Daily-Driven Cummins ‘75 C10

Jesse Harris’ Daily-Driven, Tire-Carrying, 9-Second, Cummins powered C10

By Mike McGlothlin

Wheels-up, rear-wheel drive vehicles are relatively rare in the diesel world—which means that most of them are instantly recognizable. You might not know the name Jesse Harris yet, but if you’ve seen his tire-carrying square body chances are pretty good you remember it. The hard-launching, Cummins powered ‘75 C10 has competed in Hot Rod Drag Week and Rocky Mountain Race Week, been spotted at no-prep races, and has even made it to select diesel events over the years. We finally caught up with Jesse and his wheels-up wonder over the summer to find out what makes this old-school Chevy tick.

In the family since his grandfather bought it new, Jesse acquired the Scottsdale trim C10 from his dad in 1992 and has been racing the family heirloom ever since. It hasn’t always been Cummins-powered, but once Jesse went diesel he never looked back. “I didn’t know how it would run, but it went 10.20s the first week out,” he told us. “And as for the Drag Week thing…the plan was to drop the diesel in and then come back home and take it out. That never happened.” In fact, Jesse found the truck so effortless to drive on the street that he started driving it to work.

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Bone-Stock 6.7L Cummins

Though the original Cummins powered swap entailed a P-pumped 24-valve, a 9.50-second pass that saw 140-psi of boost cracked the block, and ultimately (at the recommendation of a few close friends) led to the common-rail idea. Already familiar with EFI Live tuning on LS engines, the power management aspect of going common-rail was highly appealing to Jesse. Incredibly, the compound turbocharged and well-fueled 6.7L Cummins that now sits in the C10 is bone-stock. Only the head bolts have been replaced with ARP studs.

6.7L Cummins common rail diesel engine — Once upon a time, you would’ve found a P-pumped 24-valve under the hood of Jesse Harris’ ’75 C10. Not anymore. He went common-rail and will never go back. Unbelievably, the 6.7L Cummins is bone-stock, even though the truck belts out more than 1,100-rwhp. The only hard-part upgrade the 6.7L has received is a set of ARP head studs, which definitely helps hold down the fort with a data-logged 72-psi of boost in the mix. Jesse also limits the amount of torque the Cummins sees by keeping his shift points at 4,200-4,300 rpm.

S300 66mm compressor over S400 83mm compound turbo setup — An S300 over S400 compound turbo setup is brought up to 48-50 psi of boost during staging and produces more than 70 psi on each pass. The high-pressure, T4 flanged S300 on the exhaust manifold sports a 66mm compressor wheel and the atmosphere charger, a T6-flange S400, makes use of an 83mm compressor. The turbo arrangement crams boost through a tube and fin intercooler that was robbed from a 5.0L Cummins Nissan Titan engine. Believed to be a choke point, Jesse was already building a higher-flowing, bar-and-plate intercooler as we went to press.

Compounds & 1,400HP Worth Of Fuel A compound turbo arrangement originally intended for a Fummins swap positions an S366 over an S483, and the compact combo produces as much as 72-psi of boost going down the track. According to Jesse, he’s been told this set of compounds shouldn’t be doing this, but the moderately-sized system continues to hang tough in support of his 5-second trips through the eighth-mile. On the fuel side, a 14mm CP3 from S&S Diesel Motorsport feeds rail pressure to 300-percent over injectors. The stroker pump sees plenty of low-pressure fuel supply courtesy of a pair of Aeromotive A1000’s. Jesse’s homemade lift pump setup includes a regulated return system and a 10-gallon fuel cell located rearward of the rear axle.

Big injectors, supported by a high-flow, single CP3 has proven to be a sound recipe for Jesse’s Cummins. The combination of a 14mm S&S Diesel Motorsport CP3 and 300-percent over injectors afford him the ability to make big power with very little injector duration. Despite how raw and violent the truck’s launches look, the engine is extremely safe while all of it takes place. Just 1,100 microseconds worth of injector on-time is commanded via Jesse’s EFI Live tunes, along with very conservative timing.

A regulated return fuel supply system is based around the use of an adjustable Aeromotive pressure regulator and dual A1000 pumps. The regulator is set for 14-15 psi of supply pressure at idle and, incredibly, both A1000’s are older than Jesse’s teenage children! Once run on his old alcohol motor, they have a boatload of miles on them.

Homebuilt 48RE With Goerend And Sun Coast Parts

Like much of the rest of the build, Jesse handled the transmission work, which consists of a four-wheel drive 48RE that’s been converted for his two-wheel drive needs. Sun Coast’s stubby kit—complete with a larger, TH400 splined output shaft—makes it possible, along with a custom length driveshaft. A Goerend bolt-together, non-lockup converter with a trans-brake, dump valve manual valvebody helps him stage the truck quickly. “I got 898 passes out of the previous transmission leaving at 40-psi of boost or more,” he tells us. ”I build them to shift smoothly, not bang gears and break shafts.”

1975 C10 racing seat copilot seat — When you participate in events like Hot Rod Drag Week and Rocky Mountain Race Week, it pays to bring a co-pilot along on the adventure—and maybe even down the track with you. We have to say, it’s pretty cool to find a full race seat in the passenger side of a 9-second vehicle. Jesse’s wife is typically the co-pilot, and his sons are fairly involved with the truck, too.

