Chevy 350 Engine - Crate This!

With solid baseline runs under our belt we installed the new GMPP heads by themselves out of the box. While there was a recommended camshaft selection in our engine design to go along with the intake and spark-enhancing pieces, we wanted to see how good the heads were on their own. An added feature of the Fast Burns is that their heads are tapped with two sets of valve cover and intake-mounting holes to allow for use with Vortec or conventional small-block patterns.

After a series of test pulls, we achieved an optimum total timing advance curve of 36 degrees with the box-stock Holley HP jetting. The more efficient combustion chambers of the new heads explained why our engine required less total timing. As for the factory jetting from the Holley HP carburetor, it would take a story in itself to explain why this carburetor continued to deliver optimum air/fuel ratios out of the box; in short, as more air is drawn through the carburetor more fuel is delivered proportionately to accommodate it.

Like kids in a toy store, we couldn't wait to see the potential power our new heads had to offer, so we poured in some 91-octane and began testing. This time around we were absolutely amazed at the power increase our heads had made with the stock cam still in place: peak readings of 359 hp at 5,500 rpm and 378 lb-ft at 4,000 rpm. We knew the improved ports, chambers, and valve size of the new heads would make more power, but without additional valve timing the gains were impressive: 44 hp and 27 lb-ft.