capndar

Fire up the flamethrowers....

I drive long distances (very fast).....I see lots of discussion here about putting 4.1 rear end in the cars....I want to go the other way....what is the lowest rear end that you can put in an 05-09 Mustang...is stock as low as it goes? I am looking to lower the rpms over 80 mph...

If you don't like what I am doing, feel free not to comment and neutering the stallion, etc...if you have some technical info, I welcome your help.

Thanks

mdg

Isn't 3.31 the lowest you can go?

gman73

I think 3.31 is the lowest you can go. Why are looking to do this? I am guessing gas mileage. I have 4.10s and I drive 35 miles to work with about 85% being on the hwy. I drive about 75-80 on the hwy. Hell I just drove from San Diego to Virgina Beach, VA. At around 80 MPH my hwy MPGs were about 21 and at 65-70 it was about 24 to 25.

DarkFireGT

3.31's the lowest they come stock. You could probably go a bit lower than that, but then you might as well not drive a Mustang. My 3.31's seem pathetic enough.

capndar

Thanks....That (3.31) is what I thought.....I was looking for several benefits at over 80 mph....mpg, noise level, and I just like lower rpms in a bigger engine...drove an S2000 for a week and it drove me wild...ah well

Thanks

breathegood

How low do you want your RPMs to be? Mathematically, with a 3.31 you should be just a hair under 2100 at 80mph (assuming manual tranny, 5th gear). Any lower RPM at those speeds and you are putting an awfully big load on your motor anytime you need to climb or accelerate even a little bit. Good luck in your endevour. Let us know how it works out for you.

pascal

Another way to lower rpm is to have your 5th gear pinion replaced with another one that would give you something like .58 ratio but still ripping from 1st to 4th. I know it's costly but it's still a valid option...
You'll be on the cruise control at 80mph with 1800rpm or 2000 max.

If you have an auto, disregard this post.

capndar

PASCAL - nice idea...and that had crossed my mind....I know that in my 5.4 Expedition, the difference in MPG between 1850 and 2000 rpm is incredible...

howarmat

exactly....you want to keep it higher than 2K imo otherwise you are lugging the engine

pascal

No kiddin'
How do you think those Vettes get 30mpg at 80 with their 6.2 cube?
The 6th gear is made for hwy only.
The computer helps a lot but still...