Last time, in “The Hunt For Power” we told you how we screwed up. Oops. Well, as we said we aren’t the first gear-heads (or is it Jeep-heads) to round off a cam, and we won’t be the last. As we predicted, the third time we had to tear into Piggy’s engine to make it right, something seems to have finally stuck. As of right now, the old Jeep is running great, and we wanted to tell you how we did despite the hiccups. To do that, we ran down to Airaid where, with a little help of Donovan Shafer, the J-Truck trickled a little more oil on their fancy Mustang Dynamometer and put down some numbers. Once done, with a few pulls it became clear that the new-and-improved Pig Truck was indeed healthier but was running dangerously lean at higher rpms and engine loads, which is always a good way to burn a hole through a piston.
With that information in hand, we contacted Howell Engine Developments, and they supplied us with a new Calibration PROM for our Howell TBI system. With the new tune in hand, we returned to the dyno where the pig picked up nearly 50 hp and 60 lb-ft of torque. While the numbers are decent with a 47 percent improvement in horsepower, the seat-of-our-pants dyno is what really counts, and the “this-is-fun” numbers are way up. All in all, the Pig Truck is now much more drivable, reliable, and downright more fun, especially on turns in the dirt!
Step By Step
Since Part 2 of “The Hunt For Power,” we drove the Pig Truck (with the second cam and new rockers installed) back over to Airaid. Once loaded on the dyno, the truck made a respectable 132 hp at the rear wheels and a very nice 246 lb-ft of torque. Having said that, the air/fuel ratios were dangerously lean with a maximum reading of 22.0 (12-13 is good for hard, high-rpm loads). Airaid’s Donovan Shafer, who ran the dyno for us, recommended we talk to Howell Engine Developments to fatten up the air/fuel ratio.
After the engine modifications, we were making 132 hp at 3,200 rpm. A bit less than we’d hoped for, but from a 37-year-old engine that has never been rebuilt, that is still really good. Considering that a ’78 ’Vette was rated at 185 hp at the flywheel and we are probably at around 160-170 hp at the flywheel (taking into account parasitic drivetrain losses). We are also spinning 36-inch tires. If we wanted to maximize power, we could have gone to lighter or smaller tires or added tri-Y headers. While we made decent power on this run, we were severely lean on the top end, which can burn holes in pistons and fry valves. Something had to be done.
With the dyno’s air/fuel ratio information, we contacted Howell Engine Developments for a custom Calibration PROM. Once it arrived, we simply used a 1⁄4-inch drive wrench to open up the back of the Howell computer. Once we were inside the computer casing, we popped out the old chip and installed the new one. Take that Staples with your dumb plastic “easy” button.
Back on the dyno, the Pig with its new Calibration Prom put down similar horsepower and torque numbers as the last time she was on the dyno. This time, though, the engine was running with an improved air/fuel ratio of 14.6. That’s much safer for the mechanical longevity of our AMC V-8.
So why did we do this? Well, we could have tracked down a 5.3L or 6.0L third-gen GM V-8 for a swap and probably made more power with a cheap-and-dirty engine transplant. At the same time, there is something to be said for keeping an iconic vehicle like the Pig Truck powered by an old-school AMC pushrod V-8. Sure, an LS swap might have been more cost-effective in regards to horsepower-to-dollar gains, but we would have had to deal with custom engine mounts, adapters, and all the unforeseen issues that we skipped by sticking with AMC power. Regardless, the Pig Truck is just a little cooler, more reliable, and now much easier to get sideways in the dirt, which brings a smile to our face.
The first graph shows our initial modified numbers versus our baseline numbers, but that was running dangerously lean. The graph on the left shows our power output after we put the new PROM in the Howell Fuel Injection computer and cured the lean condition. While we did lose a little peak power, it is worth it to keep the engine from grenading and the curves are still nice and flat. Peak power is now 128 hp at 3,200 rpm and 238 lb-ft at a stump-pulling 1,700 rpm.