Worth the switch to 4.30s?

WE3ZS wrote:

Hemling wrote:
I think I need to refine my question / premise that I am operating under. I intend to tow in 3rd, exclusively. Is the reason that people use higher numerical gear like 4:30 and 4:56 ratios so that they can remain in OD longer without dropping to 3rd as much, or for increased power in the 1:1 ratio (3rd in my trans.)? I don't intend to make use of OD at all. I just want to know from those who have experience if I can expect my Excursion to hold 3rd reliably or if the 3:73 ratio is going to make it want to grab 2nd. If that's the case, I will put in 4:30s and be done. I don't care about OD.

You should care about OD, it's the gear the trans was designed to tow in. ;)
However, it may have some difficulty holding onto OD with that 9,000lb TT and the standard 3.73 gears. Deeper gears will improve the towing performance significantly, I have some real world EXperience in that department. :)
Our EX is an '05 with the same 2V V-10 4R100 that you have, but ours is a 4X4. We bought it (with 65,000 miles in'10) to be our tow rig with very limited daily driving. The original trailer we bought was an '04 Victory Lane 28SRV toyhauler that was 31' long and had a GVWR of 11,000lbs but it typically scaled at about 9,500lbs for most trips. So that weight makes a very good comparison to your planned 9,000lb TT.
Our EX came with the same 3.73 ratio but in the LS flavor and it was still rolling on the stock sized 31.5" tires (LT265/75R16E). Everything on it was bone stock as it was a former Army Corps of Engineers vehicle, so I used this setup as my baseline to plan future mods to make it a better long term tow rig.
My first mod was to perform a complete spring swap, I went with modified X/B code springs from an F-350 adding additional leaves to all 4 corners, adjustable Rancho shocks and a Hellwig rear sway bar. This gave the Ex an additional 3 7/8" of front lift and 4 1/2"+ of lift in the rear, it eliminated the near constant bottoming out of the front suspension and set me up to fit the 35" I wanted to eventually run.
During the first few years of our ownership we made several trips from home (just outside of Philly) to the coastal Carolinas and GA. This allowed me to make some very equal comparison as I modified the EX as the routing, combined weight and speeds were the same on each trip.
The first trip that established the baseline showed towing mileage results of 6.5 to 7 MPG and it could hold OD on the mostly flat mostly I-95 route but it did drop down a gear on any incline at all. On the rolling hills in MD and VA it downshift on every climb and needed fairly high throttle opening percentages to hold the 60/65 speed on those small hills. Acceleration up to highway speed was less than impressive but it was adequate.
With future plans of running 35" tires I swapped up to a set of 4.88 gears in place of the 3.73, at the same time I also swapped up to OEM 18" rims that had 32" tires. Those slightly taller tire reduced the effective ratio to 4.80. The next trip down South and back over the same route, at the same weight and speeds resulted in a towing mileage of 8.5 MPG. The biggest differences were the amount of time spent in OD, it didn't downshift a single time while on the highway. The ability to easily maintain speed on those same rolling hills and the greatly improved acceleration up to highway speeds.
The next upgrade was installation of a set of Banks headers and Y pipe. I left the balance of the factory exhaust stock, the small manifolds and horrible Y pipe seemed to be the best target for improvement. The next trip South following the new headers saw a towing mileage of 9 MPG. There was a noticeable improvement in throttle response and there was slightly less throttle opening percentage needed to maintain cruising speed.
The next mod was the purchase of an SCT tuner and 5 custom tunes from 5Star Tuning. I bought the 87 Octane Economy, 87 Tow, 87 Performance , 89 Tow and 89 Performance tunes. I provided 5Star with my trailer weight, info on the headers and had them use my planned future upgrade to 35" tires for setting up the tunes. After some experimentation with the 87 Tow and Perf tunes I found that the Perf tune suited my driving style and preferences while towing better than the actual Tow tune. I'm a fairly conservative driver and am willing to give up some speed on hill climbs if it will allow the trans to hold OD without lugging, the Perf tune works well for this. Throttle openings of up to 54% could maintain OD on climbs under high load. I found the Tow tune to be too aggressive in downshifting on climbs, it would work very well with someone more focused on maintaining more of a steady speed on the climb with less focus on economy. The first trip with the 87 Perf tune added to the growing mod list resulted in another 9 MPG. While I didn't see a mileage increase with the tune the drivability was nicely improved due to a much better than stock transmission shift schedule and strategy. Smoother acceleration, throttle-by-wire lag elimination, shift crispness and the above mentioned improved OD management were the strong points of this tune.
I then finally got my long awaited 35"s (to me they just look like the "right" size tires for these wagons :)), these new tires spec at 35.28" tall which reduces the effective ratio to 4.39. Unfortunately we didn't get to make that same route trip with this step of the EX's evolution. But a few shorter trips in other directions showed the combo to still be an excellent performer with very similar drivability and towing performance.
Our next big change was trading the TH in on a new Jayco Eagle Premier 338RETS TT, 41' hitch to bumper and tipping the scales at 11,000lbs. Several long mostly highway trips with this new TT and the EX's current configuration have returned 8 to 9.4 MPG results. Over time I have started to use the 89 Perf tune for most of the towing trips, it provides another step up in improved performance and trans management while allowing OD to be held with even wider throttle openings of up to 66%.
Between the gears, headers and tunes, all of which improved the Ex's towing performance and drivability the gears were the single biggest performance adder, without question. I strongly would recommend a gear upgrade for a V-10 EX pulling over 8,00lbs. The 3.73s will definitely get the job done, but regearing to arrive at a 4.30/4.50-ish effective ratio will deliver positive results and improved drivability and efficiency. You may see a reduction in unloaded economy with a gear change, our Ex went from 14-ish MPG on mixed city/highway driving to it's current 12.5-ish on a similar mixed driving tank. Some of that reduction is from my 4" lift and wider 35" tall tires, without the lift/tires you may only see less than or about 1 MPG decrease in solo economy. Since our EX serves as our dedicated tow rig with very little solo driving that's not a big issue for us.
If you will be towing in the 9,00lb range I would also strongly suggest that you get some method of reading the trans temperature. I use a stand alone gauge but there a several other options including Bluetooth OBDII dongles and smartphone/tablet app that will show that and many other data points of interest. Using OD for the towing work will build less heat in the trans than towing in 3rd gear, the 4R100 trans in your EX was designed to tow in OD and only needs to have OD locked out if it is hunting in/out of OD rapidly as that will build up a lot heat. Heat is the enemy of transmission health, typically users report about 100 degrees above ambient for most towing work with short durations above 200/220 during steep climbs. Short spikes as high as 250 are survivable but minimizing the time at the higher temps is the best plan. The best way to cool a hot 4R100 trans down is to let the vehicle idle in Neutral.

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