Looking for a new Ford 8.8 IRS

[blykins]

Be sure and use a calculator that includes your tire height. It makes a big difference.

I always use FMS gearsets in my stuff. Richmond gears have a tendency to whine, even when set up correctly.

I would buy either Motive or FMS, and my installer says that the FMS gears are the higher quality of the two.

I'm getting about 66mph with a 3.55 and 26.6" (295/50/15) tires.

[priobe]

Great.... nothing is ever easy

The 3.31 gear is Motive and the 3.27 or 3.55 is FMS.

Ford does not make a 3.31 damn it decision decision.

I was prefering 3.31.

I did you the calc for tire size which is 25 in.

Here is the breakdown at 60 mph

Keep in mind I am currently at 3000 rpm @ 60 mph = 3.73


1. 2500 rpm @ 60mph = 3.08
2. 2650 rpm @ 60mph = 3.27
3. 2700 rpm @ 60 mph = 3.31
4. 2900 rpm @ 60 mph = 3.55

[olddog]

Originally Posted by priobe

Great.... nothing is ever easy

Keep in mind I am currently at 3000 rpm @ 60 mph = 3.73

If the above numbers is dead accurate for your car, forget the calculators and just multiply out the ratio of the gear ratios.

3000 * new ratio / old ratio
or
3000 * 3.55 / 3.73 = 2855

1. 2477 rpm @ 60mph = 3.08
2. 2630 rpm @ 60mph = 3.27
3. 2662 rpm @ 60 mph = 3.31
4. 2855 rpm @ 60 mph = 3.55

Another important thing to consider is the speed limits that you drive in. If you are taching 2477 @ 60 mph you will have 1651 at 40 mph. Depending on your cam, it may not run there and it will force you down a gear. That could put you back up to 3000 rpm in order to run 40 mph. You want to make sure that it is pleasant to drive where you run the most, not just 60 mph.