Fabspeed Bypass Pipe-Any Experiences Welcomed.

[Johnny Danger]

Originally Posted by The Radium King

do the ebay headers and leave the stock mid-pipes/cats. that's how porsche does it in countries with less strict emmissions requirements.

north america has the added requirement for emmissions reduction at start-up, so american cars have an additional warming 'pre-cat' on the headers and a secondary air pump, as well as sensors and ecu programming that checks to make sure both are working. row does not have this requirement, so row cars do not have cats on the headers or secondary air pumps, and no sensors to confirm their operation.

you can get catless, equal length, stainless headers on ebay for $65; the cheapest you can get new catless midpipes is $500. get headers without cats, however, and you have to deal with the sensor that is there to confirm the operation of the now-absent cats (or you get a 'check engine light'). you can reporgram your ecu to row, you can buy 'foolers' (fvd sells them) or you can make your own. all the sensor does is look for 02 content in the exhaust. it can be fooled into thinking that the cat is working by distancing it from the exhaust; some guys just hang it under the car, or you can get spark plug savers that thread into the exhaust bung and get the sensor out of direct exhaust flow (make sure your new, catless headers have two bungs each). there is also supposed to be a trick that uses a resistor or diode wired into the sensor; google is your ally for cheap, easy solutions to this.

other considerations are pipe diameter; oem for a 3.2 is 1.25" into 1.75" (ebay headers vary, but 1.5" into 2" is typical); go much bigger than this (or go completely catless or to a high-flow muffler) and you get into backpressure issues. reduced back pressure is good at high rpm when the engine is trying to flow as much air as possible, but at low to mid-range some back pressure is necessary to facilitate combustion chamber scouring and make max power. i've yet to see a dyno of just a high flow exhaust that does not indicate a drop in hp/torque at lower rpms. that's why most dynos from tuners include ecu flashes to compensate or don't start until 3000 rpm to hide this fact.

other things i've read is that cats tend to kill high frequencies, so a catless exhaust can be ricey sounding. also, i've read that those who have compared row to us spec cars have found the row to only be several hp stronger, so better figger out what your $/hp threshold is. i can justify $65 for several hp; uncertain if i can justify $500 for the same gain.

ps - lobo; what's the word on the wrap - worth it? keeping things cooler at all?

With all due respect, at 600 cells the secondary cats are arguable the most restrictive (and possible the heaviest) part of the oem system . Therefore, if one is going to leave most of the system intact, it would be far better to leave the headers/pre-cats in place and remove and bypass the secondaries .

[insite]

True. Plus, no cel with properly built pipes. The secondary cat pipes weigh close to 30 lbs. The bypass pipes? 8 lbs.

Total weight savings on my full exhaust was about 80 lbs.

Originally Posted by Johnny Danger

[B]With all due respect, at 600 cells the secondary cats are arguable the most restrictive (and possible the heaviest) part of the oem system . Therefore, if one going to leave most of the system intact, it would be far better to leave the headers/pre-cats in place and remove and bypass the secondaries . [/B]

[The Radium King]

weight aside, the argument becomes where the remaining cats are located for best performance - on the headers or on the mid-pipes. porsche and cost say delete the cat on the headers.

changing mid-pipes is easier; no potential seized bolts in the block, no sensors to deal with. however, here are some links to three easy ways to fix the cel issue:

http://forums.evolutionm.net/evo-how-requests-questions-tips/215795-5-o2-cheater-non-fouler-how.html

http://www.fvd.de/us/en/Porsche-0/-/-/-/item/item_details/VID_33179399-VCD_85527367-gid_29-sort_4-display_50-item_FVD111LAMVER/EXHAUST_-_Tuning_-_Catalytics-FVD111LAMVER-Oxygen_Sensor_Extension.html

http://www.audiworld.com/tech/eng53.shtml

otherwise, everything i find on the intraweb says that the pre-cats are more restrictive than the main cats ...

