Tbarber01

Hello Guys! I have a 2006 Mustang GT Convertible Automatic. I have a stock 4.6 engine. As my first performance mod I changed the gear to a 4.10 from a stock 3.31. I just got the car back from the shop and it feels like this gear has hurt my performance! I know that sounds crazy, My speedometer is currently off about 10mph( at 50mph I am showing 60mph). I know a tuner can correct my spedo, but do I need to have a different tune other than my stock tune to get my performance back??? Any ideas?

Planeswalker

I have never had an auto, but I would imagine the shorter gears are killing your autos shift points. A tune would fix that and add more power.

friedmaster

Back when my car was an auto... I did consider changing the rear end gears, and from what I remember with my research, I think you may have gone too far with the ratio.

Going from a 3.31 to a 4.10 is a 23% increase in gear ratio, which means each gear is now 23% shorter, in a car with a 5-speed transmission. As a result, I'd expect that your car is now going a bit crazy over-shifting (as it hits the defined RPM shift points) without actually gaining much speed.

The 4.10s are a common mod for people with standard cars, as it's a 15% increase over the stock 3.55s. As far as I remember, the 3.55s or 3.73s were the right gear for the auto transmissions if you wanted to bump up the seat of the pants / noise factor a bit.

Paris MkVI

That tracks with what I always heard for the S197's - 3.73 max for the auto trans, 4.10 max for the manual trans.

You get off the line quicker, but lose top speed.

slostang

4.10's IMO went out of style with holly double pumpers....


That is way to much gear in a street driven auto car.

1bad01gt

My car is an 08 GT with 4.10's. You need to get a tuner and set the gear ratio to 3.73's. The speedo will be off a couple miles an hour, but when the tune is set to 4.10's the transmisstion shifts too quickly into higher gears.

retfr8flyr

You need to have someone that knows how to tune the auto in our cars to give you a tune for the 4.10's. In my opinion 4.10's are too much gear for the auto but lots of guys run them. The tune needs to be changed for the shift points and torque management through the gears with the 4.10's, not just the speedometer.

I don't know your location, to recommend someone in your area but if you want a great mail order tune then contact Mike Rousch at Mid Atlantic Performance 1-804-332-6685 - Email: Mike@MidAtlanticPerformance.net Mike is one of the best tuners on the east coast and he is now doing e-mail tunes.

fdjizm

+1 need a tune you just changed your rear gears and your shift point are going to need to match.

Maverick214

I have an auto with 4.10's and as others have said you need a new tune. Fixing the speedo only won't fix the shift points.

Once it's fixed 4.10's are great in an auto, I'm glad I didn't go 3.73

Feint Motion

I may consider 4.10's with a tune down the road.

Zaksgt

I had 4.10's in my 06 GT 5 speed with no problems.

retfr8flyr

Does your computer shift our 5 speed?

D6-06

Use a tune you cant go adding mods without a tuner they wont do jack **** because your engine thinks its running with the stock part so if you get a new cold air intake without a tune its not gonna do anything same with gears uts winding higher making your engine think is going faster and makes your transmission shift more. i would get a tune written or get a tuner written right away.

m05fastbackGT

First off newbie! You responded to a post which was originally submitted over 8 years ago. And second, the vehicle does NOT require a complete tune re-flash in order to run a different gear ratio.. If the person in question wants to continue running the stock calibration tune, a tuning shop can write up a tuning file which can make adjustment changes for the gear ratio, while keeping the remainder of the stock calibration tune fully intact.. Therefore, all the OP would require is contacting his tuning shop vendor and request a speedo revision adjustment to correct his speedo issues..

Paris MkVI

Necro-post, friend. These messages were posted in 2014.Many of these folks have been inactive on the site for many years. The OP hasn't posted anything since 2014.

m05fastbackGT

Certain folks obviously don't bother paying enough attention when it comes to details, such as how long it's been since thread posts were last submitted on a thread which has been inactive for many years.. LOL

tbear853

... Well, it is pretty easy to see a topic, click on it, start reading, looking for a hint of help with one's own pressing issue, and not realize the post being read was written when one was them self ... still pooping yellow.

I've got a very modest collection of really old shop assists type books, paper pages, xdrawings, etc. ... and I still find myself lost in them from time to time. Road guides, like the 1915 AAA Tour Guide ... for example. Very few maps, but the book is near an inch thick. Fine print on extremely thin paper, it's a turn by turn directory of locally chartered turnpikes and paths, how to get from A to B. One issue only covers the Southeast. One could pay tolls along the way, or pay for one toll pass at either Bristol or Winchester to get to the other .... it was like near $4. Easy to get lost in ... where was I?

Oh yeah, like old Popular Science, the section where readers wrote in to ask Smokey Yunick ("Say Smokey!") questions about thier '54 Hudson blowing out transmission fluid at high speed ... Smokey's reply sdtill has merit.

Bert

yep ... and I don't know about you guys; but if I was posting on a phone, I wouldn't be able to see ANY of those little details, I probably couldn't even read the threads, and I wouldn't be able to write much either!

m05fastbackGT

Good point about the phones lol. Perhaps I'm just one of those select few who still post from a PC