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Originally Posted by ryuujin
Can anyone give me the real mail on headers for my 2001 2.7l? I've read a lot of stuff on the 'net' etc and I can't decide if i should outlay the dollars for an increase in HP that is questionable? Can fitting headers increase HP at the wheels of 10 to 20HP (quoted in some ads). If I fit headers should I then fit a full sports exhaust including cats and muffler to gain the maximum or can I just leave the exhaust standard? Will the fitting of the headers cause any problems such as CEL etc? I would appreciate any help with this.
Regards
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Ryuujin,
Be advised, upgrading the exhaust system on your boxster (i.e. headers and cats) is a serious undertaking that requires a systematic approach. If I am not mistaken, the 2.7 engine has a similar exhaust system to the 3.2, wherein there are two sets of catalytic converters. These sets are commonly referred to as being the "secondary" and "pre" cats. Most would agree, that the "secondary" cats are for the most part extraneous, and, therefore, can be removed and bypassed. However, its the design of the "pre" cat and how it is integrated into the header that creates a challenge. A challenge in the sense, that it is a very delicate balance to increase increase air flow, at the same time maintain the necessary amount of back pressure, as well as keeping the vehicle OBD compliant ( refers to emissions, cel's ect.. ). In my experience, I found that going "catless" actually resulted in a loss of power. This was especially the case with regard a low end torque. Again, some degree of back pressure is necessary in order to maintain power. Next, I experimented with deleting the "secondary" cats and replacing the oem pre-cat/header configuration in favor of separate set of after market headers along with lower cell cats that were relocated further "downstream". Needless to say, this approach required that the O2 sensors via newly created "bungs" had be relocated, as well as the remapping of the vehicle's ecu in order to eliminate ongoing problems with cel's (check engine lights). Another problem with this application was finding high quality cats. There must be a million manufacturers with respect to headers, however, it was nearly impossible to find a real tri-metal 200 cat cell, say on the level of HJS. The third and final application, involved having a set of headers (along with the pre-cats) custom fabricated in a way that they followed the principles of the oem set-up, however, the newly designed ones involved longer, equal length primaries that flowed into a true merger collector and incorporated 200 cell tri-metal HJS cats. This design proved to be ideal. The installation was simply and straightforward. There was no need to retro fit or alter anything, the vehicle was completely OBD compliant, and most importantly, there was clear improvement in hp throughout.
