4.10 vs 3.90 gears

[FLA RAUD FAN]

Just wondering what you guys think about 3,90's vs 4.10's .

Dennis recommends the 4.10's and I will probably go with that, but I was wondering if anybody with the 4.10's feels like they are a bit high on the RPM's at highway speeds?????
The 3.90's might be a good compromise.

I have the chart Logan provided with the RPM differences between the 3.55 and the 4.10.

Does anyone have a chart with 3.90 compared to the 3.55's ????

The car definately needs more low end grunt and 4.10's seem to be the preferred choice but I kind of like the nice easy cruise at highway speeds with the stock gearing.

Let it fly....I'm listening....
Thanks, JP:argue: :argue: :argue:

[Murader03]

There just isn't that much difference between the 3.90's and 4.10's that I would worry about. I've got the 4.10's and I don't think they are to high. The MM is a heavy car, the 4.10's work best IMHO. Do what makes you feel the most comfortable with. But, as you stated, Dennis recommends 4.10"s!

[Logan]

I'd be more inclined to compare 4.10's and 4.30's... 4.10's are the minimum in my opinion for the car. 4.30's if you really wanna be a bad ass.

[RF Overlord]

^^^what Logan said^^^

FLA: I believe the 4.10 is the best compromise between performance and highway cruising...as Dennis has already determined.

I rode in Black Badger's car (with 4.10s) stuffed with 3 other (ahem *cough*) full-size adults, and his car seemed to pull us around and up & down hills effortlessly. I was watching his tach, and it didn't read significantly higher at speed than my car with the 3.55s. I just don't think you'd get your money's worth changing to 3.90s...

[CRUZTAKER]

I think I gained 400 rpm at highway speeds with the 4:10's
I was reluctantant too, and it took a day or so to get used to the higher rpm, but I only lost about 9/10th's on MPG, and from what I understand, the 4.6 motors LOVE rpms. Like all day long. So I am no longer worried. 4:30's no good for me only because I do ALOT of long highway runs, and little street racing.

And as far as the exhaust note, now people really notice me while at highway speeds...particularly in conjunction with the new megs tips!

[Blue Marauder]

4.10s are 15.5% lower (higher numerically) than 3.55s. Whatever your rpm is at a particular road speed, add 15.5% to it. In other words, if you are pulling 2000 rpm at 60 mph, add 15.5% to 2000 to get 2310 rpm at 60 mph. Don't forget, though, your speedo is also now 15.5% slow (really doing 51 mph at an indicated 60 mph) so you won't see the true rpm difference until you recalibrate the speedo with a chip. This is the same effect that you would see by putting smaller diameter tires on the rear of the car.

[SergntMac]

Originally posted by RF Overlord
FLA: I believe the 4.10 is the best compromise between performance and highway cruising...I just don't think you'd get your money's worth changing to 3.90s...

Bingo! Thank you RF. The cost of a gear set is around 180 bucks, installation varies greatly due to local labor rates, union shops, flat rate schedules, and so on. Rather than quibble over precise figures, I think an average of 500 bucks for a gear swap will serve my purpose here.

The rationale for swapping in a taller gear is to provide the power train with greater leverage against the labor of launching a heavy car. Even in normal driving, improving leverage is good, but think in terms of "less." The less the motor has to work, the less gas you burn, and the less wear and tear you suffer. The car moves forward easier, quicker and with less effort. More action at the back end requires less action at the front. Taller gears don't improve your power, but they get more done with the power you have, so, you use/need less power for the task at hand. Now, which lever delivers the most bang for your 500 bucks?

While 4:30s give lots more scoot in city driving, your highway driving would suffer. Cruising at 65-70 MPH in OD would hold your MM at the breech of your power band, and your throttle would feel "nervous" or, jerky underfoot. Your MPG would suffer too, perhaps not drastically, but you should consider it wasted fuel producing no advantage over long term consumption. You're running higher than necessary RPMs, and not getting anything out of that RPM, or, MPG. 4:30s would be a ratio fit for a more specific purpose, maybe racing on a regular basis, with little highway driving.

The 3:90 gear presents the opposite argument. A great highway cruise ratio and better MPG than the 4:30s, but also producing lackluster scoot around town, enough to ask yourself "why did I bother?" Your lever is longer than the OEM, but still rather short for what you want to achieve. In city driving, I'd expect you would still be heavy on the throttle from a standing start, and not gain any benefits in MPG. In fact, MPG may get worse, because the taller than OEM gear will tease you to drive in way you do not with the OEM gear. It's psychological now, you spent 500 bucks on a gear swap and you keep mashing the throttle to prove it. Yeah, something is different, but look at all the gas you're burning to prove it to yourself. Again, 3:90 over 3:55? Not enough of anything for 500 bucks.

4:10s provide the best of improvement with least of inconveinence, and justify a gear change. More leverage, less labor, very agreeable MPG, and delightful throttle response, both at the stop light, and on the highway.

I just finished reading another thread here on mileage, and it seems to me that the "bone stock" owners are reporting poor MPG, while those of us who have made modest changes are doing much better. With all my mods, I'm still enjoying the EPA rating of 17/23, and I believe it is because all my mods do one thing, improve leverage and reduce labor (k, maybe that's 2). To get a bone stock MM to haul azz, even just on the ramps, burns a lot more fuel and gets less results for that fuel. Improve the leverage, reduce the load, and get more bang for your buck.

500 bucks well spent on better leverage, now go out and add a Stallion Torque converter and underdrive pulleys, and double your 4:10 savings and enjoyment...As usual, IMHO

[Warpath]

Check the vendors links section of this website for a place to get Ford gears for low cost.

[merc406]

If you want out of the hole torque, go with the 4:30's.

[FLA RAUD FAN]

The 4.10's appear to be the way to go, I am just a bit reluctant and wanted some more justification from the old timers!!!
I drive 90% in town as it is, but the car seems to be so smooth on the highway I look forward to some good road trips. I only have 1000 miles now but I am preparing for my mods in the near future, thanks again for the input!!
JP

[Logan]

Just do it. I guarantee you'll be a happy camper. We all have the same concerns you do, with respect to driveability and not making our ride un-duely harsh or unreasonable to use as a daily driver.

My two pennies? Best bang for the buck mod there is.

[BigMerc]

What your concerns are, mirror exactly what I was saying before I did it. I chose to do it based on the guys here on the site, and I'm telling you you'll be very very happy. you wont notice and loss of drivability at all, makes it a great ride, I drive a lot of highway miles and at 90MPH most of the time and the difference is not noticable at all. The difference is around down it wakes the car up, very quick acceleration. Just do it and you'll be most please I assure you............now if Trilogy would hurry up I'd do that too.

[BigMerc]

around down?....how about around Town!!

[tetsu]

How about 4.56s and some short 10inch slicks on 15s? Put some skinnies on the front for added weight transfer and ROAR!!!!

With the above and a FordChip I'd reckon an otherwise stocker could pull a 14.5 in decent air 14.7 in poor.

Johnny

[Thomas C Potter]

I'm in the minority here, I vote for 3.90. My 17x8 with 255's is like having 3.90 and it feels perfect!! I know this MM is no Cobra, and it never will be w/o serious $$.

[Blue Marauder]

Originally posted by Thomas C Potter
I'm in the minority here, I vote for 3.90. My 17x8 with 255's is like having 3.90 and it feels perfect!! I know this MM is no Cobra, and it never will be w/o serious $$.

Just don't forget that your speedometer is now about 10% off due to the smaller diameter tires. When the speedometer is reading 60, you are really only going 54-55 mph. Better stay out of everyone's way!