The 7.3-liter Power Stroke community has debated the 6637 filter modification for decades. It’s a cheap and easy DIY intake that many swear by, but the team at KC Turbos has long suspected it does more harm than good. They recently put the popular mod to the test on a dynamometer to settle the argument with hard data.

Testing the Zoodad Mod

Before testing the 6637 filter, the team first tested a different popular modification known as the “Zoodad mod.” This involves cutting a hole in the core support directly in front of the factory airbox inlet to provide a path for cooler outside air.

On the dyno, the mod didn’t show any significant horsepower gains, but it made a huge difference in intake air temperatures (IATs). Charlie noted that the IATs “stayed cooler, they started cooler, and they ended cooler” compared to the baseline runs. Because of this clear cooling benefit, which is especially important for towing, the Zoodad mod was declared KC Turbos approved.

The 6637 Filter Test

Next, the team removed the enclosed S&B intake and installed the popular 6637 open-element filter in the engine bay. The negative results were immediate. The intake air temperatures were higher before the dyno pull even started. The first run showed some loss of power and torque across the entire curve.

“We lost 12 horsepower,” Charlie announced, adding that “peak torque went down 38.” A second, more heat-soaked run showed even further power loss.

Even more alarmingly, the exhaust gas temperatures (EGTs) showed a “200-degree difference,” a massive increase that can be dangerous for a diesel engine under load. Charlie declared the myth of the 6637 being a performance upgrade as “totally busted.”

The Verdict from Experience

Charlie explained that this was why his shop disliked the popular filter. He stated, “It’s one of our standard questions that we ask, are you running a 6637 filter… I can’t tell you how many customers we’ve had where it fixed their truck.”

He says they have traced issues like high EGTs, low power, excessive smoke, and even collapsed intake boots directly back to this filter. He concluded that the 6637 performs no better than an old, dirty stock filter because it’s fundamentally a hot-air intake, pulling in superheated air from the engine bay.

The Final Word

The simple fact about any 7.3-liter intake is that pulling cool air from outside the engine bay is critical for making good, safe power. It’s clear that even if some versions of the 6637 filter flow well, they will always be a hot-air intake.

Informative, data-driven videos like this one from KC Turbos are a huge help for the community, as they provide real-world proof that can finally put old myths to rest and help owners who might be running a 6637 filter understand the root cause of their truck’s performance issues.