Rear end

[Mike827]

Which gear would be better for the mm rear end...? 3.73 or 4.10 thinking about swapping out the factory 3.55

[Stranger in the Black Sedan]

I put 3.73s in but I did the labor myself. No way is it worth paying someone to do that little of a ratio change. 4.10 is too much rpm for a big boat 4 door for me when a large % of the mileage I put on the MM is highway cruising. 3.90 would be the perfect ratio for me but there is no Ford OEM or racing gearset in 3.90 so I stuck with a ratio I could still use my rotunda pinion depth tool on.

[ntd]

Which gear would be better for the mm rear end...? 3.73 or 4.10 thinking about swapping out the factory 3.55



I personally went with 4.10's Did the install myself. 4.10's really make our big cars jump off the line quicker and compensate for our engines lack of low end torque. I drive 75-80 mph on the freeway and lost @1 mpg. If I hadn't gone with a Paxton and used a Eaton I would have stayed with the 3.55. Good luck with the decision either way I'm sure your butt dyno will feel and improvement

[RF Overlord]

Unless you can do the labour yourself, it's not worth the expense to go up only one step...the difference in perfomrance is minimal. Go to 4.10. Unless you drive almost exclusively on the highway, and at "illegal" speeds, the difference in overall MPG is almost nil.

[babbage]

I paid $260 for my 3.73 install, done by a pro. I'd recommend taking it to someone whose done it before. Pay close attention to tolerances if you do it yourself. Heck lots of posts I've read -> even people who have had a shop do it and it grenades a week or two later.

I take long trips in the summer and sit for hours at 80ish... My car is faster than other cars that are NA and have 4.10's ...

Get the FRPP gear kit no matter what ratio you go with. Good time to do a Girdle too...

[Pat]

Prevailing wisdom........4:10's.

I love mine, still get close to 24MPG at 70MPH on the highway with AC on.

[Mr. Man]

I put 3.73s in but I did the labor myself. No way is it worth paying someone to do that little of a ratio change. 4.10 is too much rpm for a big boat 4 door for me when a large % of the mileage I put on the MM is highway cruising. 3.90 would be the perfect ratio for me but there is no Ford OEM or racing gearset in 3.90 so I stuck with a ratio I could still use my rotunda pinion depth tool on.


Was there a reason you didn't go with a 3.90 by one of the bizillion companies that offer it for an 8.8? Just wondering :)

[babbage]

Was there a reason you didn't go with a 3.90 by one of the bizillion companies that offer it for an 8.8? Just wondering :)

Yeah Ford Racing doesn't have it! ;)

[Mr. Man]

Yeah Ford Racing doesn't have it! ;)

Why do they have to be made specifically by Ford racing? I wanted to know why he didn't use an aftermarket co. Maybe the answer is he only uses Ford racing products. I'm just interested in his thought process.

[babbage]

Yeah Ford Racing doesn't have it! ;)

Why do they have to be made specifically by Ford racing? I wanted to know why he didn't use an aftermarket co. Maybe the answer is he only uses Ford racing products. I'm just interested in his thought process.

I was kind of kidding, sort of. FRPP gears have a nice face hob process. For me I was worried that i couldn't get the right tune from an SCT dealer, which it turs out is a non issue. (with an 'oddball' ratio..) who do you like for 3.90?

[Mr. Man]

I didn't really have anyone in mind but I guess any of the big names that make gear sets. On this site 3.90 doesn't come up that often and like you I thought the tune was the issue. As its not I really wonder why the 3.90 option isn't more popular. Seems like it would give you a compromise between the 4.10 and stock. Bit quicker off the line but realistically no loss in MPG and on S/C cars the axles and engines might stay in one piece. We all know about the failures some have had, running 4.10 and 28 splines even a few 31 spliners. Just my 2 cents FWIW:beer:

[SC Cheesehead]

Prevailing wisdom........4:10's.

I love mine, still get close to 24MPG at 70MPH on the highway with AC on.

^^^^^ What Pat said ^^^^^

70 mph on the highway = 2,300 rpm, < 1 mpg difference in mileage from stock.

This change, and a tune WILL wake up the car.