Is the ITR head going on a GSR bottom end?
If so, you will actually lose about .2 points of compression since the combustion chambers are designed differently.
Another option to consider is using an ITR TB and a Skunk2 IM designed for the GSR head. You will retain the compression, but you will get more air flow and top-end power ... if that's what you're going for overall.
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2005 s2000