LS Engine Build - L92 Cylinder Heads

After baselining the engine with the stock 6.0L heads, we bolted on a set of ported 6.0L castings from West Coast Racing Cylinder Heads. Owner Richard Reyman has this program dialed in and says it offers some excellent flow improvements over the stock heads while retaining the stock valve sizes.

After baselining the engine with the stock 6.0L heads, we bolted on a set of ported 6.0L c

Big Ports, More Flow
For years, we've been talking about the potential advantages of smaller intake ports that enhance intake velocity in an effort to make great torque for street engines. However, with the LS series of engines, these L92 and LS3 heads with their larger, rectangle-shaped intake ports seem to take exception to that concept when used on large displacement engines. If we had really looked at our own flow testing during development, we would have noticed that the CNC-ported cathedral heads offered a much better exhaust-to-intake-flow (E/I) relationship than the L92 heads. Looking at the E/I for the ported L92 heads reveals that the flow relationship indicates a need for more exhaust duration to help top end power. When we get to the actual dyno results, the lack of good exhaust port flow could be used to explain why the engine didn't quite make the power we thought it should.

The first thing we did after getting the GMPP-ported heads out of the box was stick them on Jim Grubbs Motorsports' SuperFlow 600 bench to test their mettle against the stock L92 heads. The main flow improvements for the GMPP heads occur above 0.600 inch valve lift.
The first thing we did after getting the GMPP-ported heads out of the box was stick them o
The GMPP CNC-ported L92s also include combustion chamber mods while retaining the stock valves.
The GMPP CNC-ported L92s also include combustion chamber mods while retaining the stock va
The stock L92 ports are generous, but the CNC-ported versions are even larger with a cross-sectional area of more than 3.2 square inches at the opening, and they get larger from there. To put that in perspective, the GM SB 2.2 NASCAR race head from a few years ago measures roughly 2.8 square inches.
The stock L92 ports are generous, but the CNC-ported versions are even larger with a cross

Flow Data
Valve Lift	Stock 6.0L		Ported 6.0L		E/I Percent (Exhaust-To- Intake Ratio)
Valve Lift	Intake	Exhaust	Intake	Exhaust	E/I Percent (Exhaust-To- Intake Ratio)
0.100	76	57	70	59	84
0.200	145	115	145	119	82
0.300	200	152	210	174	82
0.400	236	173	250	213	85
0.500	252	188	288	228	79
0.575	260	194	303	230	76
0.600	263	198	294	231	78

The stock 6.0L and WCRCH-ported versions come with a 70cc chamber and 2.00/1.55-inch valves. These flow numbers came from West Coast Racing Cylinder Heads and were tested on a 4.030-inch bore at a test depression of 28 inches.

Valve Lift	Stock L92		GMPP Ported L92		E/I Percent (Exhaust-To- Intake Ratio)
Valve Lift	Intake	Exhaust	Intake	Exhaust	E/I Percent (Exhaust-To- Intake Ratio)
0.100	72	59	72	55	76
0.200	148	116	144	116	80
0.300	212	161	214	157	73
0.400	264	187	267	192	72
0.500	302	203	300	214	71
0.600	322	208	326	224	69
0.700	316	212	337	231	68

The GMPP CNC-ported heads come with a 70cc combustion chamber and stock 2.165/1.590-inch valves. Both sets of L92 heads were tested on JGM's SuperFlow 600 flow bench with a 4.060-inch bore adapter at 28 inches. Intake port volume on the CNC versions is 279 cc.

Cam Specs
Camshaft	Duration (Advertised)	Duration (At 0.050)	Lift (Inches)	Lobe Separation
XER281HR, intake	281	232	0.595	112
54-428-11, exhaust	283	234	0.598	112
LS1 277 LRHR, intake	276	227	0.614	113
54-458-11, exhaust	284	235	0.621	113