Precision Performance Products shifter for 48RFE transmission — Surprise, surprise, Jesse knows his way around transmissions, too, and he built the 48RE that sits behind his 6.7L Cummins powered C10. The Chrysler four-speed takes its cues via this Precision Performance Products shifter, which shifts off of CO2. Bolted to and within the 6-pinion rear planet 48RE’s case, you’ll find a host of race parts, including a 35-spline Sonnax input shaft, a TCS billet intermediate, and Sun Coast’s larger billet output courtesy of the company’s stubby kit. Goerend Transmission supplied a varying pressure, manual valve body with a dump valve and trans-brake, along with a bolt-together non-lockup converter that’s extremely efficient.

Stolen, Wrecked, Rebuilt, and Repainted When you own and race a vehicle for three decades, it’s bound to have some history behind it. Outside of racing, Jesse’s Cummins powered C10 has been stolen, recovered, and then was almost totaled in an unfortunate collision with a State Trooper. When the latter accident occurred, Jesse decided to convert to a full tube chassis, build an 8.50-certified cage, and transform the C10 into a Cummins powered full-blown race truck. As it sits today, it’s a long way from the V-8 powered, stock frame long bed C10 it was when it first hit the track back in ’92.

Tubbed, back-halved and sporting a full tube chassis, it’s hard for some to believe Jesse’s Cummins powered C10 is regularly driven on the street—but that’s exactly the case. In fact, Jesse tells us he puts 15,000 miles on the truck each and every year. Here, you can see the mounting locations of the battery, 10-gallon fuel cell, and 8x8x1-inch Derale Performance auxiliary transmission cooler. Jesse reports that 187 degrees F is the hottest the 48RE has ever been, and that was while sitting in Chicago traffic.

1975 Chevrolet C10 Cummins powered race truck — It might be a single axle, bumper tow trailer, but it weighs as much as the truck does during Drag Week. For more localized racing (especially no-prep), Jesse typically forgoes the trailer and simply drives the truck to the venue empty. “It’s pretty cool to drive it to an event through the gate, then drive it past all the trailers on my way back out the gate, driving home,” he told us. “In seven years of doing that, I’ve only broken one drive shaft and been stranded once.”

Surviving each and every 50-psi hit the truck makes is a Moser Engineering 9-inch with an aluminum thru-bolt center section/third-member. The Pro Street Moser unit packs a ring and pinion from US Gear with a 3.00:1 axle ratio. A four-link suspension helps plant the truck on its violent, wheels-up launches and Jesse has it dialed in so well that it’s a rarity when the truck doesn’t hook perfectly.

Aldan American coil overs with Ridetech springs with Mustang II spindles — Tied in with the tube chassis out back, you’ll find a pair of Aldan American coil overs with Ridetech springs. Up front, AFCO Racing coil overs got the call, along with lighter weight Mustang II spindles.

Gunning For 8’s

Even though Jesse doesn’t necessarily follow the normal, diesel-only outlets many racers do these days, he still gets plenty of passes in each summer. In fact, whether he’s racing on a legit track or at a no-prep event, Jesse tells us he makes 400 passes a year. It’s no wonder his wild Cummins powered C10 has become so deadly consistent. In the future, Jesse plans to shoot for 8.80s—if not creep up on his 8.50 cage certification. But beyond his goals of going faster, Jesse enjoys the streetability of the truck, how drivable the common-rail is, and how little breakage he’s experienced. The fact that he racks up 15,000 miles a year on the old square body should tell you something about his confidence in its reliability.

In this shot of the Grant Products steering wheel, you can see Jesse’s means of manually controlling the Overdrive shift, the bump box, and the dump valve. After the truck’s trip through the water box and the subsequent burnout, he turns the dump valve on, which allows engine rpm to come up easier. When Jesse starts to bump in, he’s already up on boost, and the dump valve is turned back off.

1975 Chevy C10 diesel drag truck — Jesse’s C10 is known for its hard, wheels-up launches, but many don’t realize the fine line he walks in making the truck so consistent. “We don’t use boost control or rpm control,” he told us. “We’re leaving at a certain fuel quantity, and we tailor it around 48-50-psi of boost most of the time.” Leaving there, it will cut 1.17 and 1.18-second 60-foots. Leaving at 25-psi of boost, the truck dead-hooks and wheelies like crazy.

“I’m a Chevy guy not a Mopar guy, but I love the Cummins and I like TorqueFlites.”

—Jesse Harris

1975 Chevy C10 front grill

Upon returning home from 2021’s Hot Rod Drag Week, Jesse began piecing together an A/C system so he can tackle the 1,500-mile journey in improved comfort next year. How many people do you know that’ve installed A/C in their tube chassis racecars?

EFI live tuner — When you’ve owned a truck like this for so many years, not very many people turn wrenches on it. “I’ve done everything on the truck but the paint and body work,” Jesse told us. He also admitted he had a hand in tuning the common-rail engine. With help from good friend, Aaron, the two have built some highly-effective tunes using EFI Live software.

1975 Chevrolet C10 rear bumper with hitch — It might not be a Class V receiver hitch protruding from the rear bumper, but this hitch says Jesse’s C10 still tows a trailer—and it does it more frequently than you might think. What isn’t always onboard for the truck’s towing endeavors are the rear slicks. On occasions where a trailer is attached, a set of 35-inch Cooper Discoverer STT Pro mud terrains can usually be found under the tubs.

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Mike McGlothlin

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