placement of the tuned ehaust...

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impression

New Member
Feb 26, 2009
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Syadney,Australia
Gday all, well i've gotten a thumpster exhaust for my Grubee GT4 66cc and i'm getting a 49cc pocket bike expansion exhaust, the plan is to put the expansion part of the pipe in the thumpster exhaust somewhere so i get the extra performance and keep the exhaust fumes @ the back of the bike.

my question is where would be a good placement along the thumpster exhaust to place it ?


.trk
 

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NunyaBidness

NunyaBidness

Active Member
Jun 29, 2008
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memphis tn
From what I've seen, you want the expansion chamber about 10-12 inches from the exhaust port. I'm sure someone that knows for sure will chime in soon.
 
mdlee1958

mdlee1958

Member
Feb 22, 2009
204
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Fort Collins, Colorado
I had to remove 3-1/2" from my SBP tuned pipe for reasons of fitting to the bike so it wouldn't be riding just inches from the ground leaving just 9' of header length GHOST and I talked on the phone (after the amputation) and he seemed concerned until I told him that I had already taken it out for a ride and now have more power than I know what to do with. Bear in mind tho that I am riding at 5000 feet elevation. Don't know how much that figures into the equation, but I think that you have a lot of leigh-way on the header length.
 
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impression

New Member
Feb 26, 2009
244
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Syadney,Australia
mdlee1958 said:
I had to remove 3-1/2" from my SBP tuned pipe for reasons of fitting to the bike so it wouldn't be riding just inches from the ground leaving just 9' of header length GHOST and I talked on the phone (after the amputation) and he seemed concerned until I told him that I had already taken it out for a ride and now have more power than I know what to do with. Bear in mind tho that I am riding at 5000 feet elevation. Don't know how much that figures into the equation, but I think that you have a lot of leigh-way on the header length.
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thanks for the info. hmm, i wonder how far off sea level i am

edit:

WOW

Welcome to Bleep City Council

BLEEP is a city on the western fringe of the Sydney metropolitan area, in east central New South Wales, Australia. BLEEP is approximately 50-60 kilometres by road west of Sydney, 30 metres above sea level and is located at latitude bleep and longitude bleep


and the one for Sydney according to worldclimate.com
Weather station SYDNEY is at about 33.86°S 151.19°E. Height about 42m / 137 feet above sea level.

hmm, i wonder how i should be runnign the fuel mix :S

could someone explain please the sea level importance ?

I know that the lower the altitude the more oxygen within the air, but unsure how that would play upon the exhaust
 
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seca40

seca40

New Member
Nov 15, 2008
131
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Albuquerque
I believe the tuned exhaust uses SOUND pulses to back the air/fuel mix into the open exhaust port just before it closes. Sound travels a bit slower at sea level than at higher altitudes due to air density. This would change the timing of the back pressure pulse arriving at the exhaust port. Given the fact that your tuned pipe was not SPECIFICALLY designed for the chengine one more variable of a little probably won't matter that much.

Of course I could be totally wrong.

Anybody?
 
Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
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N.M.
mdlee1958 said:
I had to remove 3-1/2" from my SBP tuned pipe for reasons of fitting to the bike so it wouldn't be riding just inches from the ground leaving just 9' of header length GHOST and I talked on the phone (after the amputation) and he seemed concerned until I told him that I had already taken it out for a ride and now have more power than I know what to do with. Bear in mind tho that I am riding at 5000 feet elevation. Don't know how much that figures into the equation, but I think that you have a lot of leigh-way on the header length.
Click to expand...
I am here next to the Sandia Mountains is there any more input. How much you weigh etc. I have the pipe it just came in the mail. I am not sure what I want to do yet . Have not mounted it as I think I will be putting it on a fuul sus bike , thats not completed yet.
 
Masterm222

Masterm222

New Member
Feb 14, 2009
132
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Billings, Montana
I am looking to buy a tuned exhaust/expansion chamber for my PK80 motor. I found them at SickBikes but they are out of stock. This is a must have option for build number three as it is going on a Giant "Stiletto" chopper! Please HELP!
 
mdlee1958

mdlee1958

Member
Feb 22, 2009
204
1
18
Fort Collins, Colorado
Hi, sorry for the late reply.... been out riding. I weigh 175-180 lbs and the expansion pipe is mounted to a BGF 80cc engine. I am using the SBP shifter kit (which I highly recomend) with a 38-14 six speed freewheel. Ghost from SBP and I talked (after I had lopped off the 3-1/2") and we came to the conclusion that if the engine is doing what I ha expected then the loss of the 3-1/2" section is no big deal. Like the install manual stakes by adding or removing header length you are moving the power band of the torque curve either up or down thru the RPM range. As it sits now I am happier than a hog in slop about how it performs. Just came back from a ride up and back down the Poudre River Canyon (5000' to 7000' elev) and on the way down kissed the bottom end of 50 mph (irratating the guy in the car in front of me cause he couldn't shake me off his rear end on the windy canyon road .... LOL). Granted I was going downhill but I got off the bike in Laporte to gas up and couldn't stop laughing the rest of the afternoon.
 
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drhofferber

New Member
Jun 22, 2008
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Impression...heres the pipe you are buying mounted on my bike...and here is one i bought from spooky tooth...guess witch one kicks ...? Dennis
 

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bigbutterbean

Active Member
Jan 31, 2011
2,417
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Lebanon, PA
here is a little info on header length for expansion chambers. longer header means the pipe comes on at lower rpms, increasing low and mid range power. shorter header means higher rpms, increasing high end power. if you want better hill climbing ability, you want more header length. also, a lot of people talk about re-jetting when ibstalling a new x chamber. here is my take on it. I have the same pipe pictured in the OP. I did not re-jet nor will I. I extended the header so the chamber sits under the engine. the only change I made was to lean the throttle needle all the way out. I did that because I was running really rich. my top speed went from 22 to 28 and I'm happy with that. my hill climbing ability is decent.
 
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