What rear end gears would be best?

[capteddie]

Looking for advice...

I'm getting close to the end of my build and came across something I think I'll have to address over the winter.

I have a stroked 408 with about 475hp/530fpt on the dyno and its married to a beefed up Ford C6 automatic. The rear-end is a ford 9" with 3.73 gears. The last time I was at Ed "DV" Combs shop, he said he thinks I would need to change the gears to get better drivability and performance.

Anybody have any suggestions? Would something around a 3:07 work better?

Thanks in advance for any ideas or suggestions!!!

[WildBill3]

We run a 308,with our 408 and I think its ok iv runa 12.004 on street tires I dont feel like im giving up much on performance.And it makes a nice cruzzzin gear ,seems like all the ol lincons had them many with a posi.Good hunting for the best choice.WB3

[Ron61]

Bill is correct. In 1964 the standard gear in the heavy Galaxie with an automatic was a 300. Four speeds had 3:54. With your light car, anything lower than a 3:54 would be a waste in my opinion. I think around the 300 area would work great. And many of the old Lincons did have a posi unit, but if you don't have one you can still put one in.

Ron

[capteddie]

Thanks for the input guys...

Any recommendation where I can buy a 3rd member with 3.08 gears?

A quick search of Summit and Speedway didn't bring anything.

Thanks again!

Ed

[wtm442]

You might want to play around with a rear end gear calculator and stick in various numbers to see what happens.

http://www.idavette.net/tech/ratioc.htm

http://www.cobranet.com/calcs.htm

[Cobrabill]

I would do 3.27s.3.0's are gonna be a pooch around town with a automatic.

[Bill Bess]

The other Ed, It depends on how you intend on driving the car and what you desire as far as acceleration, throttle response, noise at highspeeds and fuel mileage etc.

Lower gear ratios will give you the quickness off the line and good for drag racing and quick response out of turns.
If you want to cruise the highways at 80 mph, with low exhaust noise, low rpms'..go with 325, 300, 308 something like that.

Bill

[mln385]

You may want to consider what cam you have and where the power builds, If your engine does not build power till 2500 or 3000rpm then with you 3:00 gears you will be riding in 2nd gear around town.

My thoughts are more 3:46-3:64 but this also depends on final gear ratio of tranny as well.

Marc

[Bernica]

Been there, done that. I'm running 3:31's with one of Dave Kee's wide ratio toploaders. Not sure how that ratio would translate with your AT, but I'm happy. Plenty off the line and still have highway cruising at fairly good RPM. The power band of your cam will also be something to consider.

[Cobrabill]

Marc-3rd gear will be 1 to 1.I'd also go with the 3.46's but on the upper end of the scale.

Where does the timing curve come all the way in?Example:If your timing is in by 2800,then choose your gear to give you 2900 rpm or so at cruising speed.

There's more to this then just picking a number and tossin' them in your rear.

[capteddie]

Thank again, everybody!!!

Let me pull out my dyno sheets and engine build spec and I'll post the info.

Ed

[wtm442]

Ed
Suggest you start the car with the 3:73 gears. They will probably be a little too high, but great for stoplight racing. After you have felt what they are like, then you can get another pumpkin with a different set of gears.

[jdean]

Go with the 3.08 or 3.27 if you drive it on the highway at all. This will be plenty unless your cam is too aggressive. Otherwise go with a 3000 stall converter and 3.73 but dont go more than 1/4 mile at a time ;-)

I had 3.27 with a C6 in my CR and it was a good compromise. Tom Wells has a C6 and uses like a 2.93 but he has a 521 BBF and still spins the wheels past highway speeds. If you decide on 3.08 I will send you the ring and pinion if you pay shipping. If you need a traction-loc for 31 splines I have that too.