On the other hand, back in the day, we use to put windows in the piston to allow engine as much breathing time as possible.
This was on reed motors. It really made a big difference. Piston life was shortened on the race bike but at these lower rpm It would probally be ok.

I'm am talking about the intake, not the exhaust.

I wish I still had the paper work on how to do this.

Food for thought

rc ign
did I mis-state something about the piston skirt and or its location if I did please show me so I can clear it up .
The piston skirt CLOSES the exhaust port .
please re read the entire thing I still dont see what you cant understand
its not a holley double pumper for crying out loud its a 13.5 mm zama .vacuum is what your refering to and yes to creat more vacuum restrict the venturi this however also restricts the amount of fuel and oxegen otherwise known as mixture that you can flow into the engine.
the thing with the floor of the port ,15degrees,and feeler gage was to give a sorce of reference to how to transfer degrees to measurment in a scale more familiar so during cutting we have a reference as to how much to cut it worked for me maybee I didnt explain it properly .I understand the top of the port controls exhaust timing thats why I told him to be so careful.did I miss something else if I'm wrong help me out I'd like to know to avoid passing bad info on to others.or explain myself better

Ralfbf
two stroke tunning by A.Grham Bell talks about it alot thats where I got clean up the bottom of the exhaust port so the gasses can get out easily which makes room for new gas charge

The part I can't understand is about the bottom of the piston skirt CLOSING the exhaust port.. Most 2 strokes are made so that the top of the piston is just flush or a little below the bottom of the exhaust port...The piston skirt does nothing about exhaust timing...If cutting the bottom of the port makes it run better, it's more from making the port slightly larger than anything else...You would do more by slightly widening the port or slightly raising the top..

The bottom of the skirt DOES close the exhaust port when the piston is at TDC.

But, I think whats being said, is that if you LOWERthe exhaust port too much--you risk the skirt actually OPENING the exhaust port at the bottom when the piston is at TDC. You've just opened the exhaust port with the bottom of the skirt--and exposed the crankcase charge under the piston to the exhaust.

Come on Ralph--keep up.

I see that, but the top of the piston opens and closes the exhaust port, the bottom never gets high enough in the bore to do anything..When the top of the piston comes down it uncovers the top of the port first, then keeps going down until the top of the piston is flush with the bottom of the port..the bottom of the skirt is way down in the cylinder and never gets high enough to do anything...Unless, like you say, the bottom of the port gets cut lower than the bottom of the piston skirt....That's why nowhere, except maybe in A Graham Bell's book, does it say anything about cutting the bottom of the exhaust port, it's already almost too low....
I think we're saying the same thing, the whole piston is what covers the port..
But the BOTTOM of the intake side of the skirt is what controls intake timing on a piston port two stroke...
Maybe we need to know where on the piston the skirt starts ?
Top, middle, bottom ?

cutting the bottom of the port is just common sense if it is in the exhaust streem ,as in porting ,you make it smooth
and free flowing if its a ridge smooth it out if it a depression ,fill it. my pistons on all three ryobi's goes past the bottom of the exhaust port to smooth this out you must grind it either flush or lower than the piston topif you grind down too far
the piston skirt will uncover a small area in the exhaust port that will be open to the crank case ,connecting the crank case to the exhaust port .if that happens you will get less than good results, this is something that I came very close to doing ,I got carried away grinding by the time it was smoothed out and polished I had gone well past my target.I didnt realize that there was a risk until after reasembling it and didnt want anyone to make a mistake based on my advice .
the bottom of the port has nothing to do with exhaust port timing ,and very little to do with duration, the top of the port controls open and close of the exhaust port the piston top controls 1\2 way on the duration. the port is almost to wide now,its very close to the transfer ports and one ring end,. if made too wide the ring could conceivably expand into the port and catch on the port as it travels up breaking the ring
the thing about the carbs ,yes I understand that you can only put a larger carb on to a certain point .after which you're too big, however, if you cant get the old gasses out then there is knowhere for fresh gasses to go.the stock carb,which I am running is around 9 mm at the venturi ,very small ,most guys do replace the carb with a larger one .the 13.5 zama that I refered to is the same one poco 242 runs on his toro 25 engines without any problems. I for whatever reason cant get one to run lean enough to use ,it maybee its too big, but poco has used them on ryobi's before with success, so I thought it was worth mentioning
I was allways taught that the area from the bottom of the piston pin bosses to the bottom of the piston is the skirt
rc pilot; I still think some of your problem stems from your exhaust port being to restrictive 128 degrees is exactly what aero nut was talking about,
yep,sometimes I get a little enthusiastic ,its one of my" endearing character features"or flaw if read another way.if I have good results with a tunning trick I like to share I dont horde them like a miser and gold,I thought thats what this forum stuff was about.
rc ign; do you have any other problems with any more of my statements ,have I explained myself sufficiently,after re-reading this thread I can see where you could get confused if you skimmed it .or took it out of the context with which it was presented .however results are what matter I picked up 300-350 rpm's doing what I described.if I'm wrong please tell me so I can make the appropriate corrections. but I dont want to split hairs Idont have time for that .

