The five-angle valve performance...
The five-angle valve performance job GES performs on its LT1 heads is visible on this intake valve opening. Less visible, but more important, is the work done on the short-turn radius in the bowl area. Intake flow is further improved by the use of back-cut Manley valves.
GES also pays plenty of attention...
GES also pays plenty of attention to intake ports. Heads destined for the 440-horse longblock get Stage 1 runner porting. Those meant for the 480hp version, as shown here, get Stage 2 porting, which means that the stock 180cc runner is hogged out to 190 cc.
The exhaust side is also worked...
The exhaust side is also worked over, complementing the bigger valve and helping the extra inflow escape after combustion.
Before proceeding to the assembly...
Before proceeding to the assembly stage, GES surfaces all its heads, a critical step that helps ensure proper cylinder head-engine deck sealing and a consistent compression ratio.
Fitting a set of factory LT1...
Fitting a set of factory LT1 valve covers back on the modified heads requires a bit of improvisation. Clearance for the roller rockers is created by cutting away part of the bracing found inside the covers.
Besides adding the readily...
Besides adding the readily apparent Comp Cams 1.6:1 rocker arms, GES beefs up the valvetrain of its ported LT1 heads by increasing the rocker stud size to 7/16-inch. "We've all seen 3/8-inch studs break," says Chad Golen. He maintains that pushrod guideplates are also a must: "Self-aligning rockers can pop off."
The manifold intake runners...
The manifold intake runners are ported and gasket matched, though GES doesn't max the port out. "If we did," Golen tells us, "We'd lose some responsiveness and torque. We're not going to max it out when we can make power with a smaller port."
Aftermarket LT1 intakes are...
Aftermarket LT1 intakes are rare, and LT4 pieces more so. Golen maintains that these engines need a fully ported intake, and GES can provide one at extra cost. Lungs intended for the 440hp engine are modded to accept a 52mm throttle body (4 mm over the stock piece); its big brother gets a 58mm inlet.
|LT1 LONG-BLOCK SPECS|
|Block:||383ci LT1 fitted with four-bolt mains|
|Oiling:||Melling high-volume pump, new factory 5-quart pan|
|Crank:||Eagle cast steel, internally balanced|
|Rods:||Scat 4340 forged, 6 inches long |
|Pistons:||SRP forged, full-floating, 11.5:1 compression|
|Rings:||Speed Pro Plasma-Moly|
|383/480:|| GM aluminum LT1, 54cc chamber, five-angle valve job, Stage 2 porting, 190cc intake runners, ARP bolts, Manley stainless steel valves, 2.00/1.56-inch, back-cut|
|383/440:||Same as above with 180cc intake runners|
|LT1 POWER CURVES|
|Horsepower||440 @ 6,000 rpm||480 @ 6,300 rpm|
|Torque||460 @ 4,100 rpm||460 @ 4,500 rpm|