| GMPP CRATE ENGINE SPECS |
| 350CI FOUR-BOLT BLOCK-ORIGINAL SPECS |
| HEADS | 76cc, 8.5:1 compression, 1.94/1.50 inch, intake/exhaust |
| CAMSHAFT | 0.450/0.460 inch, intake/exhaust |
| DURATION | 222/222 degrees at 0.050 inch |
| POWER | 315 hp at 5,100 rpm/351 lb-ft at 3,700 rpm |
| 350CI FOUR-BOLT BLOCK-IMPROVED SPECS |
| HEADS | 62cc, 9.9:1 compression, 2.00/1.55 inch, intake/exhaust |
| CAMSHAFT | 0.470/0.470 inch, intake/exhaust |
| DURATION | 224/224 degrees at 0.050 inch |
| POWER | 385 hp at 5,600 rpm/407 lb-ft at 4,200 rpm |
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.
 To make sure our heads weren't...  To make sure our heads weren't cheating on the dyno we measured their intake-runner volume, combustion chamber size, and intake/exhaust airflow numbers. All was legit, making this test even more impressive than we had expected. |  Our new camshaft complemented...  Our new camshaft complemented this street engine nicely. The idle vacuum dropped only a half inch while making 26 hp and 29 lb-ft more than the cylinder head swap only test. Don't forget the Lucas assembly lube, as the camshaft can run dry for several seconds until the engine splashes it. | |