1970 Challenger: Meet The First-Ever Non-Hack Hellcat Swap!

This Hellcat-powered 1970 Challenger RT/SE could be the ultimate melding of classic styling, modern performance, and comfort.

If you think back to your high school days, there’s likely at least one car you used to see on a regular basis that was sitting neglected in someone’s yard or under tree. You probably daydreamed about that car and wondered why on earth anyone would be so callous to treat it like that. You certainly wouldn’t. You would get it back on the road to its former glory. For Larry Rose, this ’70 Challenger RT/SE was that car. As a young man, he kept his eye on it as it sat neglected in a yard. He saw it every time he drove out to his grandma’s house in Georgetown, IL and he would just shake his head and then spend most of the rest of the drive thinking about it.

“How hard could a Hellcat swap be? …The answer is really hard, and plenty expensive.”

In most cases, stories like this usually include a few attempts at inquiring about the car, always to be turned away with declarations that it’s not for sale. Larry’s story went much better though. He kept an eye on the Challenger, and in 1989, he got wind that the car was for sale for $3,500. The bad news was that a light pole had fallen across the hood and gone through the windshield. Still, Larry knew that was the car, so at the age of 17, the Challenger became the first one he ever bought.

“The bad news was that a light pole had fallen across the hood and gone through the windshield. Still, Larry knew that was the car…”

Being a high school kid, money was tight, so Larry replaced the windshield and worked the fender back out as best as he could. He spent some time getting it reliable and drivable again, and the 383 Magnum, four-speed, Dana-rearend—equipped coupe was his ride for the last two years of high school. As you would expect, there were many nights spent cruising the local hot spots to see and be seen. On one of those trips, Larry even managed to catch the attention of a good-looking girl who he took to prom. He didn’t know it then, but she would eventually be his wife. Some say the cool car had a little something to do with that.

“Larry even managed to catch the attention of a good-looking girl who he took to prom. He didn’t know it then, but she would eventually be his wife.”

Around 1990, Larry saved up enough from his job working at a pallet company after school to have a local shop swap on a fender, repair the hood, and spray on a new coat of Lime Green paint. Shortly thereafter, though, Larry went away to college and the Challenger went into storage for a few years. School comes first, but once he had time to devote to it again, the Challenger was back on the road, and at the drag strip. It was still running the stock drivetrain, and rowing gears down the track was fun, but to get more consistency Larry swapped in an automatic. Then to get more speed, he added a nitrous system. The Challenger remained in this form for the next few years, and was a force to be reckoned with.

The RT/SE moved back and forth from the front to the back burner through the late ’90s and early 2000s as life changed and other projects came and went, but around 2005 Larry started thinking about making some really big changes. The burgeoning pro touring movement was bringing on a surge of innovation in new products to make classic cars more powerful, better handling, and more fun. For all of its history so far, the Challenger had pretty much just been a straight-line car, but Larry was warming up to the idea of getting more well-rounded.

While the 383 had been a great engine and taken a beating over the years, it was time for a freshening, so Larry took the opportunity to upgrade to a 440 6-pack. The automatic came out and a stick went back in, but instead of a four-speed, the Challenger got one more cruising leg from a five-speed swap. The really interesting stuff happened underneath the skin though. Rather than rebuild or upgrade the original suspension, Larry opted for a full Reilly Motorsports package with the AlterKtion system up front and the Street Lynx in the rear. To say this transformed the Challenger would be an understatement. It was like a whole new animal and Larry fell in love with it all over again and started driving it a lot more.

There are things you learn about a car the more you drive it, especially when you’ve become accustomed to the nice things modern cars offer. For example, while a 6-pack looks oh-so-cool when you pop the hood, keeping it perfectly tuned in all conditions can be a bit of a chore. Plus, it’s not exactly easy on fuel. Since Larry was enjoying driving the Challenger more and planning to attend the 2012 Hot Rod Power Tour, he started looking at fuel-injection options and settled on a FAST EZ-EFI system. Notwithstanding, even with the more precise fuel and ignition control, Larry discovered the often lower quality fuel available in rural areas caused a lot of spark knock, requiring him to stop and manually adjust the timing.

