Closed port v.s open port (education) calling all saw techs

[slipknot]

From my reading and learning from the pros, closed port is better for modifying I think!!

So for your piston you just need a piston, the cylinder is ok? Why not post up some measurements, post some pics of it, you main measurements you need are crown height and bore dia, crown height is from the top of the pin bore to the top of the piston, a little taller won't hurt at all, measure your squish stock and see how much room you have.

Thats an idea, but I did manage to track me down a meteor assembly and a golf....trying to decide. $42 total for the meteor kit, and $35 total for the golf from that kafar dude on ebay. Just got to look for oleo-mac 952 parts...efco, john deere, and cub cadet searches yeild nothing on ebay. leanin towards the meteor.

 

[berryman70]

I think you're on to something here.

Here is a picture of the open ports on a 510 cylinder. The roof's of the transfer ports are flat and at 90º to the port.

A curved closed transfer offers optimum FLOW fo show!

What if you reshaped the open port to redirect the flow? Anybody have some pics of a reworked open port?

 

[troutfisher]

What if you reshaped the open port to redirect the flow? Anybody have some pics of a reworked open port?

I think that can be tricky. When the transfers open, the cylinder is full of burnt gas with no oxygen. The fresh charge coming in needs to flush the cylinder from the bottom to the top, toward the exhaust port, without mixing the two.

 

[parrisw]

Thats an idea, but I did manage to track me down a meteor assembly and a golf....trying to decide. $42 total for the meteor kit, and $35 total for the golf from that kafar dude on ebay. Just got to look for oleo-mac 952 parts...efco, john deere, and cub cadet searches yeild nothing on ebay. leanin towards the meteor.

Go with the meteor.

 

[CHEVYTOWN13]

What if you reshaped the open port to redirect the flow? Anybody have some pics of a reworked open port?

Weld some material at the corner of the ports where the roof and the port wall meet. Then shape. You might be able to add curvature. Or JB weld, but that stuff can come loose??

That's a lot of work and tricky as stated. But doable I think.

 

[eyolf]

The last cyl shown, from a 510, was obviously designed with manufacturing costs in mind. The posts that suggest crankcase volume and gas flow direction are the reasons for the difference are close to right, but miss a couple of points; a better designed "open" port system will still perform quite well however.

Tuners pay attention to port timing figures (how long the ports remain open, in terms of degrees of crank rotation) as well as port geometry. Closed ports can present problems if they were designed badly, because its tougher to reshape them.

Look at pistons designed for moderate perormance levels with open ports and compare them with pistons designed for clsoed ports. Mostly the closed port models have a lot of open space around the piston pin that corresponds to the port inlet, while open ports often extend down into matching openings in the crankcase.

Open ports, more crankcase volume, less crankcase compression, less efficient fuel transfer, lower performance, less heat to get rid of.

Closed ports, probably longer duration, better crankcase compression, more power, more cool mix passed under piston crown, more heat transferred to mix under piston crown.

When I was a lad, I came in contact with guys that raced snomobiles, and some of these guys were trying everything they could think of, and often failing spectacularly; engines originally designed to be stationary power plants at something like 65hp/liter aren't able to handle the stresses and heat of twice that power level. One trick we saw a great deal was to drill holes in the piston that would match up with small finger or "boost" ports carved into the cylinder...a sort of "open" port as well.
Some even drilled tiny holes from the ring groove into the piston...the reason was to get a bit of ring sealing boost from crankcase pressure, but mostly to flow a little bit more cool mix under the piston crown. The holes in the piston matching up to boost ports helped too. But in the days of aluminum psitons and cast-ron cylinder liners, anything that could be dome to keep cylinder temps down was good.

 

[RTK]

Aren't open ports are much easier and less costly to produce

 

[slipknot]

How do you post pictures directly within the thread like that? everytime I post a picture...it makes a link to the picture...which you have to click on in order to see the picture. I hate that..:censored:

So what would be a bad design for say a woods port saw? Bsnelling has inspired me with his well thought out porting threads. Ive decided to hack on a possibly junk cylinder for my 952...I am having trouble finding a decent thread on how to bring back a scored jug w/ nikasil plating. What i feel...may be just aluminum transfer... but have to get it off to see if there is more damage...I was reading a good thread on how to but lost it.

