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

Testing GM L92 And LS7 Cylinder Heads Rocker Arms

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.

Testing GM L92 And LS7 Cylinder Heads Exhaust Ports

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.

Testing GM L92 And LS7 Cylinder Heads Piston To Valve Clearance

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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