Is the exhaust scavenging on 6 cylinder boxers less effective than other layouts?

I've been thinking about all the posts about the difficulty to gain from exhaust and intake upgrades on the 2.5l boxster engine. Since all the flat 6s share the same basic design I thought I'd post my question here. I find it hard to believe it is so difficult to get more than 204hp from this engine. After all Renault reliably get 197hp from the 4 cylinder normally aspirated Renault Sport engine in my Clio. The boxer is abour 20% larger. The Renault is only 2.0 liters with a similar basic on-off variable cam system. It revs higher though, and has less torque. My concern is increasing track performance. I noticed when timing the cams on the boxer engine that all four cams are "parked" at the same time, meaning all the valves are closed for one "beat" of the cycle. Whereas on my 944 one cylinder will always have valves open when in TDC, keeping the "beat" constant Could it be that the 1,2,3 and , 1,2,3 and rythm is decreasing the effectiveness of the scavenging putting more emphasis on other design factors of the exhaust such as back-pressure? If this is a cause for the lack of response to exhaust upgrades could some kind of X-pipe perhaps improve the scavenging?

There is a theoretical answer and a practical one. In practice, when x pipes are added to 3.4l/3.6l 996 engines(you are in the 996 section,not Boxster), the results are misleading because the cats are usually deleted. It is unclear how much high-end power is just from reducing the restriction caused by the cats ,and how much is caused by the X pipe. When they do fit cats they are often 200 cell so the results are still obscure. In the case of the Boxster it has a peculiarly small TB and small diameter intake. So you probably need to rephrase your question,put it in the Racing/Track section &/or Boxster Section. http://986forum.com/forums/general-d...-diameter.html

Quotes source post: 13576806

Headers of proper length can help exhaust scavenging. We've seen these on race engines. The exhaust system looks like a nest of stainless steel snakes. Search out pics of the Carrera GT V10 exhaust system and for a real shock to the senses look at pics of the Porsche 918 exhaust system. The intake and exhaust ports are reversed so the exhaust runners come right up and wrap around and then go into a muffler system just above the engine. The 2.5l stock exhaust system is pretty good as the engine makes good power and does so at a pretty high RPM. (I've never driven a 2.5l car but my 2.7l car the engine pulls strong right up to 6400RPMs where it makes max power and even beyond with no signs of running out of air. That's the sign of a good exhaust (and intake) system, in fact a good engine.) It takes considerable expertise and experience and testing to come up with the best all round exhaust solution. And it takes more expertise and experience and testing to improve upon the stock system. My experience (with exhaust systems on motorcycle engines mainly) is while the benefit is real the problem is the improvement is limited, confined to a narrow range of RPMs. This isn't necessarily a show stopper if one intends to use the engine in its higher RPM ranges but it is a trade off. Whether an x-pipe would help or hurt I can't say. I don't see any cross overs on any Porsche engines from the factory. One woudl think if there was any real benefit Porsche would offer this. I mean the pressure is always on to deliver more performance while consuming less fuel and emitting fewer emissions. You can't rely upon the static timing of the cams to know what they are doing when the engine is running. The 2.5l engine has VarioCam and this advances, or retards, intake cam timing at various engine speeds and under varying engine conditions/loads to help with torque at lower RPMs or boost HP at higher RPMs. I think the 2.5l engine lacks the resonance flap feature in the intake which when opened changes the effective length of the intake runners and helps improve air flow and cylinder filling at higher RPMs. Below a certain RPM (3K IIRC) the flap is closed so the default intake runner configuration can help with low speed running, engine tractability.

I chose to post here because the question is not limited to the Boxster engine. Am I right in thinking that there is a pause per rotation when the camshafts are parked, or are the lobes spaced so that the shafts can be parked at 120 and degree 240 degrees as well? If so I'm incorrect in thinking that there is a pause in the exhaust beat per revolution per bank, a pause I thought could affect the scavenging since the pressure pulses have to match the opening of the valves. A pause would cause the pressure wave to arrive late for one cylinder. That is my suspicion anyway.