No problem, we were all saying the same thing...

MY 2 cents....I do not think you have to go big as possible on ports. I think a good tuned pipe is more effective. They make carbon fiber pipes now that weigh zip!!!!! I am going that route for top performace on at least one plane. Mayby a CMP Giles 202!!! Capt,n

RC you ever see one of the peak a boo engines from A&M, you could look from the intake clear thru the exhaust port. Got the deck heigth off a bit. Maybe smog control with build in EGR

Captin!!! I tink that in order to get the most out of an engine with tune pipe your exhaust ports need to be high on the duration timing, so a low duration timing engine wouldn't benefeit from the use of a tune pipe

I think you both need to read chapter 4 in a book on two-stroke tuning by A. Graham Bell may save you a lot of work. Obviously the expansion chamber must be of the correct length to ensure the pulse waves are reflected to arrive at the exhaust port at the proper time. tuned pipes are a waste of money and time, go for the port timing bigger bang for the buck.
Ken

TKG..Didn't see those, but Dan Santich stopped by my shop many years ago on his way to race at Madera...He had spent some time with Stinger Wallace and said he could make his engine look just like Stingers...He used my porting tools and made a peek a boo engine out of his...Wouldn't run at all, we had to get a new cylinder....
I would like to see someone get another 1000 rpm from my G26 on gas without using a pipe and still have it useable at anything but WOT..
If port timing alone would work there would be thousands of performance engines built that way..Can't be done....
ALL racing two strokes use tuned pipes.....

Boxcar: Look at any high performance snomobile, motorcycle, jet ski or whatever and 95% of the engines will have a tuned pipe. Most right from the factory. I do not think I will look for that book...it may be a waste of time. But I will listen. Regards Capt,n

capn'
where r you going to run your tuned pipe I guess I should say route it? will you build a tunel like most patern planes
or just let it hang out in the breeze?
im torn about the porting question . most of the guys that I know who fly patern use tuned pipes but none that Iknow of do any porting work on their glow engines .
however I do beleive the book about how a tuned pipe works ,I also know that a dirt bike for off road use will have hotter porting thats why a pipe will work so well on them. I cant recall ever seeing a tuned pipe\expansion chamber on a stock street bike but I wasnt into street bikes that much.
then again ,a tuned pipe properly tuned should give some benifit to a stock engine with no porting so the real questionis how much can you get from it without mods to the port and will it be worth it from a time and money standpoint.
I think you stand to gain from either porting or from a tuned pipe but really get your moneys worth from using them together.someone had one one a ryobi not to long ago and reported that they thought it sounded like it was turning up more but didnt have there tach durring the run .if you give it a try let us know how it works out

A stock G26 picks up 1000 rpm with a generic 30cc Mac's pipe..
Dick Hanson runs pipes on his Roto engines, they turn 10,000 also...

One thing I have noticed with just running a pipe on a stock engine is there is gain every where.

