Testing The New GM L92 Cylinder Heads - 550 hp for Under $4,900
| Parts List | | Description | PN | Source | Price | | LQ4, iron 6.0L, used | N/A | LKQ Auto | $1,100.00 | | L92 aluminum head, complete, 2 | 12582713 | Scoggin-Dickey | 798.50 | | Rocker arms, intake, 8 | 12569167 | Scoggin-Dickey | 70.00 | | Rocker arms, exhaust, 8 | 10214664 | Scoggin-Dickey | 70.00 | | Rocker support stand, 8 | 12600936 | Scoggin-Dickey | 11.98 | | Rocker-arm bolts, 8 | 12560961 | Scoggin-Dickey | 61.92 | | Valvesprings, kit, LS6 (16) | 12499224 | Scoggin-Dickey | 52.25 | | GMPP L92 carb intake | 25534401 | Scoggin-Dickey | 299.50 | | Fel-Pro LQ4 head gasket | 1027 | Summit Racing | 41.95 | | Fel-Pro intake gasket, L92 | 1222-2 | Summit Racing | N/A |
The wider, rectangular intake port moves the pushrod laterally, which requires an offset intake rocker arm. This is the first situation we can recall where a GM production engine uses an offset rocker arm to clear a wide intake port. | 
Comparing the exhaust side of these stock heads with the fully CNC-ported LS7 heads indicates that the stock L92 heads are slightly better at lower valve lifts, which is what you want with street-oriented cylinder heads. | 
After removing the stock 6.0L heads, we took the time to check for valve-to-piston clearance to make sure we wouldn't bend a bunch of valves with more lift from the Comp cam. We needn't have worried, since we found a ton of room. This is partly due to the Gen III engine's taller 15-degree valve angle. We're used to working with 23-degree heads. |
Flow-Chart Comparison Factory L92 head
2.160/1.59 valve sizes, stainless steel
15-degree valve angle
Factory CNC-ported LS7 head
2.20/1.61 valve sizes, titanium intake, sodium-filled exhaust
12-degree valve angle | | Valve Lift | Intake L92 | Exhaust L92 | Intake CNC LS7 | Exhaust CNC LS7 | | 0.100 | 72 | 63 | 71 | 60 | | 0.200 | 148 | 126 | 145 | 120 | | 0.300 | 212 | 162 | 222 | 159 | | 0.400 | 264 | 189 | 271 | 192 | | 0.500 | 302 | 205 | 315 | 207 | | 0.600 | 322 | 214 | 348 | 219 | | 0.700 | 316 | 221 | 352 | 221 | | For this comparison, we tested the L92 heads on the SuperFlow 600 bench at Jim Grubbs Motorsports using a 4.030-inch cylinder adapter, while the LS7 head-flow numbers came from the GM Performance Parts '07 catalog, as we did not have access to LS7 heads to test. We also measured the L92 heads for their intake-port cross-sectional areas and came up with a cavernous 3.19 square inches. That is roughly the cross-sectional size of an oval-port big-block Chevy intake port, which means that intake velocity on a small-displacement 364ci engine like ours will certainly suffer. This explains why the torque dropped at lower engine speeds, especially when paired with the longer-duration camshaft. The most impressive point is that the L92 flow numbers are close to the LS7 through 0.500-inch lift, yet a pair of CNC-ported LS7 heads will drill almost $2,500 out of your savings account versus $800 for the L92s. Which would you buy? | |
| Cylinder-Head Spec Chart | | Part number, complete | 12582713 | | Casting number | 5364 | | Valve angle | 15 degrees | | Valve size | 2.165/1.59 | | Combustion chamber | 70 cc | | Intake-port volume | 260 cc | | Exhaust-port volume | 90 cc | | Valve-stem diameter | 8 mm (0.315 inch) | | Intake port | Rectangle | | Exhaust port | D-shape | | Intake-port cross-sectional area | 3.19 square inches | | Conical (beehive) valvespring* | 1.290-inch diameter at base | | *Requires offset L92 intake rocker |
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