Justin Duffy Makes A Push For Fastest 4×4 Allison Duramax Title

When you’re out at the drag races, typically, you’ll see one of two things. You’ll see an extremely clean build or you’ll see something that is a little rough around the edges. For Justin Duffy, he’s earned the title of “extremely clean”. Speaking of titles, Justin’s Duramax-powered Chevrolet has been making a push to be the fastest Allison-backed, 4×4 Duramax in the world.

At one time, he held the record at 5.76 at 126 MPH, but as of recently, it was taken away. Justin’s core mission is to have this title and maintain it and even though the 2021 season is coming to a close, he and his team are going to do what it takes to get it back. We’ve seen this truck out at a lot of events competing in the 6.70 index class but this year was his 5.90 index debut.

This was the slip when Justin took the record initially. He has outdone himself yet again as of recently with an even faster pass.

How It Happened

“I was running 6.70 last year on a stock bottom end engine. With that, we’ve been 6.20’s with the stock engine but with 5’s and that record in mind, a build was in order,” Justin explained. “Since then, we’ve put together a completely built engine and as of now, we’ve made 30 passes at around 1,450-horsepower and it is still going strong.”

Now that Justin’s rig is easily a 5.90 truck, it is wild to see how far it has come in the two years he’s owned it. When he purchased the truck, it was a completely stock grandpa-looking truck. Now, however, it is an animal. “A ton of people don’t believe what has been done with this truck and for those who have doubt, I love proving you wrong,” Justin said.

With the record in the scope, Duffy is trying his best to put the hail mary pass together before the end of the year. “I really want to get into this .70’s again before the end of the year and get that record back before we make a serious change,” Justin said. “I’ve got Chris Gelbaugh building a 48RE Dodge transmission for the truck but before that is in, we need that record.”

My goal this year was to just win a race. I want to be a competitive racer in the 5.90 index class that the Outlaw Diesel Super Series puts on. – Justin Duffy

What’s Under The Hood?

Seeing a truck that large going that fast, it has to have a healthy setup, right? We talked with Justin to get the full download on what it takes to get this Silverado in the five-second range. This starts with a 6.6-liter Duramax engine that was put together by Marty Brown. For air, Justin relies on a single S400 frame turbocharger from Reed Patridge.

“This is the baddest S400 turbocharger I’ve ever had,” Just said. “I have abused this thing ever since I’ve got it. I am at about 30 passes over 1,400-horsepower and the turbo still feels brand new.” For you guys looking for a Duramax turbo that can get you deep into some elapsed time, maybe this is something to look into.

For the fueling components, Justin’s Silverado uses S&S Diesel Motorsport. S&S 400-percent over injectors and a pair of CP3’s. A 14mm high pressure pump in the valley is backed by a 10mm pump on the belt. “Thanks to Justin Norris at S&S Diesel for always getting me taken care of when it comes to fuel demand. I trust the product and the performance proves it,” Justin explained.

Backing all of this power, and possibly one of the most important parts of this story is the built Allison transmission. In the beginning, a Diesel’s Unlimited Allison transmission backed by a Goerend Transmission torque converter is what it takes to hold 1,400-horsepower or more for plenty of passes. “Huge thanks to both Logan Lewis and Roman Blades for building the Allison transmission that I was just able to break the record for the fastest 4WD Allison transmission in the world.  5.860 @124mph.”

Justin continued, “Big thanks to the Diesels Unlimited guys for supporting me in the past, but now we put our own transmission together with the help of Blake Crenshaw.” Speaking of Crenshaw, he has his hands in the tuning of this truck too. “I have put all of my trust in Blake Crenshaw’s tuning capabilities. He always get’s the tuning dialed in and is perfect for what I need. He’ll make quick adjustments when needed and offers other opinions on how to do things and helps me with diagnostics I’ve had throughout the years.”

On the plumbing, Justin uses an HSP Diesel Performance piping kit. Ryan Daniel’s over at HSP has helped with parts anytime Justin needed it Justin praised that. Other parts include a Yukon rear center section, PPE tie-rods, DHD straight-race center link, roll cage by Kenn Kir Race Cars, GTS Fiberglass bedsides for weight savings, Auto Fab anti-roll bar, and an Old Skool Fab 7-inch stack.

Lastly, Justin wanted to thank his friend Casey Leavell for always helping. He’s helped him since day one with all of the fabrication and if it wasn’t for him, the truck wouldn’t be half of what it is today. Be sure and stay glued to the 2022 Outlaw Diesel Super Series for more action from this truck in the 5.90 index class.

For more truck features, stay tuned here at Diesel Army. What are your thoughts on this mint build? What would you do differently? Let us know in the comments below.

 

 

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About the author

Artie Maupin

Artie Maupin is from Southeast Missouri and has an extreme passion for anything diesel. He loves drag racing of all kinds, as well as sled pulling competitions.
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