FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: c9zx on June 30, 2025, 04:57:24 PM
-
Trying to decide on a ratio and a manufacturer for a ring and pinion. This car will likely never be driven more the 25 miles form home. I'm leaning towards a 3.89:1 gear but, I would like other opinions on ratio and manufacturer. I haven't bought a gear set in 15 years, and I know product quality can change over time. Thanks, Chuck S.
-
It will depend on a lot of factors and in the end, it will give a top speed and mph per 1000 rpm factor, to play with for your tolerance of noise, resonance and vibration.
If your engine will turn 6k and you have 27" tires, your top speeds will be:
3.50 = 138 mph
3.89 = 124
4.11 = 117
4.56 = 106
Divide those number by 6 and that will give you mph per 1000 rpm. So, you can decide what level rpm your most comfortable with at where you spend most of your the time driving.
Edit:
The above, is assuming a 1/1 top gear, as in a top loader. If you have a OD trans, divide the above by the OD ratio.
-
Your decision also must take into account your transmission. Also, with an automatic, a taller gear will make the converter tighter and it will stall at a lower RPM. If you have a lumpy cam, you can easily end up with a situation where the car wants to pull through the brakes at the stoplight.
A taller gear can make the car more fun since gears multiply torque and it's torque that puts the grin on your face.
-
Do some math calculations using your tire diameter, rear end gear ratio, transmission gearing, and engine performance like where it makes peak torque and where it runs out of camshaft rpm (top gear is important for road cruising but do the math to see where gears will end up)
I have done this with a few cars, most recently a HI-PO 289, 4spd manual, Detroit Locker rear that got modified into a 5 spd manual.
It was well worth the time I spent "trying" (on paper) different rear end gears, different tire diameters, and different transmission gearing.
Once I figured out what I thought would be a good rpm range to drive around with it all came together and I ended up with certain transmission gearing, certain differential gearing, and a certain tire diameter that have all come together to make the car so much better, and fun.
-
I have had great luck for street cars with old Ford gears, Yukon and Motive, but would likely do Richmond with a racer.
That being said with a hot street car, short trips, more info on the motor and desired use would be good BUT, 1st gear ratio X rear axle = either side of 10-11:1 is pretty good in traffic and horsing around.
That's focused on what 1st gear feels like banging around town, you have to look at what you think the top end does too. Some examples below.
Wide ratio 4 speed = 2.78 x 3.70-3.91 is pretty good
Close ratio 4 speed = 2.32 X 4.11-4.56 is pretty good (well pretty good around town but hit a highway and you'll be swearing and if you don't have the oats at the big end if you race it)
Of course it depends on tire size, engine build, desired use, you name it but pretty good rule of thumb for a streeter. You can likely see why most of us prefer wide ratio on an FE
-
Trans is wide ratio, converting to big input and rebuild. Engine will be 462 (if THIS block checks good). TFS heads, ED RPM intake, around 11.0:1 SCR, long tubes (Doug's), Hydraulic Roller cam (looking for peak HP at 6100-6200 RPM if possible), Harland Sharp rockers, 850-950 Holley. Unless I screw something up, it should make good power and make me smile every time I drive it. Thanks for all the input everyone. Chuck S. (OK)
-
In that case, if you intend to drag race with it, what I would do, is gear for 6500 in third gear at what ever you expect your 1/4 mi trap speed should be and let 4th act like a OD ratio.