3.55 to 4.10's

[Emperior]

I'm in the process of switching from stock 3.55 to 4.10. I spoke to dealer tech he stated the switch will cause speedometer to read less than actual speed. He said around five mph or more. He also said switch will increase gas mileage, work trany harder. Alot of MM's have 4.10's.
Is this true?

[teamrope]

Your speedometer will be off, but I'm not sure by how much. While your at it, you might as well get a tuner from either Lidio or Dennis, and have them load a tune that has the changes needed to compensate. Personally I've ran both their tunes and both are better than stock. For a daily driver I'm partial to Lidio's transmission schedule.

I noticed about a 2 MPG drop swapping to 4.10's

[red]

I'm in the process of switching from stock 3.55 to 4.10. I spoke to dealer tech he stated the switch will cause speedometer to read less than actual speed. He said around five mph or more. He also said switch will increase gas mileage, work trany harder. Alot of MM's have 4.10's.
Is this true?
The speedometer will read MORE than the actual speed by about 15.5% ((4.10 - 3.55) / 3.55). So, for example, at an actual speed of 60MPH, your speedometer will read ~69 MPH. With the stock 3.55's, you'll be running about 1800 RPMs at 60 MPH in 4th gear. With the 4.10's, you'll be running about 2100 RPMs at 60 MPH. Obviously, this will lead to some decrease in mileage.

[SC Cheesehead]

The speedometer will read MORE than the actual speed by about 15.5% ((4.10 - 3.55) / 3.55). So, for example, at an actual speed of 60MPH, your speedometer will read ~69 MPH. With the stock 3.55's, you'll be running about 1800 RPMs at 60 MPH in 4th gear. With the 4.10's, you'll be running about 2100 RPMs at 60 MPH. Obviously, this will lead to some decrease in mileage.

Red,

I agree, but I've also realized that the engine will be running higher in the power band which, IMO, improves operating efficiency; so the impact on mileage is minimized.

I've tracked mpg on my car before and after the gear swap, and to date I've seen less than 2 mpg difference, which is minimal, especially for the improved performance the 4:10's give.

[fastblackmerc]

When I switched I lost 1 or 2 MPG and RPM's were about 200 more at speed.

Do it, you won't regret it.

[Emperior]

What do you recommend the gears first or tune or it doesn't matter?

[SC Cheesehead]

What do you recommend the gears first or tune or it doesn't matter?
You can do a tune by itself, but if you get gears, you'll need to get a tune to revamp shift schedule.

IMO, if you can afford both, go for it, best two mods for the money.

[Aren Jay]

..........

[red]

Cost for the 4.10 will be about $1000 all in unless you do it yourself...
I spent about $250 on new FRPP gears and a master install kit and about $300 in labor. $1000 seems a bit high to me, though my costs may have been on the cheap side.

[ctrlraven]

I bought my FRPP gears from Blue Oval on ebay, price was under $200 with shipping and bought the Cobra clutch pak (diff rebuild), install kit and new axle bearings from Summit.

Labor? Haven't installed them yet but I'm looking at $250-500 for the job.

[fastblackmerc]

If you buy a tune from either of the top two vendors DR or Lidio they will supply you with a 4.10 Tune as well as 3.55 tune. Get that first then decide if the 4.10 is necessary. Cost for the 4.10 will be about $1000 all in unless you do it yourself, tune will be about $400.

Either way you will need the tune.

1K for installing gears!!!!!!!!!! :eek::eek::eek::eek:

If you paid that much you got screwed!

Look around for a shop that works on Mustangs, they are your best bet. Had my 4.10's installed for less than $500.00 parts included.

[doyounochef]

how much top - end do you lost with the 4.10 gears in place

[fastblackmerc]

Good question. I'd think not much. I've had mine up to 120 and still pulling.

[red]

how much top - end do you lost with the 4.10 gears in place
You can calculate this by multiplying your "top end" by (3.55/4.10, or .866). So, instead of ~140 MPH at 6,000 RPM in 3rd gear, you'd be at ~121 MPH.

[RR|Suki]

If you buy a tune from either of the top two vendors DR or Lidio they will supply you with a 4.10 Tune as well as 3.55 tune. Get that first then decide if the 4.10 is necessary. Cost for the 4.10 will be about $1000 all in unless you do it yourself, tune will be about $400.

Either way you will need the tune.

WOW $1000, I think I spent $450 total, gears and install kit, and labor :eek:

[BODYMAN]

I would do the gears and tune at the same time so there is no speedo diff and you will be very pleased a dr stage 1 kit (gears,chip)