ATKM5

Ok, so I did a search and found that by deleting the primary cats, relocating the O2 sensor to behind the secondary cats will give me about 10 whp. And as far as I understand, removing the resonator and replacing it with straight pipes will yield no gains.

My question is though, will my car get much louder if I remove the primary cats and put a straightpipe instead of the resonator???

Thanks in advance... This is going to be my first mod.

chiromikey

the only way your car will get significantly louder is to replace the rear mufflers. everything else will only give a slightly noticable change in sound if any.

AKxSpyO

REsonator delete seem to make your car a little throatier. Not too much, but noticeable. Also saves you some weight.

Zod

Emmm primary cat removal, me want! But to scared to try
Damn check engine light!
If you do manage to be successful with relocating the O2 sensor behind the secondary cat please post picks
Hope it works out for you, as I have this mod in mind and 10 whp is very nice I think for basically removing something!

LazyE55

If you want LOUD than you could do a similiar setup as me.....I have the Eisenmann Race, removed the primary cats, secondary cats, and the resonators. I have the K2 programming with the cats delete so i dunt have the CEL lights. Overall the plus side is it sounds awesome! Down side is it smells like gas....doesn't bother me too much though

ATKM5

Thanks for all your help everybody. I'm actually thinking of removing the secondary cats and resonator now... I don't know what to do.

E55 RUSS

Man I told you before how to do it...it works just fine !!!

E55 RUSS

Thats what I have also but I kept resonators, to keep away drowning noise but I have HEADERs...I must say its sounds SICK

III II I I AMG

i already got the resenator delete with straight pipes, sounds pretty cool for now... and im going to replace the cats with sport cats like evosport or kleemann..almost the same as removing it

dyno

better result with Primary or Secondary cat delete?

I would prefer Secondary delete

first, no light problem (I suppose)

second, I understood this engine works better when the system is closed enough near the header, to allow exhaust flow maintaining its high speed and passing quickly the cat filter ..(for this purpose, even the pipe has a smaller diameter before the cat and enlarges after it)
this way helps also to avoid loosing of torque at low rpm (that, on the contrary, I think it would be extremely affected by using a Supersprint-like header instead of the stock)

if this idea is correct, bigger useless stoppage would be caused by secondary cats that are encountered when the flow has a reduced speed

unfortunately, I have not directly experienced the two options

of course, the above reasoning works till we prefer the overall MB feeling of class power. When an awe tuning is concerned, we need to open everything, put away all cats, etc.. but it will be no more MB feeling

E55 RUSS

Primary cats make extra 10 rwhp...

dyno

means about 2-2,5% gain

In my last dynoed experience, but with a smaller NA V8 engine, Cat delete + a slightly more open exhaust gave: from 300at crank, to 328hp =+9% .
Cat delete should count for most of it. Hence, Secondary cats must play a big role.

dyno

Hi,
just called an exhaust manufacturer ... cost for bolt-on bolt-off system INSTEAD OF SECOND. CATS would be fair .. about 200-300 euros.

I'm a bit scared because he said that will be louder, then check light will beam ...
I said him, don't worry, my lambda connectors are on primary cats only;
you make me a bolt-on system and If I don't like sound, I'll fit back my cats

What do you think Guys, for the Dealership will be enough saying that mod was because of hurting a stone or something ?


Indeed don't know wheather to believe or not: in my other V8 engine, the difference in sound was negligible when I tried to install back the original exhaust directly to pipes (instead of cats) .. moreover, there, I had 2 cats only, not 4!

chiromikey

bottom line...if you want power, removing the primary cat is what you should do. if you want sound, remove the rear mufflers.

dyno

therefore, what for Secondary?

chiromikey

i wouldn't spend the money if that's all you're going to do.

dyno

what else should I ?

my plan is to do Lsd and Ecu next on

phatmitzu

I understood it the other way around?
Removing the prim yet keeping the secondary yells more HP gain than keeping the prim and removing the second...

Rguy271

Ive been tempted to simply gut or remove my mufflers before. This car is too damn quiet.

E55 RUSS

Its all about flow...removing secodaries to much flow in the rear will loose you torques...

dyno

right,
this is the reason why we need some real evidence!

indeed my "understanding" grew after speaking with an exhaust producer that considers wrong the Supersp. system (perhaps because they are located close to each other... but maybe also because he learned something more while accomplishing some produce for Lorinser).

I think truth depends on our targeted "tuning range".
For sure, a 2-2,5% gain is unusually low

dyno

http://www.uucmotorwerks.com/html_pr...torquemyth.htm
"...The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture,
.... the reduction in backpressure is causing more air to be drawn into the combustion chamber than before.
....the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.-"

chiromikey

i won't comment on supersprints system but search for posts on my long tube headers and exhaust system. i've got no primary cats, high flow secondary cats, straight pipes to the rear mufflers (deleting the resonator) and i can assure you i have ZERO problems in regards to losing torque or backpressure.

dyno

ok, this means that theory from motorwerks works even for F/I engines

We should ask more to this guy:

https://mbworld.org/forums/showthrea...ts#post2377331
08-21-2007, 08:38 PM #26
ProjectC55
MBWorld Fanatic!
Join Date: Feb 2004
....Frank I noticed a very dramatic difference in hp just by replacing the secondary cats back. You're not gonna believe anyone unless you do it.