The right pipe adds to the bottom the mid range and the top rpm.
When the engine is ported the bottom end power goes away and the mid and top end are enhanced. Now I know this isn't always the case but usually it's true.

The longer the stinger the higher the operating range.
Low end comes from short fat stingers

The stinger is the pipe that the exhaust actually exits.

so the only things against a tuned pipeare the size and location of the pipe cost and availability.
now I'm wondering why they are not more popular 1000 rpm's and power increase right through the rpm range
is pretty good for a bolt on mod or ,is there a bigger problem that i'm not seeing here .I know there is lots of stuff on this forum about it did a search on it lots of talk about it . and some experience.will someone try it? ,just have to wait and see.stay tuned! ha, ha,

You are right Capt. but what you did not see is all the research and testing it took to make them work. those pipes can cost you a lot of power also if not done right.
Ken

I've noticed this same thing.

A pipe on a stock gasser (G-62) adds power across the whole range. It's not peaky. I never notice it "come on the pipe" like a glow engine. I've had a pipe on a glow engine before, and you can definetely tell when the motor comes up on the pipe. Big shot of power at a certain RPM--and pulling like gangbusters from there up to max RPM.

Not so with the G-62 on a pipe. It's just smooth power from idle to max RPM. I gained 1200RPM on the top. Spool-up from low end is dramatically faster. No more midrange burble. It actually sounds quieter than the side dump exhaust divertor that I was using before.

Now I want to run a pipe on every gasser I have. Wish I had the money to buy all those pipes.

Does anyone know of a header that will bolt up to the Ryobi? [:-]

there has to be a down side here somewhere.otherwise we all would be tripping over all the tuned pipes . manufactureres would fit them to existing engines instead of making new larger engines. yes tuned pipes
can work but there has got to be a limiting factor here that we are overlooking .like I said if they are' all that" we should literally be tripping and stumbling over all the tuned pipes that came on the engines we bought and tore down .
yet,..... I dont have one.

Flyjoe, could it be because of the formula to determine the tuned length of the exhaust.
L=EDx42545 divided by RPM. Assuming a exhaust duration of 196 and 11000 RPM we would have 196x 42545 divided by 11000 = 758 mm, 758mm being the tuned length of your exhaust. A true tuned exhaust would cost more than the engine.
Ken

Yes pipes are expensive....but if you got next to nothing in a engine conversion...its well worth it. Good power...not super expensive like some engines alone. I plan on letting the pipe hang beolw the fuse, for starts. I will post a photo of setup I may copy.

The downside is that they are expensive. The pipe for my G-62 cost me about $175.

Another drawback is, they aren't always easy to setup and secure to the airframe.

More?

You can cut too much off your header and ruin it. Then you go back to the manufacturer and pay through the nose for another one.

Once you dial it in, and tune it for a specific prop and fuel--your pretty much stuck with that combination. Change the prop (RPM) and you'll have to re-tune the system again. Sometimes, that means buying another header.

Why don't all manufacturers sell their engines with tuned pipes? Because it makes the engine run harder. Manufacturers are worried about warranties. It is not just something that you bolt on and go. It takes time, and patience. It also takes a bit of engine "know how" to put a pipe on an engine and tune it right. Do you ever read the engine forums around here? How many dumb*****'s can't even tune the carb on a simple glow engine? [sm=lol.gif][sm=rolleyes.gif] You think they can handle a tuned pipe?

And, those are just a few of the drawbacks to a tuned pipe. Most of it is end-user related (lack of knowledge on the part of the end-user). Some of it is expense. A lot of it is manufacturers and warranties.

I flew the Ryobi today. 6150RPM with a Zinger 17-8. I had it a touch rich. I could hear it in the air every once in a while--it would start to break into a really good scream for a second and then it would burble back to rich. I landed and leaned it out a bit. It sounds better. I picked up probably 300RPM. I must have been flying it around 5700--5800RPM. I just need to go out and fly the darn thing as much as possible.

This is a stock Walbro carb with 13mm opening. I'm tempted to just hook the fuel jug to it and let it burn a gallon or two of fuel in the driveway.