SonicBlueV6

Thought I'd start a thread about swapping gears in our cars.
Post here if you have swapped or have any thoughts on the subject.
More info can help us decide the right course of action to take with our cars.

Questions:
How much HP & Torque can the 7.5" rearend & stock axles stand? (Thinking about the power increase if adding a supercharger or nitrous).

If you have done a swap: What ratio?, manual or automatic?, performance changes?, acceleration?, top speed?, gear whine?, cost?, would you do it again or would you do anything different?

I have an auto with a few mods & I'm wanting to do a swap. Torn between 3.73 and 4.10. I may supercharge later & I wonder if that should affect my choice of ratios. I wonder how top speed will be affected, although I care more about acceleration than top speed. Seems like my car tops out at 120MPH now.

Thomas S

I'm going to go with 3.73s and a T-Lok whenever I do mine. I don't want to go too crazy. BTW your top speed is because of the factory speed limiter. A tuner will take care of that.

DrumStyxs10

Someone will correct me if im wrong but it is not the best idea to get a higher gear ratio if you are going to supercharge or turbocharge your car because higher gears up your rpms and chargers kick in at higher rpms at least like most kick in at 2500-3000 i think so you will wear on your engine alot worse because you will always be boosting so it is best to do only one or the other i think.

ManEHawke

That is what i've noticed with forced induced cars. They tend to have lower gear ratios, I think 3.73's will still be ok.

Gearhead

The 3.73:1 ratio for the V6 should be just right. It is all about 3rd gear. When passing, that is the E-ticket ride that you need. With the stock 3.31:1 ratio, 3rd gear will take your car to 91 MPH @ 5,300 RPM (Peak HP). With a 3.73:1, the speed is reduced to 81 MPH @ 5,300 RPM. Since most passes are conducted between 40 MPH to 80 MPH, that gets you going as well as possible, considering that you are missing two pistons (darn those insurance rates).
If you care to calculate speed at RPM, here is how you do it:
Tire Diameter (stock) = (21.5 cm)(1/2.54 in/cm)(0.65)(2) + 16" = 27.00 in
Circumference = (3.14159)(27.00 in)(1/12 ft/in)(1/5,280 mile/ft) = 0.0013387 mile/rev
Speed = (5,300 rev/min)(60 min/hr)(1/1.41 3rd gear)(1/3.73 axle ratio)(0.0013387 mile/rev) = 81 MPH
1st gear is 3.75:1, 2nd gear is 2.19:1, 3rd gear is 1.41:1, 4th gear is 1:1, and 5th gear is 0.72:1
2,450 RPM is 70% of the RPM where the torque of this engine is at a peak, and is a reasonable speed for fuel efficiency.
Cruising in 5th gear with stock gears @ 2,450 RPM will yield 83 MPH
Cruising in 5th gear with 3.73:1 gears @ 2,450 RPM will yield 73 MPH
I would estimate you will take a 1 MPG hit at 70 MPH from the change.
I guess that the city mileage won't be affected.
I am planning this gear ratio, as well as buying P255x50R17's, which are a perfect match to the stock wheel diameter. On 8" wide Chrome-plated Bullet rims, these 10 inch wide tires will give me an inch of bumper for rim protection against curb stones.
As near as I have been able to learn from Ford mechanics, vehicle speed is taken off the rear of the transmission with a chopper in a hopper type arrangement. No Speedometer-Cable-gear swap is possible to correct the Speedometer after the axle gear swap. I did find a programmer made by Superchips for the 2005, and they tell me that the 2006 codes will be ready by June 2007. You should have the coder in-hand before you swap your gears. In addition to accepting various axle ratios, this also allows you to re-tune for Ethyl 93 fuel, for a few HP boost.
I think I would be careful as far as supercharging a V6 with this 7.5" axle. I think you might rip it apart. If you intend to do that, and want to do the gear swap anyway, find a take-off GT axle that already has a 3.55:1 ratio (stock for the GT) and put that in instead. I recall that Ford moved to the 8.8" axle back in 1987 to keep the V8s from ripping apart the smaller 7.5" axles. We are fast approaching those power levels with a stock V6 as-is.

Defiant

Hmm... either my local shop is full of BS or else we're all about to be disappointed: apparently the 3.73 gear set has been discontinued. Again, this is according to Joe at Mustang Magic in Deer Park NY. I did mention that I had seen gear sets for sale on the web but he seemed quite adamant that the 3.73 was not available -- only a 3.42 and the 4.10. Whiskey Tango Foxtrot, over?

Anyone else have more info to add?

--=K

Thomas S

Here ya go!
http://www.v6mustangstuff.com/05Drivetrain.htm

Defiant

Thanks for the link, Jimp... that's the same place I saw them for sale, which is what made me really confused. Has anyone actually ordered 3.73's from V6Mustang stuff (or gefracing.com - I heard they're backordered for months)?

--=K

yur1279

How is mustang magic? I've heard of them and was wonderign how your experience with them has been?

1trickpony

3.73 are still listed at the FRPP site for the 7.5. As long as their making the Ranger their should be 3.73 gears available. The 7.5 took a lot of punishment from the 5.0L awhile back, so if you stay under 300 pounds of torque I think you'll be ok with a blower. Drag radials will probably kill your rearend faster than the blower. I think a lot of guys avoid short gears with a roots type blower because you can't get it to "hook up." A vortech type blower needs short gears to get into the power band quick. They don't make real power until 4000 rpm.

