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headers, all you need to know


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Just wanted to share an article I came across concerning headers and pipe diameters.

I currently have the K&N Cold Air Kit 57-7000 and IPD Plenum.

The K&N kit alone did an amazing job of eliminating most of the dreaded "flat spot" in power

for the 3.8 liter between 4500-6500 rpm. I can not say enough about it, my favorite mod

so far. Pulls significantly harder through 4500-6500 rpm and screams to 7300 rpm. The sound

alone was worth it to me. 5500-7300 rpm shrieks like a GT3 and the performance is noticeable.

The IPD Plenum further eliminated any remaining flat spots and helped a little more on the top end.

All K&N and IPD Plenum dyno's benefit most between 4500-6500 rpm, but the pull to 7000 is

that much more sweeter.

So, since I am happy with my top end pull I was seriously considering adding the x51 headers to my 997 C4S for even better air flow.

The X51 headers have larger diameter primary pipes, so what exactly does that do and how does it benefit or change the power curve delivery?

"The stock 997S headers have ø 42mm tubes. Both the 997S X51 and 996 GT3 headers have ø 48mm tubes."

This article may be old news for most of ya, but still beneficial to those looking into headers now.

I Also realize this article is not Porsche specific, but the science and results should be the same for all cars.

full article is here: http://www.carcraft....sics/index.html

some interesting key points.

"As engine speed increases, so does flow rate. Then, as restrictions increase, velocity slows again, reducing power accordingly. Interestingly, camshaft design, compression ratio, ignition-spark timing, and piston displacement affect all this if an accompanying improvement in the exhaust system isn't included with such changes. In fact, these types of modifications can cause exhaust problems to occur sooner in the rpm range.On the other hand, exhaust systems can be too big for engine packages that don't produce sufficient exhaust-flow volume to necessitate size increase. So we're back to the flow-velocity issue. Sizing of system components, such as headers, can be keyed to engine speed and piston displacement. We'll show you how this is done later in the story.

Graph A illustrates how merely changing pipe diameter affects an engine's output. Note that the smallest diameter creates good midrange torque yet falls off at the top, while the larger primary header pipes add more high-rpm power at the expense of low-speed torque.

Primary pipe length can also skew an engine's power curve based on length changes. Primary-pipe diameter establishes the peak torque point, so changing the pipe length will rock the output curve by pivoting it around that peak torque point. Graph B shows how longer tubes tend to increase power below peak torque while hurting power above peak torque. Shorter tubes tend to affect the engine in exactly the opposite way, hurting midrange torque in favor of increasing top-end power.

Primary pipe diameter plays a big part in determining the torque curve. A pipe that is too small creates peak exhaust-gas velocity too early in the rpm curve and will limit top end horsepower. Pipes too large lose low rpm torque and create peaky output curves.

So, million dollar question???.. Sacrifice low end torque (majority of city driving), for more top end??? which would you perfer? hmmmmm

post-5327-0-96079100-1306358836_thumb.jp

post-5327-0-05004100-1306358848_thumb.jp

post-5327-0-00449900-1306361625_thumb.jp

Edited by qikqbn
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Thanks for posting the article , very interesting indeed. The article makes comment on displacement and restrictions in the engine / exhaust , but the X51 headers are used on a gas flowed head and in conjunction with different cams , as a result the effects of fitting on a standard engine are not guaranteed or indeed matched to the current state of tune in your vehicle. Having experimented with different de catted standard manifolds on a 987 of differing designs (3 into 1 collectors with longer primaries and larger diameter versus shorter unequel branch with smaller primaries) I didnt see significant differences in dyno plots between the two designs , despite a difference of 4mm on the primaries diameter. What does seem evident is that removing restrictions , such as catalysts , seems to reduce power mid range whilst allowing more power top end and for a sustained period (ie not such a sharp drop off in power to the red line) . The article gives an insight into header design but its a fact that the 2.7 and 3.4 cayman use identical headers despite differing engine capacities and valve sizes. This to me suggest the differences in primaries and the design is possibly less significant in smaller engines such as the 3.8 and 3.4 porsche than larger 6 and 8 L V8's on which the article is based. Personally I would leave manifold tuning alone and save the cash on fitting X51 headers for aftermarket items from a known supplier like supersprint. Unless you have already fitted a GT3 throttle body , this may be a more beneficial upgrade than fitting the manifolds , as it improves mid range torque and top end power. On a 3.4 cayman with smaller capacity engine the gains from upsizing the throttle body from 75 to 82 are close to 25 hp , for a larger capacity engine such as a 3.8 I would expect similar if not better gains.

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Great article Bill. Really interesting..

As I go through my life with Porsches I realize that most engine mods are a complete waste of money. There are some...Like your K & N intake that do make a difference. But not many. We men (at least me) are like children.. We fall for the afternarket BS like naive school boys.. Unfortunetly most aftermarket stuff is garbage and should never go on your car. I think that Vivid Racing is probably the biggest culprit.:censored:

I think the next time I want to "bolt something on" I will just "take something off" (that's already there) and put it back on again. Maybe that will quench my thirst for not "leaving well enough alone".