[Johnny Danger]

Originally Posted by The Radium King

weight aside, the argument becomes where the remaining cats are located for best performance - on the headers or on the mid-pipes. porsche and cost say delete the cat on the headers.

changing mid-pipes is easier; no potential seized bolts in the block, no sensors to deal with. however, here are some links to three easy ways to fix the cel issue:

http://forums.evolutionm.net/evo-how-requests-questions-tips/215795-5-o2-cheater-non-fouler-how.html

http://www.fvd.de/us/en/Porsche-0/-/-/-/item/item_details/VID_33179399-VCD_85527367-gid_29-sort_4-display_50-item_FVD111LAMVER/EXHAUST_-_Tuning_-_Catalytics-FVD111LAMVER-Oxygen_Sensor_Extension.html

http://www.audiworld.com/tech/eng53.shtml

otherwise, everything i find on the intraweb says that the pre-cats are more restrictive than the main cats ...

Ideally, if one could eliminate the oem header/pre-cat design in favor of a set of high quality aftermarket headers that incorporated both larger diameter and longer equal length primaries that flowed into a well designed merge collector, along with a pair of high flow cats (something on the order of 200 cell tri-metal HJS or Emitec cats) that were located mid stream - that would prove to be a very effective system indeed. However, in order to accomplish something along these lines, one would have to spend big buck$$ ! Especially, with the cats . Having said that, unless a person's budget would allow for this kind of expenditure, the best option would be to remove and bypass the secondary cats. The 986 boxster shares the same secondaries as 996 platform vehicles. And, at 600 cells, these cats are much more restrictive (and heavier) than the pre-cats which are 400 cell .

[The Radium King]

the ebay headers are copies of expensive headers (slightly larger diameter, equal length primaries, etc.) so the the differences between $65 and $1000 headers become very small (ie, porting, polishing - most things you can fix with a dremmel) and any power improvements negligible.

regarding the cats, please show my anything that confirms that the cats on the mid pipes are more restrictive than the cats on the headers. here's a previous post by a board member regarding cell count:


Quote:


"Anybody have any idea how many "cells" are in the OEM primary and secondary cats?

I've come across differing information. In the past, I've been told that the primary cats are 400 cell and the secondaries are 600. However, I tend to think that they're 400 cell all around."

so, either the cats are the same, or the cats on the midpipe (the 600 cell secondaries) are more restrictive. either way, best money and performance are on the ebay headers and leave the midpipes as-is.

[Johnny Danger]

Originally Posted by The Radium King

the ebay headers are copies of expensive headers (slightly larger diameter, equal length primaries, etc.) so the the differences between $65 and $1000 headers become very small (ie, porting, polishing - most things you can fix with a dremmel) and any power improvements negligible.

regarding the cats, please show my anything that confirms that the cats on the mid pipes are more restrictive than the cats on the headers. here's a previous post by a board member regarding cell count:


Quote:


"Anybody have any idea how many "cells" are in the OEM primary and secondary cats?

I've come across differing information. In the past, I've been told that the primary cats are 400 cell and the secondaries are 600. However, I tend to think that they're 400 cell all around."

so, either the cats are the same, or the cats on the midpipe (the 600 cell secondaries) are more restrictive. either way, best money and performance are on the ebay headers and leave the midpipes as-is.

Throughout my entire experience conducting exhaust mods, I've both read and have been told by virtually every knowledgeable exhaust "tech" and "tuner" that the secondary cats on the 986 were 600 cell .

[insite]

There is a lot more to it than that......

Originally Posted by The Radium King

so, either the cats are the same, or the cats on the midpipe (the 600 cell secondaries) are more restrictive. either way, best money and performance are on the ebay headers and leave the midpipes as-is.

[The Radium King]

yup, and a lot of that has to do with tuning the exhaust to maximise exhaust gas scouring at lower rpm, improving low rpm flow efficiency while maintaining backpressure, etc., all of which supports locating the cats further downstream and improving the headers.

ps, the quote about both cats being 400 cell was made by JD in a thread from about a year ago, so caveat emptor to all.

http://986forum.com/forums/showthread.php?t=25644&highlight=600+400+cats