I'm sure you know this, but for others that do not, this is what Ford did for the 2010 GT500. 1-4 is the same for getting it on, but 5 and 6 were made smaller to lower the RPMs for better HWY MPG. That's pretty cool and a very smart thing to do. 6th is like .5x I think.

 

You could go with taller tires to further reduce RPMs at speed.

 

Riiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiigh t, and then we'd have a Caterpillar Mustang.

 

hahahahahaha

 

Dude, I'm not suggesting putting monster truck tires on it (although that does conjure up a troubling image that could scar me for life). But, you know, a little more meat to fill out the wheel wells.

 

Lowering the rpms a few hundred is not going to to put less wear, noise etc on your car. If these are your goals, you won't achieve them. Think about it you'll have to be in 4th gear way more often which defeats the point. You'll be constantly shifting if a stick since you won't be able to pass cars on the highway unless you are going 90mph. Bad idea, won't solve your problems. Do what everyone else who drives a Mustang does, turn the radio on.

 

another mod you should consider, because you mention reduced noise, is to install Dynamat extreme in the doors, floors, trunk, spare etc. It makes a world of difference in the feeling of quality for the car, its quieter, cooler in summer, warmer in winter. I think your idea to change the diff gear is fine, at 331:1, but changing 5th to a high overdrive is better. Does anyone offer lower (numerically speaking) 5ht gear cogs?

 

I would consider 3.31 as the tallest gears only.

When Ford was putting things together, they specifically matched gear combo's with tranny ratios to achieve a certain RPM at 55-60 MPH.

at that speed, your motor is in the lower edge of the optimal HP/TQ powerband...hence the motor is less likely to get lugged and place stress on the crank.


deeper gears place you farther into that powerband, so it's never an issue. I've seen 3.03 gears for a 8.8 axle for sale. But that would effectively kill your 5th gear.


I'm not sure why you are wanting tall gears...other than MPG's. yeah, 3.31 will get you slightly better MPG's...but it will cost you performance. Any MPG gains you see will be pretty minor. On the order of 1...maybe 2 mpg gain.

The 4.6 and 5.4 motors love to sit at 2,000 - 3,000 rpm all day long. When I drove my 1,000+ mile roadtrips, I used to get 21 mpg at 75 mph in my 4 door F-150 with a 5.4 3v...75 mph equated to about 2,200 rpm in it.





I think you'll find that a swap to tall gears is pretty much worthless. It will run you roughly $500 for the install, and you will spend more time in 4th gear if you have any hills/mountains at all.


best of luck

 

Ford has made (and may still make) ratios at least as low as 2.73:1 for the 8.8" rear.

 

What they've said is pretty much true.

You can lower the rear diff ratio to 2.73, 3.08, or 3.27. It will cost $500-800. How many miles will you have to drive to recover that cost?

Changing the rear ratio also puts you lower in the power band, just like they said. Puts a lot of strain on the engine, and may not actually net you better mileage overall. In some situations it would. But once you get in traffic and have to slow to 60, you'll be in 4th and it will cost you fuel.

One of the biggest mistakes with the '05-'09 Mustang is the 5 speed. Why not a 6 speed? It's not rare or expensive technology, especially with a V6. 5th is a .68-.72, pretty much what 5th is now. But 6th is .50-.60 - which wuld be perfect for long cruising across the midwest or southwest.

If you do a lot of long haul driving, you should consider making the change. Contact somebody like Mike Forte and have his send you all the parts you'll need.

Unless you have an auto. Then you're stuck with what you got.