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Posts: 338
Registered: October 2007


Porsche 987 Gen 1 - All Models Manifold / Header De Cat

Reviews Views Date of last review
2 9008 Tue January 28, 2014


Recommended By Average Price Average Rating
100% of reviewers None indicated 10.0


This article is focussed on the benefits of de catting the standard manifolds as an alternative to aftermarket items.

In order to comply with emissions , the rear silencers must be stock or at least have working cats. Avoiding the CEL primary lambda failure fault codes is discussed later in the article.

The dyno plots included in the article are intended to demonstate the additional gains of fitting free flow manifolds , when other mods have already been put in place. As a result , the individual gain from the manifolds is less than would be expected if this was the only mod in place. This follows with all the figures quoted on aftermarket tuner sites for exhaust systems.

Some useful tools:

Flared nut spanner 19mm/22mm - for undoing lambda sensors

Wobble socket square drive and 1/4 inch square drive extension bars (also wobble socket design)


The porsche Boxster chosen for this development is a MY 2004-2006 version, fitted with the M96.26 variocam engine in 3.2L displacement. This model is unique in the porsche 987 model range as it is fitted as standard with equal branch (performance) manifolds.
Porsche literature at the time of release makes specific note of the 3.2S manifolds being a performance design , compared to the branch arrangement of the 2.7. The branch arrangement of the 2.7 was later used in both the 2.7 variocam "plus" and 3.4 engined M97 engine variants found in the Boxster (from 2007 onwards) and all cayman models.

Manifolds in Detail / Comparison

Below is a picture of both the standard branch manifold and the equal branch performance manifold. Both items use exactly the same 400 cell ceramic catalyst of the same dimensions , so the "performance" element is by virtue of the branch design. Manifolds are interchangeable as are the later 3.4 and 2.7 variocam plus units found on 2007-2009 cars , all use the same gaskets.

3.2 S manifold on the left and 2.7 / 3.4 on right

The inlet throat of the extract tubes is also the same size and construction on both items, only the overall bore is slightly larger on the 3.2 at approximately 45mm versus approx 41mm of the 2.7, though I suspect this has more to do with engine displacement. The diameter of the outlet that connects onto the rear silencers is also identical on both manifolds at approximately 55mm. The 2007 and later cayman / boxster manifolds are the same design as the 2.7 but use a 42mm tube on the header into the cat housing. The outlet from the cat onto the rear silencers is the same as all others at 55mm. With the sizes so close on the early 2.7 and later 3.4/2.7 M97 engine, its difficult to be certain they aren't the same size.

From the pictures it can also be seen that the 3.2 uses slightly longer extract tubes , a common design to improve mid range torque.


Removing the ceramic cats is relatively straight forward , but I should stress its not a reversible procedure , so once done , the manifolds are de catted for ever more , unless you pay to have new cats fitted.

In order to prevent CEL fault lights for the secondary lambda probes , you will need to either have the emissions checking turned off in the ECU by reprogramming , or as I did , fit dummy cat inserts into the second lambda position. These were supplied by Maxspeed Motorsports in Canada , and fit in between the manifold and the lambda probe to back out the sensor from the air flow and provide a mini cat prior to the lambda probe. The result is no fault lights , even with complete removal of the primary cats.

I would advise its best to keep the rear silencers standard or at least have items with hi flow cats installed to ensure emissions compliance and local government emissions tests can be passed.

Maxspeed "screw in" adpater for secondary lambda probe

Internal view showing fine tri metal "mini" cat

Removal of existing manifolds

Some safety precautions - Wear leather faced gloves when handling hot manifolds or bolts. Safety glasses are advisable when spraying release agents or working under the car looking upwards / using a wire brush.

I found the ease with which the manifolds can be removed depends on the service life of the car, how much salt its been exposed to and age of the vehicle.
1. With the car ideally on a lift , make sure the engine and exhaust are up to temperature.
2. Starting from the ends of the manifold , using a long breaker bar and metrinch type socket , gently crack the bolt seal on each of the 6 manifold bolts where they connect to the engine block , by first tighetening each bolt by 1/8 th of a turn. I found that a liberal application with freeze spray and penetrating fluid helps this process.
3. Starting again with the bolts at either end of the manifold undo each bolt so the initial tension is released.

4. Continue again through this process until all six bolts are loose , but keep the manifold bolted to the block.
5. Now jack up the rear of the car and remove the rear road wheels and the plastic covers on the wheel arch liners that cover the lambda probes.
6. Remove the lambda probes from the manifolds. Again this is best done with the manifolds hot , so you may want to slacken these soon after the manifold bolts in step 1. I found a flared nut spanner is best for this task when used with an extension tube to get better leverage. Use freeze spray and penetrating fluid to prevent the probes seizing as they are undone.
5. Apply liberal coats of penetrating fluid and use a wire brush to agitate any rust from the threads of the three manifold to rear silencer flange bolts , on each side of the exhaust.
6. Using a wobble extension or universal coupling in conjunction with 1/4 inch drive extension pieces its possible to get a socket onto each of the three nuts securing the manifold to the rear silencers.