 

[TRI955]

After reading through this thread, I am now worried. I replaced the piston in my 242xp recently with a Meteor. The original piston had "windows" in it around the wrist pin, the new Meteor piston does not. The saw runs great with the new piston but now I am second guessing myself now. The two pistons look identical except for the "windows" in the OEM piston. I guess my question is, will this hurt anything? Am I losing performance?


Mike

 

[mountainlake]

A open port piston with a full skirt wouldn't even run in a closed port jug. Steve

 

[Cliff R]

"I guess my question is, will this hurt anything? Am I losing performance?"

If the windowed piston were used in the factory P/C, it was done for a reason. It provides a path for airflow. In the intake charge we also have lube oil. Lube oil is used to protect the wrist pin bearing and wrist pin, and the air movement removes heat as well.

You loose the airflow and the heat dissapation with the new piston. Does it effect engine power, not sure? You'd have to have done some timed cutting before and after the piston swap with no other changes.

I'm not into porting these engines, or modding them other than minor muffler mods and improving squish if I'm removing/replacing P/C's.

From what I've noticed, the open port designs tend to produce broad/smooth power, and still like to rev, but pull down more in the cut.

The closed port models, enjoy high rpm's, and seem to have stronger power in the upper rpm ranges.

The best comparison I have is between my 51 (open transfer) and 55 (closed). They both love to rev, and the 51 is smooth clear across the speed/load range. The 55 is quite a bit stronger in the cut, and doesn't pull down as easily as the 51. It enjoys and stays at higher rpm's, but seems to have a narrower operating rpm range in direct comparison to the 51.

All of my "Pro" Husqvarna's are closed port, and all of them have excellent power to weight ratios, and strong top end power when in use. Both my 262XP and 268XP easily rev to 14,000rpm's no load and still "2 stroke", but I don't set them that high for firewood cutting.

I had a Husqvarna 61 for a while (1983 model open transfer), and it was a TURD in comparison to my 262XP. I couldn't stand running that saw, sort of like driving Corvettes all the time, then getting into a Geo Metro, so I installed a 268XP top end on it. Completely different saw afterward, and I made the mistake of letting a good friend use it, and I got back cash instead of my saw!....LOL.....Cliff

 

[mountainlake]

You might gain power with a windowed piston in a open port jug, a lighter piston and more room for the mix to get to the cylinder but less piston volume to push the mix through. Would have to try it to find out. I'd think full skirt pistons are cheaper to make. Steve

 

[TRI955]

Its funny how you came back to read this thread and learn something after runnin your suck in post #6 at me...your post.....
"slipknot is a glorious beacon of light" LMAO!!! Who comes up with this stuff!?!?
I do obviously...dont you like to gain knowledge....for FREE?
So whats up with that? Its a public thread...say what you want..just thought i'd point that out to ya. The 242xp is a very rare/legendary small saw....but ya kinda answered you own question when you said it runs great!

Sorry about the other post, was just playing, didn't mean to ruffle any feathers....eerrr....quills!?!? Rep sent your way!


Mike

 

[berryman70]

I think that can be tricky. When the transfers open, the cylinder is full of burnt gas with no oxygen. The fresh charge coming in needs to flush the cylinder from the bottom to the top, toward the exhaust port, without mixing the two.

One reason I've been interested in this thread, I'm working on a open port saw right now, I know they are more limited on performance but I'm trying to get as much out of it that I can. I have to raise the transfers so I'm wondering about keeping them flat on the top, I've already widened them towards the intake.

 

[slipknot]

Thanks to all that replied to this thread. You guys know your stuff. There are some other smart guys that I wish would have shed some light on the subject, or at least heard their opinions. Maybe they were too busy in other threads or busy period. Oh well, atleast now i know the difference now, and what they look like. How about some more pictures to give more examples of jug designs. I like seeing whats on the inside.

 

[nanuk]

I remember a thread...

where someone was porting an open trans cyl... and he had ground the intake side of the transfers all the way from the bottom to the top.... all of them. lots of grinding.

can't remember if he said how much it helped.

I'd guess directing the top 1/4" or so toward the rear would help some, like in a closed port.. but doing the whole transfer would appear to have some extra benefit...

But not having done it myself, and again... can't remember who had the info, and whether there was a great benefit... not sure it's worth the effort.