I finally pulled the trigger and bought the GT-Pro Downpipes with siamese X pipes. So everyone understands, my first goal was to wake the beast sound wise and hp/tq gains second.
Last Saturday, Jerry from Eurocharged came down south and I also got them to custom tune the car.
I dynoed the car to show the results. It was a dynojet and I have the dyno files if someone cares to look at them. All dynos were done on the same day.
GT-Pro treated me right and the fit of both items were right on. The only point of contention was the slip-on to attach the downpipe to the X pipe was not strong enough per the shop foreman. I had to splurge and get a $3.00 coupler that was welded to the X-pipe. The foreman then used to slip-on on top of the coupler. He felt the slip was not strong enough and overtime would cause a leak.
Here's a pic of the X pipe:


The first Dyno sheet attached is stock versus tune. gains are 48rwhp/17tq. Be aware that I had sent my ECU this year to Jerry for tuning so the results of 380hp stock does not mean I have a freak car . Jerry stated that the car did not have the time to adapt down (he flashed it back to stock Saturday for comparison purposes). Most other C63 seem to dyno at about 360 which is about an expected 20% loss so we could infer that his tune could be as big as 58rwhp or 72 at crank.


The second Dyno sheet is stock versus pipes. At max level, gains are 15rwhp/17tq. Interesting to note however that the gains at close to 4Krpm
are 30rwhp/22tq. I went for a quick ride and could feel a stronger pull at mid range. Comparing this to Fluid's pipes, the max increases are not as good, not sure if the design has anything to do with it. Super had also tested downpipes and found no gains so I am actually very happy to have picked up a bit of hp.


The last Dyno sheet is tune versus tune + pipes. gains are 13rwhp/17tq. Seems consistent with dyno sheet above. At close to 4K rpm, it seems the tune is working hard as the pipes do not show a gain as much as above.



The car now makes 441rwhp/398tq which would translates to 551hp or 100 more than stock. I am a happy camper .

Sound wise, it is like all others have stated. It is not for the faint of heart. The cold starts are scary. Under 2.5Krpm, the car is just like stock with no droning at all.
Above this, it barks really loud. My only issue is in between 2.5KRPM and 3KRPM, it sounds really rough. Above 3KRPM, the sound somehow changes and it sounds much louder but keeps the stock AMG DNA. I will look into Super's solution to mitigate this minor problem.

As a side note, you E55 guys are lucky. There were quite a few of you guys there and with headers, pulley, tune, intake, Jerry worked his magic and cars were pushing 560rwhp. Holly Crap .
An M6 was also there with ASR exhaust and he pulled 454rwhp/345tq. I went for a test drive and the SMG gearbox is a monster. Each gear change was brutal and the car was fish tailing and looking for traction even in third gear.
The top dog was a Renntech SL65 and it pulled close to 590rwhp.
Excuse the long email but I think it was worth it to demonstrate the gains that can be achieved with just a couple of $$ grands.

 

The car makes 441rwhp UNcorrected, post SAE graphs and use those to determine crank numbers with 18% DT loss not 20%.

How much did you spend total if you don't mind me asking? Seems like you got the noise of LT headers without the gains in HP and torque. There are tune only cars making more TQ, SAE on dynojets on 93 octane and within 5rwhp as well.

 

Great write-up!

I did pick up nearly 2 MPH at the track with catless down-pipes vs x-pipe only in nearly identical conditions. I reported my before and after dyno results were minimal due to much better conditions before.

Anyhow, I would love to see the SAE data. Do you happen to have the Dynojet runfiles?

Thanks again for taking the time to document this. Independent user data is king!

 

Not sure why SAE versus uncorrected matters. A stock car makes 451hp per the factory and has been tested on a dynojet many times at around 360rwhp which translates in 20% loss. 20% is at 361, 18% is at 370, immaterial difference.
I am comparing apples to apples which is uncorrected. The delta is what matters.
If you want to argue that I only gained 90hp versus 100hp, be my guest. I could care less.
I will not advertise the price I paid for the pipes but it is not even close to what Fluid advertises. I refuse to pay the MB tax.

 

Super,
Thanks for the kind words especially coming from the king of writeups.
I do have the files but do not know how to translate them.
I am happy to send them to you if you wish.

 

You can download the software directly from dynojet.com called WinPEP. It will allow you to view the runs in many different ways. I'll PM you my email address. I'd love to check out the files myself, I've got quite a collection of C63 dynos now.

 

Very nice write up and gains.

 

Looks like GT-Pro cleaned their unit up with less pieces/welds and a cleaner X section. Good job Brian!

Emeric: Great writeup. Always glad to get independent results and thanks for taking the time to do this.

 

It only matters if you actually want to know how much HP and TQ you're making. Uncorrected numbers mean nothing as far as "my car makes XX/XX" you can see a 30-50rwhp swing uncorrected vs SAE during different parts of the year. SAE correction smoothing set at 5 (to eliminate false spikes) is the industry standard for dynoing.

Also since the numbers will correct down (on both before/after pulls) the deltas will also be smaller. Obviously highly important when making a comparison right?

Again the 18% only means something if you care about accuracy, and let's face it, you're reporting numbers? From what I've seen most stock C63s with non P31 package put down 370-375rw SAE on a DJ on 93 octane in 5th gear. 360rw sounds more like a 91 number.

Anyway, glad you're happy with the car, but going off what's posted I would have rather gotten some LTs. Thanks for sharing.

 

RStevens63: Thanks for the clarification. I will download the S/W and post some SAE graphs.
I am in FL so I am running 93 Octane.
The reason behind not going to headers is costs. MBH headers installed will cost at least 4.5K and this was about a quarter of that.

 

Is this still true? I now have K2 (Kleeman exhaust manifolds and 200 cell primaries) and looking for a little more to get a little closer to LTs while passing our annual OBDII emissions and not sounding like LTs.

Could be because of the redesign. Super's was the original version. Yours has a smoother transition at the X.

Original version:


According to OrientBlue3, they are now made my Stillen.

 

I still have the issue around the 2K to 3K range where it sounds really rough. I recently compared it to someone with headers and he does not have that problem. He sounds louder at higher rpm.
Thanks for reviving the thread as I need to post uncorrected numbers.

 

Man...there is where I do most of my driving. I thought an x-pipe would smooth the sound out?

 

Really enjoyed your write up and learned a lot even though I am late to the party. Awesome gains and I too would be a happy camper. You really got your moneys worth....very nice and congrats...

 

just get some LTs and call it a day

like i have always said , dyno #s don't do justice until real world experiences are proven . find someone you have raced before the goodies and race them again to see the true gains .

congrats on your new found power

 

Opps....I thought you were just reviewing the X and I just realize you also have catless DPs. I wonder if your sound is a result of being catless?

 

I would agree that the sound issue is mostly because I am catless because the headers car I compared it to had one set of aftermarket cats.
I am still debating on adding the silencers but have not had time to do it yet.

 

Glad to see he's making a better quality product now and others do not have to experience what I had to with my X pipe.

 

Which version do you have? Supposedly, from what I read, the new "Siamese" version should yield a smoother sound since the gas flow does not cross-over. That is what I read in the net so take it for what it is worth.