grubbee exhaust mod

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breno

breno

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Aug 19, 2010
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I was wondering if anybody thought it may be beneficial to make this exhaust work the other way around.
I think this would make the shape look the way it is supposed to.
Wouldnt even mind extending the header pipe a tad more. From what Ive read extending the header pipe should assist in a little more low down torque.
Has anyone played with these exhausts??
 
cory151

cory151

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All I know is my muffler was loose and my low end and midrange power was up. It killed my top end and sputtered but I feel thats probably because of a really lean condition.
 
BarelyAWake

BarelyAWake

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Jul 21, 2009
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Boss's kid got one fer his grubee 66... there's distinct but marginal performance increase over the stock can, not nearly the power provided by other tuned pipe systems (I blame the lack of a headpipe & perhaps the shape of the chamber) and w/o additional support I'd worry about all that weight jus' dangling off the exhaust studs...

...and it's FREAKIN' LOUD OMG - I can't even hear my own engine at all when riding near him, he loves it laff
 
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Black_Moons

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Oct 25, 2010
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Really? Odd, Over the pipes I tryed, that exhaust got me a HUGE incress in my low to midband proformance over stock, but oddly seemed to lower my top rpm a little. Like 50% more power easily.. though I have the CNS racing carb, And I port matched the exhaust before puting it on.. And have a port matched intake.
Also, its actualy not that loud on my bike. Have not got the other longer expansion chamber exhaust to compair it to.. yet :)
 
BarelyAWake

BarelyAWake

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Me an the kid did a buncha 1/4 mile runs before & after... which is always a challenge fer me 'cause I outweigh the lil punk by ...a bit lol Test riding his bike vs mine, with the stock can vs the full length, grubee vs a full length expansion chamber/header - the only difference at first being I port matched even my stock system (both 66cc w/44t);

his vs mine
stock/stock - I'd have a bike length on him
stock/full length - I'd have about 4
grubee/full length - I've 2 bike lengths on him (his was also port matched at this point).

Not sayin' that the grubee expansion doesn't provide a much needed gain in performance, kid's bike also ran a ton better in general and his take-off improved greatly - it's not a bad pipe at all, but I suspect header length times the pulse far better than w/o one is all *shrug*


edit: BTW - I later put the stock can back on that bike (yanked the full length sys for another build) and the kid flat-out destroys that one now blarg ;)
 
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breno

breno

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I too do agree with the grubbee pipe there was a substantial differecnce over the stock pipe even with them both port matched. Only there isnt to many variations in exhaust pipes here in oz to choose from hence the grubbee.
The only other way I could get a full length proper exhaust pipe, I would assume would be from SBP, etc. and getting it sent over from America.
Which leads me to having a play around with the grubbee exhaust i.e welding bending whatever is necessary.

Would it be worth while say giving it an extra 4-6inchs of header pipe??
Turning the expansion chamber backwards which would make it appear its facing the normal way?
Adjusting the stinger pipe length??
I have no real experienece when it comes to playing with exhausts but i'm capable of cutting, adjusting, welding, etc.

At the moment the power is all up the top end roughly mid-top end power. My goal is to move that band lower in the rev range. I just dont kow how to really go about it.
 
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BarelyAWake

BarelyAWake

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I couldn't tell ya if it'd be "worth it" to ya to chop up & play with yer system, but if ya do decide to modify it - you could ofc take the stock headpipe, cut it off the muffler, port match it and use that as I did with my sys (see pic below). There's some babble about alternate full-length exhaust systems, various expansion chambers & whatnot in this thread, which was supposed to be about cats, but we ended up rantin' bout a buncha stuff heh: http://motorbicycling.com/f13/catalytic-converter-mufflers-15857.html
 

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scotto-

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
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Ridin' inSane Diego, CA.
I'm thinkin as for modifying the Grubee easily would be to cap the stinger (or chop and cap it) and weld a mid-bleed stinger thats a little bit larger in diameter, and about an inch and a half long. It would make the pipe a bit quieter if nothing else. Just a thought. Here's a pipe I made a while back for a 47cc Tanaka....from a pipe off of a Yamaha 250cc Quad





click on pic for larger image....it's mounted on a chinese 49cc 2-stroke in pics
 
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breno

breno

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That would be a benefit in itself to quiten it down a little more even if it didnt affect the performance ppl can hear me coming from a mile away.
 
scotto-

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
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Yes, mid-bleeds are much quieter than end-bleeds, especially sitting at idle. Don't get me wrong, it will still be fairly loud at WOT, but not nearly as loud as it is now. Cheers m8!
 
scotto-

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
6,505
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Ridin' inSane Diego, CA.
Black_Moons said:
Hmm, Hows the midbleed affect proformance?
Click to expand...
Let me just say that the various mid-bleed pipes that I own (and there are several) blow the end-bleeds of similar shape and size out of the water! I don't know why or how this is....it just is. I honestly don't know the theory or total concept of this mid-bleed thing, but I do know they produce exceptional power and performance like no other. And they are quieter than an end-bleed expansion chamber.
 
breno

breno

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Thanks for taking the time to upload those pics scotto. Thats an interesting way of doing it, personally i've never seen it b4. Would love to have a spare pipe to play around with.
I ended up turning the exhaust the other way around and slighlty extended the header approx. 1inch with 28mm pipe and added a 3" stinger aswell. Happened to shave the slant head 0.008" amongst all this too so I cant really tell which made the difference but theres a def. improvement in bottom-mid end grunt and the top end feels a little pokier aswell over all a good result.
 
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