whats your idea for best exhaust and transfer degree and duration
- Thread starter mrfubs
- Start date
Well since it seems that everyone else understands my posts and wish to learn instead of just jump in and stir the pot anytime there's an intelligent conversation going on like an arrogant attention starved kid who thinks he's better than everyone else, but it's not your fault, it's everyone else's fault... I understand, and I'm sure your rubber rainbow pants will get you just the kind of attention you're looking for on your unicorn ride...now it makes sense but you have heard it elsewhere but the information was given to confuse not to teach. its not your fault. google my words then google rubber rainbow pants > lolmore likely to get a match with the rainbow pants.
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when did we start argueing? i would love to go riding w u. i h ave to much opinion and testosterone. i apoligize if i lost my sense of humour.
posting here wastes my time. without you dave i have little reason to be here. i have stuff to keep me busey. i apoligize again.
will chat later i hope.
sub
when did we start argueing? i would love to go riding w u. i h ave to much opinion and testosterone. i apoligize if i lost my sense of humour.
posting here wastes my time. without you dave i have little reason to be here. i have stuff to keep me busey. i apoligize again.
will chat later i hope.
sub
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roger mentioned raising exhaust and lowering intake, as well as cleaning up the transfers. All that in addition to ramping the piston. You should really only do one or the other unless you want a really high power band (my bike is tuned for 8500 rpm, and trust me, it's no faster than my new one out of the box, but the new one uses more gas, is louder, and takes off way faster.
The one tuned for 8500 RPM only has raised exhaust, reed valves and intake window on the piston & 4 3/8" holes next to the wrist pin to reduce weight (and give me a much larger harmonic sweet spot), an SBP pipe attached via flex pipe (internal ridges disrupt exhaust flow though, go with as smooth a pipe as possible). This motor's been through **** though as I learned how to tweak and I learned several things:
#1, exhaust tuned length. It's set for 8500 RPM (about 36" or so), but the ridges in the flex pipe disrupt flow and leak like crazy (my white shoes are now pitch black). Needs to be re-done with either copper piping or bending/welding handlebars
#2, the RSE Reed valves are much, MUCH too small for these engines, 50cc high performance reed engines use huge reeds with quad valves. Get the arrows if you don't go custom.
#3, not enough compression with the stock head (~80psi), needs to be shaved down to nearly flat with the aluminum heatsink or use an aftermarket head.
#4, lighter pistons are better. the lighter you make the whole assembly, the less vibrations you will suffer from. My piston weighs about 96 grams (stock is 108g iirc). You can purchase a titanium wrist pin for about $12 that will cut off 8 grams of weight.
#5 the transfers are terrible, TERRIBLE angles. This is quite possibly the biggest loss of power from an out-of-the-box motor. If you want instant power, fix the angles.
#6 the intake manifold and port (non GT5a engines) are much too small. high performance 50cc engines use 25mm carbs, the NT carb out of the box has a 14mm venturi with a 3/4" (19mm) mounting point. A 19mm dellorto PHBG clone can be had for about $44 and comes with all mounting hardware. Get yourself a GT5a cylinder (REQUIRED! you will need the bolt spacing) and weld up a 1" O.D., 3/4" I.D. intake manifold [the largest possible on our engines without extensive modification]. Stock intake is 3/4" O.D., 1/2" I.D. so even the 14mm stock carbs are bigger than the manifold they're attaching to.
#7 Performance vs Reliability. If you want raw performance, use the stock CDI, it's tuned for maximum power every stroke. If you want to save your bearings (which you should have replaced with american or japanese 6202 bearings anyway), get the jag CDI (or lightning?), it retards at high RPM, putting less pressure on the rod and bearings because the 'bang' wont be as strong when the piston starts descending. Has almost no effect on vibrations, that has to do with the weight you're throwing around.
#8 Get a proper piston. The Hoca Minarelli has been found to fit, but needs cast iron rings or better cylinder plating, is already ported for reeds and weighs just as much as the stock piston. The rings will seal properly, retaining pressure and being thinner, reduce wear and sliding resistance. Get a titanium wrist pin to reduce vibrations
The one tuned for 8500 RPM only has raised exhaust, reed valves and intake window on the piston & 4 3/8" holes next to the wrist pin to reduce weight (and give me a much larger harmonic sweet spot), an SBP pipe attached via flex pipe (internal ridges disrupt exhaust flow though, go with as smooth a pipe as possible). This motor's been through **** though as I learned how to tweak and I learned several things:
#1, exhaust tuned length. It's set for 8500 RPM (about 36" or so), but the ridges in the flex pipe disrupt flow and leak like crazy (my white shoes are now pitch black). Needs to be re-done with either copper piping or bending/welding handlebars
#2, the RSE Reed valves are much, MUCH too small for these engines, 50cc high performance reed engines use huge reeds with quad valves. Get the arrows if you don't go custom.
#3, not enough compression with the stock head (~80psi), needs to be shaved down to nearly flat with the aluminum heatsink or use an aftermarket head.
#4, lighter pistons are better. the lighter you make the whole assembly, the less vibrations you will suffer from. My piston weighs about 96 grams (stock is 108g iirc). You can purchase a titanium wrist pin for about $12 that will cut off 8 grams of weight.
#5 the transfers are terrible, TERRIBLE angles. This is quite possibly the biggest loss of power from an out-of-the-box motor. If you want instant power, fix the angles.
#6 the intake manifold and port (non GT5a engines) are much too small. high performance 50cc engines use 25mm carbs, the NT carb out of the box has a 14mm venturi with a 3/4" (19mm) mounting point. A 19mm dellorto PHBG clone can be had for about $44 and comes with all mounting hardware. Get yourself a GT5a cylinder (REQUIRED! you will need the bolt spacing) and weld up a 1" O.D., 3/4" I.D. intake manifold [the largest possible on our engines without extensive modification]. Stock intake is 3/4" O.D., 1/2" I.D. so even the 14mm stock carbs are bigger than the manifold they're attaching to.
#7 Performance vs Reliability. If you want raw performance, use the stock CDI, it's tuned for maximum power every stroke. If you want to save your bearings (which you should have replaced with american or japanese 6202 bearings anyway), get the jag CDI (or lightning?), it retards at high RPM, putting less pressure on the rod and bearings because the 'bang' wont be as strong when the piston starts descending. Has almost no effect on vibrations, that has to do with the weight you're throwing around.
#8 Get a proper piston. The Hoca Minarelli has been found to fit, but needs cast iron rings or better cylinder plating, is already ported for reeds and weighs just as much as the stock piston. The rings will seal properly, retaining pressure and being thinner, reduce wear and sliding resistance. Get a titanium wrist pin to reduce vibrations
Use a computer with some proven formulas for the parameters you are working with......the 2-stroke is all about port timing. Much to gain with porting and a proper expansion chamber, large carb.....and case reeds + high compression head. That's what comes to mind.
this is good info, but I'm slightly confused. I hope someone can help.
Blowdown is the amount of degrees that the exhaust it open before the transfers open. Its purpose is to let the pressure in the cylinder reduce to or below the crankcase pressure. If the pressure in the cylinder is above the pressure in the crankcase when the transfers open, the enterance of the fresh air and fuel is delayed-not good. At higher rpm the piston is moving faster, thus there is less time (in seconds) that the ports are open and the less time there is for the cylinder pressure to drain before the transfers open.
So wouldn't you want more blowdown with the engine that runs higher rpm?
Edit: nevermind, i figured it out. A person can increase exhaust duration and therefore increase blowdown, but one also must increase transfer duration to get the most out of the increased exhaust. Increasing the transfer duration decreases blowdown.
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