For those who haven’t been following along (and why wouldn’t you be?) the folks at KC Turbos are giving away their beloved 7.3L Ford F-250 Super Duty. The truck has been in the company’s fleet for a while and was put to use for product development and CARB testing. Instead of just selling the much-loved truck, KC Turbos is giving it away to one lucky winner. Here’s the good news: If you don’t win this truck, you can still build your 7.3L the same way.

Bone Stock to Badass

Naturally, it won’t be leaving the stable before receiving a full makeover and some moderate go-fast goodies. After corresponding with you guys—the diesel enthusiasts—it became clear fans wanted to see a classic resto-mod that retained the 7.3L’s original charm and allure. Kind of like an “OEM+” type of build, it would incorporate a leveling kit on 35s rather than a huge lift and large wheels. In alignment with the overall build style, fans prioritized 500 hp at the wheels, equating to clean, usable power optimized for towing and reliability. In order to hit 500 hp at the wheels, KC installed its all new KC300x Gen 3 Stage 2 turbo, Full Force 238/80 injectors, and every supporting mod to make sure it could make that power reliably. While a high-strung, disaster-prone diesel truck makes for great entertainment, that wasn’t the objective for this build. We can all agree that blowing up this 7.3L would just feel wrong.

Breaking 500 HP

By the end of episode 5, the team had finally broken the 500-hp barrier. Doing this required adding all the fuel with an Airdog lift pump setup, Full Force Diesel 238/80 fuel injectors, a CNC Diesel Fabrication high-pressure oil pump, and Driven Diesel regulated fuel return system from Dennis Schroeder. The team at KC Turbos knew that their KC300x Gen 3 Stage 2 turbocharger was capable of more than the 505 hp that it put down, so it was time to start removing restrictions to let the turbo breathe a little better.

The first thing they decided to try was pretty simple: cutting off the stock muffler. From previous experience, the team was doubtful doing this would result in any significant power gains. To their surprise, however, they saw a nice increase of 22 horsepower at the wheels and 45 additional lb-ft of torque from peak to peak. More impressively, at 2,500 rpm, they noted an increase of 35 horsepower and 70 lb-ft of torque.

How did they get these crazy gains just from chopping off a muffler? Charlie Fish, KC Turbos’ founder, R&D expert, and dyno wizard theorized that the muffler was horribly clogged from 25 years of soot, carbon, and oil buildup. Running oversized fuel injectors for an extended period with the factory exhaust certainly didn’t help and likely contributed to such a large restriction. While adding a new OEM muffler likely wouldn’t see these massive gains, a good quality aftermarket unit would probably gain some—though not as much as just junking the whole thing.

With both the airbox and filter removed, and the stock muffler cut off, the truck was only making 527 hp. Something was amiss as the company had routinely pushed 7.3L trucks to the 550 hp mark. There had to be more restrictions.

Andrew Arthur from AA Design and Performance Tuning was on-hand for the dyno session and theorized that the factory downpipe could be part of the issue. The team installed a full 5-inch turbo-back exhaust system from MBRP and headed back to the dyno. The results? The team noted a fat goose-egg—no gain at all from adding the new exhaust. Although the truck sounded notably different, there were no improvements in terms of boost pressure, exhaust back pressure, intake air temperature, exhaust gas temperature, horsepower, or torque. There was nothing measurable—just the normal variances between dyno runs.

Adding Restrictions To Increase Power?

The team quickly huddled to work on the next move. The factory air filter was already removed and the stock airbox was propped up in the air (as to not suck dust and debris from the engine bay). Doubtful it would help but desiring to try anyway, the guys installed a fresh S&B cold air intake system on the 7.3L. As it turns out, adding an air filter back to the equation actually resulted in a measurable horsepower gain. An educated theory suggests that the S&B intake was doing two things—drawing cooler air and delivering it in a smoother manner to the engine.

It’s difficult to judge spool-up perfectly (because if you roll too hard into the throttle at the start of a dyno run, the truck will downshift). Because of this, the team at KC Turbos often tells people not to focus too much on the very start of the dyno run. However, adding the S&B intake made such a big difference that the turbo actually showed signs of spooling faster and adding 6 psi of boost pressure (and up to 53 psi total on a max-effort tune).

