I was just checking on this during this week. The OEM LS1 tapers down to 71 mm and most "ported" throttle bodies keep the stock size throttle blade. The LS2, from what I was told, uses a 4 bolt body, which mounts to the F.A.S.T. manifolds that are available now (don't know about the FAST 78 manifold) so an adapter is needed to use an LS1 unit on the later FAST's (as well as the fuel rail). I am sending my OEM LS1 unit out to a vendor who bores them to 78 mm and makes a new throttle blade, and also claims it flows better then the BBK 90 throttle body...we will see.
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