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Old 09-24-2014, 04:47 PM   #1
Join Date: May 2013
Location: Georgetown, SC
Posts: 210
986 motor upgrade...3.4 996

Down to final steps of a 3.4 swap into my 1998 Boxster ( including a 6 speed trans). I have a number of questions I hope someone can help me with or answer for me.

1. I have enclosed a picture of my exhaust headers. Note the inside diameter of 58 mm. Also note my fabricated intake manifold (Blue silicone piping) 3 in. ID.

My question is how far away from the throttle body should my MAF be placed?? I am using a BMW MAF holder (black tub)with a Porsche MAF. Should this BMW tub be as close to the throttle body as I can get it or much further away as it is in the stock Boxster close to the air box??

2. I would like to fabricate a pipe to eliminate my CAT. If I do this can I eliminate my post CAT sensors??

3. The stock DME is Motronic 5.2.2 and is the same DME model that was in the 996 the motor came from. Will I still have to flash the DME before the car

will run?? I know if I drop the post CAT it will need a special chip what if I do not drop the post CAT ??

4. I would like to post a mistake list detailing some of the mistakes I had made on this journey if there is any interest out there...is there??

Attached Thumbnails
New 996 motor plug.JPG
996 exhost.png

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Old 09-24-2014, 07:06 PM   #2
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Location: DE
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FWIW, I have a '98 spec box with no cats at all. The 2nd set of O2 sensors are plugged in, but hanging in space. No CE light and no cat or O2 codes. Pretty sure ECU is 5.2 also. Based on this, I think it would work ok without the cat if you keep the post cat sensors electrically attached.
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Old 09-24-2014, 07:14 PM   #3
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Location: chi-town
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went thru this
1.try to google 996 set up and try to position it relatively in the same spot. Im running my MAF next to the airbox
2. yes with ROW flash. SAI delete is a "must" with ROW
3.You need a flash. if not car will run like $#@%# and be too lean. Go with 3.4 ROW
4. go 4 it
99' with 3.4l engine. ROW tune. SAI delete
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Old 09-24-2014, 08:46 PM   #4
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Fun project. If it were my car I would place the MAF as far away from the throttle body as possible. Also use an intake screen upstream to smooth turbulent air before hitting the sensor. The MAF is pretty sensitive and getting it into clean air without valve lash acoustic wave interference gives you the smoothest A/F ratios across the RPM range.

2009 Cayman 2.9L PDK (with a few tweaks)
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