Or maybe I should do what I did when I was a little boy and just get lots of cool "stickers" :clapping:

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Great article Bill. Really interesting..

As I go through my life with Porsches I realize that most engine mods are a complete waste of money. There are some...Like your K & N intake that do make a difference. But not many. We men (at least me) are like children.. We fall for the afternarket BS like naive school boys.. Unfortunetly most aftermarket stuff is garbage and should never go on your car. I think that Vivid Racing is probably the biggest culprit.:censored:

I think the next time I want to "bolt something on" I will just "take something off" (that's already there) and put it back on again. Maybe that will quench my thirst for not "leaving well enough alone".

Or maybe I should do what I did when I was a little boy and just get lots of cool "stickers" :clapping:

I LOVE stickers ! :jump: LOL . I hear stickers are good for 10 more hp. Phillip, Turbo's like yours are much easier to squeeze more power out of,

and when i had a turbo (mitsubishi) I was like a kid in a candy store buying every upgrade possible. I did see major gains in power, but I also

inherited major frustration from all the little things that started going wrong too. Seemed like I was always fixing or adjusting boost problems like little

leaks or vacuum lines popping off all the aftermarket stuff. I feel your pain. You still have an awesome beast with or without the upgrades.

bert987 ... interesting info, I did not know 2.7 and 3.4 use same headers on cayman's.. Wow, larger throttle body.... hmmmm Is there programming involved?

One other thing that stood out from the article and also stood out from a gold meister tech I talked to at Porsche is this...

The article and tech confirmed that basically the headers are a part of a system designed by porsche as a unit.

Headers alone will not necessarily give you the results you want. They may shift when and where your peak torque hits,

but the hp may not be what you expect. So basically consider the entire system and not just single upgrades or parts...

now, about that throttle body... ;)

Edited by qikqbn
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Great article Bill. Really interesting..

As I go through my life with Porsches I realize that most engine mods are a complete waste of money. There are some...Like your K & N intake that do make a difference. But not many. We men (at least me) are like children.. We fall for the afternarket BS like naive school boys.. Unfortunetly most aftermarket stuff is garbage and should never go on your car. I think that Vivid Racing is probably the biggest culprit.:censored:

I think the next time I want to "bolt something on" I will just "take something off" (that's already there) and put it back on again. Maybe that will quench my thirst for not "leaving well enough alone".

Or maybe I should do what I did when I was a little boy and just get lots of cool "stickers" :clapping:

I LOVE stickers ! :jump: LOL . I hear stickers are good for 10 more hp. Phillip, Turbo's like yours are much easier to squeeze more power out of,

and when i had a turbo (mitsubishi) I was like a kid in a candy store buying every upgrade possible. I did see major gains in power, but I also

inherited major frustration from all the little things that started going wrong too. Seemed like I was always fixing or adjusting boost problems like little

leaks or vacuum lines popping off all the aftermarket stuff. I feel your pain. You still have an awesome beast with or without the upgrades.

bert987 ... interesting info, I did not know 2.7 and 3.4 use same headers on cayman's.. Wow, larger throttle body.... hmmmm Is there programming involved?

One other thing that stood out from the article and also stood out from a gold meister tech I talked to at Porsche is this...

The article and tech confirmed that basically the headers are a part of a system designed by porsche as a unit.

Headers alone will not necessarily give you the results you want. They may shift when and where your peak torque hits,

but the hp may not be what you expect. So basically consider the entire system and not just single upgrades or parts...

now, about that throttle body... ;)

Having done both manifold experiments and also throttle body upgrades , I know from dyno plots that the throttle body gives real world Hp figures that can actually be felt and used on the road. Personally i dont fall for the marketing hype or the price tag that suggests something is worthwhile because its expensive. The TB upgrade on my own car achieved between 8 and 12hp gains with more results mid range than at peak power. Torque also increased by a significant amount . The mod has been verified by at least one other and suggested to be more worthwhile than manifold and ECU tuning put together...Its certainly worth a try , particularly if you can source a used throttle body and plenum , rather than paying new prices. In terms of value for money its an outright winner , direct bolt on (though you will need silicone reducers to fit the GT3 plenum to a 997 3.8 manifold and requires no ECU retune, the car does this compensation all by itself.

From my own experience I would suggest the X51 manifold design is more likely to give a sporty sound than the 3 into 1 design of the standard item , and may well be more to improve the customer satisfaction than any significant improvement in Hp. If you look at any "performance" manifold its usually equal branch and a common collector rather than a branch design which to me suggests the increase in bore of the X51 is to give a deeper sound and compensate for the losses of the branch design. I've also found the branch rather than equal length design gives a more sporty sound as there is more occasion to hear sound collision in the manifold (ie crackles pops etc). I fully agree that the exhaust should be considered as a system rather than looking to improve it piece meal , particularly if performance gains are desired.

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