The following week, we trekked back to HP Performance and installed the new stud and adjusted the valve. The new ring-and-pinion went in (same 3.55:1 ratio as before); then, we strapped the Cobra to the dyno once more just to see how things were. Once the run was stopped, Stolen Goods and its Boss 347 engine had improved power output to 358 hp and 386 lb-ft of torque. The tune-up was still dead-on, so no changes were deemed necessary.
Now that the snake was back in action, it was time to burn rubber, so we set off for Gainesville Raceway in Gainesville, Florida, home of the NHRA Gatornationals and the first outing for our recently finished project car. The two-hour drive on I-75 went off without a hitch, but it rained the whole time and the track called it right before we got there.
On our way home from the cancelled...
On our way home from the cancelled track test, we noticed the engine wasn't running up to par. After swapping the spark plugs, the problem still existed, and pulling them out again revealed that the No. 7 cylinder hadn't been firing, as evidenced by the pristine condition of the spark plug.
After stopping for a bite to eat, we noticed that the throttle seemed to be hesitant, as if the engine was loading up with extra fuel. We thought the plugs might possibly be fouled. After about 40 minutes of interstate driving, the Cobra was down on horsepower, and it definitely wasn't running properly. We pulled over at the nearest rest stop to check things out.
Your author had experienced symptoms similar to this in another project car, and it turned out to be a wet mass air meter and harness. After surveying the meter and air filter on Stolen Goods, it was immediately apparent that both were well soaked in water. Since the car wasn't making any odd noises and the gauges checked out, we wrapped the meter and harness with a towel and completed our journey home.
We picked up a new set of NGK BKR6E spark plugs, but before we swapped them in, we pulled the meter, air filter, and harness to make sure everything was clean and dry. We also cleaned the mass air sensor's element in case the water on the air filter had brought in any oil from the filter. A quick twist of the key and we could still tell the engine wasn't up to snuff, so we swapped out the plugs. Interestingly enough, the front four plugs were perfect, while the rear four were gas-fouled. We also noticed that we weren't getting a positive snap when we put the spark plug wires on, so a little WD-40 was in order for the boots. Time for a test run.
The engine still wasn't running correctly, so we pulled the plugs again to find that the fuel-distribution problem was gone, but the No. 7 plug had not fired at all. After pulling the valve cover, we realized that the very same intake rocker arm stud had snapped again, but this time the rocker wedged itself sideways, which restricted the pushrod's movement and explains why we didn't hear the pushrod tapping the valve cover.
Since we had a deadline to meet, we pirated a rocker-arm stud from another car and reassembled everything. Unfortunately, Stolen Goods still ran poorly, and pulling the plugs again revealed that the No. 7 cylinder still wasn't firing. After consulting with engine builder Tom Naegele at D.S.S. Racing, we were looking at the possibility that the pushrods were too long and the rocker didn't have enough travel, which ended up binding the assembly, and the stud took the brunt of the force applied.
Things were going great with...
Things were going great with the project until we encountered some severe valvetrain noise, so into the engine we went.
Stolen Goods suffered two...
Stolen Goods suffered two rocker-arm stud failures, both of which occurred on the exact same intake valve and cylinder. It appears there may be a bit too much side loading, and we think the pushrod length may have something to do with it.
To get to the bottom of this...
To get to the bottom of this mystery, we needed a set of digital calipers and a compression tester. The test revealed that all cylinders were on the money except No. 7, which came up with a goose egg. This could be a bent valve or just a misadjusted rocker arm.