been thinking about 4.10 gears for my 09 gt,, what can anyone tell me about them,, i see american muscle has the ford ones for 149,,,not bad for a nice lil upgrade,thanx,,sully
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2009 mustang gt ,5 spd,,,vapor metallic w black ford racing stripes,, pypes o/r h pipe ,,,borla stinger axlebacks,,,8 inch shorty antenna,,,Honeycomb blackout panel,,tinted windows,,,,in oct getting ,,kooks longtube headers,,,,steeda cai,,,, and sctx3 93 octane tune,,,from brenspeed,,,,,,,,,,,,,,,,,,,,,,,,,,,, JOHN" sully ' SULLIVAN
2008 Vista Blue Mustang GT Coupe, FRPP Hot Rod Cams, FRPP 4.10s, Eiback Pro Lowering Kit, Steeda UDP, Steeda CMDP, Steeda CAI with 94 Octane Custom Dyno Tune, Solo Performance Axleback Exhaust, 20" Foose Nitrous Legend wrapped with Falken FK-452.
I do alot of highway driving... and love my 4.10's 2200 rpm at 60mph
You'd be run over doing 60 mph on a highway in NJ...
I went from 3.31's to 3.73's. I've very happy with them. I do about 50/50 city / highway driving. But you know what they say, "Don't fear the Gears Man". Why stop at a mondaine ratio like 4.10's. Have you considered 4.56's?
It's personal preference and driving habits more than anything else. If you spend a significant amount of time on the highway you'll take a decent hit on mpg. If that's not a concern or you do a decent amount of city driving (You actually could see an improvement in city mpg with a numerically higher ratio gear) you could get away with 4.56's or 4.30's are another option. If you do a search you'll get a ton of hits on gear threads. Everybody has their opinion but you should figure out what you want.
Here's a link to an rpm calculator. Engine RPM Calculator
Scroll to the bottom section on that page.
Stock tire height is 27.1, final gear ratio is 0.68.
If you go with 4.56's you'll only be turning ~2307 rpm @ 60 mph...
Gears are great bang for the buck but they need to be chosen correctly. You have to take some things into account or you may not end up with the result you are looking for. For example, if you are going to supercharge it some day the 4.10 are pretty steep, you will blow the tires clean off in 1st gear. If you will be changing over too or already have a smaller diameter tire (height) it will dramatically change the overall gearing of the car. Case in point, I have 3.55’s but they work almost like a 3.73 because my rear tires are shorter than stock (but a lot wider). And lastly if you spend time on the freeway or are sensitive to what RPM’s you will be driving on the freeway at it needs to be taken into consideration. I intentionally geared my car to run 2400rpm’s at 80mph (and 208mph topped out). Everything else was secondary. And I don’t spend a lot of time on the freeway or use my car to commute. I can’t stand a “buzzy” car when cruising down the freeway.
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I drive my car around 25,000 miles per year and do a lot of highway and still like my 4.10s. 3.90s might be slightly better all around but anything less than that is unjustifiable in my opinion. (Unless forced induction is planned later)
4.10 gears whats your opinion? 
