ADVrider

Go Back   ADVrider > Bikes > Thumpers
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 04-15-2010, 02:27 PM   #1
svejkovat OP
Studly Adventurer
 
svejkovat's Avatar
 
Joined: Jun 2009
Oddometer: 856
How quiet can you make a 2 stroke?

Performance is absolutely not an issue. A one cylinder water cooled KX80 Kawasaki dirt bike motor being used in a fun scooter project. The 2 stroke it's replacing is rated at 2.5hp. The KX80 weighs the same (actually a few oz less!) and is rated at 16hp.

I'd be very happy with 8hp if I could make it stealth quiet. Seems like it would be possible, especially being water cooled, with a standard (non expansion) enduro muffler and a little more attention paid to silencing the intake. Would I have to do any retuning to the engine?

Anyone ever tried to calm a two stroke beast? Just how quiet can you get these things? I had a Yamaha 80cc "Mini Trail" when I was a kid. That's how quiet I'd like this to be. Obviously I want more than 2.5 hp out of it or it's not worth the effort. An enduro pipe would probably spread out the power band a little bit as well, no?
svejkovat is offline   Reply With Quote
Old 04-15-2010, 02:31 PM   #2
KLXplode
Desert Hunter
 
KLXplode's Avatar
 
Joined: Feb 2009
Location: Arvada , Co
Oddometer: 980
Step one: Take off muffler
Step 2: Sell twostroke
Step 3: Buy a fourstroke
__________________
Formerly known as ridehard_ridefast

The Collection:
-1985 Bronco II: Top chopped off. Off road lights/bumper. 2 12" subs. 5 Speed manual

-1993 Kawasaki KLX650R(Green Goblin). Trying to plate

"Trials is an amazing sport. You can get hurt really really bad without even leaving the campsite!


"Its not how fast your going, its about how fast your fast comes to a stop"
KLXplode is offline   Reply With Quote
Old 04-15-2010, 02:38 PM   #3
svejkovat OP
Studly Adventurer
 
svejkovat's Avatar
 
Joined: Jun 2009
Oddometer: 856
????????

I googled it as well. No one is really interested in losing any performance for the sake of noise reduction, so 100 percent of online info focuses on tweaking the silencer, or wrapping the expansion chamber with insulation in order to get a db or two below max limits for sanctioned events. Helps me none at all.

I guess I'll have to just start experimenting. I hate to do it blind. If I didn't have this particular motor I would not even think to do this, so selling it and buying a four stroke is not an option. It's a '96 model, and selling it to get a watercooled 80cc four stroke would put me 500 dollars in the wrong direction. In fact, an 80cc fourstroke racing bike is still going to be waaaaaaay too loud for my aims and I'd be in the same spot of trying to repipe it.

Anyone know of a more suitable forum where I might pose this question?

svejkovat screwed with this post 04-16-2010 at 08:27 PM
svejkovat is offline   Reply With Quote
Old 04-15-2010, 02:41 PM   #4
KLXplode
Desert Hunter
 
KLXplode's Avatar
 
Joined: Feb 2009
Location: Arvada , Co
Oddometer: 980
Quote:
Originally Posted by svejkovat
????????

I googled it as well. No one is really interested in losing any performance for the sake of noise reduction, so 100 percent of online info focuses on tweaking the silencer, or wrapping the expansion chamber with insulation in order to get a db or two below max limits for sanctioned events. Helps me none at all.

I guess I'll have to just start experimenting. I hate to do it blind. If I didn't have this motor laying about I would not even think to do this, so selling it and buying a four stroke is not an option. It's a '96 model, and selling it to get a watercooled 80cc four stroke would put me 500 dollars in the wrong direction.

Anyone know of a more suitable forum where I might pose this question?
Leave it on here for a few days you will get some responses. It just takes time, like you said mess around with different silencers, mufflers, and insulation. . Keep looking.
__________________
Formerly known as ridehard_ridefast

The Collection:
-1985 Bronco II: Top chopped off. Off road lights/bumper. 2 12" subs. 5 Speed manual

-1993 Kawasaki KLX650R(Green Goblin). Trying to plate

"Trials is an amazing sport. You can get hurt really really bad without even leaving the campsite!


"Its not how fast your going, its about how fast your fast comes to a stop"
KLXplode is offline   Reply With Quote
Old 04-15-2010, 03:44 PM   #5
Fubars
What would Scoobydo?
 
