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4.09 vs. 3.73 opinions wanted

CNCLester

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I currently have my DD driver 2016 manual GT. Looking for a little more acceleration from my GT (3.31 gear) but keeping it N/A - never going Power Adder route. Already have the Power Pack 2 but maybe I've grown used to it and as always want a little more without breaking my budget. Just asking if I went gear change, would 3.73's be enough or go all out to 4.09's. Anybody out there with 4.09's please chime in
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CNCLester

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I have a friend who has a 14 gt mt82 procharged. We installed 3.73 in his car and it comes out of the hole really good. With that mt82 I would not go any shorter as your 1-2 shift is going to come quickly, but will be fun as hell when you let her rev. I have 4.09 in my 18 mt82g4 and they are perfect for me.
To answer your question on labor time I'll say this. I can remove the s550 diff in an hour and a half. Proper gear setup will take 2 to 4 hours depending on if you have to set pinion height more than once to get proper mesh pattern. Then 1.5 to 2 hours to reinstall diff. If you buy another differential as I did, you can install the gears on a bench with a simple holding fixture and swap them out in 2 hours. Then if you don't like it it's simple to go back to what you had.
 

SJulian10mm

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3.73's with a Power Pack 2 is a very potent combination for NA street cars. Braski ran an 11.86 with a Power Pack 2, Big / little's and an IRS re-work and cat back exhaust. That's moving pretty good for just a Power Pack 2 as the only power adder.
I have this settup and have been really happy with it for both track and street. 3.73s are perfect with the added RPM. I generally shift at 7000 when giving it the full beans...that leaves me a few hundred RPM of error room. 1-4 rip considering how simple the settup is.
 

RoadCone

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I have a 4.09 with a Tremec (2.97) and love it. Once in 4th I can let the car eat..... I also ran it with MT 82 and cobra Jet intake.... I think a 4.56 would have been optimal for the NA 1/4 mile.
 

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Do not get 4.09s or listen to anyone recommending them. I had 3.37s and they are geared low as it is. But good for the street. You will regret 4.09s unless you want to be using 6th gear at 55mph.
 

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Thanks for all this feedback! Now I keep going back and forth since this is going to be a one time job obviously. Looking to do this in the spring so I have a lot of time to think it over. I'll definitely take any more input up until then. My mind says 3.73's. Just hope that 10% difference can really be felt.
 

Mikepol2

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My car came with 3.73's, but I have a 4.09 set ready to install when I have a little more cash. But here are some speed / rpm calculations for 3.73 vs 4.09 for my car with GT350 wheels and tires:

MPH at 7K RPM:
Gear / 3.73 / 4.09
1st / 47 / 43
2nd / 73 / 66
3rd / 108 / 98
4th / 153 / 140

MPH at 2K RPM:
Gear / 3.73 / 4.09
1st / 14 / 12
2nd / 21 / 19
3rd / 31 / 28
4th / 44 / 40
5th / 54 / 49
6th / 71 / 64
 

TheLion70x77

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Thanks, I guess I've heard one too many times to never fear the gear lol!
4.09's would be a blast with the Power Pack 3 and a little more ideal due to the added rev range than with Power Pack 2. Torque curve is much flatter with Power Pack 3 than power pack 2 making throttle modulation more ideal with the shorter gearing. Power Pack 3 with 4.09's would provide impressive acceleration.

Power Pack 2 is really better with 3.73's and makes the most of the stock intake manifold / gearing. I plan to eventually retire mine from daily and run 4.09's with a Power Pack 3 and 305 4 square setup (extended studs and spacers up front) for a street able track car. However over the next couple of years it will remain a track able street car (more street oriented) as it is set up now as that's primarily what I use it for.

If you want more punch without doing a gear swap or adding power, I highly suggest you start looking at efficiency. More is not always the best way to go about it. Many times people completely over look losses, forgetting that power is already there but is wasted on inefficiencies or OE design intents that are more focused on CAFE than raw performance. There are several key areas to look at that when combined make a substantial difference (more than just the next level up Power Pack would by itself).

