THE SRT CUMMINS
23 MPG / 723 HP / 1669 FT/LB TORQUE / 11.8s E.T. / 1295 MAX EGTs
Over the past few years you may have noticed one of our project trucks featured on our Instagram feed – a black 2003 Dodge 1500 SCSB powered by a 12-valve Cummins. That truck (dubbed the "SRT") was the brainchild of Pusher owner / founder Jacob. We sat down with Jacob and went over the SRT - from his inspiration to the ins-and-outs of the build.
“As a teen I always loved the Dodge SRT10s and Ford Lightings, but as an adult, I could just never quite justify the poor fuel economy that comes with them, especially if you towed anything” said Jacob, “My older brother always had fast cars, trucks, bikes, etc. and I was always right next to him during his builds - eventually having many of my own. Although none of the fast trucks we built really did “dual duty," working as both a race truck and a practical daily driver. That was until we ran into diesels and started to understand the immense versatility and capability if setup properly.”
“I knew weight savings of this combination would equate to better fuel economy, but I also wanted to build this truck for a few other reasons. I’ve always been curious what it would be like to drive a vehicle that’s 1,000 pounds lighter and 18” shorter than anything else available with a large displacement diesel. And I also wanted to prove out the upper power capability of our Low Mount Compound System, for 1994 to 2002 Cummins,” he added. “Don’t get me wrong, we’ve built and assisted customers with countless builds across all of our products, but my personal trucks had not exceeded 550HP specifically with the Low Mount System.”
The building blocks
Jacob found a 2003 Dodge 1500 SCSB with a Hemi parked in a local ship yard that, in classic Hemi fashion, had dropped a valve. It had a straight body, good interior, and was black; all the prerequisites were met. After he brought it home, he bought a 1994 Ram 3500 automatic from a friend. The 12v had never been modified and had 223,000 miles on it. Between the two trucks he had all the components he needed to make the swap about as easy as it could be.
Going with a 1994 donor truck gave him a 47RH transmission which requires very little input to operate. To handle the power he had planned, he rebuilt it in-house with all of the normal upgrades mostly from RevMax: triple-disc torque converter, billet flex plate, billet shafts, billet servos, Alto clutches, Kolene steels, valve body, and a Mag Hytec pan.
Even though he knew its history, he completely disassembled the engine to verify that it was good to go. Everything looked great in the rotating assembly, as a well taken care of Cummins typically does. From there he put in a Max Spool 194/215 Cam with common rail lifters, and welded on the cam gear. He also used Max Spool heavy duty push rods to handle the .100” larger valves from Mountain High Performance and 110-lb valve springs. He also ported the head in house to take advantage of the larger valves. Lastly to keep the cylinders sealed up, he used ARP 425 head studs and o-ringed the head.
For fueling, he chose DAP 7x.0115 injectors with O24 delivery valves and 4k governor springs. He maxxed and balanced the pump netting 440CC’s and used a FASS 150 with a sump to feed it.
The frame on these trucks is stout, its fully boxed and is very rigid for a 1500. The weight of the engine dropped the front ride height right to where he wanted it, so he just used 2” drop shackles in the rear to even things out. The only real chassis mods were to run CalTrac traction bars and remove the overload leaf spring to get the truck to squat easier. The first trip to the track he found that the factory limited slip differential couldn’t handle the job, so he put in a Detroit locker along with some lower 3.21 gears. The factory brakes were good (these trucks came with big rotors to start), so he simply upgraded the rotors to drilled and slotted rotors and dropped in some new calipers and pads.
Jacob had always been fond of the two door SRT10 trucks so the original plan was to build “the SRT Dodge should have built”. However, the further he got into the project the more he realized the ground effects that come along with those trucks, especially the wing, didn't fit his style. They took away from the truck feel a bit and would make it more vulnerable to damage during the minor off-roading he planned to do from time to time. He opted to compromise - a mix between a custom grill he built, the factory style sport front bumper, an SRT10 hood, and a simple roll pan modified to let the exhaust nest in it slightly.
Air delivery is clearly Jacob's speciality - "I still love the older diesels, they’re still very capable and relevant these days so we've continued to put a lot effort into parts for them. Since we used a 12-valve engine, I wanted to use as many 'off-the-shelf' products of our own as possible. I started with our 3.5” Mega Twin Intake System, to equalize air across the cylinder head. I then installed our Low-Mount Compound Turbo System, which compounds the factory HX35 with a BorgWarner S475. Factory chargers tend to get a bad wrap because you can’t make a ton of power with them as a single, but that’s the nature of a relatively small turbo. The cool thing about the factory chargers on any of the Cummins or Duramax equipped trucks is they work perfectly in compound setup to about 700hp."
Thanks to a spacious engine bay, almost all of the components in the Pusher Low Mount System were bolt on, with the exception of the final charge tube and the down pipe. Jacob made up some custom parts to connect to the intercooler inlet and exhaust locations in a 3rd gen body. To monitor engine vitals he used the Edge CTS2 monitor with a host of their sensors, which showed him that the turbo setup topped out at about 68 PSI in the quarter mile, and generally within 20F EGTs between cylinders.
Notes & Results
"The nice thing about this swap is that the Ram 2500 & 3500 have the exact same body as the 1500, so it was no problem to get the Cummins to fit – it was just a matter of building all the mounts (motor, transmission, etc). I didn’t want to do anything too crazy – just put together something easily attainable with mostly bolt-on parts. This truck wasn’t built to be a track queen, it was built to be used. The truck cruises nicely on the highway, with the 3.21 gear. I see about 1600 rpm at 70 mph, which makes it a really nice ride. Most notably a quiet ride, courtesy of the compound system; that second charger really quiets down individual cylinder fire and drone; it pretty much acts as a muffler. I’ve driven all over Florida, picking up equipment, towing my boat – even handling preschool drop-off – it’s a super easy, reliable daily driver. Being that is sits fairly low, it corners really well too."
The final SRT boasted an unbelievable amount of useable power. It dyno’d 723 hp / 1669 ft lb SAE at 61 lbs boost, and never exceeded 1250F EGTs during the pulls. Even at the track, after a big burnout and a long tree, the truck barely touched 1400F going through the traps on a humid 85F day in Florida.
"It’s definitely fun having a truck that comfortably runs 11.8s ET’s which is good enough to take down a lot of the Mustangs and Corvettes I run across on the street, but still be practical with air conditioning and a comfortable interior. You can definitely imagine that I’ve seen a few surprised faces from inside a muscle car over the years. To top it off, I average 23 mpg during mixed driving."
So what’s next for Jacob?
“We’ve found even with the short wheel base and lighter truck, it’s hard to put the power to the ground at the track, let alone on the street. My main interest has always been pushing the daily driven envelope, I want to be able to play with my truck any time and not have to watch my EGT gauge more than the road or work so hard to keep it straight. This truck has proven its worth the work of the swap. Next time I want something that’s just as fast on a back road as a prepped track – so I’m going to go with a 4WD common rail, aiming to hit 1,000HP with minimal smoke. That way I can run all terrains and move up the ladder to play with the next level of cars I run across on my daily drives.”