Back-pressure pipes?

[The Lone Rider]

After seeing Jerms Magna with what looked to be hand made custom pipes, I am keen to make my pipes much louder (like his ones..)

I quite like the pipes on mine though, I just want loud and proud.

So.. what is this just inside my pipes?

To me it just looks like metal plates with rivets holding them on. I've read a Magna exhast mod on a website that said all you need to do is drill out the rivets and take out the plate (then it went on about adding some things to it to further modify the sound) but I think that was for a 750cc magna (which has different exhasts from what I've seen).

One person I've talked to warned that that plate might be creating "back pressure" that is needed for the engine to run properly.

So.. in the end, what are they and would it be worth drilling out the things that look like rivets and try popping out the plates to see how it sounds?

Thanks in advice for the help

[The Lone Rider]

This is the link I was referring to.

http://www.magnariders.com/html/TipT...k_Muffler.html

Does anyone have a Magna 750 that they can take a couple of close up photos of the ends and sides for me?

[imdying]

Engines don't like or need back pressure. Pressure waves on the other hand are a different kettle of fish.

[The Lone Rider]

Today I've drilled out the rivets and it sounds a bit louder, but one of the black plates comes out a little (but so far I haven't been able to get it all the way out. Only an inch from the chrome pipe). It has a long tube coming off it and I assume that must be the baffle.

[xwhatsit]

Engines don't like or need back pressure. Pressure waves on the other hand are a different kettle of fish.

You are the exhaust designer, so you'd know the score, but I always thought some designs use back pressure for increased scavenging effect? Also, doesn't a bit of restriction (same with reduced carb intake size) boost low-end power (at the expense of top)?

[imdying]

You are the exhaust designer, so you'd know the score, but I always thought some designs use back pressure for increased scavenging effect? Also, doesn't a bit of restriction (same with reduced carb intake size) boost low-end power (at the expense of top)?

I'm no exhaust designer, but that scavenging effect you're talking about are the pressure waves I mentioned. The trick is to keep the scavenging effect, with as little as possible back pressure. Neat trick if you can manage it

Just cut those cans open, make it loud

[The Lone Rider]

Can you please explain the scavenging effect?

I think I've done as much work on it as I want, save for two things. Firstly, the black back plates comes loose so I'm gonna put one rivet back into one hole on each pipe to hold it still, and then I'm gonna get another drill bit from a friend or work and make the other 3 holes I made bigger to compensate for the two I closed.

Are there any legal things I need to be aware of to pass a WOF etc.. now that my pipes seem to be much louder?

My ex gfs words were "I can hear your engine from my room now. I couldn't used to". This is good.. our unit is the first one on the drive by I park my bike all the way at the other end under a car port and do my work nearby there to

And.. new story.. I just dropped her off at school and as I drove off, I swear the noise level of my pipes set off a car alarm

[imdying]

Scavenging effect... it's complicated. Essentially, you can use the pulses inside the exhaust (headers for the most part as I understand it) to help the piston remove spent combustion gases from the combustion chamber via the exhaust port. As the headers do most of that job, the muffler isn't too critical.

My bike is reasonably loud, but being a twin it's a nice beat, so getting a WOF wasn't a problem. Legality aside, you don't want to ride something obnoxiously loud, it's not fun. You'l know in your mind if it is too loud, if it is, weld some metal back in

[xwhatsit]

Scavenging effect... it's complicated. Essentially, you can use the pulses inside the exhaust (headers for the most part as I understand it) to help the piston remove spent combustion gases from the combustion chamber via the exhaust port. As the headers do most of that job, the muffler isn't too critical.

My bike is reasonably loud, but being a twin it's a nice beat, so getting a WOF wasn't a problem. Legality aside, you don't want to ride something obnoxiously loud, it's not fun. You'l know in your mind if it is too loud, if it is, weld some metal back in

I know you're not an exhaust designer, but I read with great interest your other thread

What's the reason, then, that people re-jet their carb when de-baffling or replacing the end-can? Is that just down to increased flow due to low back pressure?

[imdying]

Depends on the situation, it's not always necessary. Sometimes motors are a little lean due to emissions compliance, and it's a good as time as any to fix it.

[The Lone Rider]

Legality aside, you don't want to ride something obnoxiously loud, it's not fun. You'l know in your mind if it is too loud, if it is, weld some metal back in

I'd say right about that I wouldn't want it any louder

[The Lone Rider]

I've finished my exhaust mods, mainly because I fear anymore problems in doing it than what I've already run into would result in me needing to buy a whole new pipe set.

I simply drilled out the 4 rivets on the black back plates, then increased the hole size to 8.5mm to allow for big venting.

In the process of doing that though, the lower exhausts plate came loose and hung out when you start the engine. The pressure pushed it out. This gave the bike a very loud sound but it was a tad whistley for my tastes. Also because the plate was hanging out a bit, the noise dispersed sideways and created a 'FFrrrreeeeee" sound in my ear everytime I drove past a solid object. It's loudness was good though - as I drove by people looked.

So, because it looked gay and the side dispersal pissed me off, I drilled two 3mm holes in two sides of the plate between the vent holes I put in and shoved in aluminium rivets. Now all I need is some heat resistant black paint as there are a lot of scratch marks on the plate from me working on it (I blame it on living in a flat and not having somewhere to work on things like this).

Im summary, my bike sounds a tad noiser with a low, hard breathing puffing sound while idle. And about the same sort of difference while riding. It certainly is not loud enough (like it was with the plate hanging out) to make people look up at me.

Anyone have more ideas?

[Shorts]

Im summary, my bike sounds a tad noiser with a low, hard breathing puffing sound while idle. And about the same sort of difference while riding. It certainly is not loud enough (like it was with the plate hanging out) to make people look up at me.

Anyone have more ideas?

I drilled the end plate on my bike not long ago. I have a similar effect. Its loud enough to be noticeable, but not loud enough to be annoying, I think if your can is sectioned, getting drilled holes further up into the can would help reduce that puffing sound. As it is on my muffler, I have only opened the last baffle. Much like opening only the front door of a house trying to get good airflow through. If you want good flow, then open all the doors inside the house, as well as the front and back door. That will allow the greater flow overall rather than just extra air escaping from a single chamber.

I would be trying to drill the inner baffle now but I am having trouble finding a footlong drill bit lol

[The Lone Rider]

I don't even know how to get the baffles out without destroying and cutting anything

[Shorts]

I don't even know how to get the baffles out without destroying and cutting anything

I'm in the same boat. This stock garbage can is completely weld-sealed.


It may just be better so sit on it as it is until you've got another muffler in hand or you're ready to take a leap to get a new muffler should you totally destroy this one. That's kinda what I'm doing now. I don't have the cash for a nice slip on, so I'll just live with the current setup until a new is "needed".