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| Perhaps the greatest flow improvement in the LS3/L92 head is making the short side radius downturn more gradual with a straighter shot at the valve. This is something that head porters aim to do when modifying a head. You can see the LS3 head on the right has a much straighter shot at the valve in the area marked in red. A finer casting sand is used on the LS3 port cores and you can even see the difference in surface smoothness in the picture. Smoother means better flow. |
The LS3 has a cylinder head that was particularly well engineered by taking advantage of GM’s motorsports experience. The LS3 head uses a casting called the L92 which is an optimized version of the first generation of LS castings. The L92 used an intake port shape that was originally developed by Katech for the factory Corvette C6R engine used in ALMS. Instead of the tall and narrow “Cathedral” intake port of the older LS1 and LS2 the L92 port uses a more traditional rectangular intake port. The port was wider higher and straighter than the cathedral ports with a rounder more direct short side radius.
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| The LS3 port on the left is higher, larger, smoother and straighter than the old LS port on the right. |
This was accomplished by moving the push rods 0.250” to the side and using offset rocker arms so the rest of the valvetrain could be undisturbed. The exhaust port was not as radically changed but was made slightly larger and higher with a more gradual short side radius. The exhaust valve guide boss was also reshaped for better flow. Although the basic port geometry was derived from the C6R motorsports program, GM continued to refine the port design using powerful computational aids such as GT Power, Unigraphics based CFD and NASTRAN as well as extensive flow bench testing to arrive at the final port shape.
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| Although a multi angle valve seat is something the Japanese have been doing for years, the LS3 is one of the first GM engines to use this flow improving trick. A wider valve bridge was needed to prevent cracking between the intake and exhaust valve seats. |
Even things like the use of fine grained casting sand for the port cores and three angle valve jobs were employed to improve flow. Larger valves than the early LS engine were employed at 2.165” intake and 1.59” on the exhaust side to further increase flow. The results are ports that can outflow many DOHC 4 valve designs!
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| The LS3/L92 heads have bigger valves as shown here. |
