After crawling underneath my SLK 55, I realized that one of the most inefficient aspects of the exhaust system is the factory connection to the secondary catalytic converters. The factory chose to go from 2.50 inch piping from the primary cats, then "squished" the pipes for ground clearance, then reduce the piping to 2.25 inches before heading into a choking 90 degree bend, then feeding into large ceramic substrate secondary cats (see pics).

What I decided to do is replace the large factory ceramic substrate secondary cats with 200-cell metallic substrate cats by ECT. The install includes using 2.50 inch stainless mandrel bent tubing from the primary cats all the way to the new secondary cats. As you can see from the pictures, the piping was not "squished" but rather tucked up into the enclosure to ensure adequate ground clearance. I want to keep the car as "green" and quite as possible which is why I chose to stay with secondary cats. I know that many out there do a full 2nd cat delete, x-pipe, etc., but I did this mod in conjunction with AMS short tube headers and the car now sounds and performs incredible. Not too loud - just right.

AAA Performance Exhaust did an outstanding job installing the cats. All stainless piping. Notice the nice welds that are nicer than the factory robot. No 90 degree bends! The tech used the same factory hangers and supports. After the job was done, the car was started and put back on the hoist to check for any leaks which was done by the tech wetting his hand and running it over the welds to feel for any windage. Then he took metal polish and polished up the piping. There is no way that the factory would ever halt the assembly line to do this type of custom work - hats off to AAA Performance Exhaust! If you are in Los Angeles area, this is where to get your custom work done.

AAA Performance Exhaust
West Los Angeles
2600 S. La Cienega Blvd
Los Angeles, CA 90034
888-314-8268
Ph: 310-736-4717
Fax: 310-839-1720

 

More pics:

 

More Pics:

 

Car must sound a bit nicer now. But why not delete the secondary cats altogether if you were going to do some exhaust work anyway?

 

You really don't gain much by deleting the secondary cats entirely. With the 200-cell 2nd cats combined with the improved piping, I gather I am giving up very little HP (1 to 2 HP) to going with full 2nd cat delete.

The primary cats are the most restrictive. If you want that last drop of HP, then long tube headers, primary cat delete, muffler delete, and X-pipe is the way to go - the drawback will be a VERY loud car at 1/4 to full throttle. I want to do my best to stay green (and smogable in CA) and stay within a sensible decibel level which keeps the rozzers away...

 

That's cool, but how come you still keep the resenator?

 

I wanted to keep the car fairly quite. The AMS headers did make the car quite a bit louder; but in a good way by enriching the noise - not obnoxious, but rather more exotic, if you will. The 200-cell cats made it just a bit louder still. Removing the resonator would have been too much for me, but that's my preference. I get in enough trouble with police as it is.... The stock resonator is a straight thru design and doesn't rob that much HP, unlike the ones found on 1970's era Cadillacs which made them sound like vacuum cleaners.

I have a .avi movie of the car on the dyno at full throttle (before the cats upgrade) which I will post on youtube and this forum. Then all can judge for themselves if they want to go more or less extreme in terms of muffling.

 

Hello A'la,

Glad to hear you followed our suggestions. AAA did great job on the install from what I can tell and the smoother piping as well as improved flow of the 200 cells should give you more power as well as improved sound. It may take another 2 weeks for the sound to fully adjust but other all it looks like your exhaust system is about as free flowing & great sounding as it can possibly get while still being 100% street legal and retaining the stock primary cats. Great job!

I also agree on keeping the stock resonator, it will help smoothen out the sound from all that extra air flow from the headers & cats. At the end of the day it needs to still sound like a Mercedes and not a nascar. I like the approach you took for sure, definitely the most refined route, beside the entire back half of the stock exhaust system is completely free flowing so theres no power to be gains. All the gains are in the headers & cats.

can't wait to hear videos of the car after headers and also after new cats. Are you thinking about doing another dyno comparison after the upgraded secondary cats? I think you will pick up more than just a few HP, especially with that high flow 2.5" mandrel piping setup. Keep up the great work.

 

After cutting the second CATs off, how bad is flow choked out? Are they pretty clogged and restrictive with ceramic packing? Thinking about cutting mine out, just don't know if it's worth the effort and money. In the past, most my second CAT deletes have resulted in a bit more responsive throttle and deeper tone. Would love to know if the 2cell metal CATS would work as primary with no CEL's.

 

AMS does not recommend removing secondary cats all together. First off, its illegal to do so, also the gains of doing so compared to high flow 200 cell are minimal at best. Also the 200 cells still give you much better sound quality than going straight pipes.

Its tough to say whether 200 cells will throw check engine light... usually they won't but again it depends on how sensitive the ECU is to changes in the various gas levels. Typically I would recommend upgraded headers & 2nd cats, but not primaries, leave primaries stock as they do clean up most of the bad emissions that come directly out of the heads.

Great job A'la, you did an excellent job, can't wait to hear videos with our headers & those secondary cats, im sure the car sounds fantastic.

 

Actually, the 2nd CATs are only in place for CA Emissions. Thank goodness i live in FL. Was trying to free up the flow by removing Primary with something that won't run into CEL's. Guess no one here has tried it as of yet.

