hooleyboy

There has been alot of talk in the past about this car needing back pressure, Some even went as far to say they a Res-delete would make you loose some HP. I would think they would say the same about secondary cats removed. Well I guess this thread debunks that. Its just about the cheapest horsepower as you are going to get. Cut two pipes and weld two pipes and there you have it.

bumpnzx3

sounds pretty nice. good gains also- looks as though you gained across the board, rather than loosing a little then coming on pretty strong on the top end like i would have expected.

bmjdevelopment

Outstanding sound. Not having guys that can do this, where should I go to get this done. Could I go say to a place like Midas??

genome

thanks for the sound clips.

this is very nice to know.

hooleyboy

I wouldn't say go to midas. but any custom exhaust shop in the phonebook could do this i would think. Most important you would want someone who can weld good.

rploaded

+1 for not going to a run-of-the-mill car shop. You really need to find a place that knows what they are doing. I had my cats removed, res deleted, new flow through muffler installed and rear tip mufflers removed, etc etc. All of this only ran me 425$ And the welds are spot on (Meaning it should look OEM). You will have to do some movement of the hangers etc to do a full job on the exhaust. Spending a few extra bucks at a custom shop is the first step to success - the results will speak for themselves.

Signed: Ex garage DIY exhaust hacker......

viper501

Sweeeet

hooleyboy

This i feel will be a soon must have mod for C55ers, and its cheap, you dont have to buy any parts to get HP. I was looking at gains just under the evosport headers that cost me some good loot, I bet those headers are helping make the power though.

wawy

Hey hooleyboy,

First of all another good post and something we need more of! 19wtq and 13whp just seems like a lot to me for just removing the secondary cats and I’m just wondering a few things:

- Did you by any chance inspect them to see if they were clogged? I believe there is/was a recall out for the C55 for this sort of thing. If this was the case then I can easily see how removing them could yield 19wtq and 13whp!

- As you alluded to, I can’t help but wonder if some of the gains you realized were in fact mostly due to the Evosport Headers and removing the secondary cats just allowed them to perform to their true potential. I'm wondering if someone doing this to a stock C55 without aftermarket headers/high-flow manifolds would benefit as much?

- Just for clarification you said you “chopped them off and repiped them with a 2008 M5's exhaust” so you did the dyno after adding the M5 exhaust then or before? Did the M5 exhaust free up some HP/TQ??

- I was surprised that “After i installed these wheels I deff seeing a lose of power at the wheels on a dyno. Anyway” especially considering they are 18s. Do you know if they were heavier than your stock C55 rims?? This makes me wonder how much I may have lost going to 19s. Now, the Renntech’s are supposed to be very light but still – it would kind of defeat the purpose of what I’m trying to achieve……..

- Finally, I will be getting headers in the future (I don’t know which ones) and if there are indeed a lot of gains to be had by removing the secondary then I will indeed have to try this….

hooleyboy

We inspected the cats to see if they were clogged as we suspected it after some smelly exhaust on the dyno pull. IMO i thought the car always kinda stinked when i'd get on it. Cats looked like they were in ok shape lots of tiny cells though.

I kinda think that with the headers it did help with the gains a bit. I would say that with my findings on the dyno, these gains would only be realized if someone had headers. So i think that is a factor to think about.

As for the wheels I went to a 18x9.5 wheel with a 255 tire. I dont know the exact weight but if the drag strip tells me anything, As soon as i put the new wheels on my trap speed at the drag strip went from a 108mph to 103mph. To me thats a sign the rotational mass is greater with the aftermarket wheels. Your monolites even being 19s, are at least 10lbs lighter per wheel than my rims. I know nothing about physics so I cant say what that would mean on a dyno. IMO lighter is better in most cases.

Yes we did dyno before and after chopping the m5's exhaust up. What you're seeing in the dyno is baseline pull then secondary cat delete with m5 stock pipe fitted. 2.5 inch pipe i believe.

Evosport headers are a good way to go IMO. just about the most affordable ones out their. C55 headers are the same as SL55 headers. So if i ever get an Sl55 I taking these headers with me.

dorikin_86

Sounds awesome!!!!

I gotta do this to my car...just not sure how I would pass emissions in CA

Quicktwinturbo

I'm at work n my work doesn't have speakers so I can't hear your car sounds.. But I had a friend with an slk55 with cats removed.. His car sounded like a Harley / Cam'd mustang.. which i didn't like it very much... Way too loud imo...

Its crazy that you can gain those whp /wtq though! Thanks for the infor!

spr

Hey Hooley do you get any drone whatsoever in the cabin on the freeway or while driving from the full exhaust, e.g. no sec. cats or resonator?

hooleyboy

I had drone, but I also drove around with no spare tire or mat in the trunk. Ask USMC_C55 He has my exhaust now.

mikekuriger

Drone would not be good for me either, so I'm thinking of just doing the 2nd cat delete and leave in the resonator and stock mufflers at the tips.

madC55

Don't have pics, but I have a C55 with true duals and X-Pipe. I would go lay in the driveway to describe where they are chopped but it is freaking puring here in cow town (burbs outside philly). All I know is whatever is up towards the front that has the sensors is still there, everything else is custom back to the stock mufflers and tips.

Sounds nasty.

RLx02

Just got my secondaries removed today. The sound is AWESOME. Even with the res delete it sounds pretty quiet inside but finally I can hear my exhaust scream from the inside. But when you're just driving normally its barely, i mean, barely louder than before. I don't know from my butt dyno if its faster or not; but I do have heavy *** 19" rims weighing me down too.

Maddydaddy

The only thing holding me back is the fear of highway drone. I am at 2800 rpm at 80 on the freeway. How is the interior noise at that constant rpm?

AMS Performance

If you get the high flow cats, it will give you most of the gains with almost zero drone. If you do headers & high flow 2nd cats, keep stock exhaust & resonator. It will still give you very nice exhaust note as if you had an aftermarket catback.

Maddydaddy

I should have noted that I have already removed the resonator.

RLx02

Well, when I bought the car the resonator was removed and there's barely any drone with that removed. After the secondaries came out I can barely notice a difference with the secondaries gone. Its well worth the money to get 'em chopped off if you love that throaty v8 sound.

mb_c55amg_guy

mike, what do i have to do to get my exhaust to sound like yours from the you tube video....the exhaust guy is clueless...as i dont know what to tell him to do.

RLx02

have him cut off the secondary cats and the resonator with straight pipes. A lot of shops won't do this as its illegal in many areas to mess with emissions though.

Kompressor21

I just got my secondary cats deleted and wow it soudsn and feels amazing..
I have to say this is the best mod I did to the car that was so cheap.
I will do a video to show how it sounds..
Sounds unbelieveable!

hooleyboy

what ever you do, if you go with a cat delete make sure you keep the stock clamps in their currant location.You are going to want them at some point.