When you add boost to the legendary Jeep 4.0-liter inline 6 engine, magic happens. If you put that magic inside a yellow and brown box of delicious defunct automaker and take it to an automotive competition, you might just win.
But it’s more likely you’ll end up mid-pack in competition as the crowd favorite, especially when they get a peek at that interior.


Bask in the warm tones of that plastic dash. Touch the spongy softness of those padded, faux-chrome-striped door cards. Spin the retro suicide knob on the steering wheel. It’s interiors like this that inspired Riley Hawk’s Scion xB from SEMA. The laptop charger and cables indicate the modern nature of the powerplant, but hey, chill out, man. Relax. Take it all in for just another moment. Have another ‘lude and feel your mustache grow.

Faux wood covers the dash, and a Spirit badge adorns the glovebox. Tilt steering, column-shift automatic, air conditioning, front bucket seats. It’s a killer machine. It’s got everything.

Photo courtesy Team External Combustion.

Just two months before the event, Team External Combustion found this AMC Spirit complete with the company’s venerable (and ancient) 4.2-liter engine. That’s the father of the 4.0 HO motor that earned legendary status among off-roaders.

Photo courtesy Team External Combustion.

Tight on time, they weren’t ready to try and test the budget-stroker setup you can make by mating the 4.2-liter crank and rods to a 4.0 block and head, never mind that this 4.2 was in unknown condition. They opted instead for something they knew would work.

External Combustion is the team behind the autocross-stomping Jeep Cherokee XJ-R. That Jeep, despite having incredibly unsophisticated suspension (stick axles at both ends), had the honor of setting fastest time of day at the Grassroots Motorsports $2013 Challenge. That Jeep’s turbo engine is more or less replicated for the Spirit. It uses many cheap, Chinese-made turbo components and plumbing. Megasquirt hardware controls it, using the camshaft signal for the trigger.

They had only just got it running the night before the 2014 event and are still having transmission issues with the original Spirit 904 automatic. (The engine bolts on using the 4.0’s flex plate, provided you elongate one hole.) It hasn’t visited a dyno yet for official numbers. Greg Stewart, a representative from the team, gave me an estimate: “The XJ-R makes 274hp/322 tq at 12 psi from a 50-trim T3/T4 turbo. The Spirit is running 16 psi from a 60 trim, but the trans slips in every gear. Fuzzy math of 10hp per psi say it should make 314/362 at the wheels.”

For 2015, the team has purchased an Aisin-Warner AW4 automatic transmission to replace the 904 and will swap in a Ford 8.8 rear end with a limited-slip differential to replace the super-tall 2.31 open diff. That’ll help with actually delivering power to the ground. If the engine “doesn’t blow up right away,” they’re also contemplating adding nitrous. The target is a sub-12-second quarter mile.

The suspension was essentially stock. The short build time led them to simply cut the front springs; they’re hoping to eventually find stiffer ones that will work. The rear leaf springs stayed, which gave the car oodles of sexy rake. “The control arms up from have poly bushings. We installed GM upper ball joints, which are taller, to try and correct the camber curve. We welded the old ball joint holes closed and drilled new ones,” Stewart said.

Its total lack of suspension tuning certainly didn’t help, but neither did the all-season tires. They’re big tires for sure, with tons of flexing sidewall and huge, howling, squirming tread blocks. Those tires give the car an excellent vintage street racer look, but they’re not at all grippy enough for a competition environment. They also rub the fenders a bit.
 

As it sat, the car finished mid-pack for both the autocross and drag racing portions of the event, covering the quarter mile in 14.755 seconds on its best run. The scales at the event showed a 2835-lb. curb weight, with 59 percent on the front axle — no doubt in partial thanks to all that rake. After one of the autocross runs, they inspected the tires to see the result of the rub up front.
 

I have a feeling wheels and tires will change for next year, too, but they’re not actually planning much for the suspension just yet except for adjusting the rear spring shackles. Fingers crossed that they don’t touch the interior.
 
Team External Combustion is: Jeff Hutton, David Seavey, Pat Murphy, Tony Sestito, Greg Stewart and Matt Harkins. Seavey and Hutton are the owners of the Jeep, but the Spirit belongs to the team.
 
Photos Copyright 2014 Hooniverse/Alan Cesar unless otherwise noted.