4.09 Rear Gear Set

[Mr. Happy]

Anyone compiled a speed in gear delta with these gears?

I would suggest using this site to figure it out: http://www.kabamus.com/garage/gears.html

Huh

He's asking if anyone has calculated the top speed difference in each gear between 3.73 and 4.09. I know it's hard to figure that out in a thread about changing rear end ratios ;)

Rear gears need to be matched well with the Coyote manuals, but the autos seem to run the same no matter what gear you have. Guys have tested this over and over, and there's no appreciable difference between gears with these cars' automatic transmissions. Best to run 3.15s or 3.31s and keep your gas mileage up.

For a manual NA Coyote, run 3.73s with a Boss, CJ, or even possibly a Voodoo IM. For the stock IM, run 3.55s.

Where these 4.09s are really going to help is on launching the GT350 harder. As we all know, the car has pretty weak torque below 3,500RPM, and first gear is extremely tall. After it gets moving, it builds speed like crazy, but it needs help off the line for the guys who really want to drag race them. It would probably be a little more fun on the street too. It would be worse for a road course with 4.09s, which is what it's designed for. Like Hack said, buy a second center section with 4.09s and swap them out depending on your application.

I would wager that the 4.09's will help pretty much everywhere (street, strip, road course) since it increases the thrust in each gear. Yes, you'd need to shift more around a road course, but you're going to be accelerating faster in those gears. Actually, looking at the gearing and most tracks, you'd be able to leave the car in 4th gear more often since 4th would run out in the low 130's and 5th would be the low 160's. 3rd would only be used for tight corners.

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[FTD]

Did a quick max speed in gear calculation, promising results. This is with OE size tires.


GT350 - 3.73
1st: 55.44 MPH
2nd: 80.78 MPH
3rd: 111.94 MPH
4th: 145.08 MPH
5th: 180.33 MPH

GT350 - 4.09
1st: 50.56 MPH
2nd: 73.65 MPH
3rd: 102.08 MPH
4th: 132.31 MPH
5th: 164.46 MPH

GT350R - 3.73
1st: 53.48 MPH
2nd: 77.91 MPH
3rd: 108 MPH
4th: 139.97 MPH
5th: 173.98 MPH

GT350R - 4.09
1st: 48.78 MPH
2nd: 71.06 MPH
3rd: 98.49 MPH
4th: 127.65 MPH
5th: 158.67 MPH

 

[Mr. Happy]

Did a quick max speed in gear calculation, promising results. This is with OE size tires.


GT350 - 3.73
1st: 55.44 MPH
2nd: 80.78 MPH
3rd: 111.94 MPH
4th: 145.08 MPH
5th: 180.33 MPH

GT350 - 4.09
1st: 50.56 MPH
2nd: 73.65 MPH
3rd: 102.08 MPH
4th: 145.08 MPH
5th: 180.33 MPH

GT350R - 3.73
1st: 53.48 MPH
2nd: 77.91 MPH
3rd: 108 MPH
4th: 139.97 MPH
5th: 173.98 MPH

GT350R - 4.09
1st: 48.78 MPH
2nd: 71.06 MPH
3rd: 98.49 MPH
4th: 127.65 MPH
5th: 158.67 MPH

You copied over 4th and 5th for the GT350 4.09 from the 3.73 column. Just an FYI. 1-3 is correct though.

 

[FTD]

You copied over 4th and 5th for the GT350 4.09 from the 3.73 column. Just an FYI. 1-3 is correct though.

Fixed now. The forum didn't like the formatting; copy and paste was not very easy.

 

[MAV]

Anyone compiled a speed in gear delta with these gears?

Adapted from a spreadsheet I found on the Internet...

 

[Nataphen]

4.09s may be the GT350's ideal all around gear then. I may swap mine if I'm still wanting a little more after all the other parts and tuning. I have to get the car first though.

 

[Voodooo]

I plan on installing them when I remove my rear cradle to do the bushings. But id still rather 1/4 mile the car first to see what the trap rpm is.

 

[Hack]

It looks like it could really use even more gear - like a 4.56 or possibly something over 5.xx. 4.09 just doesn't make much difference looking at the speed in gear. I agree that 4.09 might be faster on a track - depending on how long the straights are.

First gear is just way too crazy tall. I should say - it's fine, but really set up for a road course and not optimized for acceleration on the street.

 

[ITLRUN]

The gear set will be cheap enough... The install will be a PITA with the lower air tray, fluid cooler and the fact that it's an IRS.

The 99-01 Cobras and 03-04 Mach's loved a 4.30 even as a street car. Never fear the gear!

 

[04Terminator]

Like Hack said, buy a second center section with 4.09s and swap them out depending on your application.

Is that possible? I'd be up for the whole assembly. Nobody locally I trust to do the job.

 

[Nataphen]

Is that possible? I'd be up for the whole assembly. Nobody locally I trust to do the job.

I'm sure it's possible to get one. It may be more than you'd want to pay. More than likely, you'd have to swap 4.09s into your stock chunk, then you'd have to buy another OEM replacement one with the 3.73s. I doubt that they'll make a unit with 4.09s installed. I may be wrong though.

 

[Hi-PO Stang]

I am sure it would be expensive , but maybe Ford Motorsports will sell the main body housing of the IRS with the 4.09 or 4.56 gear installed

 

[04Terminator]

Fingers crossed!

I am sure it would be expensive , but maybe Ford Motorsports will sell the main body housing of the IRS with the 4.09 or 4.56 gear installed

 

[200MPHCOBRA]

Anyone made a move on this yet? I would love to see one of these things geared down to get this thing in the power band faster..

 

[stanglife]

Another thing any experienced gear changer will notice is that Ford gears never come with a pinion depth written on the pinion, this is why it is common practice to use the size pinion shim that came out of the car, doesn't guarantee it'll be dead on, but that's what you have to start with when there's no reference depth given with the gear set. That being said the Ford gears are very good gear gears when it comes to set-up using the original pinion shim. I always make a note of what my car takes and just put that shim under the next ratio I'm trying, this way I'm not having to press off the pinion bearing again to steal the shim.

I'm a little late to this thread but wanted to say, ^this^.

I've done my own gears ONLY when I'm replacing an original gear with another FORD gear - and the rear end is in good shape with low miles. When those conditions are met, out of the 5-6 gears I've done, they've always when in with the original shims, zero problems, zero noise.

Now, if you're changing brands, someone has been in the rear end multiple times before you or the car is getting new carrier bearings - it gets more complicated and there are many more things to measure...I take it to someone that's done thousands of gear setups, not worth my time and a new learning curve.

So, IMO, if you have a home shop and are handy, you can likely do the OEM to FP gear swap with no issues. Of course, there's always the chance it will not be perfect - check the pattern - but IME, it's been pretty smooth.

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