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Discussion Starter · #1 ·
here's some incomplete but interesting data. i have an 06 CS and a friend also has one. i have been tinkering/modifying mine with various exhausts and lately an IPD 82mm plenum. i have dynoed my car once in the stock configuration. also i have done 4th gear roll ons with my friend in both the stock config and ipd plenum /catless log tube header config (his car is unmodified).

the roll on comparison, when both cars were stock, showed the same acceleration from 3 to about 5500 rpm (4th gear). numerous tests showed neither car would walk away from the other from 50 to 95 or so. yesterday we did the same test with my car modified with the headers,plenum and TB. his car walked away from mine every time.....very definitive test. there were a couple runs where we got pat 5500 rpm and i think i started to produce more power but it was unclear because we shut down too soon (safety reasons). so all i can say is I am now making less torque from 3k to about 5k for sure

the catless long tube headers have produced a CEL and i'm not sure what effect that would have

bottom line is i think the TB and plenum reduced mid range torque
 

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Remap is a must if you have done the above mods. Your engine is breathing so much better now and without a proper remap, you might be running a little lean.
 

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I would theorize it is the catless headers, not the intake side, causing your drop in mid range torque. You're also not providing information on what exactly you've done to the exhaust tract after the headers, which has proven to be a place where these cars can gain (or lose) real power.
 

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Remap will make a huge difference. Without it, the lack of cats and removal of one of the intake flappers kill torque. Also you need to pull to 7300, the plenum does not show gains until after 6000. Softronic has a very good tune for that combo, I ran it for a couple of years. Dyno after the remap and parts on my car showed an no point weaker than stock, and overall almost 30whp higher.
 

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Discussion Starter · #10 ·
i have the stock catback. although it's claimed that the stock cat back costs power, I haven't seen any data and i tend to doubt it. the restrictive part of the exhaust seems to be the first cat. also, replacing just the cat back has shown to provide pretty much no power increase.
 

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Discussion Starter · #11 ·
Remap will make a huge difference. Without it, the lack of cats and removal of one of the intake flappers kill torque. Also you need to pull to 7300, the plenum does not show gains until after 6000. Softronic has a very good tune for that combo, I ran it for a couple of years. Dyno after the remap and parts on my car showed an no point weaker than stock, and overall almost 30whp higher.
i wonder if i go back to the stock plenum and keep the headers and do software, if i can get a significant increase between 3500 and 6000 rpms? that's where i really want it
 

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i have the stock catback. although it's claimed that the stock cat back costs power, I haven't seen any data and i tend to doubt it. the restrictive part of the exhaust seems to be the first cat. also, replacing just the cat back has shown to provide pretty much no power increase.
So you say you haven't seen any data with regards to the stock exhaust. You cannot have searched these forums. Have you any data to support your own claims I wonder? :)

The 987.1 has 2 of its 4 catalytic converters in the mufflers, just search. Removing them is the best and CEL-free way to free up power. I think you started in the wrong end my friend. Catless headers is a good way to lose torque, unless you have other mods to compensate. You haven't even a canned tune, so you are SOL.

On the 987.2 there are no cat. converters in the mufflers, all 4 of them are in the headers/manifolds and as such the headers are the most restrictive part of the exhaust. Which leads me to think that maybe you are confusing your generations?

I would go back to stock headers, find an aftermarket exhaust, keep the plenum and maybe even do a tune if I were you. Then you will get back the torque and increase power, and no CEL's since the muffler cats aren't monitored. Win-win. :cheers:
 

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Discussion Starter · #13 ·
yeah i've had two aftermarket cat backs.....dynoed one of them. it had no effect on power
 

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Put the car on a dyno. I had perfect A/F ratio on a previous car without a tune. The ECU can accommodate quite a bit. I believe OP is correct in plenum removing mid-range torque.
 

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Discussion Starter · #16 ·
somebody needs to make a larger plenum and retain a valve and get the best of both conditions....
 

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I have Softronic flash + NHP sport cats on headers + Stock exhaust + smaller 74mm IPD plenum

is it worth upgrading to 82mm version if I don't go aftermarket exhaust (for legal and personal reasons)?
 

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You're definitely losing low end TQ with the Catless Headers. Not enough back-pressure I would reckon.

Will improve/fix that problem with the tune. The Stock ECU will not be able to accommodate for all the extra air/flow that the Headers/IP/TB are producing!
 

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You're definitely losing low end TQ with the Catless Headers. Not enough back-pressure I would reckon.

Will improve/fix that problem with the tune. The Stock ECU will not be able to accommodate for all the extra air/flow that the Headers/IP/TB are producing!
Exhaust back pressure is a myth, just google it. Other than that I agree with you. :)


Back to topic:

If removing cats, I would personally always start furthest down the exhaust stream. The reason is quite simple: cat. converters require heat to operate properly, the closer to the engine they are the more effective they will be. The further away from the engine they are the more time it will take for them to reach operating temperature, and I also believe that they are more likely to clog up or malfunction over time because of that. But you have to look at the overall layout of the exhaust as well: Porsche's do not have that much of exhaust piping to begin with, therefore my "rule" is probably not as valid. Which is why I have a second "rule" as well: if/when removing cat. converters always start with the ones that aren't monitored to save you a CEL. :cheers:
 
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