Stu have you tried a Disco spud on the stock Ex mani?
Was the LPG tuned properly with the stock mani?
I think both inlet and ex manis are the bottleneck
however Z18et exhaust mani is no more restrictive than
the CA18DET facotory one and that is good for 330hp ate.
The inlet manifold leaves much to be desired like all early model EFI manis and I think both manis and head
inlet valve size hold the key to more HP while torque
will never be an issue with this engine.
Stu do you run cast pistons and at what boost?