The 1997-98 engines were the 1st run of the LS motors and has some oil control issues and excessive piston slap upon cold start (piston design). The heads are also perimeter bolts style for the valve covers and the coil packs differ as well. These year engines don't interchange easily with the '99+ engines. Stay away from them IMO. The best swap engines are '99+ all said and done. These engines have center bolt style valve covers and a different PCM/wiring harness, coil pack style, slightly better flowing heads, a better casting block with superior oil control and a few other subtle differences.
For the LQ9 you can bolt on a set of LS3/L92 heads with LS3 intake and get very close to 460-480rwhp+ with a cam/headers/tune depending upon what dyno you are on. These heads have massive ports that sacrifice some low/mid range power for a healthy top end charge. If you want heads with more down low power TFS or AFR heads are a great choice and they flow great up top as well. TFS has a budget friendly 220cc "as cast" head that make only 10rwhp less than the fully CnC ported unit. They are cathedral style heads so they would need an LS1/LS6/FAST style intake.
LS7 intake only works on LS7 heads or small bore custom LS7 heads. An LS7 production head must be run a 4.125" bore or large due to the 2.20" intake valves. The LS3/L92 heads have 2.16" intake valves and clear a 4" bore; however they are actually pretty shrouded up against the cylinder wall and aren't optimal. The TFS/AFR castings run a smaller intake valve and would be preferred.
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