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 :sunny:

[The Lone Rider]

This is the link I was referring to.

http://www.magnariders.com/html/TipTrick/Stock_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 :lol:

Just cut those cans open, make it loud :yes:

[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 :D

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 :D

[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 :yes:

[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 :yes:

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

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 :yes:

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

[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".

[The Lone Rider]

Well today on the way driving home from seeing spiderman 3, the rivets came out and now I'm back to the horrible whistly sound. I'm quite sick of figuring out ways to get the thing to stay put. I might just take it to a store and see how much pipes cost. :(

[The Lone Rider]

I have a set of pipes being made for me from Mr. Muffler in Christchurch. I went in there today and he was heating up one end of a pipe and hammering it down to fit a clasp he was making to fit on the header pipe. So far looks good. I wish I brought a camera.

[xwhatsit]

Cool. As the Australians would say, Emmachizzit?

[The Lone Rider]

They said just over $100 for it all. I'll know 2morrow hopefully as he said to come back in Tuesday morning.

[The Lone Rider]

Work still not done but I have some photos.

Left - Lone bike in its special work area (no pipes on it)
Middled - Bottom end on bike with loose pipe end that will be added shortly
Right - Bottom end fitted on bike, loose end draped over to get an idea

The top pipe (shown as the loose end) is going to me moved up further in angle to create more "size" and appearance then shown in the right picture.

[xwhatsit]

That looks really good. So those are still the standard headers?

Fark that's going to be loud. Does it sound any good sans silencers, or just kind of helicopter-ish?

[The Lone Rider]

Yeah thats stock headers.

I don't know what it sounds like with the new pipes as they aren't done and I don't want to fire it up until it's done (you know... the thrill of the birth of a new beast).

As I think I've explained before, the end pipes slide off the headers, and I've tried the bike with them completely off and I expect it to sound fairly similar with the new end pipes. I DO have a sound clip of it, but I recorded it with my mp4 played and fuck me I can't figure out how to get it to play on a computer as it's encoded in some .wav format I can't find anything about. It doesn't sound like a helicopter.. dunno what you mean by sans silencers.

I'm moving into my new house next week, and just so happens that the plan is to set up recording studio in the room that is across the hall from the garage. So once thats ready I can easily run a microphone cable to a stand to the garage and fire up the bike.

[The Lone Rider]

Went in today and the pipes are all made up save for the bracket to hold them steady to the bike. It looks awesome.

Fired it up... ooooo baby that was some meaness.

He had a cheap dick smiths SPL sound level meter, which the bike measured 85dbSPL in idle and 99.5dbSPL with some revs (not moving)

But, you also have to keep in mind its a cheap meter that isn't calibrated and we were in a box shaped brick wall, cement floor and ceiling building (meaning some narly sound reflections off all surfaces)

[The Lone Rider]

Got the bike today.. all done

FARKKKKKKK... loud. Reached 108db revving the bike while stationary outside in his parking lot.

I'll put up some picks once I give my bike a good wash, and attempt to put my flame decals on the bike.

[The Lone Rider]

Heres one pic of the new pipes (in another thread)

http://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=62092&d=1180223684

and heres an attachment. I have a video of it turned on idling that I will put up later.

[The Lone Rider]

Here is the video - bike is just idling. Also this was taken with a still camera set to video so it is ok quality and in .mov format (Quicktime is needed). Camera doesn't pick up bass frequencies too well, but you can get the idea :P

http://files.filefront.com/Custom_Honda_Magna_Pipes/;7627647;/fileinfo.html

[The Lone Rider]

Hmm, I got an email saying someone had replied to this (i have this thread under subscription), but it doesn't seem to be here

Techincally it is pipes with rooted baffles as there are none in there.

The owner of the shop I bought the bike off of has seen and heard them and likes them, same goes for several people at my work. I am planning to get someone to drive it around for me sometime though. Might have to get someone to when Spank is down here on the 9th or whatsiz..

[avgas]

sounds nice man, real nice

[The Lone Rider]

Thought I might add to this post not to have custom pipes for a bike made up like mine unless you want to be slapped with a big fine for modified noisey exhaust. Then again, at the time I forgot super loud pipes aint a good idea if you're driving somewhere at 1am in the morning. Just dont do it eh?! :P

[Brian d marge]

learn from this lesson obe won :yes:

I dont want to rain on any parade ( i did the same thing myself , with a triumph back in the day)

but u have slash cut drags ( with a length of??? for what rpm ?? )

yes they will produce more power ( at 1 point in the Rpm range) and yes 108 db is loud

and all for ??

a small increase in power at an unusable rpm ( my triumph kicked it up the top of the rpm range ,,shame I could never use it !)

imdying is quite right , you don't want back pressure , but you do want negative energy wave ?? ( cant remember off top of head at this time of nite) to arrive back at the port over a wide rpm range ( hence the taper or change in dia of pipes )

the reason escapes me why you jet up , I have it here somewhere but it isnt because the returning wave blocks the port ,,, some one can help me here !

If you find that the performance drops of at some lower revs , , try putting a mini can after the header and before the tail pipe , and if its too loud ,, find a pipe similar size to the header , drill heaps of holes in it and wrap absorbent material around it and slip it inside the tail pipe ,,,that way you will have the same look ,( which I think you have done a good job there ) and the db s will drop ( depending on the amount of absorption )

We did a dyno run on an Enfield with a super trapp exhaust ( nice cam shape ) and it lost power ,, and sounded nicer


Stephen

reaLLY SOUNDING LIKE AN OLD FART ......

[imdying]

Some of the aftermarket 4 valve Ducati exhaust systems are pretty neat... they're sectioned up into heaps of different sized pipes, with tapers at various points.

At a guess you jet up because when you increase the scavenging effect, you increase the volumetric efficiency of the motor, which means more air, requiring more fuel?

[deanohit]

At a guess you jet up because when you increase the scavenging effect, you increase the volumetric efficiency of the motor, which means more air, requiring more fuel?

I think your right there mate.I know on the over muffled dirt bikes today,by putting a freer flowing exaust with fewer baffles on,you are increaseing the amount of air your engine can process.There fore you need more fuel flowing to reach the full potential of the engine an often a performance air filter, it all helps, with some bikes gaining more than 5hp.Hope y'all can sort of under stand this.

Dunno if I can make head or tail of it meself

Edit:Try sucking through a straw, then a vacum cleaner pipe. Thats what it will be like for you engine.

[rudolph]

My frind had a 750 Magna with 4 Cobys on it

[The Lone Rider]

Everyones missed one important thing, other then performance. The new pipes look and sound kinda cool even if they are loud :P Last post was to say yeah, you'll get pinged for it though and have to pay $$ whenever you get caught.