5 Star Tuning 7.3L Motorhome Tuner Review

For the 2021 model year, Ford is now offering the new “Godzilla” 7.3L in motorhome chassis. Out is the dirt aged 6.8L V10. While the old V10 was tried and true, the new engine is a welcome change. On paper, for motorhomes, the 7.3L shows a nice improvement of 45hp, but torque has a smaller gain of about 15lb. ft. Those numbers in a large motorhome sound like footnotes, but the driving experience is very different. In this article we will explore the before and after tuning driving experience. The tuning was specifically meant for motorhome applications. The particular motorhome in question here is a 32 foot long class C motorhome, which is one of the longest motorhomes available on the E450 chassis.

When evaluating engine performance in something this heavy, sundials may be an appropriate measurement tool. The prevoius 6.8L lacked highway cruising torque. When driving up north in Michigan for camping adventures, any incline with the motorhome, especially if towing a car behind, would have the transmission downshifting one or two gears. At 70mph, downshifting 2 gears has the engine singing at 4,400rpm and making a lot of noise to boot. When travelling over long distances, that noise tires the brain. There are ways to quiet the engine with sound damping, but the sound level never approaches anything considered quiet. Transmission shifting was a planned event. If done just right, the single downshift could be achieved, but it required laser focus on the road and evaluating every hill you approached to decide when to stab the gas pedal just the right way to get a single downshift. For so many years it was the only option and unless a person spent the big money for a diesel super C, this was all we got.

The 7.3L has entered this world like the Kool-Aid man. Ford fanatics love this engine and for good reason. With the 6.8L being an overhead cam engine, it was much larger. The 7.3L is more compact and runs essentially on simpler technology. Obviously there are modern tech advances, but as Chevrolet knows, having a pushrod engine allows the overall engine size to shrink. There are already multiple tuners who have made big power with this powertrain. One interesting note about the 7.3L for motorhome duty is the power ratings are very different from the trucks. Motorhomes cap out at 350hp @ 3,900rpm. The trucks head north to 430hp @ 5,500rpm. Wait, why does the motorhome get nerf’d? Having a detuned version of the motorhome spec engine isn’t anything new. Many OEMs use a “RV spec” engine setup, which typically has the engine prioritize low end torque over high rpm power. Also, the platforms these workhorse engines go into lead hard lives and are run at max capacity often. The folks at 5 Star Tuning did provide a set of graphs which really highlight the difference. The difference is massive.

First up the motorhome dyno graph:

The stock tune falls off a cliff right at redline, when according to the tuned version, it was nowhere near giving up for power production.

Next up the F250 graph:

The lower line there is the stock graph before tuning. Just taking a look at 4,000rpm there is a huge difference with the F250 engine making 320hp and around 420 torque. The motorhome engine is making 225hp and around 300 torque. Talk about a massive detune.

Many times in automotive there can be legitimate reasons why detuning needed to happen. I say legitimate in the sense that a company may have needed to meet some target and this was the easiest and cheapest way to get there. It could also be that there is some bottle neck in the system that prevents Ford from giving us motorhomies all the horsepowers.

Driving the new 7.3L in exactly the same type of motorhome was a vastly different experience. Gone was the screamy engine with lots of downshifts. In was the mellow bellow and endless cruising in 6th gear. Endless in the sense that the vehicle wanted to stay in 6th gear almost no matter where the throttle was. There seemed no logic in the downshift pattern and was unreliable. Power feels smoother, but no real power advantage. When looking at dyno chart you can see the new engine has about a 15–25ft. lb. of torque advantage over the old engine. With something this heavy its barely noticeable.

The engine rev limiter calibration is odd as well. The RV drives just fine, but when accelerating at wide open throttle, the powertrain oddly cuts off and upshifts right where the engine seems to be still building. The transmission was super lazy at any requests for more power and the low RPM rev limit seemed to be confusing the computer where there wasn’t enough RPM for a big downshift so instead of giving me one downshift it just did nothing. Odd. I was starting to miss the old 6.8L at this point. However, the new engine was getting about 1.5mpg better fuel mileage and that is a big deal with a motorhome. Was there a way to raise the rpm limit or get the transmission to shift better?

Five Star Tuning has been around for years tuning everything from pickups and cars to RVs and side by sides. They currently have a software flash available for the new 7.3L. Power increases mainly come from removing most of the RPM limitations on the stock tune while keeping the 87 octane requirement. They will tune a custom file if you hot rod your motorhome, but my guess is most people are just in it for the basic tune. The tuning shipped to the house cost $562.48. That’s not cheap. When examining their dyno charts, the power gains are pretty small across the board until the 3,900rpm stock cutoff point and then it gets real. According to the dyno charts, the 7.3L is hitting peak torque right at the stock 3,900rpm rev limit. From there it looks like Five Star is doing more than they really are. Giant power gains are quoted over 100+ hp and torque. Hard to call it false advertising, but all they did was somewhat raise the rev limit and not even up to the stock 7.3L truck rev limit. It is hard to fault 5 Star as they figured it out and have a fix for the lackluster output from the factory.

