Piston port

[Jackson]

What does piston port do for a motor that does not have any in it ??

[Mark75H]

Adding piston porting to a reed valve motor does not seem to make any measurable power increase.

The theory is that reeds could be letting in mixture earlier in the stroke than straight piston port allows.

[Bill Van Steenwyk]

Some years ago when embarking on trying to improve the performance of a Yamato 80, one of the first things Harry ZAK did after the bolt on's like pipes, improved ignition, improvement of flow thru the factory reed valves, was to finger port the sleeves and pistons. This was done BEFORE any port work on the sleeves themselves such as raising/eyebrowing the exhaust's etc. Quite dramatic improvements in performance were seen by this modification. I seem to remember about 3-4 MPH improvement in boat speed just from this one modification. That being said, the improvment was not done prior to the installation of two expansion chambers, so the improvment might not have been as dramatic without the chambers. As with a lot of modifications, changes were also made in the pipe lengths after initial testing which improved the performance even more. In other words, a lot of times when you change one thing, if you change something else to take more advantage of the first, dramatic improvment can be realized.

Sometimes "theory" belongs in books from whence it comes. A lot of performance improvement would have never taken place if the only thing ever "turned" were pages of books or listening to those who are "experts".

Those who are afraid or for other reasons never experiment usually don't run up front, all other things being equal. There is much information available about two-stroke tuning and performance. There are also computer programs available to help.

[Skoontz]

I only can share the experiences I had when racing Bultaco motorcycles. Up to 1980, all Bull's used piston ports. Then 1981, they installed reed valves to try and improve perfection. They failed miserably, although the use of the reed valve on the piston port motor produced 15 more lbs of torque from 5,000 to 8800 than the piston port motors. At 8800, through 9600 they tended to peak and loose power. The reeds would break causing the crank case to fill with gas to the point where raw fuel would spit out the stinger of the pipe. They took out the reed valves in '82, and had planned on doing more R&D, but after a strike the factory went BK and thus ended the company.

I know they would have played with that reed valve until they saw improvement and always wondered the how what and why's of the PP vs the reed.....

[Bill Van Steenwyk]

I have never owned a strictly piston port motor, except perhaps in a garden type tool or chain saw. In other words, never one that I had an opportunity to try to improve performance of. That being said, some of the fastest motors I have ever seen run, ONCE THEY GOT ON PLANE AND GOT GOING, were strictly piston port motors. I will clarify by saying the strictly piston port engines for their time, and against competitive engines in the same time frame, were very viable race engines. The down side was they were very touchy carburetion wise (jetting) to allow them to plane off without loading up, and also props used had to be right on. As far as I know, and based on conversations with those who ran them, by having the fixed piston port to allow fuel to enter the crankcase and then the cylinders, there was very little flexibility on the low end of the RPM range. Motors with rotary and reed valves were and are more "flexible" and you don't have to be as closely "right on" insofar as props and jetting are concerned in the lower RPM ranges when first starting off when the boat breaks over on plane and the engine takes the full load.

If you will remember the early road race bikes, Yamaha, Suzuki, Kawasaki, etc., were piston port engines in some of their models, and all did well and had lots of power from a start to top speed, BUT they all had gearboxes to assist in keeping the engine in the piston port narrow power band. A lot of the early Kart engines were also piston port, but they used slipper clutches that allowed the engine to maintain RPM in the range where max power was developed or at least a lot more than lower in the range. When the engine RPM got high, the clutch locked up and then was basically direct drive like could be compared to an outboard lower unit. In the early 70's Stan Leavendusky built an "M" engine for Eileen made from a 100CC Kart engine complete with a slipper clutch and chain drive. She had to lube the chain by pushing on a pump with her knee a couple of times a lap to squirt oil on the chain. We used a pump and hose/bag assembly from an early windshield washer aftermarket assembly filled with oil. Had to start it with an electric starter and battery that was not nearly as compact as they are now, and really never got it propped out right, but it was a fun project and got lots of attention at the races in the early 70's.

Guess the best way to summarize is most of the race engines used today use some type of valve to assist in getting the air/fuel mixture into the crankcase and then to the cylinders, and don't depend on a fixed opening such as in a piston port engine, whether it be in Stock, Mod, PRO or OPC, so that should tell you something. Finally, there are still some engines out there with finger ports in the sleeves and ports in the piston to assist in getting extra fuel into the cylinders, but this type "help" is used in conjunction with the other types of induction valving mentioned earlier.

