z4m Exhaust modification
- Thread starter pixelloft
- Start date
Guys
We've got the back box off to do this but the guy about to do it has a concern, and I'm with him to be honest:
The tail pipes are double skinned. By the look of the pics on here the pipe has just been welded to the outer skin. Now this outer skin is not air tight and in fact has two 10mm square holes either side of the tailpipe. So instead of the gas coming out or the tailpipe you will have it coming out of these two side holes. Even worse some of the gas coming from the back box will now come through these holes. This could potentially cause a couple of problems - one you may get exhaust gases coming inside the car. Also if you had a particularly strict MOTer they could fail it as an exhaust blow.
Any thoughts?
We've got the back box off to do this but the guy about to do it has a concern, and I'm with him to be honest:
The tail pipes are double skinned. By the look of the pics on here the pipe has just been welded to the outer skin. Now this outer skin is not air tight and in fact has two 10mm square holes either side of the tailpipe. So instead of the gas coming out or the tailpipe you will have it coming out of these two side holes. Even worse some of the gas coming from the back box will now come through these holes. This could potentially cause a couple of problems - one you may get exhaust gases coming inside the car. Also if you had a particularly strict MOTer they could fail it as an exhaust blow.
Any thoughts?
Make a hole through both skins and weld the bypass pipe to the inner skin so it vents into the tail pipe proper not between the skins. This may require a bigger hole in the outer skin, but this can be filled again. It will be under the car and out of sight, so the ugliness will be hidden!
We discussed this at Kustom101 before doing the mod. The best option is to cut through the outer trim (it isn't really a skin just a trim piece) and weld directly to the actual tail pipe. Now i decided not to bother with this, because it was more of a fiddle and the exhaust gasses are already right at the rear of the car. Also, the fit for the pipes is tight. If i notice black deposits building up where they shouldn't be I will do it as described, but looks fine so far.
Went with the outer skin too. The guy welding it said to make a big enough hole to be able to get the weld gun in would be tough. He said you'd probably have to take it off completely which would be a right ball ache.
Anyway we ran out of weld gas so only got one side done. The drive home with only one back box was fun though
Anyway we ran out of weld gas so only got one side done. The drive home with only one back box was fun though
I've been modding Z3 MC silencers for a few years now, and IMO the best way to improve both sound and performance is to open a window on the upper surface and selectively "gut" them to change their "reverse flow" configuration into "straight-through" flow. Provided that you keep the OEM tailpipes you won't get any droning and they will sound quite civilised until you give it some beans when the sound is tremendous! You can then weld the window to close the silencer to reseal. You will have no problem passing the MOT. You will also shed quite a few Kgs in the process. Dependent upon how you do the gutting, there is a significant performance gain to be had.
here are a couple of clips of the modded silencers on my Z3 MC:
http://www.youtube.com/watch?v=CK_q...DvjVQa1PpcFN9kelo0jVducIawSaY-jBM0aISkhKhsI0=
http://s103.photobucket.com/albums/...s/?action=view¤t=outsidecarto4krevs.mp4
I've just obtained a pair of Z4MC silencers and I shall soon do the same for my newly acquired Z4MC.
here are a couple of clips of the modded silencers on my Z3 MC:
http://www.youtube.com/watch?v=CK_q...DvjVQa1PpcFN9kelo0jVducIawSaY-jBM0aISkhKhsI0=
http://s103.photobucket.com/albums/...s/?action=view¤t=outsidecarto4krevs.mp4
I've just obtained a pair of Z4MC silencers and I shall soon do the same for my newly acquired Z4MC.
glad it all came good in the end I think that someone here on this forum has already gutted a pair of M boxes and reported that it made only a minimal increase in volume and in their opinion wasn't worth the effort.
exdos said:
Are you sure it's not just for cosmesis and to differentiate the ///M from the rest? :roll:
That said, I have seen some fairly modest Japanese cars with two small tail pipes instead of one, so presumably that is for some form of performance gain...
Spitting and popping is unburned fuel on the overrun entering the hot end of the pipes and igniting. I wouldn't expect more popping from different back boxes as the sound originates way before that, although you may amplify the sounds you do have I suppose.
Have you tried exaggerating your throttle pedal movements so you open the throttle more than you need, then slam the throttle closed more rapidly?
This will dump more unburnt fuel giving more spitting. It's going to ruin your fuel economy
and I can't comment on what consequence this may have on the lambda sensors or cats if they end up contaminated from this...
I usually find that the harder I drive it, the hotter the system gets and the more pops I hear
My Westfield pops and bangs from both ends when it's really excited as it spits fuel back through the carbs too
Have you tried exaggerating your throttle pedal movements so you open the throttle more than you need, then slam the throttle closed more rapidly?
This will dump more unburnt fuel giving more spitting. It's going to ruin your fuel economy
and I can't comment on what consequence this may have on the lambda sensors or cats if they end up contaminated from this...I usually find that the harder I drive it, the hotter the system gets and the more pops I hear
My Westfield pops and bangs from both ends when it's really excited as it spits fuel back through the carbs too
Yes, this will work on any back box and will give you a lot more noticable spitting and popping on overrun. The reason is that the mufflers remove these sounds with baffles etc. If you take off your back boxes altogether and start you car up you will hear how much the car spits and pops... its is terrifying (but pretty cool sounding). Now what you are doing is bypassing some of that neat un baffled sound straight through into the world.
I hope this helps.
Mine spits and pops all the time now, whenever i lift off, even at very low speeds. Its great fun!
pixell how about some furher away pics of the car now??? like square from the rear..... Really pleased someone got use of my old boxes.... they were just gather dust on the attic..... They are incredibly heavy as well..... Awesome work Btw.... i take it you wont be selling these on for some other aftermarket options now??
Thanks Byron,
Just tried to snap a few pics on my iphone but having just replaced the back, the lens is doing something strange and blurring parts of the image. Anyway, here are a few pics after i just clay bar'd it and polished... Also... just fitted my newly recovered steering wheel from Jack at royal steering wheels. Also, while i removed the steering wheel i painted the spokes and interior door handles with hyper silver for something different (black, silver then clear).
