the mysterious 2 stroke camshaft

GoldenMotor.com

Goat Herder

Gutter Rider
Apr 28, 2008
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What a tuned pipe does if proper by dimensions. It can produce more bottom end or more top end . A fatty type tuned pipe gives the best of all desired worlds. Products - MX - FMF Racing


A tuned pipe sends back to the engine the unburnt charge that is normally just blown out and wasted. What this means if done proper the effect is more charge crammed into the cylinder on the compression stroke = more power.

http://www.fmfracing.com/Products/MX
 

tire

New Member
Sep 29, 2010
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College Station, TX
but to what magnitude are these powers realistically increased? 5%? anything less than about 15% would not seem financially worthwhile in proportion to the cost of the motor kits to begin with (assuming a chinese 200$ kit).

in the car world exhaust catback systems and headers are big sellers but don't deliver much bang for the buck power-wise (despite false ads and a widespread public misconception). basically on most stock powertrains there are bigger fish to fry rather than messing with the exhaust. is this not as true with our 2 stroke motors due to the expansion chamber having a more direct effect on compressing the air charge before the compression/detonation cycle?
 

tire

New Member
Sep 29, 2010
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College Station, TX
thanks for the links, though i have those basics down so far. and that animation of the expansion chamber was just how i had it in my head, good deal, i'm not hopeless.

goatherder, you may be right. i doubt there are practical ways to dyno these tiny motors. it'd probably be cheaper to use Seat of the Pants Method and just mix and match components until better results are achieved. pardon me as i make a transition from the car world!
 

Mac

New Member
Dec 3, 2009
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Maine
A expansion chamber is certainly the BEST bang for the buck, the SBP pipe is a bolt on Breather, coupled with a good air cleaner, power up about 30%. Remember, get the motor running well before you mod it up, clean the ports with a dremmel, take out the casting marks etc, still dependable.

Mac
 

Drewd

New Member
Jul 25, 2008
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Colorado
Two common mods that definitely improve power provided your carb is adjusted/jetted appropriately and your exhaust is tuned to correct length

1. High compression heads (either slant head or mechanic mikes billet head)

2. Tuned exhaust
 

Kevlarr

New Member
Jul 22, 2009
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Mi
The thing you have to remember is that even a 5% increase in power on one of these two strokes does make a difference. Problem is with these motors there's no one big mod that can be done to gain a lot of power but when you start adding up the little improvements like porting, balancing and an expansion chamber you'll notice it. My motor went from cruising at 25 with an absolute top speed of 28 mph with everything original, added an expansion chamber and that moved up to cruising at 28 with the occasional burst to over 30. Switched to a 36T sprocket and that number moved to cruising at 30 but it would never go faster then 32 even downhill. Balanced the crank, ported the intake, shaved 2mm off the intake side of the piston skirt and ditched the lower gasket which got me to the point that now I can regularly cruise along at 35 with the occasional burst up to near 40 and that's lugging a not so light anymore bike with my added 230 lbs.
 

tire

New Member
Sep 29, 2010
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College Station, TX
would it not be more practical to start with a more powerful stock motor? take what i have read about the 9 hp morini motor that costs 600... after buying a 150$ chinagirl and upgrading about 150-250$ of hardware, air filter, exhaust, blueprint crank, piston, the price difference would be small and the power of the chinagirl would still be in the range of 2.5-4 hp while the 600$ motor is 9 hp out of the box.

should i ever build another small motorcycle or big MB, i may consider a big thick frame (small framed motorcycle or scooter frame) and a legit 4 stroke motorcycle v-twin or quality 2 stroke. i suppose until i have a shop to work from i can't be trying my hand at building a legit 60 mph scooter/motorcycle...

i think i just miss my yamaha road star. :-(
 

Kevlarr

New Member
Jul 22, 2009
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Would it be more practical to go drop cash on a new Vette instead of finding an old 70's small block car, rebuilding the body, rebuilding and trying to squeeze every ounce of power out of the original motor? Probably but you wouldn't learn anything and it wouldn't be nearly as much fun. :D
 

tire

New Member
Sep 29, 2010
121
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College Station, TX
i'm not sure that the price/power ratios are quite comparable in your analogy, but i get what you're saying and i would normally agree kevlar. however, i don't have as much time nor facilities/tools as i would like. :-(