There are lots of very sharp folks that post here and I am sure you will get some more answers and helpful hints.

[88workcar]

What does piston port do for a motor that does not have any in it ??

sss

[Fast Fred]

the power Band of a piston port Moda is narrow, vary narrow. older style dirt bikes.:cool:

[Jackson]

I was going to cut a port hole in my piston below the last ring, in line with the boost port like a nissan 25 has . Do you think that it will work??? Thats what iam calling piston port. I put the piston in the block and mark the top of the piston where the boost is at and then moved my marks down below the rings about 3/8in" And then cut a hole a little bit smaller than the boost port. What do you think??? I have not done this to all pistons and have not put motor together yet. Before I did so I wanted somebodys EXPERENCE on this.

[mac19f]

"Adding piston porting to a reed valve motor does not seem to make any measurable power increase."

So why were there so many 3rd port Quincy engines built? I know OF Christner verified all his modifications on a dyno. Was he selling an unnecessary modification?

The 3rd port modification replaced the "mumps" extra reed valve modification so they took out the extra reeds and added a piston port.

I have 3rd ported engines and can say fairly comfortably there is a difference at top end. The 3rd ports add nothing perceptible to the low end. The benefits only show up at very high intaking velocities.

[Frank Volker]

The Quincy flatheads (loopers) had both reed valves and piston ports--or "3rd" ports" as we called them. The 3rd port addition increased hp over the entire band from about 6500 to 9200 RPM when tested on an FA (15 cu in) engine. I seem to recall an improvement of around 5-8%.


Frank

[tsrt]

my 18hp with tunnel run 46mph without and 56mph with piston port on gps

[Skoontz]

The Quincy flatheads (loopers) had both reed valves and piston ports--or "3rd" ports" as we called them. The 3rd port addition increased hp over the entire band from about 6500 to 9200 RPM when tested on an FA (15 cu in) engine. I seem to recall an improvement of around 5-8%.


Frank

Intersting Frank, that is a very similar power band to the Bultaco, even though the Bull was a single cylinder.

[Mark75H]

So why were there so many 3rd port Quincy engines built? I know OF Christner verified all his modifications on a dyno. Was he selling an unnecessary modification?

Yes, O.F. is quoted as saying in his opinion the results were disappointing, but people asked for it anyway. Additional improvements to Quincy 3rd porting of deflectors and pipes etc for deflectors stopped when emphasis shifted to the Looper; this is also a quote from O.F. There was hope that more would come of deflector 3rd porting, but O.F. did not have time to work on improving the deflector and the Looper.

As Ron quotes Revson ... Revlon was not selling beauty, they sold hope

As a post script, combined 3rd porting and reeds were tried on 2 racing motorcycles as well, also without amazing results - quite possibly within the 5% Frank mentions.

[88workcar]

A 5% gain could mean winning, rather than 2nd place.

[David Mason]

Sometimes "theory" belongs in books from whence it comes. A lot of performance improvement would have never taken place if the only thing ever "turned" were pages of books or listening to those who are "experts".

Those who are afraid or for other reasons never experiment usually don't run up front, all other things being equal. There is much information available about two-stroke tuning and performance. There are also computer programs available to help.

There is no website, there is no computer software package, there is no book that can teach you what you need to know to win races. Experience is by far the best teacher. In my opinion and my opinion only, which I am sure most would disagree with, you can take your books and computers and research all you want. If you want results go practice it in reality. You will soon find out that theory is simply someones opinion.

I also have no comment as to whether third porting works or not. It depends on your engine and a lot of other factors. What works on a Nissan might not work on a Yamaha or an Evinrude, or a Merc. If you think it will work, try it. Best lessons learned are the hard ones.

[Mark75H]

A 5% gain could mean winning, rather than 2nd place.

The same gain is possible with careful blueprinting, part selection and balancing.

In circle racing it is probably not enough to make up for a bad start, other driving error or bad luck.

[Bill Van Steenwyk]

Jackson:

To clarify you asked about a piston port to be installed in an engine. Some of the explanation given by both myself and others touched on what was known as a "piston port" engine design. What I meant by that was that the engine I was describing had no other induction timing system except that the piston itself would activate by opening and closing an intake tract from the carb so as to transfer a fuel/air mixture to the cylinders. This opening is usually in the crankcase and the carb or carbs are attached directly to that opening wiith no other valving to time the opening of that tract other than the piston skirt passing the opening and allowing air/fuel mixture in. In other words, no reed or other type valve like a rotary disc. That is the true definition of a "Piston Port" engine.

