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Did you do the same research into the plenum and/or throttle body? Which specific ones are you looking into? I could definitely consider it now that you said sound. I'll be getting a pro-tune anyways, another 5whp can't hurt.
Doing your own labor is really key; I wish I had the space and the skills (honestly I could acquire the skills/tools, I'm an engineer by training but space in ny metro area is like unobtanium) - my shop though is usually reasonably priced thank God.
Yeah you're preaching to the choir I literally bought this car because Carreras went turbo
the throttle body I was referring to is a factory part but was corrected and the 991 already has the biggest one.
IPd is the only one that makes the plenum. I have a hookup on these if you’re interested, PM me.
Larger diameter exhaust and intake parts do not = more power. They often produce the opposite.
I don't like being the professor in threads like this so I would encourage people interested in mods to look up concepts like volumetric efficiency and cylinder filling. The wider the intake and exhaust ports and manifolds, the slower the intake and exhaust gasses flow, the less fuel/air and exhaust moves into and out of the combustion chamber, and the less power you make. In a NA engine, when it comes to intake gasses, you need not just capacity (diameter), but velocity. And you get velocity by constricting airflow, not enlarging it.
Think about putting your thumb over the end of a garden hose -- the water flows at a higher velocity as you reduce the diameter of the passage through which it flows. This is four-stroke engine 101 level stuff. Bolting up bigger headers or a bigger throttle body will usually not make power -- not unless the engine has design flaws or you've modified other parts of the engine so that bigger intake/exhaust becomes necessary. An engine is a system, and all the parts have to be designed to work with each other.
Turbos of course are a different story, and with them you can just dial up the boost and make huge power gains.
Larger diameter exhaust and intake parts do not = more power. They often produce the opposite.
I don't like being the professor in threads like this so I would encourage people interested in mods to look up concepts like volumetric efficiency and cylinder filling. The wider the intake and exhaust ports and manifolds, the slower the intake and exhaust gasses flow, the less fuel/air and exhaust moves into and out of the combustion chamber, and the less power you make. In a NA engine, when it comes to intake gasses, you need not just capacity (diameter), but velocity. And you get velocity by constricting airflow, not enlarging it.
Think about putting your thumb over the end of a garden hose -- the water flows at a higher velocity as you reduce the diameter of the passage through which it flows. This is four-stroke engine 101 level stuff. Bolting up bigger headers or a bigger throttle body will usually not make power -- not unless the engine has design flaws or you've modified other parts of the engine so that bigger intake/exhaust becomes necessary. An engine is a system, and all the parts have to be designed to work with each other.
Turbos of course are a different story, and with them you can just dial up the boost and make huge power gains.
While I agree with this in theory... and proved it with my last review; these headers did prove to make gains with no tuning at all. Largely the sport cat - which was never made for performance. Car drives noticeably better.
Larger diameter exhaust and intake parts do not = more power. They often produce the opposite.
I don't like being the professor in threads like this so I would encourage people interested in mods to look up concepts like volumetric efficiency and cylinder filling. The wider the intake and exhaust ports and manifolds, the slower the intake and exhaust gasses flow, the less fuel/air and exhaust moves into and out of the combustion chamber, and the less power you make. In a NA engine, when it comes to intake gasses, you need not just capacity (diameter), but velocity. And you get velocity by constricting airflow, not enlarging it.
Think about putting your thumb over the end of a garden hose -- the water flows at a higher velocity as you reduce the diameter of the passage through which it flows. This is four-stroke engine 101 level stuff. Bolting up bigger headers or a bigger throttle body will usually not make power -- not unless the engine has design flaws or you've modified other parts of the engine so that bigger intake/exhaust becomes necessary. An engine is a system, and all the parts have to be designed to work with each other.
Turbos of course are a different story, and with them you can just dial up the boost and make huge power gains.
Good post, and many very valid points. I think it also proves how good the OEM stuff is from the perspective of the parts working in efficient harmony with one another.
That isn't to say it cannot be improved, but for the best experience a full and complete package might be the best way to do...and most costly.
Larger diameter exhaust and intake parts do not = more power. They often produce the opposite.
I don't like being the professor in threads like this so I would encourage people interested in mods to look up concepts like volumetric efficiency and cylinder filling. The wider the intake and exhaust ports and manifolds, the slower the intake and exhaust gasses flow, the less fuel/air and exhaust moves into and out of the combustion chamber, and the less power you make. In a NA engine, when it comes to intake gasses, you need not just capacity (diameter), but velocity. And you get velocity by constricting airflow, not enlarging it.
