SM_ATL

I am thinking about adding a few more hp to my 991S and had already tried headers and sportcats on my previous 991, so I thought I would study X-pipe center muffler bypasses.

Fabspeed and Agency Power offer products that look pretty similar. Fabspeed is a bit more expensive ($1,595 vs $1,295) and a little more heavy (claims to reduce the car weight by 7.45 lbs vs "about" 20 lbs for Agency Power) but looks better finished -as always with Fabspeed products, they just look perfect-.

Fabspeed Xpipe muffler:


Agency Power Xpipe muffler:


At this point, there is not much to discriminate one product from the other (one seems better finished but is a bit heavier and costly...) and sound clips on the internet are not reliable enough to form an opinion on the acoustic merits of each products.

Both manufacturers have been kind enough to publish dyno curves for their product (with only the Xpipe muffler in place, not sure though if the reference is the standard exhaust or the PSE in both cases). I spent a little bit of time digitizing the power curves:



and looking at the hp improvement at different rpm's



This is where to comparison becomes a little more difficult. I know very well that dyno data has to be taken with a (BIG) grain of salt, but the Agency Power hp gain seems too good to be true around 4,000 rpm. Around 5,000 rpm and above, I would say that there is again no significant difference between the two products.

In both cases, you will not see a very significant peak hp improvement, but the gain you can observe from 3,000 to 6,500 rpm is probably well noticeable when you drive (on average +29 hp for Agency Power, +16 hp for Fabspeed). I know that I should have digitized the torque curve and rather talk about the gain in ft.lbs, but I was too lazy

So what conclusion should I draw:
-$1,300 to $1,600 is not a huge amount of money if the gain (let's say in hp) actually ranges from +16hp to +29hp. This seems in fact to be a good bang for the buck if you compare what you would get from other mods: X51($$$!!! -OK, not the same philosophy and more hp), tune (not available yet, but probably less impact and more potential warranty issues), etc.
-Somehow the Agency Power product seems too good to be true: more than a 50hp gain at 4,000rpm, 12+ lbs lighter and $300 cheaper...
-I am very tempted to give it a try BUT I would lose the on/off functionality of the PSE that I like a lot, especially when I cruise over very long distance and that I have my 991 in 'GT' mode, all soft and cushy and sipping a minimum amount of gas On the track, there is no doubt that I would be happy with the mod.

I'll sleep on it for a while and maybe contact the vendors to get more direct feedback.

If forum members have had experience with these products (or similar products on 997's or others), please chime in!

paver

Look at Supersprint exhaust systems. I don't know if they even offer anything for a 991, but they are highly regarded and their systems are said to truly deliver the gains they report. I looked hard at a system for my GT3 and everyone I talked to confirmed their quality. In the end, I didn't buy any system only because I didn't need to spend the money but would have definitely gone w/Supersprint.

paver

you may want to look at M&M too. Race Parts Warehouse sells it. The owner Eddie is a good guy. He stands behind what he sells.

http://racepartswarehouse.net/index....product_id=120

rijowysock

the fabspeed one is an error:

fabspeed eliminates side cans, making S and base exhaust basically the same (no side cans)

the other one keeps the side cans (notice 4 outlets and 2 inlets)... so you're only eliminating the middle muffler basically and keeping side cans


they will have totally different sounds as one is eliminating both middle muffler and sides and using those resonators to reduce sound/drone.

the other is just a center bypass....


i hope this makes sense... thats why the diff shape... i talked with several companies when the 991 came out and had the idea of making a universal center muffler since the base and s are totally different.. if you made an exhaust that eliminated the side cans you could then come off the cats and make it work on both cars, hence half the investment cost... and double the customers..


hope this helped!

the fabspeed would eliminate side cans, meaning 40+ lbs lost there and 7.45 on the center.. i emailed them about this error in the past..



the fabspeed would be louder and more pops and burbles...

the other would just be a little deeper.. not much more pops and burbles over the stock S exhaust that already does that...






i would go fabspeed, great quality but also tons of weight savings and downshifts would sound amazing.

SM_ATL

Thanks for the advice. I'll check both references your provided.

Thanks, good catch on the Fabspeed pic (I just posted without checking...).

