Piston port

[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.
aka "five window intake" ya you need them

[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