01-27-2011, 12:34 PM
for the past 7 years i have been playing with exhaust systems for this car, in an effort to get the right sound, the right look, significant weight loss, not lose power, and maximize performance - it has been a very long and very expensive journey, with over $11k invested in a dozen different cat-backs, and of course the header - all along the way i learned a lot about how the engine works, what things have what effects, what myths there are out there about different systems, and what they do, and don't do - i tried just about everything, and compared a lot of data on a number of different systems - there was always some form of compromise with every system - either it didn't fit the way i wanted, or interfered with something else, or didn't sound right, or had the notorious midrange torque dip that any free flow system showed
so, i went about making my own system - this allowed me to get the fit i wanted, with the muffler nicely centered and tucked up high, and the pipes formed to fit perfectly - the tone was greatly improved, accentuating the low notes, and muffling the high ones - weight was decent, and there was none of the nasty torque dip - so, finally i had landed on something that almost made me happy
i say "almost", because in spite of the obvious performance increase of the rs barn header, and all credit given to the development of that, i was never happy with the sound it made - when it was cold, it had too much of a "kazoo" sound for my tastes - when it warmed up, it wasn't bad, using either the rs barn cat-back, or the one i ended up developing - still though, the OEM header sounded better - it just didn't flow as well
for almost 5 years i lived with the sound, because i could not give up the performance - with the advent of the supercharger though, i was again thrust into the arena of exhaust systems - in developing the kit, i had to reinstall the factory header - i fell in love with the sound again - once i was done with that though, and knowing that a forced induction engine is not as prone to torque loss issues with exhaust system changes, i wanted to see how much more power there was available, and so the rs barn header went back on - immediately i could tell that it flowed better up top, and could make more power - i was still running the factory catalytic converter, and so the lower end gains that we had seen on charts were not there as much, but you could tell the upper end was less restricted - unfortunately the sound again became a problem - in addition to that, the engine no longer ran right with the header, and needed way too much fuel - also, the DME is not capable of managing the rapidity of the changes in flow, due to the free flowing nature of the header - this presented a couple of problems
1. there was no way the header was going to pass any sort of emissions testing - the visual inspection was an obvious issue, but the output measurements would not be close to passing
2. in order to provide enough fuel off idle, the low end of the maps became too rich for the longevity of the engine, and would ultimately result in fuel wash - as this is a street car, that was unacceptable
so, back to the OEM header
not wanting to give up any power now, and realizing that there was upper end restriction in the OEM header, i went about doing some measuring and redesigning - i took the system apart, and started looking at how it was built - i found that the primary tubes were not all that different from the aftermarket tubes - ok - that's good news - then i looked at the secondaries - again, the volume worked out fairly nicely - that left the collector - aha!
porsche, in designing the system, had crimped down the tube at the collector, and then inserted a reducer sleeve - this dropped the cross-sectional area to just under 3" - they did this to improve low end torque - this made total sense, since that is what the engine needed most - it worked too - unfortunately this created a restriction up top that choked down the engine
now, what to do? i got inside each primary and resized the tubes and cleaned up the manufacturing anomalies that hindered flow (slag, bumps, reduced entries) - i did the same thing to the secondaries - this was a number of hours of tedious machining, but this would help with flow and heat - then it was time to rework the collector - this meant removing the crimped down area, reshaping the secondary exits, and creating a new merge point that more closely matched the oval exit tube which had about 4.9" of cross sectional area - there wasn't a lot of room in which to work, but we got it done! when i was finished, i ended up with 4.524" of cross sectional area - that is a 50% increase in cross sectional area over what was there before
then it was off to the ceramic coaters to have the outside of the entire header coated, and then the inside also coated with an extremely high temp thermal coating - this will promote scavenging, and also reduce under hood temps - it will also smooth out the tone even more
