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increase torque/low-end power with muffler? ideas/criticism

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bevlak
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PostPosted: 13:00 - 06 Oct 2018    Post subject: increase torque/low-end power with muffler? ideas/criticism Reply with quote

Hi all

Just wanted to ask everyones opinion on the above. So I've bought a little cg125 that I'm turning into a brat/cafe type thing for city commuting. Just a daily rider type thing but want it to look nice.

When I bought it, it had a totally rusted and holed muffler, but the header pipe was fine so I chopped the muffler off and stuck on one of those straight through cafe style mufflers. Obviously this being a 125 this is not a great idea in terms of low end power so I was trying to figure out a way I could keep the look but get back some of that low end power so I can pull off from lights at least faster than a granny on a mobility scooter.

As you may have guessed I'm a novice at customising, but I really enjoy building things so after a lot of googling it appears (correct me if I'm wrong) that a longer exhaust will increase low rpm power but restrict the top speed.

As above, it's for zipping to work on through heavy traffic so not bothered about top speed, more Interested in acceleration. Its rarely going to be getting to 50mph in town so as long as it can go that fast I'm happy. With this in mind I thought I could build a baffle type insert for the muffler that would effectively increase the distance exhaust has to travel, having the same effect as a longer exhaust but still give me a short length visually.

I've attached of picture of an idea I was thinking of building to fit inside the muffler can. Can anyone tell me if my thinking is right here? Will this give me a little more low end power? Ideas welcome!

Cheers[/img]
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Riejufixing
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PostPosted: 13:35 - 06 Oct 2018    Post subject: Reply with quote

A muffler? That's one of those woolly things like a big scarf, isn't it. You could chop a bit off and stuffit up your exhaust pipe to give the effect of a silencer.
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bevlak
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PostPosted: 13:45 - 06 Oct 2018    Post subject: Reply with quote

Riejufixing wrote:
A muffler? That's one of those woolly things like a big scarf, isn't it. You could chop a bit off and stuffit up your exhaust pipe to give the effect of a silencer.


good one
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Riejufixing
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PostPosted: 14:11 - 06 Oct 2018    Post subject: Reply with quote

Interesting drawing - the "straight through look" is maintained, but it's difficult to predict what would happen to performance. My guess is that you would not need so many "stages", but more will lessen pressure fluctuations through the rev. range. You'd probably need to experiment, but that really needs power measurement. Whether there's anything commercially available in the way of "straight through-looking" silencers, I don't know.
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bevlak
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PostPosted: 14:24 - 06 Oct 2018    Post subject: Reply with quote

Riejufixing wrote:
Interesting drawing - the "straight through look" is maintained, but it's difficult to predict what would happen to performance. My guess is that you would not need so many "stages", but more will lessen pressure fluctuations through the rev. range. You'd probably need to experiment, but that really needs power measurement. Whether there's anything commercially available in the way of "straight through-looking" silencers, I don't know.


hmm ok thanks for this! I can make the design in above drawing for next to nothing, ive got mig and scrap metal lying about... so might just do it and see what happens, can always take it off if its crap i guess! As above the main thing is just a bump in low end power - at the moment im having really sluggish pull off from standing, but picks up fairly well after that.

So you think that having more chambers will create less fluctuations? I think I'll try out the design as I have it first and see what it runs like. I'm aware messing with this is going to mean resetting carbs/jets - do you know which way this is likely to go? My guess is it will make it a little richer, but could be wrong here!

Thanks for your help Smile
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Nobby the Bastard
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PostPosted: 15:19 - 06 Oct 2018    Post subject: Re: increase torque/low-end power with muffler? ideas/critic Reply with quote

bevlak wrote:
So I've bought a little cg125 that I'm turning into a brat/cafe type thing for city commuting.


Can you show us some pictures of this abomination? I want to show them to my kids so they know what not to do.
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stevo as b4
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PostPosted: 15:38 - 06 Oct 2018    Post subject: Reply with quote

Why do you think you've lost some low end power compared to the std exhaust in the first place?