 

The factory secondary cats are ceramic substrate like the primary cats, but much smaller (and there is that 90 degree elbow before the cats that also acts to reduce the piping down to 2.25 inches). If you look at the photo of the primary cats, the substrate material is identical (the honeycomb inside) in the stock secondary cats. The 200-cell cats are much more porous (you can kind of tell by looking at the photo of the new cats – sorry I did not take a picture of them straight on), but you can see them on ECT website under the metallic substrate section (available on Ebay thru seller ppe).

http://www.ect-catalyst.com/02metallic.asp

Here is what the car sounds like before the cats upgrade with just the AMS headers. Try to tune out the whining noise of the dyno machine. This clip was done on a cheap camera - they sound much better in person, but you can kind of get an idea. The car is just a bit louder now after the cats mod; it sounds awesome.

http://www.youtube.com/watch?v=YiC4Co2ENSI

http://www.youtube.com/watch?v=NuSJVGEkKhI

 

sounds great, can't wait to hear some stationary, as well as, drive by vids of the car with the freer flowing 2nd cats, should sound very clean. congrats!

 

hey f1 - how did the dyno turn out?

 

Yes, I will post some other videos as soon as I get a monkey to hold the camera as I do a drive by.

As for the dyno, yes I did see gains with the headers. I did not dyno the car after the cats mod and probably won't since it cost $125 per hour to rent dyno time and a tech. I figure another 2 to 4 hp on the cats mod (at the flywheel)?? The gains are pretty much what I expected on the headers; perhaps 1 or 2 HP less than I hoped for, but it was 69 degrees day of the "base" run and 90 degrees day of the "post" run (blame global warming), so it is harder to tell. I do not have the funds or time flexibility to have a perfect controlled environment like, say, the McLaren F1 team. Overall I am very happy with the HP results, fit/finish, and especially the sound - the car sounds much more exotic than before.

I need to get the dyno graphs in electronic format from the dyno shop, then I will start new thread on the results.

 

22 degree difference will definitely hamper the results a little bit but the gains sure did seem healthy considering the circumstances. good job

 

So what were the gains ?

 

Like I mentioned, the heat conditions varied quite a bit unfortunately. Figure about 9 to 11 HP at the wheels. About 13 to 15 HP at the crank. My goal was to get between 40% to 60% of the power of long tube headers (without all the noise, easy installation, and staying smogable in CA) for 20% of the cost. It worked. The incredible sound was just icing on the cake. The car sounds incredible - more 2008 Maserati-ish than 1969 Chevelle-ish.

 

I am totally with you on keeping the resonator in there, it really is more towards maserati cultured sound. Im guessing that you cant feel the power from the headers as its about the same as a/c on/off. Im in UK and based on your findings I would say secondary cat delete with decent swept bends would be a great mod for sound with a touch of power and very cheap. If they are price well the headers would be nice, what do they retail at.

 

Contact Abedin Motorsports (AMS) directly for pricing. I locked in a price about 7 months ago, but he is a good guy, so his prices should be comparable to what I paid - way cheaper than long-tube headers. And if you have access to a good custom exhaust shop, you will save over $1k on secondaries and install.

I will post new drive-by videos soon; it really is a nice blend of low and high pitched frequencies. Keep the stock resonator and mufflers in place, then adjust according to your taste. You will not be disappointed.

http://www.abedinmotorsports.com/

 

you take it to get smogged in California,do they ever check carb numbers on the cats installed?When the car sounds non stock?
It is a common question on the E55 and the regular W210 forums.Since you are in Ca. what has been your experience as far as smog testing a non stock system goes.
Thanks
great write up and nice work
ohlord

 

Good question. I have not had that problem when smoging my cars in the past. My 944 Turbo is very loud - much more so than stock - and didn't have a problem with the independent smog shops. The biggest issue I have had is passing the "visual" test; when ever I have had simple cold-air intake systems or aftermarket cat-back systems, it usually gave the tech pause. I usually reinstall the factory airbox and muffler before testing. Here the cans, resonator and primary cats are stock. The AMS headers look very factory fitting (not snaking equal-length piping).

As for the ECT cats, they do have serial numbers and are cataloged with the company. It is hard to tell with the pics above, but the serial numbers are etched into each one. The car should pass the sniffer just fine since I didn't remove the primary cats which do most of the emmissions clean up. Also, the car is not much louder than stock when it isn't under load. I don't believe that the rollers used on CA smog machines offer up much in load resistance; certainly no where near the resistance of a dynomometer. I believe they just need to bring the car up to a steady 3k or 3.5k rpm.

 

Here is a short clip video of the sound of the exhaust with the AMS headers and 200-cell secondary cats. It was done on a cheap Casio camera in my garage so it has a bit of a "hiss" in the background. It sounds so much better live, but hopefully you can get an idea. Notice the nice blend of high and low pitch frequencies. I'm between 3k and 4k rpm with about 1/4 throttle blips. The AMS lightened pulley really lets it spool up and down quickly. I will post other drive-by videos and hard launch soon.

Best to click on "watch in high quality" just under the volume icon
http://www.youtube.com/watch?v=Nn_0IdzTRfI

 

I like it! Can't wait to see what mines going to sound like!

 

Has anyone in replaced the primaries with 200 or 300? any check engine light or smog check issues?