Fubars's Avatar
 
Joined: Aug 2003
Location: Ventuna, California
Oddometer: 1,736
You could try a Kawasaki KDX200 stock muffler. They're kinda heavy, though.
Fubars is online now   Reply With Quote
Old 04-15-2010, 03:59 PM   #6
HeadTrauma
\_(ツ)_/
 
HeadTrauma's Avatar
 
Joined: Aug 2008
Location: Antelope Valley, SoCal
Oddometer: 1,260
If you're not adverse to doing some exhaust fabrication, a non-expansion exhaust from a engine roughly as quiet as you're looking for would probably work. Potential sources could be outboard boat engines, lawnmowers, etc. You could even use multiple mufflers from a smaller quiet engine to get adequate flow. Yes, you would probably have to address the engine's jetting.

Quote:
Originally Posted by ridehard_ridefast
Step one: Take off muffler
Step 2: Sell twostroke
Step 3: Buy a fourstroke
That wouldn't help at all. Four-strokes seem to have more energy in the low-frequency ranges in the exhaust that are harder to muffle and carry further....hence the term "thumper."
__________________
1995 XR628R -Lots of goodies...room for more.
"Another breakdown, suicidal shakedown,
Feels like I'm livin' on a chain gang."
HeadTrauma is offline   Reply With Quote
Old 04-15-2010, 04:07 PM   #7
Navin
Beastly Adventurer
 
Navin's Avatar
 
Joined: Sep 2009
Oddometer: 7,551
http://www.thedbsnorkel.com/
Navin is offline   Reply With Quote
Old 04-15-2010, 04:07 PM   #8
Flatulator
Banned
 
Joined: May 2006
Oddometer: 733
If this scooter has plenty of room for a big airbox and big pipe ... you could make it VERY quiet ... without even losing much performance at all

... even more so if the pipe and airbox could get hidden inside a plastic compartment ... (don't know what scoot you're talking about)

example ? ... the KDX200 ... a very quiet bike that is 2.5 times bigger displacement .. so you could make quieter than that with out much trouble

... don't worry about starting from scratch ... since virtualluy nobody does what you're trying to do ... your path is unknown (to you)

in steps >

cut/rotate/fit/weld the stock KX80 pipe to fit on the bike fairly nice .. dont make the overall volume/length much smaller than stock

adapt the largest (stock)OEM muff from a 2 stroke that you can find cheap ... (KTM200/250/300 EXC? - all quiet bikes)
- stock Banshee muffs are quiet too

consider doing a 180 'return' for the muff ... (so it lays over or under the pipe - with another .. mmm .. 180 (or so) ... for the final exit

If you want to keep as much of the stock power as possible ... keep the final exhaust exit the same ID as the stock KX80 had ... don't go smaller

Do an image search for aftermarket moped/scooter pipes to see what I'm talking about (with the 180 returns).

airbox ? ... make it as big as possible ... do some multiple internal baffling's to prevent 'straight shot' path of air(noise)

Too much power and noise ? ... add a few inches of overall pipe length if you have room ... make a stop to keep the powervalve (it has one?) from opening

The KDX200 used a double walled pipe for its first 20 inches to help kill noise

It could be whisper quiet ... and haul ass
Flatulator is offline   Reply With Quote
Old 04-15-2010, 08:01 PM   #9
LILBIT
Ride you must.
 
LILBIT's Avatar
 
Joined: Oct 2007
Location: Lake Placid, FL
Oddometer: 1,675
Quote:
Originally Posted by ridehard_ridefast
Step one: Take off muffler
Step 2: Sell twostroke
Step 3: Buy a fourstroke
Ignorance. A two stroke is easier to make stealth. The sound waves do not carry as well as an opened up thumper. Any offroad race that does DB checks can attest.

A smaller diameter longer muffler with a DB Snorkel. On the bike it will still seem noisy. The pipe(not muffler) and cylinder do that. From 50ft at a reasonable RPM things will be much different.

I had a KTM 300 with a snorkel and good packing. Riding here at my house trail my wife would have to come outside to hear me unless i was flogging it. Even at RPM it was not annoying.
__________________
I eat my candy with the pork and beans-
LILBIT is offline   Reply With Quote
Old 04-15-2010, 08:20 PM   #10
ADVCoop
Studly Adventurer
 
ADVCoop's Avatar
 
Joined: Aug 2007
Location: Acme, PA
Oddometer: 771
One reason two strokes can seem loud is the thin pipes. I have had some success with wrapping the pipe with header wrap. Sometimes you have to re-jet and it kind of looks like crap so I haven't done it in awhile. I like how the DBsnorkel works but I'm cheap. I have also welded elbows on the silencer end to direct the sound down, that helps some too.

