By our third pull, we had...
By our third pull, we had things pretty dialed in, and the engine produced 396.7 hp and 377 lb-ft of torque. Average torque and horsepower was up as well.
The first thing we checked was ignition timing, and we noticed it was moving around--it's not supposed to. After swapping out all of our electrical components for new ones, we still had the same misfire between 3,300 and 3,800 rpm. We then performed compression and lead down tests, which showed that the engine was healthy. It was late on Friday and we decided to call it a day.
The following Monday, we planned a carbureted induction setup to rule out a bad wiring harness, injector, or other EFI-related problem. Over the weekend, Hedrick also wondered if the cam was walking in the block, as it would explain the erratic ignition timing. As we pulled the engine down, we noticed that the camshaft was indeed moving nearly a quarter inch in the block. This will affect how the distributor gear and the cam gear mesh, which can alter the timing and cause a misfire.
After the engine dyno's break-in...
After the engine dyno's break-in program was complete, Hedrick made a few half-throttle pulls to creep up on the engine. Oil pressure and temperature, along with the air/fuel ratio was carefully watched to make sure we didn't toast our fresh motor. Our first pull, with 29 degrees of total timing, netted a peak horsepower of 390.4 at 5,500 rpm and peak torque of 378.1 lb-ft at 5,000 rpm.
While we don't recall any issues with the cam gear during installation, it was evident that there was no endplay on the cam and gear, and this tight fit caused the cam bolt to back out, which allowed the camshaft to slide back and forth in the block. Hedrick determined that the brass bushing behind the cam gear wasn't sitting on the gear correctly, so he took it and the cam retaining plate to his machine shop and milled them down until the bushing was flat and the combination offered 0.005-inch endplay. He then degreed the cam (you'll see that in an upcoming tech article), and HP Performance's Jason Combs and Jimmy Hartley reassembled the engine--this time with a carburetor.
We're going to throw the EFI setup back on the engine, but since we had the time, we opted to test both so we could compare the two setups. The carburetor is a Holley 650-cfm four-barrel with vacuum secondaries, and the intake manifold is a Professional Products Typhoon dual-plane, air-gap-style intake. We don't know if it's optimum, but it was sitting around so we went for it.
We'd like to thank Mark Hedrick and Jimmy Hartley, along with Tony Gonyon and Jason Combs, who went above and beyond to get our stroker small-block running tip top and make this test happen. There are always risks when assembling your own engine at home. That's why there are professionals like Horsepower By Hedrick, who offer professional machining and assembly services. If you're not up to the task, they are, and they build their reputation on the fact that they do it right the first time.
In any case, check out the next installment of our stock-block stroke swap to see how the carburetor fared against the EFI setup.
The first thing we did was...
The first thing we did was check the base timing, which we had set at 10 degrees. We saw the timing changing upwards of 10 degrees while the engine was idling. Something was amiss.
On our fourth pull, we detected...
On our fourth pull, we detected a slight engine misfire, and the dyno chart showed the engine's dismay. Note how power and torque dropped off at 5,600 rpm.
After changing out spark plugs,...
After changing out spark plugs, distributors, computers, and ignition modules, we began to perform several mechanical tests, including compression and leak down tests. Everything checked out fine, so we went back to the ignition timing and its erratic movement. We decided to remove the fuel injection and install a carbureted-induction setup to rule out the wiring harness. As we pulled apart the engine, we discovered that the camshaft was moving a good bit in the block, which disrupts the mesh of the distributor gear against the cam gear. Unfortunately, we could not reassemble and retest the engine before we met our deadline, so be sure to check back in the next installment as we'll compare the carbureted setup against the EFI and finish our tuning and engine dyno testing.