 59 ab bored .125, H and H cam, egge and so forth. My transmission is 1939 style top loader 3 speed. Most to the time will be spent at 55 to 65 MPH, and occaisionally 75 on the interstate. Rears tire will be 28 to 30 inch tall. My rear gearing choices are typical for an 8 inch. 3.00, 3.24, 3.55 etc. I don't know where at the flathead runs it's best with some acceleration left on tap. I am keeping the three speed. Which gearing would be best?
david
 
I was just looking up mine for changing gears.
I'm running 2.78 8 in with 205 70 15 and running 2k at 55 mph.
To use my new white walls 710 15 28.88 dia. I would need 3.25 gears to stay the same.It come out 2k 52mph.
I can pull the hills good.
 
This is cam problem. A stock cam will give max torque in the 1800-2200 rpm range. How much tork depends on displacement and CR. A small engine doesn't have alott of torque in the first place and a cam makes it worse. A bigger engine will produce more torque but the cam kills off the low end. A cam like the L-100 works best at around 2400 up and gas mileage is pretty good (18-21 MPG) in a well tuned engine. Your trans is direct in third so gear it for cruise. 3.55 would be a good starting place.
 
I would think a 3.24 with a 28 tooth cluster in the trans would be a good compromise.

I have a A-V8 with a slightly warmed up 59AB and 7.00-16 Tires (30.4" Dia.). I am running a "Changer" with 3.46 O.A. rear end ratio and 25 tooth Zephyr Gears and it is just fine. I would not want to run a taller rear ratio with this combination however as there is not a lot of low gear ratio with the 25 Tooth Gears.

My Experience.,

Chris
 
You must log in or register to reply here.
Back
Top