Larry and his wife Kara were sold on the Power Tour, so Larry decided that the next evolution of the Challenger needed to be in the direction of easy long-distance touring. He wasn’t willing to give up on performance however, not by a long shot. Thanks to the modular design of the AlterKtion K-member, Larry knew he could easily swap to a different engine family, including a Gen-III Hemi. After some planning sessions, Larry placed a call to Cleveland Power and Performance to get one of their running pallets with an ’08 6.1L Hemi and complete wiring harness. While he was at it, he figured it was a great time to add a Magnuson supercharger. To preempt grenading the five-speed, Larry ordered a Tremec six-speed to handle the grunt. Larry and Kara attended more Power Tours with the Challenger in this configuration, and Larry discovered how much fun a boosted Gen-III can be on the drag strip. We guess you could say that was his gateway to late-model drivetrain performance.

That brings us to 2016. While all of those upgrades were cool, we know what you really want to know: How hard could a Hellcat swap be? If the Challenger already had a blown Gen-III in it, how hard could it be, right? Wrong. The answer is really hard, and plenty expensive. Even more so because of Larry’s choice of transmission.

While sitting in traffic on the 2016 Power Tour and getting a severe left leg workout, Larry looked over at Kara and stated, “We should just buy a new Hellcat with an automatic trans.” Kara shot that down stating that they really didn’t need another car. “Fair enough,” Larry thought, so he countered with, “Well, what about a Hellcat engine upgrade instead?” That sounded fine to Kara, so at literally the next gas stop, Larry called up Cleveland Power & Performance and asked to be placed on the waiting list for the next available running pallet with the eight-speed automatic. The next week, they called Larry back and said they had one ready to ship out, if he was sure he wanted it. Larry assured them he was, and the Hellcat pallet arrived at his shop literally ready to run. For a couple of months, Larry would crank it up on the pallet just to show it off to friends, but when it came time to actually put it in the Challenger, the headaches began, particularly pertaining to the TorqueFlite 8HP90.

“For a couple of months, Larry would crank it up on the pallet just to show it off to friends, but when it came time to actually put it in the Challenger, the headaches began…”

Before the stick shift brigade gets their pitchforks, if you haven’t driven one, you’ve got no argument to stand on. The 8HP90 is a marvel and to be perfectly honest, the best transmission option for the Hellcat and easily among the best performance-oriented, non-dual clutch self-shifting transmissions on the market. Sure, there was a point in time where a manual transmission was the only way to go, but those days are gone.

Starting with the roots, the 8HP90 debuted in the BMW 760Li behind a V12 engine, so it was engineered for precision behind power. Weighing less than 10 pounds more than the five-speed automatic it replaces, the eight forward gears work to keep the Hellcat engine in its most efficient rpm range with tight ratios of 4.71, 3.14, 2.10, 1.67, 1.29, 1.00, 0.84 and 0.67:1, with a 3.30:1 Reverse. Thanks to that 4.71 first gear, the Hellcat uses a tiny 2.62:1 rear axle ratio, yet delivers a 12.34:1 torque multiplication factor in first gear. For perspective, to achieve the same value with a 1970 street-spec Hemi Challenger, the standard 2.45 first gear would require huge 4.88 gears. Eye opening, huh? And while six-speed drivers may enjoy the connected feeling they get from the stick shift and clutch pedal, there’s no beating the 160 milliseconds shifts in Track mode. And that, friends, is why Larry decided to enter untested waters and keep it for the swap.

We say “untested,” because the 8HP90 is not a currently supported swap. Yes, there are at least two swaps we know of running around with one, Roadkill’s General Mayhem and the Gas Monkey Garage 1967 Dodge Dart “Shartcat,” but that doesn’t mean the info is accessible out there for everyone. Also, it’s a different case if you don’t want to hack your car up as much as they did. So with no harness or ECU available other than the stock parts, trying to integrate 2015 systems with 1970, plus a few aftermarket systems, opens up a world of complications. As far as we know, Larry’s is one of the few Hellcat swaps currently drivable and he’s still about 95 percent of the way to having it all figured out. The only current nagging concern is the ECU defaulting to limp mode after 130 mph. Larry speculates it could be a VSS issue related to the 3.54 gears in the Dana 60 causing the ECU to believe the vehicle’s absolute speed is too high, which, if determined to be the case, creates another issue since no one produces a 2.62 gear set for a Dana 60. That’s also why you see the stunted power numbers in the Fast Facts, since the Challenger cannot hit full rpm on the dyno. Still, in current form, Larry reports the Challenger is totally drivable and road-trip reliable. If you’re looking for the easier route, Larry advises using a GM 4L60 series with a standalone controller.

“Larry’s is one of the few Hellcat swaps currently drivable and he’s still about 95 percent of the way to having it all figured out.”

