http://cgi.ebay.com/ebaymotors/Porsche-944-Porsche-944-Callaway-Turbo-951-C-300-HP-st
10-26-2005, 09:20 PM
#16
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To answer your question, nothing. Yes that probably happens at certain exhaust pressures/velocities. This of course leads into discussions about tri-Y headers versus 4-1 headers, chamber volumes, etc. Entire dissertations could be written on sizing an exhaust system to optimally tune for a particular displacement/RPM/etc.
As a variation on the above idea, alternative solutions might include a "staggered" manifold (one that adds cross-sectional area as it passes each exhaust port) or figuring out a way to run a "header" for each exhaust port to a common collector (such as in a 4-1 header) but that'd be a heck of a 3D puzzle getting it to fit between the head & frame rail and from front-to-back still getting the turbo in there (not to mention it'd be a fabrication nightmare!). It probably would represent the best solution from an efficiency standpoint though.
Actually if you look at the photo above, there is some effort by Callaway to slope the tube coming off the exhaust port to the back (kind of like the idea I had, just not as much) and direct the flow somewhat to prevent backup. This wouldn't eliminate interfence between different flows though (as in your example). I really do think some sort of individual header assembly with four seperate pipes going to a common collector with the turbo & wastegate mounted off that would be the best solution. Or of course you could always just run four little teeny turbos like GT5s or something. . . One for each exhaust port!
First one to engineer and build that idea gets a prize!
As a variation on the above idea, alternative solutions might include a "staggered" manifold (one that adds cross-sectional area as it passes each exhaust port) or figuring out a way to run a "header" for each exhaust port to a common collector (such as in a 4-1 header) but that'd be a heck of a 3D puzzle getting it to fit between the head & frame rail and from front-to-back still getting the turbo in there (not to mention it'd be a fabrication nightmare!). It probably would represent the best solution from an efficiency standpoint though.
Actually if you look at the photo above, there is some effort by Callaway to slope the tube coming off the exhaust port to the back (kind of like the idea I had, just not as much) and direct the flow somewhat to prevent backup. This wouldn't eliminate interfence between different flows though (as in your example). I really do think some sort of individual header assembly with four seperate pipes going to a common collector with the turbo & wastegate mounted off that would be the best solution. Or of course you could always just run four little teeny turbos like GT5s or something. . . One for each exhaust port!
First one to engineer and build that idea gets a prize!
10-26-2005, 11:36 PM
#17
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this is why I believe Porsche decided on the crossover, so it does not waste exhaust gases which are pretty important to a turbo engine....theres really no room for a 4-2-1 manifold and turbo on the right side of the engine bay without extensive modifications, and even then the cold side would have to run near the hot exhaust tubes....so before you knock Porsche's design, think again! full boost at 3100 (as per FWM) on a turbo making 220 hp 20 years ago is pretty damn good i'd say
