rse reed valve drill holes in piston or raise the piston skirt and extend intake port

[FurryOnTheInside]

that is what i feared...now i have no clue on where to drill the holes on the piston, what size holes, how many holes, or if i should have multiple rows of holes, or how many holes in each row... but, have you tested it? are you sure on the grubee 48cc engine specifically, even if i put the holes in the piston, i wont see any performance increase with the reed valve? if anything, i hope the reed valve will at least help with fuel economy since there will be no "spit back" coming out of the front of the carburetor soaking the air filter with oil (my last gas bike did that).

I'm reading the same page you are (in your link) and jaguar who's site that is, is pretty unambiguous about the holes in the piston, even showing a diagram of how he drilled his piston. I'd say there's more than a clue there.
I haven't seen a thread anywhere discussing if there'd be a difference in these piston mods with the Grubee 48cc vs the HT 48cc, though I've never actually searched for one.
I think this thread suggests that the reed valve gives a performance advantage if you're running a single speed bike (wider power band), may or may not give a performance advantage on a geared bike (where jaguar and Fabian's replies contradict), and gives a stealth advantage for all bikes from less intake noise.

I apologise to the OP if I've been helping keep the thread off topic, but thank jaguar and Fabian for their replies. I had temporarily forgotten about the intake noise and was a little starry eyed at the figures like "38%" on the page the OP linked. I think I value sound moderating mods more than power or economy mods personally, so some of this was moot for my purposes but good fun to read and think about and I'll definitely revisit the topic when the time comes.

 

[Fabian]

should i drill holes in the piston skirt in the intake side OR shorten the piston skirt 5mm on the intake side AND make the intake port longer by 5mm.

If you are installing a reed valve intake, just port match the bottom of the piston to the top of the intake port when the piston is at top dead centre, and it's job done.

The next point to consider is one of redundancy if drilling the intake side of the piston with a bunch of holes that makes it look like Swiss cheese. Normally, the piston is used to block off the intake port when descending down the cylinder bore; preventing air/fuel mixture from being blown back out the intake port. If a reed valve petal fails (because nothing is 100% reliable over greater periods of time) and by good luck it passes through the engine without any damage, the only thing that allows the engine to keep running is the original piston port timing.

When the piston is drilled to look like Swiss cheese, you now rely solely on the reed valve to provide intake port timing, and should a reed valve petal fail, the engine will struggle to run; giving negligible levels of power, if the reed valve passes through the engine without incident.
If the piston is left in a condition where it still can act as the mechanism to provide intake port timing, at least you can still ride the bike home, or continue to your destination, should a reed valve petal fail.

 

[Deleted member 12676]

my god Fabian, you are recommending having both piston port intake and reed valve?
It is one or the other. If you install a reed valve it is an absolute must that the piston skirt be drilled.
If you want reliability then just keep the engine as it is without a reed valve. But I tell you from experience that reed petals last a very long time and when they start to fail it is not all at once because the corner frays little by little and when it is too much you will notice a power drop but it will still run.

 

[Fabian]

my god Fabian, you are recommending having both piston port intake and reed valve?

Yes i am, and that's how my bike runs and with good effect.

It is one or the other.

It just happens to be both and it works well.

If you want reliability then just keep the engine as it is without a reed valve.

Mt engine has given good reliability with a reed valve intake.

I tell you from experience that reed petals last a very long time

That has been my experience

when they start to fail it is not all at once because the corner frays little by little and when it is too much you will notice a power drop but it will still run.

That has also been my experience, but i have heard of complete reed valve petal failures in Japanese motorbikes, so it's reasonable to assume that there is potential for it to happen with aftermarket reed valve intake systems for the Chinese 2-stroke bicycle engine.
Keeping the intake piston porting allows redundancy should a reed valve petal suffer a complete failure, unlikely as it may be.

 

[Deleted member 12676]

Thinking about both together;
reed valve preventing backflow at lowest RPM would help power but during the RPM range where the piston port intake works well it only serves as an intake restriction and would reduce power. Since these bikes aren't used at the lowest RPM (since they have little power there and the speed is so so slow) it is totally unecessary.
Fabian do yourself a favor and stop smoking so much weed and drill some holes in your piston!
If you are going to do something, do it right.

 

[Fabian]

The alternate opinion exists and it could possibly drill some holes in your theory!

 

[max350]

Most discussions will end up like this ................................. on this forum

 

[keatonx]

You CAAAAN have a reed and piston port at the same time if they're working at the same time, like in the suzuki case reed system (has a piston port, but a reed petal under it). Gives more low+midrange. In series like Fabian is doing tho, won't have much benefit unless the rpm is super low and the piston port has too much area. It would have the disadvantages of both (flow resistance and a small timeframe for flow).

 

[HeadSmess]

with a tiny lil intake port of 16-18mm diameter, putting anything in the way is going to be a restriction... aka, after market reed valves.

the reed valve allows these high performance kx 80's to take a carb that would just bog out and die at most RPM if fitted to a standard piston port. make up for the restriction by simply having them larger. can get more air on each gulp. putting them in the crankcase helps.

for all out power at a specific rpm, then piston port reigns supreme. most people cant ride a narrow range engine with ridiculous power. race bikes may be powerful, but its useless if the wheel spins... they come on smoother than the standard bike. piston port suits constant rpm use, like marine or aero...

noone even mentioned disc valves remember the early russian one has disc/drum induction through the crankshaft... and disc induction is the best of all.

as for drilling holes... piston port requires the piston skirt be yay high, to achieve the correct duration, determined by desired rpm, carb, intake length, blah blah...

reed valve requires the largest opening possible. i would be setting the piston at BDC, scribing top of intake port, remove piston...and remove everything from below that line.... then chamfer edges nice to remove burrs and stress points...


hmmm...

 

[Deleted member 12676]

the only benefit Fabian has is a stronger idle.
the rest of the RPM range runs weaker because both systems hinder each other when both are in place.
the reeds restrict intake flow and the unholed piston restricts intake duration.