On the topic of “not supported,” the Hellcat technically isn’t either, because even though it’s a Gen-III Hemi, it’s most definitely not the same level of install. Even though Larry had already installed a 6.1, the Hellcat was not a direct drop-in. For one, because of the lines routed from the rear of the supercharger, the engine had to be moved forward ¾ inch. Then there’s the six heat exchangers and all the requisite plumbing. For example, to cool the intake air and maximize density, a 250-watt thermostatically controlled electric pump moves 45 liters of coolant per minute through two intercoolers built into the flanks of the supercharger and two radiators positioned at the front of the car. You can’t just shove them any old place they fit; they need strong airflow and Hellcat-equipped cars are designed with this in mind. In fact, when Larry spoke to Chrysler engineers at a show once, they said one of the biggest issues he would likely face would be getting enough airflow to the coolers to keep the Hellcat out of limp mode. Working within the envelope the ’70 offers, Larry’s solution was to position the coolers within the fenders for the best airflow and add slim auxiliary fans. While he has not attempted open-track use, this solution has been effective for regular street use and Power Tour.

Wiring is its own adventure with a swap like this. The complex multi-tiered electrical system in the production car features multiple computers that all retrieve data from each other. The challenge is figuring what you can eliminate and what you can’t. For example, disconnect the wheel-speed sensors and you’ll trigger a code and disable the traction control, stability control, and speedo, but the car would still be drivable. On the other hand, the car would not crank at all if the ABS module were unplugged. That’s why Larry’s Challenger has the Hellcat ABS module mounted and plugged in, even though it’s not actually doing anything. As for the rest of the wiring, Larry reached out to numerous resources to confirm what was critical to operation. If the Challenger had a modern dash swap, it would be lit up like a Christmas tree with warning lights from triggered codes, but none are mission critical.

Despite the fact that it’s already a driver and has taken home the Mopar Muscle Editor’s Choice award at the 2017 Mopar Nats, the saga of the ’70 Hellcat is actually an ongoing one as Larry irons out the technical details to get his RT/SE as turnkey as a brand-new Challenger. The plan is to have all the details ironed out so that he can offer the swap to customers of his shop, Larry’s Automotive in Newburgh, IN, with minimal hassle and using only the necessary components. Plus, if you haven’t noticed by now, Larry loves to upgrade and change this car, so this is hardly the last iteration. If you want to see more technical build details and follow the progress, check out his Instagram @70Hellcat because even though the Challenger will be making 707-plus hp once the bugs are smashed, Larry hinted to us that he’s already pondering what he may do next to make it ever faster.

 

FAST FACTS

1970 DODGE CHALLENGER RT/SE

LARRY ROSE; NEWBURGH, IN

ENGINE

Type: Gen-III Hemi Hellcat

Block: Hellcat, cast iron

Rotating assembly: 6.2L Hellcat

Cylinder heads: Hellcat/Apache cast aluminum

Camshaft: factory Hellcat .561-/.551–inch lift, 278/304 degrees duration

Valvetrain: Hellcat 1.65:1 ratio stainless steel rocker arms

Induction: Hellcat 2.4L twin-screw IHI supercharger

Exhaust: TTI headers with Magnaflow pipes and mufflers

Ignition: stock Hellcat coil-on-plug

Cooling: custom/Hellcat

Oiling: Hellcat wet-sump with factory piston oil squirters

Output: 680 hp, 585 lb-ft of torque

Built by: Chrysler/FCA, Saltillo Engine plant (Arizpe, Coahuila, Mexico)

DRIVETRAIN

Transmission: Hellcat 8-speed 8HP90 TorqueFlite, factory shifter.

Driveshaft: custom from the Driveshaft Shop

Rearend: Dana 60 with 3.54 gears

CHASSIS

Front suspension: Reilly Motorsports AlterKation with adjustable dual-action coilovers,

rack and pinion conversion

Rear suspension: Reilly Motorsports Street Lynx with adjustable dual-action coilovers

Steering: Reilly Motorsports power rack and pinion

Brakes: Wilwood 14-inch rotors and 6-piston calipers up front; Wilwood

14-inch rotors and 4-piston in the rear, Wilwood master cylinder,

Hydratech hydroboost

WHEELS & TIRES

Wheels: 18×10 & 19×11 Boze Alloy

Tires: 305/35R18 Michelin Pilot (front) & 345/30R19 Nitto NT05R

drag radials (rear)

 

You can find more photos of the build here

 

SOURCE: Mopar Muscle

AUTHOR: Christopher Campbell