My KX125 is quieter stock than my nephews TTR125 with FMF PowerCore 4 exhaust on it that's for sure.
__________________
2006 Husqvarna 610 - 1999 BMW F650 - 1982 Suzuki PE175
ADVCoop is offline   Reply With Quote
Old 04-15-2010, 10:19 PM   #11
KLXplode
Desert Hunter
 
KLXplode's Avatar
 
Joined: Feb 2009
Location: Arvada , Co
Oddometer: 980
Quote:
Originally Posted by LILBIT
Ignorance. A two stroke is easier to make stealth. The sound waves do not carry as well as an opened up thumper. Any offroad race that does DB checks can attest. .
I know i know, Im just saying what I would put in it. Im a fan of 4strokes. Im in a family with XR's and I used to have a yz250. I know plenty.
__________________
Formerly known as ridehard_ridefast

The Collection:
-1985 Bronco II: Top chopped off. Off road lights/bumper. 2 12" subs. 5 Speed manual

-1993 Kawasaki KLX650R(Green Goblin). Trying to plate

"Trials is an amazing sport. You can get hurt really really bad without even leaving the campsite!


"Its not how fast your going, its about how fast your fast comes to a stop"
KLXplode is offline   Reply With Quote
Old 04-15-2010, 10:36 PM   #12
TNC
Candyass Camper
 
TNC's Avatar
 
Joined: Mar 2007
Location: Tejas
Oddometer: 4,618
At our state circuit enduro last month, I'm a check captain for two checks during the race. I got to see about 300 dirt bikes come through our checks...twice. I was amazed at how quiet the KTM200's were. There were stupid quiet. The exhaust note was unbelievably low. I'm assuming these bikes had stock exhausts, because just about every KTM200 that came through was this quiet. I'd go find someone with one of these models and see how KTM made these bikes so quiet. I got see/hear everything from 80cc race bikes to 600+cc bikes, and these particular KTMs were absolutely the quietest.
TNC is offline   Reply With Quote
Old 04-16-2010, 05:31 AM   #13
plugeye
mc caregiver
 
plugeye's Avatar
 
Joined: May 2007
Location: Garland, Texas
Oddometer: 3,575
please post your results,
this is real interesting
plugeye is offline   Reply With Quote
Old 04-16-2010, 05:48 AM   #14
gplassm
Studly Adventurer
 
gplassm's Avatar
 
Joined: Apr 2009
Location: Western Mass
Oddometer: 586
I feel that the two strokes are easier to quiet down than the four strokes. I have an '04 KDX 200, with a stock pipe and silencer, and a Db Snorkel attached to it. As some have mentioned, while sitting on the bike, the bike sounds almost just as loud as it does without the Snorkel, but from 100 ft away the device makes a big difference. I am not able to offer actual sound measurements, but I did ask my wife to stand on the porch and listen as I rode into the woods both with and without the Snorkel attached. She said that the Snorkel made a big difference in sound reduction.
You have several main areas to look at: The silencer, the pipe itself (wrapping will help), intake (if you can find an airbox that has an intake snorkel, it will make a huge difference), and general vibration and noise containment for the entire engine bay. Stuufing foam into every crevis will help stop random vibrations and frequency resonances form metal parts. If you can "box in" the entire engine compartment with something like ceiling tiles, you will reduce noise emmision significantly. It may help to get the silencer exit as close to the ground as possible, and point it downward.
__________________
Street bikes for the street. Dirt bikes for the dirt. Let's keep it that way.
gplassm is offline   Reply With Quote
Old 04-16-2010, 06:12 AM   #15
28marcb
Gnarly Adventurer
 
28marcb's Avatar
 
Joined: Jun 2009
Location: Jacksonville Fl
Oddometer: 139
+1 on above post.

I can get my two stroke exhaust quiet enough that I can rev my engine with my ear a foot away from it. What becomes the culprit at that point is engine noise from the exhaust manifold area, exhaust springs vibrating and the expansion chamber...

A db snorkel in combination with a ktm hockeystick or kdx 220/200 stock exhaust can will get your volume down to where you're probably happy, but the engine noise will be much more substantial at that point..The pipe wrap might be a starting point for that..
__________________
Ktm 525sx (sold)
Wr 250x
Dr 650
Ktm 690R
28marcb is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 09:09 AM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014