What your are describing is what I and others here have called a "third port" or also sometimes call a "finger port". Notwithstanding other modifications mentioned such as balancing, blueprinting, special parts, it would seem that most of the actual experience of installing the type port you are speaking about DOES result in a power increase, including mine. As David Mason spelled out it may help more or less, depending on other parameters of the engine design, but based on the actual experience related here, you could do a lot worse for a lot more money insofar as a power increase than piston porting as you describe it.

If you have the desire and capability I would go for it. Either way you are going to learn a lot about engine design, and the satisfaction you will feel if you get the average 5% gain described in the earlier posts will be priceless. It would also surely be less expensive than the other modifications mentioned, and that is what everybody wants, more bang for the buck.
If it does not give you a power increase, but instead hurts the perfomance, (which I doubt) all you need to put it back like it was is a new piston without the openings you have put in it. The extra transfer port in the sleeve should not hurt anything with a stock piston back in the motor. GOOD LUCK

[88workcar]

He is refering to a current model 40hp - 60hp- mercury I think.

[Fast Fred]

finger ports, the 4th and 5th ports, them work.:cool:
aka "five window intake":cool: ya you need them :eek::cool:

[Tim Kurcz]

Indeed, piston port engines demonstrate narrow powerbands which make them less than tractable for outboards (without some means of slip).

Tech question: Why exactly will a piston port engine make more peak power than a reed valve engine?

T

[Mark75H]

Eating and drinking contest winners have the ability to gulp, huge gulps at once ... much larger gulps than us normal folks.

Motors being basically fuel and air eaters, also bow to their relatives who can do the big gulp thing.

The piston port motor is the crown prince of gulpers. The reed valve motor sips thru a straw ... quite possibly a BIG straw or a handful of straws, but a suction straw none the less.

Smacking the gulper open all at once can get the crankcase effectively at atmospheric pressure and chomp it closed before it goes back down ... the reed valve system requires pressure differential across the reed to open it to allow flow ... therefore the crankcase can never be AT atmospheric pressure ... it must be slightly below at its highest.

[Tim Kurcz]

"the reed valve system requires pressure differential across the reed to open it to allow flow ... therefore the crankcase can never be AT atmospheric pressure ... it must be slightly below at its highest".

Actually the "big gulp - straw" theory for piston ports is mostly overcome because reed valves are free to open earlier than the fixed timing piston port.

As Sam points out, reed valves require differential pressure to work. More simply stated, reed valves induce drag and turbulence in the air/fuel mixture flow. Any restriction to flow in an atmospheric engine reduces power.

The tradeoff for outboards (and many other applications) is worth it: Broader torque band and better response (with little spitback) and in-line packaging make a better driving engine - albeit at the cost of a little top end power.

[Tomtall]

As long as we are on the subject of induction I was always curious about the pop-it valves used in the Martin outboards. Why was this design never worked with more? Just curious.

[Tim Kurcz]

Hi Tom,

Complexity, durability, and cost are most likely the culprits. The Martins were limited in RPM due to relatively light spring pressures. "Floating" the valves often caused destruction of the brass followers in 200's. Two examples I owned had steel replacement followers.

[Mark75H]

Modern materials could probably make something like the Martin scheme work better than they did, but would still have some limitation. The results could be something like rotary valve timing.

[88workcar]

Should all three ports be cut like a mod 50

[Fastjeff57]

Hate like the devil to disagree with my good buddy Sam, but he's wrong here: reed valves produce superior crankcase filling than a piston port.

How do I know this? Dirt bikes. I've personally added reeds to piston port motors and found they produce not only a wider power band, but superior top end as well. The reason is LATER filling: a properly designed reed valve set up allows every cc of air coming in to get in, where a piston port does not--the port closes too soon. (If it didn't the thing would load up like crazy!) The top end improvement is dramatic, in fact.

Back in the Golden Age of dirt bikes (the 70s and 80s) we tried every conceivable induction setup, as did the manufacturers. The result is that virtually every dirt bike out there is now a reed valve design.

Jeff

[Mark75H]

The result is that virtually every dirt bike out there is now a reed valve design.