1. Sprung Mass
2. How tire diameter affects final drive and matching a sticky street tire to handle the torque
3. Engine air flow path
4. Engine friction losses
5. Engine fuel dilution due to oil vaporization (big issue with the 5.0 and all high revving engines)
6. Engine oil formulation and how it interacts with Hydrogenated DLC coatings and a good high efficiency / high flow oil filter

When you combine an oil catch can, TriboTEX DLC coating, Penzoil Ultra Platinum and a VelossaTek ram air duct with a Power Pack 2 the results are impressive. They are even more impressive when you reduce the rotating mass the engine has to spool up and reduce the final drive ratio a bit for effective gear reduction. It's really impressive, but each change plays a critical role and it's the combined effect that works, any one thing alone makes a rather minor difference. In engineering, substantial performance gains are most of the time made by a sum of small changes that seem benign or trivial on their own.

There are multiple things at work that are highly beneficial when running a low mass wheel / lower profile tire setup:

1. Handling dynamics increase as your CG is 1/2 inch lower without screwing up roll center, bump steer or chamber gain curves
2. Tire side wall has less flex (more linear breakaway) and there's less sprung mass for the suspension to manage (better response over bumps and better transition).
3. Going from a 255/40R19 + 275/40R19 staggered setup (stock) to a 275/35R19 four square setup reduces your final drive by 4%. 4% is almost exactly half way in between 3.73's and 4.09's. So it's like having having 3.91's which don't actually exist.
4. Handling is much more balanced than with staggered tire setups. Think Performance Pack Level 2 which uses 305 four square tire setup.
5. Using something similar to the RTR Tech 7's 19x9.5 (there are many flow formed wheel options in the 23 lbs range) and lighter 35 profile tire, you shave 48 lbs of rotating mass which equates to about 144lbs of sprung mass (unsprung mass has about 3x the effect of sprung mass on acceleration). Not only are you reducing the total rotating mass, but your lowering the Moment of Inertia due to where the mass is concentrated. The combined effect is like increasing power to the wheels and it's very noticeable.

I find the gearing to be just about perfect with the Power Pack 2 (7,150 rpm rev limit) and the shorter final drive due to the smaller tire. Your still 1 mph faster in each gear even with the smaller diameter tire setup compared to the stock engine calibration (6,800 rpm rev limit) on the stock tire sizes. The only caveat would be if your not lowered, the gap will look goofy. But if your ride height is dropped 7/8" or more, it will look like a factory Performance Package Level 2 or the GT350 factory setup as far as tire gap which is in my opinion good looking. It screams performance street car, not a poser car that lacks a functional suspension.

I was really amazed at how much of a difference the combination of low mass wheels and 4% final drive increase made even with no other changes (already running Power Pack 2, TriboTEX DLC coating and an oil catch can before I got my summer tires finally and put them on my RTR Tech 7's I saved from back when I had my Ecoboost Mustang).

I also highly suggest running TriboTEX DLC coating in your 5.0 with the Power Pack 2 and a oil catch can. There's about 10~15 hp across most of the power band and better throttle response + fuel economy to be gained through reducing internal engine friction losses. Oil catch can is essential to preventing fuel dilution and power fade, but TriboTEX reduces oil consumption slightly due to better ring seal. Even the stock 5.0 suffers power fade when it gets hot, heck even Car and Driver noted that in their lightning lap testing, it was the only car tested that day that experienced power fade despite nothing being over temperature on their test car. Must be a Ford thing...

Even with the short 3.73 gearing, 275/35R19 four square tire setup (Pilot Sport 4S), I still manage up to 27~29 mpg cruising at about 70~75 mph on the highway, I can post some pictures of the fuel economy bar graphs if anyone needs proof. Much of that has to do with the DLC coating, the 5.0 has a lot of friction losses, more than Chevy's 5th gen LT1 as the 5.0 operates at a higher average RPM and has 2x valve train and 4x the number of timing chains. There's a lot of lost power and fuel economy to be regained through reducing friction losses and DLC coatings are the key. The greater the losses, the greater the gains. TriboTEX makes DOHC high revving architectures more viable as your not off-setting the advantages of DOHC and higher RPM operating as much with friction losses. Use the Diesel concentration, not the regular as you need to make sure there is enough raw material to fully coat the vast plethora of friction surfaces, otherwise the coatings will not full form and you won't see any benefits.