i get it all back tomorrow - i am very excited about what this will all do in the end - i think i will finally have the ultimate exhaust system for the 968 of my dreams - it will be completely street legal too, as i am still running the factory cat (aftermarket cats won't pass tailpipe tests) - it will only work on my setup, and isn't for anybody else, but it should really give me what i have wanted for all these years
no, i wil not be reproducing this - this is purely a one-off
so, i went about making my own system - this allowed me to get the fit i wanted, with the muffler nicely centered and tucked up high, and the pipes formed to fit perfectly - the tone was greatly improved, accentuating the low notes, and muffling the high ones - weight was decent, and there was none of the nasty torque dip - so, finally i had landed on something that almost made me happy
i say "almost", because in spite of the obvious performance increase of the rs barn header, and all credit given to the development of that, i was never happy with the sound it made - when it was cold, it had too much of a "kazoo" sound for my tastes - when it warmed up, it wasn't bad, using either the rs barn cat-back, or the one i ended up developing - still though, the OEM header sounded better - it just didn't flow as well
for almost 5 years i lived with the sound, because i could not give up the performance - with the advent of the supercharger though, i was again thrust into the arena of exhaust systems - in developing the kit, i had to reinstall the factory header - i fell in love with the sound again - once i was done with that though, and knowing that a forced induction engine is not as prone to torque loss issues with exhaust system changes, i wanted to see how much more power there was available, and so the rs barn header went back on - immediately i could tell that it flowed better up top, and could make more power - i was still running the factory catalytic converter, and so the lower end gains that we had seen on charts were not there as much, but you could tell the upper end was less restricted - unfortunately the sound again became a problem - in addition to that, the engine no longer ran right with the header, and needed way too much fuel - also, the DME is not capable of managing the rapidity of the changes in flow, due to the free flowing nature of the header - this presented a couple of problems
1. there was no way the header was going to pass any sort of emissions testing - the visual inspection was an obvious issue, but the output measurements would not be close to passing
2. in order to provide enough fuel off idle, the low end of the maps became too rich for the longevity of the engine, and would ultimately result in fuel wash - as this is a street car, that was unacceptable
so, back to the OEM header
not wanting to give up any power now, and realizing that there was upper end restriction in the OEM header, i went about doing some measuring and redesigning - i took the system apart, and started looking at how it was built - i found that the primary tubes were not all that different from the aftermarket tubes - ok - that's good news - then i looked at the secondaries - again, the volume worked out fairly nicely - that left the collector - aha!
porsche, in designing the system, had crimped down the tube at the collector, and then inserted a reducer sleeve - this dropped the cross-sectional area to just under 3" - they did this to improve low end torque - this made total sense, since that is what the engine needed most - it worked too - unfortunately this created a restriction up top that choked down the engine
now, what to do? i got inside each primary and resized the tubes and cleaned up the manufacturing anomalies that hindered flow (slag, bumps, reduced entries) - i did the same thing to the secondaries - this was a number of hours of tedious machining, but this would help with flow and heat - then it was time to rework the collector - this meant removing the crimped down area, reshaping the secondary exits, and creating a new merge point that more closely matched the oval exit tube which had about 4.9" of cross sectional area - there wasn't a lot of room in which to work, but we got it done! when i was finished, i ended up with 4.524" of cross sectional area - that is a 50% increase in cross sectional area over what was there before
then it was off to the ceramic coaters to have the outside of the entire header coated, and then the inside also coated with an extremely high temp thermal coating - this will promote scavenging, and also reduce under hood temps - it will also smooth out the tone even more
i get it all back tomorrow - i am very excited about what this will all do in the end - i think i will finally have the ultimate exhaust system for the 968 of my dreams - it will be completely street legal too, as i am still running the factory cat (aftermarket cats won't pass tailpipe tests) - it will only work on my setup, and isn't for anybody else, but it should really give me what i have wanted for all these years
no, i wil not be reproducing this - this is purely a one-off
94 Midnight Metallic Blue Cab Porsche 968 w/deviating cashmere/black interior and WAY too many mods to list - thanks to eric for creating www.968forums.com
"It isn't nearly as expensive to do it right as it is to do it wrong."
(This post was last modified: 01-27-2011, 12:46 PM by flash.)
