kb24forlife24

Hey guys,

So I've had my current exhaust setup (muffler/resonator/secondary cat delete replaced with X-Pipe) for about 2.5 years. I LOVE it.

However, I never really get the crackle and pops when lifting off the throttle. I'm thinking that it is due to the X-Pipe smoothening out the sound. Is that true? If I replace the X with a straight, the two pipes would no longer be connected but I'm pretty sure I'll get a lot more crackles, right? Or is an H-Pipe better? Or should I just keep it the way it is? Decisions, decisions hahaha. Any input is appreciated. Thanks!

Amir_AMG

replace the primaries with some high flow cats my car "pops" like crazy now but it might have to do with the headers too

Fatz

Here are my thoughts on SnapCracklePop, and thunk.....

The SCP is due to unspent fuel reaching the exhaust pipes then exploding. The heat of the pipes cause the ignition of the explosion. How far from the exhaust exit the explosion happens, the amount of fuel overrun, and the speed of the exhaust gas are the primary drivers of whether the sound is a SC or P. It sounds more like a "thunk" if it explodes just after leaving the exhaust manifold/headers.

When you back off the throttle, there is a cycle where the ECU triggers a fuel amount based on where the throttle "was", which is more than needed. The excess is expelled, on the exhaust cycle, into the exhaust pipes. Then "BOOM".

So, IMO, the SCP is, in order of impact, is driven by the tuning of the ECU, how much back pressure, and how fast the exhaust travels in the pipes. The speed of the exhaust, for a given engine parameter set, will be determined by how open/reflective/restrictive exhaust components are, the size of the pipes (bigger is slower but presents less back pressure).

The x pipe will have little to no effect on SCP. It also doesn't smooth the exhaust. It probably adds 1db of volume to the exhaust note. It creates a small alternating vacuum cycle on the exhaust pipes, essentially sucking the exhaust gases from the engine exhaust port.

The increased flow allowed by headers and hi-flow cats will allow the unspent fuel to get closer to the exhaust exit before igniting. If your ECU is already aggressively tuned and AFR is as it should be (don't know what is correct) then the unspent fuel is probably igniting in the exhaust manifold..... Makes for a noisy engine....

kb24forlife24

So would the primary cats really make the difference Fatz? I can't delete them for smog purposes but as Amir said, maybe high-flow cats would work.

Hey Amir, what brand/part # did you get for the cats(Pictures or videos would be great)?

Fatz

The hi-flow cats would allow the unspent fuel to travel farther before getting enough heat to ignite. So the short answer is "highly probable". I say "highly probable" because of all the other factors previously mentioned.

Like Amir, I have headers; my mid pipes are 2.25"; x pipe located in the channel; aggressive tuning. SCP is pretty much on demand.

I believe I have the same cats as Amir - Magnaflow spun core high flow 200 CEL.

ALFAitalia

I've never had a Merc with exhaust crackle so I bow to your guys superior knowledge of the marque......however! When ever I've had crackles or pops on the overrun in other cars its always been one of two causes. Number one in my case has always been changing to an exhaust with less back pressure. This means that there is less backpressure holding the fresh charge in the cylinder on the valve overlap cam phase ......unburnt fuel escapes to be burnt in the exhaust on the overrun which is burnt when there is enough unburnt oxygen to burn the fuel in the manifold/exhaust. This also gives the lack of torque that you can feel at low revs with a race type exhaust . The other time is when the mixture is too lean with the throttle lifted. Too lean to ignite in the combustion chamber so does not burn until it builds up in the exhaust where, every few strokes, it all burns at once....pop! This can also be caused by fitting an open exhaust without ecu tuning to match.....factory settings can only cope with so much change to factory parts. Wild cams with masses of overlap can also cause it but those sort of cams would make a car peaky and unpleasant to drive on the road.

Fatz

CLK200K, those are good points. Pops should only occur when those "overrun" conditions are created; i.e. backing of the throttle quickly or between gears under hard acceleration. If it just happens haphazardly, there is a problem.....

An open exhaust will yield lower torque at low RPM as you said. On the other hand, the torque at mid band is about the same and an open exhaust will allow the engine to rev to mid band more quickly; so, in a given period of time the engine is in it's power band longer permitting faster coverage of a given distance. This is true I believe as long as there is enough torque to get the car moving quickly and the gearing and shift points are such that they can keep the revs in the power range.

I love theories.....

kb24forlife24

Amir, do you pass CA smog with your current setup?

megacrazy

What size piping are you running again?

I get lots of snap crackle and pop especially when lifting off the gas. Speaking from experience I would say larger piping will give you more pops and exhaust disruptions in general.

kb24forlife24

Dual 2.25" piping

megacrazy

That's what I thought. I have everything intact except for the muffler. So secondary cats -> xpipe -> resonators -> tips. 2.5 in piping. My bet is on the size of the piping and not any other BS. I have a 4 cyl with 3in piping that's popping even more haha.

kb24forlife24

That's what amazes (confuses) me. You have only no muffler but I have only primary cats and you get more pops. I don't feel like ripping up my exhaust again haha

megacrazy

Haha yeah...I mean the only other difference would be the resonators I added...

I'll record a vid one of these days of the pops while driving.

kb24forlife24

I gotta hear them crackles!

megacrazy

Aight I'll see what I can do

Amir_AMG

I have 2.5" magnaflow spun core 200 cell high flow cats...my car will NOT pass smog in CA or anywhere with a visual...My car is located in Maryland and it is registered in CA (I dont have to update registration while I am active duty)

If I do need to pass smog I will just pay it off every two years

Fatz

Is your 4 cylinder modified in any other way or does it just have 3" pipes instead of what diameter stock?

Does the "BS" in your post mean what it used to mean (cow pooh)?

irokdastar

mine pops and crackles with oem all oem cats just x pipe and dual all the way back . I have an 8cyl I am not sure how it translated to 4 cyl . where is your x pipe mounted . is it right after the cats or under the drive shaft ?

kb24forlife24

My X-pipe is right where the secondary cats were

irokdastar

can you upload pictures of your setup and a video . I think your pipe is too big . check this out and look at the chart. looks like 2" is best for your application .


http://www.exhaustvideos.com/faq/how...378906250#easy

irokdastar

H

kb24forlife24

jkiddd33

I drove your car. It crackles and pops....

kb24forlife24

Haha not the way I want it to though. Your car crackles by just slowing down. I need to force the car to pop and it's not that noticeable

DanielFD

cats cats cats. My BMW crackles and pops a bunch. BMW used some really high flow cats on my V8. Also this depends on advance timing. most tuners advance timing to extract performance from the combustion. Whos got a tune?