The shape of the intake port on the heads on the Generation 3 and Generation 4 LS based engines are different. The Generation 3 heads have a "cathedral" port. The Generation have a "rectangle" port. The difference between these heads are simple, the amount of cfm the heads can flow determine how efficient they are and how much power they can handle. The port of the head must also match the shape of the intake for proper air flow. The LS7 & LSX heads have a different bolt pattern which make their heads and intakes not so interchangeable with the rest of the LS family. The bolt holes are raised on the LS7 & LSX blocks compared to the lower bolt holes on the Gen 3 & 4 heads.
What this means to you?
We get alot of phone calls asking if a LS7 intake will bolt onto a LS3 head because they received a killer deal on an LS7 FAST intake. Unfortunately it will not fit due to the bolt holes not being in the same location, nor the port angle and shape. Be sure to take a look at the port of your heads as well. In the below LS intake manifold guide we were sure to include all of the possible LS engine RPO (Engine code) codes possible. Example: the LS1 has a cathedral port head, compared to the LS3, which has a rectangle port head. Here at ICT Billet we make adapters that will allow fitment of various LS cylinder heads to a variety of intake manifolds.
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