The tuner arrived in a few days. The tuner box itself is a very simple device. Plug it in, get a code from your vehicle and send that off to Five Star. They will then send you back the tune files and you load them onto the device. Take the device back to the vehicle and program it. In theory this whole process takes about 72 hours as Five Star says they need 48 hours to process new tunes. They took a lot longer for mine and required multiple follow up emails and calls. The programmer froze during an update and hold times for tech support at Five Star were so long I gave up. Eventually, I got the new updated software and the tuning files. The process on the motorhome was simple and took about 15 minutes when you have all your ducks in a row. Started up and no engine codes so we were good to go. So, how does it drive?

Hands down the largest improvement is the change to the RPM limit. That change seems to help the ECU better determine what gear is available. Five Star says they have made changes to the transmission calibration as well. That is very noticeable and not necessarily in a good way. Without tow mode engaged the RV tends to hold gears for no reason at odd speeds. Cruising through a 25mph zone in my small town and the engine is up around 2,100rpm. Just wasting fuel at that point and it is loud in the cab. Typically, OEMs will use speed and load based mapping and it feels like the load based setup was deleted and is only using speed based maps. Using onramps, the transmission still struggled to respond to wide open throttle downshift requests. When I put my foot to the floor, I want a lower gear….now. That doesn’t happen every time, even with the new tune. Sometimes it will, but the request takes seconds. In 5 Star’s defense that may not be something that can completely fix.

From behind the shoe, the throttle seems to have been remapped for a much more aggressive response. Where the old map was lethargic to tip in, the Five Star Tune likely added a higher percentage of throttle to give the feel of more performance. It works. More torque everywhere is the output here. Some of the is evident in the dyno graph, but the motorhome just seems to move around with much more authority. I would never say this thing is fast, but it doesn’t feel like a slug now. Merging onto the freeway with my Jeep in tow, I felt much more confident that I could get up to speed and not be a rolling roadblock. The power builds nicely all the way up to the new redline which is 4,600rpm. The engine still feels like it could go a bit higher, but it is so much better than the stock tune in the upper RPM power I’m not sure it is needed. However, as I think back to the F250 dyno chart, I’m left wondering what it would be like with another 100ft. lbs of torque.

As I stare at the collection of bugs on the front cap, I’m left wondering if this tune was money well spent. On one hand, the power gains up top are undeniable. On the other, there are still lots of transmission calibration issues and some questionable decisions on gear holding when not in tow mode. I received a response back from 5 Star and they indicated that as long as the request wasn’t ridiculous they can do minor tweaks to the trans calibration if their initial tune doesn’t work 100%. I am sure this comes with a limit and they probably can’t fix everything as Ford limits what can be done, but at least there is an option to fine tune the tune so you can put a tune in your tune. Unfortunately, as of this article my motorhome has been broken into and is completely inop. at a dealer. I won’t be able to test the revised calibration tune for months.

The verdict: For motorhome duty, this seems like an easy way to drastically improve engine performance. Regardless of how they got there, 5 Star can offer performance improvements in this application that only forced induction usually produces. With the ability to get modified custom tunes for the transmission, it would be hard to argue against it. The only question in my mind is what did Ford do for the detune? They set the RPM rev limit for a reason. Going up 700rpm in rev limit doesn’t seem to phase this engine in the slightest. Does it cause durability issues for other components? It would be nice at some point to find a Ford engineer who could enlighten us all as to why. Maybe one day.

So, here is a rating (1–10 scale):

Part Quality — 7

There’s nothing special about the tuner box. It looks old and dated, but it doesn’t need to be flashy for a simple tune install.

Ease of install — 7

This would be a 10 for ease of install because the process is super simple. Customer service was lacking though and timing was much longer than expected. Hounding a company for parts is frustrating.

Cost — 9

I struggled to rate this on cost. The performance improvement is a rev limit change. That is the meat and potatoes here. I know that Five Star has done some remapping of fuel curves, but that lends to a tiny fraction of power compared to what happens after the rev limit change. If you ever wanted to add almost 100hp to a car you are talking big money and this is cheap relatively speaking.

Performance — 7

Power improvements are game changing, but trans calibration possibly got worse than stock. Holding gears for long periods of time is annoying and unnecessary. Save that for tow mode. Good news is that can be changed. If I had a chance to evaluate before this article the rating likely would have improved.