One thing I am asking myself is whether these aftermarket exhausts provide some torque/hp gain compared to the PSE (I have it on my car). Porsche does not claim any performance improvement for its sport exhaust but mentions "reduces backpressure for a sporty sound and improved torque curve" in its official Service Information manual.

Ideally, I would like a system that would provide some power gain (I would be fine with 15-20 hp & ft.lbs) and that would be valved with a 'quiet' mode that could be as loud as the PSE when ON and could be MUCH louder in 'loud' mode.
The icing on the cake would be that the valves would still be controlled by the PSE switch... Weight reduction is not a major priority.

Maybe I would go back to the Fabspeed headers I had on my first 991. Not the same thing of course, but they provided a bit more sound in both 'quiet' and 'sport' mode with the PSE and (a little bit) better throttle response.

Thanks for your help... or other suggestions!

LotF

Don't mess with it. Leave it stock. The engine management computer is in control. Unless the car can be reprogrammed, you are limited to the stock control settings. There is no replacement for displacement. What you want is a bigger motor.

RCMA991

This looks like an option. Though more than an x pipe, Akropovic makes great stuff. Like the open and closed valve feature

http://www.akrapovic.com/en/Automoti...ProductFilter=

SM_ATL

You are right about the engine, I do not want to mess with it. Maybe when a truly reputable tuner will have worked on it and after several months of positive feedbacks from other guinea pigs/users. I am not so concerned about a bolt on exhaust mod though. I am not looking for a big change, and the 991S is plenty fast. I would not trade it for anything else (except of course for a 991 GT3 ). I just want to make it feel/sound a bit more raw in 'sport' mode and keep it nice and docile for commuting or cruising on the interstate.

Thanks, I will check this further. Akrapovic makes great exhaust. I have also been impressed by video's of IPE's exhaust for the 991 but have not seen much feedback or details online...

rijowysock

unfortunately having all of that would be impossible.


the bypass will lose low end tq and gain high end... if u have a manual you will notice low end loss because speed bumps you could "coast" over in 2nd will need 1st...

you cant have loud and quiet unless pse and then the loud isnt that loud...

rijowysock

stock ecu will account for the better air flow and adjust, hence why it has sensors... most systems can account for a certain amount of change and diff fuel.. but after a certain point you need a tune to get the most out of the system.

Supersprint-Evolve

Thanks

Supersprint has developed an exhaust system for the new Porsche Carrera S 991 3.8.

The car used for the development was fitted with the optional Porsche Performance exhaust, which has a sportier sound and is equipped with bypass valves that allow a quite louder sound once open.
As you guys know, the opening/closing job is managed by the onboard electronics based on the driving style (revs and throttle) and the car setup (normal, sport, sport plus), but it's also possible to bypass this control and force them open with the exhaust button on the dashboard.

On cars not equipped with the optional sport exhaust this button is not found on the dash, unless fitted afterwards. The bypass valves are instead found on the normal exhaust system, but it's not possible to force them open. The open valve mode is also quiet than the same mode with the sport system.

The prototype built by Supersprint it's also fitted with bypass valve, compatible with the OEM management system. The target to reach was to keep a sufficient level of comfort with the valve closed, for long journeys and downtown driving, but make the open mode sound extremely aggressive and ultra-sporty.



We choose a set of 90mm, thin lips round tail pes, slash cut in a way that they follow the line of the bumper and are perfectly integrated in the shape of the car:

It's possible to order the tail pipes in the usual chrome finish but also in matt black or satin silver.





Anything you need to know, just drop me a PM or email me at paul@supersprint-evolve.com

YellowPMan

No exhaust is going to give u the quoted bhp at the wheel without an ecu upgrade...if claiming 29bhp you may get 3-7 bhp at the wheel...total waste of money without ECU re-map. Even in the supersprint post above ..no claims of huge bhp gains..just a great sound !!

Supersprint-Evolve

I'm keen to highlight that Supersprint will give out the quoted figures - they have their in-house Maha dyno and publish all their figures (the cars are not ECU tuned when being tested). They have a reputation for accurate, if conservative, results.

YellowPMan

Is that at the wheel or crank?

handful

This is very true. Many years ago I purchased a cat back exhaust from Dinan for my E46 M3 and the cat back included an ecu flash, otherwise the fuel to air ratio gets thown off. If I remember correctly, Dinan quoted a +10 increase in HP and few pounds increase in torque.