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The Chevy small block, among its many virtues, has always maintained a fan base due to a certain quality: its "swapability." GM has never been one to under-utilize any powerplant, and has a habit of engineering them to accept any number of variant parts designed to optimize performance, cost and fuel economy. The 241 and 243 heads -- or LS1 and LS6, respectively -- are perfect examples of this modular approach; which head you chose depends on your budget and designs for power and future modifications.
LS Head Castings
General Motors produced seven versions of the LS engine, most of them with different heads. You can identify which head you have by looking at the three-digit stamping next to the valve cover; for example, the LS1 used head castings 339 and 806 through 1998, and 853 and 241 from 1999 through 2004. The 243 head came on the more powerful LS6 engine from 2001 to 2006, and was used in C5 Corvettes. Later engines like the truck-spec LQ9 and LQ4 used the exact same port design as the LS6s 243 heads, but had 6 cc larger combustion chambers.
Basic Differences
There are three basic differences between the LS1 and LS6 heads. The first has to do with port shape. The LS6 and the later LQ9-LQ4 heads used reshaped intake ports and D-shaped -- as opposed to oval-shaped -- exhaust ports for better flow: 200 cfm intake and 70 cfm exhaust for the 241s, and 210 intake and 75 cfm for the 243s. The second major difference is that the LS6 heads used hollow, sodium-filled valve stems for reduced valve train inertia and better heat transfer from the exhaust valves to the head. The LS6s 243 heads also had a slightly smaller combustion chamber: 65 cc to the LS1s 67 cc.
Head Comparison
Judging by head flow alone, stock LS6 heads could potentially produce about 5 percent more power than stock LS1 heads, and maybe a bit more because of the smaller combustion chambers bump in compression. The LS6s hollow valve stems give the heads a bit more high rpm potential, and the sodium-filled valves can stand up a bit better in turbocharged applications. But if youre looking for a good turbo or supercharger head, you might consider the cheaper and more readily available LQ9-LQ5 heads, casting numbers 317 and 873. They use the LS6 ports, but their larger 71 cc chambers will give you the slight drop in compression you want for forced induction.
Buy vs. Modify
If you have a set of perfectly good LS1 heads, theres no sense in tossing them for the 243s if you have any experience in basic porting. Gasket-matching, bowl-blending and smoothing out the shortside-turn radius will easily net you another 10 cfm in flow or more, and porting is practically free if youve got a die grinder and a few bits. The LS6s sodium-filled valves are available through GM -- part No. 17801930 -- and are a direct retrofit for the LS1 heads, as are the LS6s valve springs. But if youre going for absolute power, particularly in naturally aspirated form, youd do better to start with a set of LS6 heads and have them ported for max flow.
