Boyesen reeds.

[Lozza]

The pipe helps scavenging too but anyways.................
Yes Graeme is correct tip surface area helps a great deal, but(as what Steve Tassinari from V-Force realised) tip deflection also plays a big role.Old school thought was big deflection = big power but the V-Force cage PROVES that lower tip deflection is the go .Having the petals frimly closed well before BDC sets a better low pressure pulse in the crankcase as the piston starts to ascend.

[LWC82PE]

you can buy universal carbon fibre reed sheets (carbon tech brand) from Serco in Qld. depending on reed size you can get up to about 4 sets of reeds from the pack. they sell it in 2 thicknesses. it costs about $70-$80 approx for a pack but it actully works out to be quite cheap when you can cut out at least a couple sets of reeds.

[PE MAN]

is this what you use in your pe leith... i am about to change my reeds in the PE or check them out at least anyways. seems the only people who make reeds for the old girls are boyesen. i mean they cant be that bad can they. should feel an improvement over the stock reeds, no? i might give them a try anyways. they dont cost much.

[Kane Mcguire]

since 1980 the first mod i have done to every 2 stroke is to fit a set of boyesen reeds.(prob 50 bikes) EVERY single bike ran way better right throughout the rev range. if the reeds were stuffed that i replaced, then that would would explain some of the improvements. statistically unlikely for all. my motto is 'theory means stuff all as compared to actually trying it!!' 

[Lozza]

A dyno will prove that all wrong.

[frostype400]

I know that pe400's run better on stock metal reeds over boyseens.

[mainline]

i found the 175 was better on boyeson's than stock?

[Kane Mcguire]

dynos are only one part of the process. when a dyno can do laps on the back of a bike it will gain more credibility. for eons magazines have tested items on mx bikes on dynos.  but then when actually on the track with a rider a different outcome occurs.

[DR]

I agree K20, while Boyesens may not offer up any more actual horsepower they do make the engine more responsive which has the effect of seemingly more power. Everything I've ever fitted them to definately ran crisper and felt better. For the price, I believe they are worth trying as everyone has different ideals. If you don't like them simply pull them, I'm sure someone will take them off your hands

[Lozza]

dynos are only one part of the process. when a dyno can do laps on the back of a bike it will gain more credibility. for eons magazines have tested items on mx bikes on dynos.  but then when actually on the track with a rider a different outcome occurs.

That is a silly statement, you can tell everything by the shape of the curve.The shape of the curve will give a instant snapshot of how the bike performs on the track. Magazines test bikes in usualy stock form, they only report what they see they do not tune the engine. Which is why the dyno king usualy has not got the fastest lap time.

[evo550]

Have been watching this with interest and still confused .... sheez guys
Can the Institute recomend where to buy these wizz bang replacements 
I'm sure this was discussed in the last forum and a member has some new bute material 

It all about sucking in as much air/fuel, compressing it and making it go bang. The more air/fuel the bigger the bang.

With a two stroke there are three main barriers to sucking it in; the reeds, the transfers and the crankcase pressure.

This one's got me wondering. If the fuel mixture is drawn into the crank as the piston heads upwards, wouldn't the volume be limited by the volume of air being displaced above it?
Ie, if you have a piston at bdc on a 250cc machine wouldn't the volume of air drawn into the crank be 250cc as the piston ascends, since it's not a force fed system, 250cc is about all you could acheive.
Worded badly I know, but it's the best I could do on a Monday morn.

[ChrisACT]

This one's got me wondering. If the fuel mixture is drawn into the crank as the piston heads upwards, wouldn't the volume be limited by the volume of air being displaced above it?
Ie, if you have a piston at bdc on a 250cc machine wouldn't the volume of air drawn into the crank be 250cc as the piston ascends, since it's not a force fed system, 250cc is about all you could acheive.
Worded badly I know, but it's the best I could do on a Monday morn.

Gas compresses.  Gas has momentum.

As the fuel air mixture is drawn into the crankcase, there is momentum involved from the previous cycles.  Basically, the fuel air mix is still flowing into the crankcase well after the piston hits TDC.

Then there is also the scavenging effect of the pipe which draws the mixture through the combustion chamber, including drawing the mixture through the transfers which in turn draws more mixture into the crankcase.

It actually draws fresh fuel air mix right through into the exhaust pipe but the returning shockwave from the expansion chamber then forces it back into the combustion chamber before the exhaust port closes.  So you have fuel air mix coming from both directions helping the charge the combustion chamber (at least when it's on pipe anyway).

That's why expansion chambers are so critical to get right.

[Lozza]

This one's got me wondering. If the fuel mixture is drawn into the crank as the piston heads upwards, wouldn't the volume be limited by the volume of air being displaced above it?
Ie, if you have a piston at bdc on a 250cc machine wouldn't the volume of air drawn into the crank be 250cc as the piston ascends, since it's not a force fed system, 250cc is about all you could acheive.
Worded badly I know, but it's the best I could do on a Monday morn.

At BDC the exhaust port is wide open so there is a bloody big volume above the piston. Case volume is normaly bigger than the cylinder volume with transfer ducts included.

As Chris said a 2T engine is force fed in scavenging and plugging. generaly a 250 would displace 325-330cc per stroke. A fuel particle takes 20 cycles to go through the engine.

[PE MAN]

well i just ordered some boyesens. so see how it feels once they are on. whats the worst can happen... for 45 dollars ill just hang them up in the shed as i lesson learnt if they are no good an look around for the carbon sheets as leith was saying. id say trying to find a new pair of metal ones would be hard

[evo550]

This one's got me wondering. If the fuel mixture is drawn into the crank as the piston heads upwards, wouldn't the volume be limited by the volume of air being displaced above it?
Ie, if you have a piston at bdc on a 250cc machine wouldn't the volume of air drawn into the crank be 250cc as the piston ascends, since it's not a force fed system, 250cc is about all you could acheive.
Worded badly I know, but it's the best I could do on a Monday morn.

Gas compresses.  Gas has momentum.
OK not argueing, just asking. My understanding of vacum is that its a case of atmospheric equalization, as the piston travels, up a vacum (negative air pressure) is created in the crank, the area in the crank then tries to equalize itself with the air pressure outside the crank, by drawing air in, once equalized the vacum no longer exists, air stops flowing in.

As the fuel air mixture is drawn into the crankcase, there is momentum involved from the previous cycles.  Basically, the fuel air mix is still flowing into the crankcase well after the piston hits TDC.
At 8000rpm, there are 133 revolutions a second, so if my maths are any good the fuel has 266th of a second, before piston goes from tdc to bdc

Then there is also the scavenging effect of the pipe which draws the mixture through the combustion chamber, including drawing the mixture through the transfers which in turn draws more mixture into the crankcase.
I thought the fuel mixture was forced up through the transfers through positive atmosphere pressure (compresion) created by the piston traveling down.

It actually draws fresh fuel air mix right through into the exhaust pipe but the returning shockwave from the expansion chamber then forces it back into the combustion chamber before the exhaust port closes.  So you have fuel air mix coming from both directions helping the charge the combustion chamber (at least when it's on pipe anyway).I thought the returning shockwaves where timed to travel back up the pipe to reach the exhaust port just as new fuel charge potentially made it's way out, before the piston closed off the exhaust port.

That's why expansion chambers are so critical to get right.