Regarding the intake, the VelossaTek Ram air duct and GT grill mod is crucial for high speed driving (3rd gear and higher). The OE air duct setup is designed for fuel economy purposes by dumping hot radiator back wash air into the intake. Also there is no direct flow path, so the stagnation zone is in the WRONG spot for performance driving. OE's use "hot air intakes" for that reason, fuel economy. Honda is even going so far on their new cars to actually use a heater element on the intake! Hot air produces better fuel economy and lower emissions, but less power. If you look at the Ford Performance Power Packs section, i detailed a slight mod for the VelossaTek to make it work optimally with the Power Pack 2 GT350 intake by closing up that gap with some aluminum flashing material and foil tape.

Finally is the oil and filter. I highly recommend Penzoil Ultra Platinum. GTL base stocks are extremely robust and clean. They hold up very well and are comparable to mPAO's and match or exceed PAO's, but at a reasonable cost. Also PUP contains MoDTC, an organic moly compound that works extremely well with hydrogenated DLC coatings for wear AND friction reduction. Pair it with a good oil filter that is 20 micron rated. The Ford Performance FL820 has 2x the media of the OE FL-500S filter, is rated as 99% for 20 micron vs. 80% at 20 micron and out flows the OE filter while retaining clean side by pass and silicone anti-drain back valve for cold start oil flow. It's an affordable and very ideal combination.

Select oil viscosity based on your temperature applications. 5W-20 is fine for most street, drag, auto x where your not sustaining high rpm for more than for a minute for two at a time. 20 weights are in a temp range where their film strength is optimal. Optimal oil temp for this viscosity is around 210F-230F. For aggressive street use on back roads or light duty track, 5W-30 provides a little more protection and is ideal for frequent elevated temps in the 240F~260F range, typically where your sustaining higher RPM for 5 to 15 minutes at a time. For hard core track, use PUP 0W-40 where temps are in the 280F to 300F range (right at the edge of the yellow on the inferred oil temp gauge) and your at high RPMs nearly constantly and heat is at a maximum. Oil viscosity selection is all about temperature.
 
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Schwerin

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I loved the 4.10 with my Mach1 and since the gearing is so similar to the 3650 in the new M-82 I'm really thinking of getting the 4.09 for my Bullitt. Even for daily driving it was great. There was barely a noticeable MPG change going from 3.55 to 4.10 in the Mach1 so if you already have 3.73 it will be even smaller.
 

TheLion70x77

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Also might want to consider 3.91's for Power Pack 3 (7450 rpm rev limit):

3.9 Effective Ratio Speed
1st Gear Ratio 3.657 14.908 ↔ 41.2 MPH
2nd Gear Ratio 2.430 9.906 ↔ 62.0 MPH
3rd Gear Ratio 1.686 6.873 ↔ 89.4 MPH
4th Gear Ratio 1.315 5.361 ↔ 114.6 MPH
5th Gear Ratio 1.000 4.077 ↔ 150.7 MPH

vs. 4.09's
4.09 Effective Ratio Speed
1st Gear Ratio 3.657 15.634 ↔ 39.3 MPH
2nd Gear Ratio 2.430 10.389 ↔ 59.1 MPH
3rd Gear Ratio 1.686 7.208 ↔ 85.2 MPH
4th Gear Ratio 1.315 5.622 ↔ 109.2 MPH
5th Gear Ratio 1.000 4.275 ↔ 143.7 MPH

3.91's with Power Pack 3 are still somewhat street able for periodic trips if your running a DLC coating and good oil (which aids in fuel economy and power to the wheels) as it's a smaller step down from 3.73's than the jump to 4.09's. You can use the gains in fuel economy to off-set the losses of shorter gearing and higher average operating RPM's. Those speed ranges are with a track size tire profile in the 35 to 30 side wall just for reference.