The original design uses a captive bolt in the manifold part , so a socket cannot be placed on both sides of the flange.
Its not uncommon for the nuts to be so badly corroded that a socket will no longer fit , this is where a metrinch socket will still allow drive on the remainder of the nut. If the nut cannot be gripped with a socket , use a nut splitter or cold chisel and hammer to break the nut open. Do not worry if the flange bolts shear as these will need to be replaced anyway.
7. With the bolts from the flanges undone / sheared , the manifold can be lowered away from the car.
8. The studs that are left in the manifold flange can then be either pressed out or drilled out. I suggest using a cnetre punch before drilling to ensure concentricity.
9. To de cat , simply attach a wood drill bit onto an electric drill and drill through the ceramic cat from the flanged end. Suggest wearing a dust mask when doing this. Break up the cat using the drill or long screwdriver until everything is removed. Put a few old bolts into the cat housing and rattle them around to clean off any remaining cat materials and then either blow out with an air line or use a sand blaster to clean up finally.

Ceramic cat (400 cell):

Cleaned manifold - de cat


Basically the reversal of removal, though suggest using new bolts , nuts and gaskets , as well as some copper slip to lubricate the threads. Fit the manifold losely in place first , then torque down , starting from the middle bolts and working outward. Torque setting is 12 Ft Lbs for the manifold to block.
Next bolt up the rear silencers to the manifolds , make sure you fit the gasket before the first bolt !
Fit all 3 bolts and loosely tighten before final torque Ft Lbs.

Install the lambda probe extenders using an adjustable wrench or large spanner. Then pre twist the lambda cables in the reverse direction (anticlockwise) by about 5 full turns before inserting into the thread. This way , when the probe is fully inserted the cable will not be twisted.

Start engine and check for leaks .

Refit lambda probe covers in wheel arch and refit road wheels , torque wheel bolts to 96 Ft Lbs


Dyno plots suggest the effect of fitting de catted 2.7 Manifolds to a 3.2S (retaining original rear silencers with cats ) the Hp gain is approximately 5 hp. As you would expect its more biased to top end power and results in the peak power , being sustained for longer. The interesting thing about this mod is the exhaust sounds much more raspy and race like with 2.7 manifolds (headers) than with 3.2 items , even when comparing like for like with both manifolds de catted. I put this down to the design of the manifold more than the tube diameter being 4mm smaller.

As a comparison here is the data from supersprint for their exhaust :

After this mod , I went on to repeat the excercise using 3.2S manifolds rather than 2.7 items , to see if a further gain was possible. The result was an increase of approximately 2hp over the 2.7 items. This suggests the 3.2 manifolds are indeed an upgrade on the standard and would also be a factory upgrade on a cayman. The sound of the exhaust with 3.2S manifolds (de catted) is also quieter than with 2.7 items , possibly due to the design. I estimate its around 10 dB quieter

Final peak power with 3.2 S decat manifolds , cayman plenum with ECU map gave 307 bhp flywheel and 270 ft lbs torque. Thats not far off the 310 bhp and similar torque (272 ft lbs) of the current dfi 3.4 !


There are gains to be had from de catting the primary manifolds both in terms of Hp and sound. The procedure is non reversible and does limit any additions of de catted rear silencers if you still want to keep the emissions passable. If however, you were planning to buy de cat manifolds anyway , this is a very cheap alternative to achieving a similar result at a fraction of the cost.

I suggest that fitting standard 3.2S headers to a cayman or later boxster M97 engine or 2.7 will result in an Hp gain and a deeper sounding exhaust note , regardless of whether the headers are de catted or not. Obviously there will be a greater gain on the de catted items than with cats in place.
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Keywords: 987 Gen 1 - All Models Manifold / Header De Cat


Site Upgrade Donor

Registered: July 2009
Posts: 259
Review Date: Sat October 22, 2011 Would you recommend the product? Yes | Price you paid?: None indicated | Rating: 0 
Have you Installed this Product or Mod?:
Brilliant write up. Thanks Berty!
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Porsche Enthusiast

Registered: July 2013
Location: Greenfield, IN
Posts: 151
Review Date: Tue January 28, 2014 Would you recommend the product? Yes | Price you paid?: None indicated | Rating: 10 
Have you Installed this Product or Mod?: Planned
Am interested in doing this to my Gen II 2.9 Boxster...any comments? Are the procedures the same? HP and Performance?
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