Live Tuning for the Win

At this point, Andrew Arthur took over and worked his magic behind the keyboard. While he tried a bunch of different things, the main improvement was seen when he was able to increase the injection control pressure (ICP) thanks to the high flowing CNC Diesel Fabrication S2 high-pressure oil pump. Andrew said if it was not for the small change in ICP, the truck likely would not have gained much more horsepower.

There’s a big misconception on what live tuning is and what it changes. Diesel truck tuners don’t need to perfectly dial-in boost and air-fuel ratios or worry about knock sensors. Maximum 7.3L diesel horsepower comes from a combination of injection control pressure (ICP), injector pulse-width (PW), and timing. All of these are already known to the tuner. Even with an abnormal setup, tuners can typically work around the situation.

Why bother with live tuning? Because there is so much more that can be personalized, as live tuning tailors exactly how the truck responds: throttle inputs, transmission shift points, torque converter lockup, and even smoke output. Live tuning is the next level and can drastically change how you feel about your truck.

After live tuning, the crew went for a drive with Bill Cohron from Power Hungry Performance (a 7.3L legend in his own right) and Andrew Arthur. Andrew proceeded to scare the crap out of everyone with a monster burnout. He left thoroughly impressed by how well the nearly completed build ran and drove.

Data Logging the Build

Any build worth its salt is based on a collection of solid performance data. The team at KC Turbos prefers working with the Edge CTS 3 and the company’s EAS system upgrade. The EAS system allows them to not only record boost pressure higher than stock, but also log fuel pressure, exhaust gas temperature, and so much more. Harvesting data is so critical that installing an Edge monitor was the first modification that was made.

With the engine sorted, the team has also started working on the exterior of the truck, giving it a fresh look before selecting a winner. New headlights and grille give the truck a clean factory look. The thought of doing a full 6.0L Harley swap was floated, but in the end, it was decided that these period-correct updates were the way to go.

Stay tuned as KC Turbos finishes its legendary 7.3 Giveaway truck and hands the keys over to the lucky recipient.

Last But Not Least: You Tube Comments

• I didn’t know loading everybody up and going for a ride on the dyno was a thing.
• Old 7.3 aren’t supposed to drift like that… Right on!
• Easy on my truck boys
• When you can’t build a race car you play with diesel sh*t. So stupid.
• This hpop , injector, icp testing is exactly what i been wanting to see. Having same issues with icp falling off under hard acceleration. Think ill do injectors first, hpop second if it doesnt fix the icp issue, then a kc turbo stage 2.
• I absolutely love this truck.
• So why did it run way slower with way more power after the tune… Response: After the tuner was commanding more power, it was dropping ICP or injection pressure. So it was making more power, but inconsistently. Also, with the additional power the transmission was struggling more and we know now it was on its way out.

The Legendary 7.3 Giveaway Episodes

KC Turbos has been documenting the whole build process on its You Tube page, from its baseline dyno run (where it made 204 hp) to the finished product—and all the snafus, mysteries, and fun experiments in between. Rest assured that you’re not the only one dealing with a disobedient diesel truck.

We’re Building The ROWDIEST 7.3 Powerstroke?!? – Legendary 7.3 Giveaway EP. 1

How NOT to build a Diesel truck! – Legendary 7.3 Giveaway EP. 2

We Installed The BEST 7.3 Tuner Money Can Buy?!? – Legendary 7.3 Giveaway EP. 3

Can This 7.3 Make 500hp On Stock Fuel?!? – Legendary 7.3 Giveaway EP. 4

Breaking 500HP With THIS Fuel Pump!?! – Legendary 7.3 Giveaway EP. 5

How To Gain 0 HP With A 5” exhaust!?! – Legendary 7.3 Giveaway EP. 6

We Tested The WORST 7.3 Intake! Zoodad and 6637 Dyno Testing – Legendary 7.3 Giveaway EP. 7