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Time for another GMS "review"!

I have a very unique use profile and installation. I have gone through 2 after market "mufflers" and had the OEM Race exhaust originally. The first exhaust I had was the one of the Magnaflow Center Exhaust. I also HATED that exhaust, as it created horrible nasty harmonics in my Coupe and my wife REFUSED to ride in the car with it installed. The worst harmonics was at 3000 rpm or so... To try and keep the wife happy, I moved to a "Valved" exhaust from Capristo. It is a 2.5inch Cat Back exhaust, so it replaced the midpipe with a larger diameter. It provided me the best of both worlds, quiet when I wanted it, and louder when I didn't. The negatives of the exhaust is that it is HEAVY and Expensive, but it is made and has functioned well for 3+ years. The other major negative is that it does REQUIRE you to cut a portion of the bumper to fit (more on that later).

The purpose of moving to the GMS exhaust was primarily 2 fold. First, higher flow catalyst and Second, improved heat removal. One option would have been to buy the Capristo catalyst, which is roughly $2000. However, the capristo uses the same form factor as the OEM with the crazy 90 degree bend at the turbo exit. I liked the GMS version from an engineering perspective better and wasn't THAT much more expensive, plus I could wrap the exhaust to provide some additional decrease in thermal loads. You can read the installation notes in my previous posts, but I was able to get it installed. I ONLY purchased the Turbo Outlet tube, Cat, midpipe and Akrapovic adapter. As I noted before, I had to cut a portion of bumper to fit the Capristo, so I couldn't go with the GMS muffler/exhaust portion. I contracted to a custom fabricator to interconnect the Capristo exhaust with the GMS exhaust piping. It wasn't cheap, and it is a very VERY tight fit, but they were able to get everything connected. It did require cutting the GMS midpipe slightly to get better alignment and the adapter to get to the proper 2.5" pipe size.

I have now had the car for about a week and spent about 2 hours driving the car in street use, and a full track weekend. I am running with the STOCK ECU, and the original oxygen sensors. I was worried that there could be an issue with the GMS exhaust causing a CEL with the OEM ECU, but I have yet to experience that. I really really like the combination of the GMS and Capristo exhaust. On the street, the larger exhaust (mainly high flow cat) will tend to tame the massive boost and kick you get when the turbo spools up at lower RPM. Yes, it isn't as "quick" or "physical" off the line, but a much smoother application of power. On track is really where the high flow cat shines, IMHO. The boost pressure seems to build MUCH quicker (based on the digital display), and I found that my shift memory was off about a fraction of a second. I basically had to shift slightly before the yellow RPM blinked on the dash. If I didn't I'd hit the rev limiter on the engine. I also felt the engine KEEP pulling all the way to "red line". On track I don't appear to accelerate any faster (based on preliminary GPS speed traces on my VBOX), but things feel more linear to power input. Overall my lap times were MUCH better than previous times, but that is mostly due to far deeper braking, much higher speeds through some high speed sweepers (larger rear tires and bigger balls), and simply pushing the car closer to its true limits.

Now sound is very subjective, and I don't feel the GMS exhaust should be installed for SOUND reasons. This is a performance upgrade, not acoustic. If you are on track, then it is a good solid upgrade. I'll get some video's uploaded with sound at some point... My Capristo manual control doesn't seem to be working, as I can't swap between "Full Open", "Performance" and "Quiet" modes. I think when I moved the ground & antenna wires around, it made the antenna much less sensitive.

The weather was quite cool, so I haven't been able to corelate between previous runs and this one to see if temperatures have come down any.... Will update when I have time
 

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OK. I make a before/after Video.
I think in 2 or 3 weeks....at the moment it is too cold in my garage.
It is Stelvio Weather......
View attachment 114161
It would be great if you bothered measuring sound pressure. Exact absolute level is not very easy to obtain, but if you use an dab(Edit: dB, not DAB) app on your phone, with the phone and car placed exactly the same place, rotation etc., it should be possible to see if it’s for example +2.5dB louder than OEM. Measuring outside in a large open outside area would be beneficial. Audio measurements requires surprisingly high accuracy to get properly valid results.

Did I mention I have an Akra, and considering the same order?:)
 

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Discussion Starter #368
And this one is off to USA.

http://instagr.am/p/CLJ9IK9lNIE/
Now with orders covered and 1 extra set made for stock, we can continue with development of revised GMS 3" dual center out - resonated. Now featuring oval rear silencer with single in dual out and Y-pipe split section in the silencer. This will allow us to run optional dB killer inserts that we are developing as well.
 

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2017 4C Rosso Forte 8/20
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Today I have change the Stock/Akrapovic to GMS/Akrapovic.

Before:

After:

The sound is louder and deeper.
If you drive the sound stay loud and deep.
With stock exhaust the sound was gone over 3000RPM.
The engine climbs to higher rpm very very very fast and very very very easy.

The best upgrade I have do for the 4C-Engine.
On 20.03. the Trackday-Season is starting here.
So I can see the result on the clock.

@Rudi.
I think the Adapter to the Akrapovic can be 1.0cm or 1.5cm longer.

AlfaDevil
 

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Today I have change the Stock/Akrapovic to GMS/Akrapovic.

Before:

After:

The sound is louder and deeper.
If you drive the sound stay loud and deep.
With stock exhaust the sound was gone over 3000RPM.
The engine climbs to higher rpm very very very fast and very very very easy.

The best upgrade I have do for the 4C-Engine.
On 20.03. the Trackday-Season is starting here.
So I can see the result on the clock.

@Rudi.
I think the Adapter to the Akrapovic can be 1.0cm or 1.5cm longer.

AlfaDevil
This is perfect thanks!
 
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