my 70 cougar is almost done, and im planning on doing a locker and gears in the 9".
motor is a 302, gt40p heads, e303 cam, edelbrock intake, and supporting mods with a FMX trans behind it.
what gears do you recommend? i was thinking 3.73’s… and this trans will only be in here for a few months till i go with a t5 swap. and i believe i have 3.00’s in the rearend right now…
thanks
forgot to add, car is never gunna see to much freeway or commuting. just a street car and racing on weekends…
I’m not too familiar with fmx but this site might help you out.
http://www.gearvendors.com/hrfordratios.html
I’d go with 3.55’s at least though
I have heard that a person should work backwards, meaning that you need enough gear that gives you enough RPM’s in 5th gear at the minimum freeway speeds.
My 1968 XR7 has a 3.50 9 inch rear end. I am about 1700-1800 RPM at freeway speeds. I forget what it is exactly. I am running a carburetor on a 302.
There are calculators that allow you to plug in various criteria such as tire diameter, rpm, ring and pinion ratio, final drive ratio of transmission, etc.
Been there done that haha. Heres the link to the calculator I use.
3.73 or 3.89, depending on your tire diameter choice.
You’ll be bummed out if you take it to the drags and run out of motor before you trip the traps due to too steep of a gear. But, since you’re using a 302, you really need to give an engine that small some leverage and run a lower ratio.
Use the gear calculators linked and let us know what you decide.
If you’re ultimately going to be using an overdrive trans, I’d say to go with at least 3.50 gears. With the AOD behind the 393W in my Crown Vic, 27.3" tall tires and with 3.55 rear gears, it is only turning about 1800rpm at 60mph in overdrive, and only around 4700rpm going through the quarter-mile traps at 106mph in Drive! But then again, I also get around 15mpg when street driving it! If I were to go with steeper rear gears, my gas mileage would suffer.