Defiant

Hi Roy

Well, all they really ended up doing this time around was revving the car a lot and Mike (one of the techs) took it for a quick test drive to try and pinpoint the location/cause of my rear end rattle. They were very patient with my million and one questions and didn't treat me like a "dumb girl" -- they talked shop with me without missing a beat and explained everything I didn't understand.

Joe (the owner) quoted me around $250 for a gear install, plus parts... not too bad a price based on what I've heard. I will be able to give you a more thorough review of their workmanship if/when I get 4.10's and a T-Lok put in (those won't kill my poor V6, will they?) I do about half and half local/highway driving and rarely go faster than 80 mph so I'm not too worried about the higher RPMs. I just want a quicker launch off the line from light to light and a speedier merge into highway traffic. I have an XCal2 so I'm not worried about the speedo or any other adjustments.

They have a pretty sweet project car at the shop... black '05 GT manual tranny with 4.53 gears (I think) called "Retro Magic". I followed it down the block when I was leaving and darn that thing sounds MEAN! Nonetheless, I still got props on my Coffin muffler, which the guys there had never seen before.

--=K

Gearhead

Hi Kim,
I would be very curious how a locking or limited slip rear end would work in your V6. The 4.10:1 axle ratio definitely is low for the V6. Peak horsepower @ 5,300 RPM in 3rd gear would be just 74 MPH, so you might be doing a 3rd to 4th shift to complete a pass (you have a manual transmission, right?). P.S. the numbers I mentioned here and above are for the manual; not the automatic.
At 80 MPH in 5th gear and with 4.10:1 axle ratio, you would be turning 2,940 RPM, which is essenially the engine's peak torque speed (3,000 rpm). That is going to drop your mileage by a few, since a relatively lightly loaded engine will yield it's best economy somewhere between 30% to 50% below peak rated torque, say about in the 2,000 RPM to 2,500 RPM region. When under full throttle however, an engine gets its best efficiency at peak rated torque, but we aren't normally under constantly high loads, like towing a trailer, going up a mountain pass, etc..
Then again, it sure is nice to lay a little rubber in 1st gear without having to snap the clutch, right?
Maybe the 4.10:1 is just right????
See you later; Brian.

yur1279

i'm so clueless with gear stuff, ect. What happened to the 3.73's? Also, can you put the T-lok on while keeping the rest stock??

ManEHawke

As far as I know nothing has happened to the 3.73's, and you can definatley get the t-lok with nothing else.

Gearhead

When my V6 (manual transmission) arrives in late September or early October, I do plan upon the 3.73:1 ratio. I think that gives you the best combination of quick 3rd gear passing capability with very little impact to 5th gear fuel economy.
Brian.

1trickpony

I wouldn't worry about taking the 4.0L up to redline. The dyno's I've seen show it makes good power (90% of peak HP) at redline. Its not an old 5.0L that falls on its face at 5000 rpm.

ex-Galaxie500

Are the V6's with the 7.5 rear ends having the same problem a lot of the GT owners are experiencing with swapping out their gears? GT Gear Thread

ManEHawke

Thats a bad problem, not sure if anyone here has them installed yet. Hopefully it isnt a hit & miss problem.

JesseV6

Gerhead, What would you reccomend for the V6 Auto? Im torn between 3:55 and 3:73's I do a lot of highway driving but I'm looking for a noticeable change.

Gearhead

Hi Jesse,
The Automatic has these ratios:
1st = 3.22:1, 2nd = 2.29:1, 3rd = 1.54:1, 4th = 1:1, 5th = 0.71:1
The stock axle ratio for both the manual and the automatic is 3.31:1
Speed at maximum horsepower in 3rd gear = (5,300 rev/min)(60 min/hr)(1/1.54 3rd gear)(1/3.31 axle ratio)(0.0013387 mile/rev) = 84 MPH.
with the 3.55:1, the speed in 3rd @ 5,300 RPM = 78 MPH
with the 3.73:1, the speed in 3rd @ 5,300 RPM = 74 MPH
So if we assume that the typical pass is over by about 78 MPH, then the 3.55:1 would be best, and if the typical pass is over by about 74 MPH, then the 3.73:1 would be best.
5th gear cruise at 70 MPH would turn the following:
3.31:1 stock rear end = 2,048 RPM
3.55:1 optional rear end = 2,197 RPM
3.73:1 optional rear end = 2,308 RPM
So I would be pretty hard pressed to say we are going to swing the fuel economy more than about 1 MPG downward on the highway. I doubt that the city driving economy would be affected.
Another way to look at this is to look at 1st gear 5,300 RPM speeds. This would give the propensity of the car to chirp 'em off the line:
3.31:1 = 40 MPH
3.55:1 = 37 MPH
3.73:1 = 35 MPH
To summarize:
1st Gear Burnouts would be best using the 3.73:1
3rd Gear Passing would be best using either 3.55:1 or 3.73:1
5th Gear Economy isn't going to be hurt too much with either the 3.55:1 or the 3.73:1
I think in the overall, I would go with the 3.73:1.
Thanks; Brian.
P.S. I accidentally stated two notes ago that the peak torque of the V6 is at 3,000 RPM, where it actually is 3,500 RPM.