Jak63AMG

Hi guys, I just took my car to dyno after installing straight pipes for both secondary cats and resonators. The gain is pretty good at +18 WHP and +16 RWTQ. I was expecting some power loss at low rpm but there was none.

_AMG_

Nice gains!!
I had this same setup before switching over to the X pipe. Didnt notice any difference in power when switching over to the X. The sound just got alot smoother especially around 3-3.5k rpm.
The straight pipe setup sounds great though, very loud!!

Jak63AMG

Thanks, it is very LOUD, sometimes it makes me hesitate to floor the throttle at public roads

tbal

Wheres the sound clip! Wow thats some good gains from just a res delete, if they are anything like the e55/e63 ones they weigh a good amount too...

olszowa12

That's some nice gains. I wonder if there are any gains with just the secondary cats deleted.

MB_Forever

Good gains.... I was expecting maybe 8 to 10 rwhp gain from removing the secondary cats, but this is even better

Sincity

Nice gains! Can you feel the difference? I thought max 8 WHP. Must be very loud since the resonators are also removed. Drone?

AMS Performance

The reason for this is the 63 AMG 2nd cats are not actually 2.75" diameter... if you look closely, at the entry & exit of the cats they are crimped down to 2.35" OD (roughly 2.25" ID). For this reason, even those the stock piping is 2.75" in reality, its only 2.25" until you eliminate both the primaries & secondary cats. The primaries also crimp down to 2.25" at the exits as well before they expand out to 2.75".

An X-pipe will probably give you slightly more low end torque and a bit more scavenging, but you are probably only talking another 2HP/TQ so its not anything you can really feel by seat of the pants, but it does help smoothen out the tone quite a bit.

You can get almost similar results with high flow 2nd cats, you will probably drop by about 2-3HP, but again, not bad for such a simple effective mod. This plus high flow air filters & charcoal delete is almost 30 crank HP. Gotta love these big block AMGs

Sincity

^ I thought our pipes are 2.5"?

AMS Performance

Technically, the diameters are constantly fluctuating. They go from 2.35" OD to 2.8" OD depending on where you are in the exhaust system. Unfortunately they are not consistent. Some of the 63s have 2.76-2.8"OD, others slightly smaller. ML63 for example does have 2.8" diameter, but the primary downtube from the headers is only 2.0" OD, and the exit to the primaries is 2.35" OD (2.25" ID). Same is true of the 2nd cats on the ML63 (2.25" ID).

It may not sound like much, but as diameter increases the cross-sectional area increases exponentially. Its hard to understand what significant jump that is, but I will try to explain it in simple terms. If you go from 2.25" to 2.75", although that is only a 0.5" increase, the entire cross-sectional area has increase by exactly 50%.

Apply this to headers, the Kleemann 63 headers for example have an exit flange of 2.6" ID, compared to the stock 1.85" ID. This increase of roughly 0.75" increases the cross-sectional area by a whipping 97%. Although this does not mean flow will necessarily increase by 97%!! This does illustrate just how much restriction is removed and why headers do so much on the 63s when compared to earlier 55s. In addition, the 63 ports are massive compared to the tiny M113 V8s, probably by a good 70%+ (again same principle applies).

But I digress ... anyways, just thought I would share that to better explain why the gains were higher than most expected.

Jak63AMG

I haven't push the car really hard after the installation so can't tell the difference yet. As for drone, I don't notice any, at idle it sounds almost like stock but past 2500 rpm the bark is more pronounced than stock.

Sincity

AMS: That is great info. Thanks!

Jak: Tks.

SonnyakaPig

+1

I also wanted to add that I find it interesting that AMG uses h-pipes in their resonator.

I noticed that the SLS also has an h-pipe.

Are h-pipes more for sound than performance?

_AMG_

+1

Nicely said!!
Its kinda like they squished and slightly bent the pipe up so it makes it over the cross member.

AMS Performance

Yes AMG, very similar to that. Benz does that quite a bit for manufacturing & packaging purposes. Also, 2.75" is not an industry standard cat size where as 2.25 & 2.5 are. For some reason they chose to squeeze a 2.25" inlet/oulet cat on a 2.75" system (again probably to save space & money).

You can still get amazing power out of the stock system if you just know which key bottlenecks to address.

If I am not mistake I think the inlet to the OEM catback may also be crimped on some models so that could be another key area to address. Best thing to do is just buy a set of digital calipers, lift the car up on a rack, then go through the entire exhaust looking for any bottlenecks. Subtract roughly 0.1" from the OD to get to the ID and you can get an idea of the flow rates you are dealing with. Its really not that hard to figure out once you use a bit of common sense and basic understanding of the forces involved.

I wouldn't be surprised if you could pick up an easy 30-40HP @ crank just by upgrading all the restrictions in the stock system (and that's on stock exhaust manifolds). I have mentioned many of the bottlenecks, but there could be a few more I overlooked.

The biggest restriction ultimately is the 2.0" Primary downtube leading into the stock cat, but even with that ... if you were to open up the rest of the system to a TRUE 2.75" you would make plenty of power without sacrificing any torque.

Just don't go 3.0", that becomes too big of a jump on stock manifolds. Long Tubes .... that's a different story

Sincity

When Gintani posted their exhaust and headers, they showed a pic of the stock exhaust that is crimped/flatten at an elbow. I want to say it is between the resonator and muffler.....but don't remember exactly.

I can't believe AMG/MBZ would do something like this. Afterall, this is a "specialty" car.

Even Money

You're correct, just after the resonator.

AMS Performance

You have to understand things from their perspective ... manufacturers are looking at every place humanly possible to save money. If you have to spend $1000 more per car putting the highest quality exhaust system ... then multiply that by 1000 cars, that's $1mill in revenues they just lost. Every little bit counts therefore they dive into their parts bins and see what they can put together last minute and just "make it work". Furthermore, they were already trying to sandbag the C63 a bunch anyways, so why try to make power, if anything they tried to weight the car down and detune it as much as possible.


With that said, I have also received questions on PLM headers vs. Kleemann headers and the two are not the same although people claim they make similar results (untrue).

The PLMs have an increase cross-sectional area increase of only 17% at the almost stock sized exit flange, where as the Kleemans have 97% increase (plus a high flow cat). So if PLMs make 15HP/TQ as dyno proven, and high flow primaries can add an extra 10-15hp easy, then It would not be a stretch to assume that 25-35HP @ crank claim is reasonable. It won't give you the same as long tubes (50+) but it will give you a happy medium between the two extremes. In summary, unlike the M113s that preceded it, its kind of pointless to get direct bolt ons on the 63s, best go mid tubes (log or tubular) or long tubes.

2cents,
AMS

elijah

Thanks AMS for all the great info

Sincity

Thanks again, AMS. Your contribution to this thread has been very beneficial.

Jak63AMG

AMS, your information is highly appreciated

DD GT3 RD

I am very interested in this.

Since you had the tune before deleting the 2nd cats and resonator, im assuming your tune didnt turn off the cel light that would come on from the o2 censors?

Has a cell light come on now?

Does anyone know if the cell light would come on just from deleting the Secondary cats?

Jak63AMG

It will come on when you delete your primaries but some tune can by pass that. For secondary cats there are no o2 sensors so there will be no CEL light at all.

DD GT3 RD

Ohhhh I like this

also the 2nd cats and resonators are on the stock mid pipes correct? so does an after-market mid pipe just replace this? Anyone know the cheapest one?

Jak63AMG

Any reputable exhaust shop can do this.