So do the modern alky outboards, but it is not because they close later and stay open longer than piston port which "the port closes too soon"

It is because they give a wider power band

Look at piston port timing again ... there is no way a reed can stay open longer than a piston port intake port

[Fastjeff57]

..."Look at piston port timing again ... there is no way a reed can stay open longer than a piston port intake port"

There sure is! The reed will actually continue flowing air past itself as the piston starts up! The ram effect is what does it. A piston port would have HAD to close long before then.

Agreed that the powerband is much wider with reeds, and much more 'friendly'. We used to load up the engine if the throttle was opened too much at too low a speed. The thing would sit there and "Elsinore" on us for a time before it would clean out.

Ah! Fond memories...

Jeff

[88workcar]

Fellas, this is a great old memory and arguing thread, but, the question that was needing an answer is this, does it help to cut a corisponding hole into the piston, inline with the boost port? And also, does it help to cut out the other two ports as well?

[Original Looper 1]

Sam, usually over half the time you are right in your analysis of the functioning theory of 2-cycle racing engines.

However, this time I must disagree with you and agree with Fastjeff57. As the evolution of the engineering of the modern 2-cycle reed valve racing engine has progressed, in theory and reality, many of us that have been a part of the modern designs conclude that the rpms that these latest engines are experiencing lead us to believe that the reed valves never totally close anymore at the top end of their rpm cycle.

When Chris and I were doing some of our last R&D development work on the Quincy Z engines at Quincy Welding in the early 80's, we put a quartz cover on the reed valve of our 125cc M alky engine. We then added the use of a high speed strobe light and monitored the valve variations in conjunction to the rpms at 12,000 rpms. We discovered, like I am sure others did, that the reed valves no longer completely closed above 11,500 rpms.

To think now that the latest reed valve racing engines are turning 13,000 to 13,800 rpms, I can only believe that the advantage of infinite opening time of the reed valves at those extreme rpms can only lead to, as Jeff puts it, a far more superior, unobstructed flow track for the inertia of the fuel & air to create a net advantage flow capability over the past designs of fixed rotary valve or piston port timing.

Chris and I saw the transformation and progress of the reed valves take place almost totally in all uses of racing, along with our progress in the Quincy Z engines around the late 1970's to early 1980's. Some of the factories and designers have almost unlimited funds to take any design system, such as reeds, rotary or piston port, to the highest pinacle of engineering probability. What do almost all of them now use exclusively? The modern reed valve design.

What more can I say?


Paul A Christner

[Fast Fred]

them is wiseco pistons, the finger transfur ports are a bit lower off the crown than need be, but i did not want to hit the new top pin that was in stalled.
them is Stinger pistons:cool: finger ported Stinger:eek::cool:

[88workcar]

Yes Fred thats correct, The question is, on a 40 - 60 merc that does not have the holes in the piston, would you see a gain by putting them, and should you put all three or just the Boost?

[Fast Fred]

the merc would see a gain in power, the ports in the merc are behind the liner so the piston does not need the center hole.:cool:

[Powerabout]

What was the layout of the last 500 GP 2 strokes? ( although they have gears)
They must have been the pinacle of 2 stroke design considering the effort put in for racing only.

[Mark75H]

Racing outboards designed completely and only for racing have often been the pinnacle of 2 stroke development. More than once, outboard racing motors were converted to take the lead in other fields.

Just because there are more motorcycles sold each year and their makers would seem to have unlimited resources, doesn't automatically put them at the forefront of motor development.

It might be just as good to look at current Arens and Rossi 2 strokes to see the pinnacle of 2 stroke development; motor development did not stop when the bike makers got out of 2 strokes.

[Fast Fred]

pistons with ports:eek:
<a href="http://tinypic.com" target="_blank"><img src="http://i30.tinypic.com/w2o941.jpg" border="0" alt="Image and video hosting by TinyPic"></a>

[Fast Fred]

<a href="http://tinypic.com" target="_blank"><img src="http://i30.tinypic.com/2vb8ys9.jpg" border="0" alt="Image and video hosting by TinyPic"></a>

[Fast Fred]

<a href="http://tinypic.com" target="_blank"><img src="http://i30.tinypic.com/35a8az6.jpg" border="0" alt="Image and video hosting by TinyPic"><

[Fast Fred]

<a href="http://tinypic.com" target="_blank"><img src="http://i25.tinypic.com/bi5avt.jpg" border="0" alt="Image and video hosting by TinyPic"></a>

[Master Oil Racing Team]

Excellent illlustrations Fast Fred.:cool: