Andy Forest Comparison of tubular headers -v-  Harvey Smith original subaru Mark II Ported headers
			The test below was carried out on a set of Mark II ported headers only.  Subsequent to this test and with further investment in flow bench testing we found that the O/E Subaru uppipe was in fact a restriction and did not promote smooth gas flow into the turbo throat.  After various experiments we came up with our own design of uppipe and with more testing we were able to further modify the porting, particularly at the collector.  This improved gas flow across the board with far greater velocity to promote early spool and response.  We invited three customers who had recently had Mark II headers to return for the fitment of Mark III headers and uppipe paying only for the uppipe with free fitting. We were surprised that there was a very noticable improvement on the first installation and considered it might be a fluke but after completing the other two Mark II to Mark III swaps with uppipe these results became the norm. Please note :  The tests below are on the older Mark II headers, now superceded by Mark III ported with performance designed uppipe.
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		My M/Y95 WRX Wagon was originally fitted with GT Spec tubular headers and these were swapped for Mark III ported with uppipe and the improvement in spool and responsiveness was very noticable without any apparent loss of top end ability.