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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E30 (1982 - 1993)

E30 (1982 - 1993)
God's Chariot. The E30 was produced primarily from 1982 through 1991. The cabriolet was the one exception which was produced through 1993.

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  #1  
Old 09-21-2008, 03:27 AM
nich.j.anderson nich.j.anderson is offline
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Location: Westminster, CO
 
Join Date: Sep 2008
Posts: 19
Mein Auto: MKIII Jetta VR6, E30 318i
Cool Homemade Exhaust

Yo,

Working on getting a beat up '84 318i running properly, that I just got. But somebody cut out the muffler. The reason I've committed to her is something for that I can fix up and try out all my ideas on with out worrying about driving her to school the next day. Anyway, I've got this '84 318i and it idles at 3000 rpm and I'm under the hood trying to check vacuum and timing and the such and I have an open header right there. So I'm using this as an excuse to play around with some different ideas, based around exhaust muffling. I've been talking to my Physics teacher about compression waves and reflection, and mathematically you can reflect waves back on them selves to cancel them out and do it with out significantly decreasing the flow of gases. I think this is what flowmaster and borla use in their mufflers.

I'm going start fabricating a muffler, and I'm playing around with a few ideas, may be dumb, good what ever, let me know you're take on this. BTW I'm a student in high school (12th grade), work a couple days a week, obsess over cars, and am a self taught welder ($88 harbor freight special). I'm in AP Physics, Auto, and taking both 12th and 11th grade english, so I don't feel bad bragging about AP Physics, but you'll have to excuse my grammar. At school we have a Millermatic hooked up.

Here's my ideas, whether they make sense, or if I'll even be able to go through with it we'll see.

I have an old cherry bomb from my friends olde F-100. It has 2.5 inch inlet/outlet. I want to cut it open and use the center pipe and some off the baffling. I want to make a muffler that I can take apart bolt together like an oil pan. I cut the center pipe (from the cherry bomb) in half and line them up next to each other so the entering waves will have to pass through the perforated center section and the baffling to get to the other half of the center section to then leave the muffler.

Sounds like I forgot about the reflection part of the muffler, but this is where I would like to get fancy. I'll have to include pictures to really get what I mean across but for now I'll refer to the placement in terms of an XY plane. If Y+ is the inlet side and Y- is the outlet then the muffler will be a rectangle longer in Y then X with the inlet being -X,+Y corner. The two halves of the center section will be lined up longwise, parallel with Y axis. But I would like there to be a wide section in the +Y Section where I would like to put a valve that opens based on either pressure acting against the valve against a spring, or a vacuum servo. I would like this valve to allow the compression waves to travel down a path of obstacles designed to reflect the waves to silence as opposed to baffling. The path, I picture, would travel +X then -Y then -X then exits where the gases normally do in the center of the -Y side. So I'm looking at a four chambered muffler. First one has the inlet into the muffler, and the valve to let pressure into the reflection type chamber, and an outlet into the cherry bomb baffling center sections chamber, then both baffling and reflection chambers empty into the last chamber which has the out let out of the muffler.

I'm going to cut open that cherry bomb and start making the main box. In the mean time anyone who's in the exhaust field should give me some pointers. I haven't looked at the specific science to reflection yet. Also bounce some ideas about the valve, and how to properly seal everything. I want to have the spring and servo mounted on the out side of the muffler and to have to whole thing serviceable, so I can keep changing things, because I'm never content. Bounce some ideas on the whole concept too, should I just screw valve? Should I just put a big red noisy cherry bomb straight on ? I don't think so, but let me know what you think.

I'll post pictures as I work on it and update.

Thanks,

Nick
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  #2  
Old 09-21-2008, 08:08 AM
e30:) e30:) is offline
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sounds like you have a good plan, haha sounds to tecnical for me but at least your not just some kid who is saying your gonna make a muffler.... looks like you have a pretty good understanding of things. good luck and post some pics as you make it, im interested to see how it looks/works.
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  #3  
Old 09-21-2008, 09:47 PM
nich.j.anderson nich.j.anderson is offline
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Location: Westminster, CO
 
Join Date: Sep 2008
Posts: 19
Mein Auto: MKIII Jetta VR6, E30 318i
Thumbs up

Thank you for sticking up for me, but in all honesty as holes like him just drive me. Shop class in grade 9 first year of high school, I obsessed over cars, was just getting into different concepts and theories. I would bring theories about power from revs as opposed to from displacement to class to talk about and all the rednecks in my class who grew up working on trucks and muscle cars with their dads would shoot me down and tell me I was retarded. They had the experience under a car, and I didn't, there were very few arguements I could make against them since I was a "***** canadian who likes ***** import ****". But since then I've learned to work on my own car. Learned to weld. Worked in a junkyard in canada where I took apart VWs day in day out and I've learned a ton, and those as holes are now my best friends who all help me out with my ideas, and I help them with trouble shooting and modding their cars.

I don't think I'd have been as driven to learn as much as I have with out them. So anyone in the position to shut Cliffmac up, please don't, for my sake.

And I don't think I'm smarter then everyone. One thing I'll definitely never over come is my lack of common sense, and my ability to over analyze to the point where I make a simple problem complicated. I'm just now trying to learn about the very technical side of mufflers, so what I've posted is just a blurry out line of the ideas I've learned so far, and therefor sounds like BS. I'll think about it till it drive me crazy just to prove you wrong.

So if anyone has any specific knowledge about inside a muffler, please let me know. Let me know the basics. Tell me how my idea is pointless or can't or won't work, and if you're really smart tell me why. I would love to hear from people who work in the exhaust industry.

Thanks all, and especially Cliffmac,

Nick

Googled "Exhaust Valve" and found an article on GM.
http://www.superchevy.com/technical/...dod/index.html
"To mitigate this difference, a pressure-activated valve in the muffler adjusts the exhaust path to deliver an appropriate amount of noise reduction. It was found that such an exhaust system had packaging limitations that precluded its use in the Buick Ranier, which has a shorter wheelbase than the vehicles currently slated to receive DOD."
Looks like I'm not the only one thinking about it.
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Last edited by markseven; 09-22-2008 at 09:19 AM. Reason: Clean Up
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  #4  
Old 09-21-2008, 11:20 PM
nich.j.anderson nich.j.anderson is offline
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Location: Westminster, CO
 
Join Date: Sep 2008
Posts: 19
Mein Auto: MKIII Jetta VR6, E30 318i
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