Checking pushrod length is simple if you happen to have one of these tools from Comp Cams. Each tool comes in a specified rod length range and each complete turn is equal to .050 of an inch. It is imperative to measure for the correct pushrod length with a cylinder head swap.
Here's the proof. The dotted line represents the power and torque band prior to the head and cam swap. The solid line represents the new power and torque after the swap. The power and torque curve is not only a beautiful thing to see, but the peak horsepower numbers are beyond impressive when compared to the stock numbers. The horsepower peaked at 441 at 6,200 rpm, while the torque peaked at 410 lb-ft at 4,800 rpm. That's a 97hp gain over the initial stock numbers and a 40 lb-ft improvement over the initial pull. The '58 Chevy truck where this engine will end up will cruise down the highway with decent power and get decent mileage all at once. That's having your cake and eating it too.
If the OE computer is the brain of the engine, then the wiring harness is the spinal cord. The spinal cord that was used in this engine build was the Painless Performance fuel-injection harness (PN 60218). This particular factory-style harness is designed to work with the stock ECM and plug into all the sensors and controllers that are vital for the engine's function. Not just any stock ECM will work; check the serial number on the back of the Delphi ECM to find out if it is compatible with this harness. For more specifics, call Painless Performance's tech line, or check its Web site for compatibility. During the tuning phase, we did encounter one problem. The ECM that came with this engine would not take a tune and function properly.
Originally the ECM and engine was set up from the factory to work with a fly-by-wire throttle body. We changed the throttle body to a cable control. Either the fly by wire ECM would not co-operate with a harness designed for a cable set up or the ECM was just plain bad. Once we switched out, the fly-by-wire ECM and used a cable ECM it took a tune and worked beautifully. As an added bonus, if you do purchase the Painless harness for the LS-based engine, Painless will re-flash the factory ECM for you, removing things like the vehicle anti-theft and other problems, and it will be guaranteed to work with their harness. That free service alone is worth hundreds of dollars or hours of trying to figure it out on your own like we did.
The attractive truck intake is bolted back on and the rest of the engine is wired up again and ready to test. Side note: The stock pushrods were about to be re-used, however Steve was wary about the excessive amount of pre-load that was put onto the lifters. A shorter pushrod (7.325-inches long) was used and the results were much better.
Back in the dyno room control center, Steve mans the power while Ernie re-tunes the engine on the fly and re-flashes the computer. After a few pulls and re-maps of the tune, they found the sweet spot and made a final pull.