Either a 275/35R19 squared setup on 19x9.5's (more of a street setup with occasional track) or a 315/30R19 squared setup on 19x11's (more of a track setup with occasional street), your tire diameter is 26.5~26.6" instead of factory 27.7". That gives you a 4% final drive reduction so keep that in mind if you run a taller tire you'll gain more MPH and 4.09's with a taller tire would be the same a 3.91's with a shorter tire. Power Pack 2 and 3.73's with a 26.6" tire is like running 3.91's on factory tire diameters with the Power Pack 2. It's kind of a half way point between 3.73's and 4.09's.

I'm looking at it from an acceleration standpoint for all gears but 1st. I don't care about 1st gear for road race, roll race, auto x or anything other than drag race and low profile tires aren't exactly drag tire material. If you want a good drag car, run drag radials or better yet a full set of big / littles. Braski (project Midnight) ran an 11.86 on a full set of big littles, cat back exhaust, Power Pack 2 and IRS updates. Nothing else, with stock clutch in a 2015 PP GT, so it can move.

Here's what Power Pack 2 gives you with 26.6" diameter 275/35R19 four square light weight tire / wheel setup for a dual purpose car that's more street oriented:

Rear Axel Ratio 3.73 Effective Ratio Speed
1st Gear Ratio 3.657 14.205 ↔ 41.5 MPH
2nd Gear Ratio 2.430 9.439 ↔ 62.5 MPH
3rd Gear Ratio 1.686 6.549 ↔ 90.0 MPH
4th Gear Ratio 1.315 5.108 ↔ 115.4 MPH
5th Gear Ratio 1.000 3.884 ↔ 151.8 MPH

This is the gearing / tire setup I'm running now (and Power Pack 2) and LOVE it for a dual purpose setup. Running a good oil (PUP 5W-30) and TriboTEX, I still get 27 to 29 mpg on flat or slightly down hill cruising in the 70 mph range, so it's plenty street drive able. But as I mentioned, once the car becomes more of a weekend toy than a dual purpose car that's daily driven in a few years, I'll switch to Power Pack 3 and a shorter final drive with a wider tire / wheel setup. Usually what works best on the track is not what works best on the street, but some compromised hybrid setups can work reasonably well for both.

See, the thing is, Power Pack 3 makes higher average power than Power Pack 2 or the LT1 with bolt-ons (stock tune), by quite a bit, but requires more RPM to do it. Power Pack 2 is nearly identical in power band to the LT1 with an intake just shifted 550 rpm higher instead of 850 rpm higher like Power Pack 3. Simply upgrading to Power Pack 3 will not help your 1/4 mile over Power Pack 2 on the same car because your gearing isn't optimized for the higher rev range and some tweaking can go a long way.

The 2016+ SS is the star performer stock to stock and trounces the GT many times over, the 2015-2017's anemic OE tuning (both engine tuning and suspension tuning) is a big part of that. I used the SS factory setups in it's various configurations as well as the GT350's setups to learn from and optimize my gearing in the GT in the 40 to 110 mph speed range while using the Power Pack 2. On a track your going to be using mostly 3rd and 4th in the GT with occasional 2nd on a hair pin turn and 2nd / 3rd in the SS with occasional 1st on a hair pin turn. So optimizing gearing to use the power band at those speed ranges is what I focus on and it works very well in practice.

Here is the factory SS gearing for reference:
Rear Axel Ratio 3.73 Effective Ratio Speed
1st Gear Ratio 2.660 9.922 ↔ 54.6 MPH
2nd Gear Ratio 1.780 6.639 ↔ 81.7 MPH
3rd Gear Ratio 1.300 4.849 ↔ 111.8 MPH
4th Gear Ratio 1.000 3.730 ↔ 145.3 MPH
5th Gear Ratio 0.760 2.835 ↔ 191.2 MPH
 

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Bluemustang

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I like the way you think Lion. I enjoy reading your posts, keep em coming.

This makes me think about what my effective gear ratios are now with the 3.55s and the 6R80 transmission.
 
 




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