I'm guessing your mixing up fluffy low end Carburation due to your chopping the OEM exhaust up, with a loss of low end power.

How much more torque ib/ft do you want it to make compared to how it is now? 10ibft, 20, 30?

If you can't jet it right for the open pipe, just take it to a dyno and in less than an hour and a couple of dyno runs they'll know what jets are needed to achieve whatever air/fuel ratio the CG engine likes to tun best at.
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Sister Sledge
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PostPosted: 18:04 - 06 Oct 2018    Post subject: Reply with quote

My Scorpion tail part looks like that inside except remove the right hand section. The outer pipe part of the drawings is holed and wadding placed between that and a shiny outer can. I'd show a photo but I've just riveted it back together..

Not sure about low end 'grunt' on what you're riding. I doubt you'd notice to be fair..
Sounds more like a wrong setting on the carb. Failing that the engine is tired.
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Riejufixing
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PostPosted: 19:52 - 06 Oct 2018    Post subject: Reply with quote

stevo as b4 wrote:
If you can't jet it right for the open pipe, just take it to a dyno and in less than an hour and a couple of dyno runs they'll know what jets are needed to achieve whatever air/fuel ratio the CG engine likes to tun best at.


How much, as a matter of interest, for "a couple of dyno runs"?
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redeem ouzzer
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PostPosted: 20:23 - 06 Oct 2018    Post subject: Reply with quote

[quote="Riejufixing"]
stevo as b4 wrote:


How much, as a matter of interest, for "a couple of dyno runs"?


Depends who you know. For me about £30. But it’s cheaper and more effective than guessing.
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Ste
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PostPosted: 20:36 - 06 Oct 2018    Post subject: Reply with quote

Photos and videos of the bike OP is talking about: https://www.flickr.com/photos/30068069@N08/
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RhynoCZ
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PostPosted: 21:22 - 06 Oct 2018    Post subject: Reply with quote

If you choke the exhaust a bit, you're going to get more low range torque, but the bike will starve for air at higher revs.

Make a baffle, simple stuff, and keep making the holes in it bigger and bigger until you are satisfied with the performance.

OR pay a specialist to tune it up for you as is.
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bevlak
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PostPosted: 21:51 - 06 Oct 2018    Post subject: Reply with quote

RhynoCZ wrote:
If you choke the exhaust a bit, you're going to get more low range torque, but the bike will starve for air at higher revs.

Make a baffle, simple stuff, and keep making the holes in it bigger and bigger until you are satisfied with the performance.

OR pay a specialist to tune it up for you as is.


Thanks everyone for the advice, I'm going to give it a go based on my design and will report back

Don't think it's worth paying for a Dyno test, it's only a 125 after all, and it's for going to work on, not really worth it for me I'll give it a go and report back ! Nice one guys!!
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Riejufixing
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PostPosted: 22:45 - 06 Oct 2018    Post subject: Reply with quote

Ste wrote:
Photos and videos of the bike OP is talking about: https://www.flickr.com/photos/30068069@N08/


Smile

Blast. That was supposed to be in a "huge" font. I have had to add this explanation. I like it.
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bladerunner
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PostPosted: 02:40 - 09 Oct 2018    Post subject: Reply with quote

your running a pod filter AND a less restrictive carb...it runs lean as is with the airbox and std pipe so first thing I'd do is lift the needle a notch or 2......thats move the E clip down the needle by a notch or more! then its upjet by 10% and see how that goes Smile a CG whilst not ever impressive in the HP stakes can rev until it valve bounces thru the gears and offer what can be expected lower down the range without trying to "tune the pipe"
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bevlak
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PostPosted: 09:15 - 09 Oct 2018    Post subject: Reply with quote

bladerunner wrote:
your running a pod filter AND a less restrictive carb...it runs lean as is with the airbox and std pipe so first thing I'd do is lift the needle a notch or 2......thats move the E clip down the needle by a notch or more! then its upjet by 10% and see how that goes Smile a CG whilst not ever impressive in the HP stakes can rev until it valve bounces thru the gears and offer what can be expected lower down the range without trying to "tune the pipe"


Thanks for this bladerunner - This kind of leads me onto a different issue, When I bought this bike I noticed that the carb serial number didnt match the bike model according to the haynes manual. Currently running 38 slow and 100 main, but this is coming out very rich (sooty plugs) So if anything it looks like I'll have to reduce the jet sizes (might be wrong here, but all evedince seems to point to a rich mix) I've got a gunson colortune coming in the post so I'm going to try using this to get a better idea whats going on here

cheers

s
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MarJay
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PostPosted: 09:18 - 09 Oct 2018    Post subject: Reply with quote

Why not start with a decent bike in the first place? All the good aspects of the CG will be lost.
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bevlak
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PostPosted: 09:19 - 09 Oct 2018    Post subject: Reply with quote

MarJay wrote:
Why not start with a decent bike in the first place? All the good aspects of the CG will be lost.


bit late for that wouldnt you say?
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bevlak
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PostPosted: 09:34 - 09 Oct 2018    Post subject: Reply with quote

Riejufixing wrote:
Ste wrote:
Photos and videos of the bike OP is talking about: https://www.flickr.com/photos/30068069@N08/


Smile

Blast. That was supposed to be in a "huge" font. I have had to add this explanation. I like it.


in case you're interested, heres a newer photo
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bevlak
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PostPosted: 09:43 - 09 Oct 2018    Post subject: Reply with quote

Fourte wrote:
My Scorpion tail part looks like that inside except remove the right hand section. The outer pipe part of the drawings is holed and wadding placed between that and a shiny outer can. I'd show a photo but I've just riveted it back together..

Not sure about low end 'grunt' on what you're riding. I doubt you'd notice to be fair..
Sounds more like a wrong setting on the carb. Failing that the engine is tired.


ok I'm gonna try out this colourtune first and see where i get to. another problem is noise - there's no way this thing is getting past an MOT without a baffle of some sort. I tried repacking the exhaust with wire wool but it's definitely gonna be too loud.

Kind of unrelated, but funny: When i was giving it a little test ride up the alley at the end of my street the other day it was making a big racket. Some old fella at the end of my road comes out his house and says to us "piss off you noisy bastards, im trying to watch pornography in here!"

Laughing Laughing Laughing
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bevlak
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PostPosted: 13:18 - 09 Oct 2018    Post subject: Reply with quote

mpd72 CPT wrote:
bevlak wrote:


in case you're interested, heres a newer photo


Is that a protest sign in front of the bike?

"Another awesome..." I'm curious now..,! Smile

I wouldn't worry too much about improving the engine when the brakes and tyres look seriously lacking. Could you not spend the time and effort converting it to a front disc setup from a later CG or CB?


Tyres are brand new, I like the way they look. So I'm sticking with them. Yes I could convert to front disc but don't fancy spending £200 on new forks and brake just yet. Just want to get it running right first I reckon!
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Riejufixing
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PostPosted: 13:27 - 09 Oct 2018    Post subject: Reply with quote

bevlak wrote:
When i was giving it a little test ride up the alley at the end of my street the other day it was making a big racket.


You want to be careful doing that, and aware of what could happen.. insurance?
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bevlak
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PostPosted: 13:28 - 09 Oct 2018    Post subject: Reply with quote

Riejufixing wrote:
bevlak wrote:
When i was giving it a little test ride up the alley at the end of my street the other day it was making a big racket.


You want to be careful doing that, and aware of what could happen.. insurance?


what can i say im a rebel Cool
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Riejufixing
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PostPosted: 13:28 - 09 Oct 2018    Post subject: Reply with quote

bevlak wrote:
another problem is noise - there's no way this thing is getting past an MOT without a baffle of some sort.


I'm confused. Is that with the straight-through pipe, or with your invention?
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