Think about putting your thumb over the end of a garden hose -- the water flows at a higher velocity as you reduce the diameter of the passage through which it flows. This is four-stroke engine 101 level stuff. Bolting up bigger headers or a bigger throttle body will usually not make power -- not unless the engine has design flaws or you've modified other parts of the engine so that bigger intake/exhaust becomes necessary. An engine is a system, and all the parts have to be designed to work with each other.
Turbos of course are a different story, and with them you can just dial up the boost and make huge power gains.
What you say has a certain element of truth but is not always true in all cases. Especially when an OEM is not only concerned with ultimate performance, but also longevity, sound quality, emissions, differing fuel quality, different climates of operation, differing levels of maintenance, etc. Yes the engines are a system, but they are also a study in compromises.
Good stuff. I have a 991S X51, I am interested if sports cats/headers and/or an IPD plenum would have similar benefits on my car. I am not sure what is left in the X51/GTS cars but I assume a good set of headers might make a difference.
Good stuff. I have a 991S X51, I am interested if sports cats/headers and/or an IPD plenum would have similar benefits on my car. I am not sure what is left in the X51/GTS cars but I assume a good set of headers might make a difference.
A plenum is not compatible with your car but headers would have a good benefit!
@R-Rated. I'm in the process of installing the same FVD headers in my 99.1 S and I found your posting very interesting. A big thanks for sharing.
I know this thread is old and you probably do not remember but just in case... As you lightly touch it, the increased diameter of the exhaust tubes greatly reduces the access to some of the E12 Torx bolts for the flange to head. I'm really struggling to get the Torx tool to get into the bolt head. Do you remember if you used a special E12 Torx tool or anything that did the trick for you?
I'm thinking about replacing the original Torx bolts by stainless steel Hex socket ones and use a long Allen socket. This should work better with the limited clearance. As you noted, the FVD flange is significantly thicket (8mm more) than the original one (2 mm) so the new bolts will account for this.
Any help is very welcome and appreciated.
These headers together with the tune make a big difference on the car’s overall behavior. The car is a lot smoother when starting from a stop and the additional torque at mid and high revs is clearly there. Completely change how driving the car feels. I (and my neighbors) also like that the exhaust noise still very civilized even if slightly improved.
Having said that the benefits of the particular design (very short runners) of the headers are as great as the pain to install them if you do not have this specific tool of similar. Also, unlike the factory headers, the exhaust-side flange does not come with the three welded bolts. So, unlike what the instructions state, you need Grade 8:
4 x M8-1.25x40mm Bolts
2 x M8-1.25x30mm Bolts
6 x M8-1.25 Locking Nuts
12 x M8 Flat Washers
To bolt the new header to the exhaust. That’s a problem if you discover this once you are taking apart the car.
Last, FVD should provide a real documentation specific to these headers and for the car model. Currently, there is a single page generic documentation that is basically useless. Considering the greatness of these headers and the price tag, there is definitely room for improvement for the documentation. You need a very narrow TORX E12 socket with a very short universal join. Standard TORX E12 sockets will not work for at least 2 of the bolts.
Last edited by Chuck245; 09-16-2024 at 03:38 PM.
Reason: additional info
Cliff's Notes on 911 exhausts: the only power to be gained with aftermarket headers is on the 1975-1994 911's, which didn't use headers, but unequal length manifolds. You can't improve on the early headers. You can't improve on the 993 headers. And you really can't improve on the 991's. These are all equal-length designs. You can use aftermarket headers to move the power curve around the RPM range a tiny bit, but it's so minuscule I don't really understand why anyone bothers.
With all due respect you have clue what you're talking about. If that was the case why would race cars (Porsche) change the headers then? Overall circumference, length, design, weight, etc. makes all the difference when it comes to power delivery. The restriction of gas flow when exhausted from the motor on stock headers compared to aftermarket is worlds apart. These cars exhaust are so restricted it's crazy they even run! When you open that flow up it makes a major difference. I certainly felt it with. my C2S when I put my SOUL (200 cats) headers and valved exhaust on mine. The mid-range punch was considerably noticeable! Then the Softronic tune made it even better. When I run stock 991's I pull them like nothing. Cut open a muffler on one of these things and you'll see what I'm talking about. Thats why they sound like a vacuum cleaner!
03-04-2018 | 06:15 PM
