What s "PDP"

[Gerald Arana]

Can someone explain what "Perry Direct Porting" is and how it's done?

Thank you, Jerry

[Paul Smith]

We went from simple crossflow, one intake and one exhaust, to the current, modern, and highly effective schunural porting.

There was a brief transition period when engine makers tried to achieve some of the  benefits of schneural porting without making a whole new engine.  Thus, PDP was around for a little while.  I guess if you buy PDP engine, and it's healthy, you will have something between crossflow and schneral preformance. 

[Gerald Arana]

We went from simple crossflow, one intake and one exhaust, to the current, modern, and highly effective schunural porting.

There was a brief transition period when engine makers tried to achieve some of the  benefits of schneural porting without making a whole new engine.  Thus, PDP was around for a little while.  I guess if you buy PDP engine, and it's healthy, you will have something between crossflow and schneral preformance.
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Thank you Paul.

Now I understand what they were trying to do.

Cheers, Jerry

[Motorman]

SuperTigre 35bb eliminated the baffle on the piston and angled the transfer port severly up. Of course with the same port timing this dramtically cuts down on port area. To get some of that area back, they added small ports on both sides of the main port that were angled to the back of the cylinder. It didn't really work because the perry ports were too small, they were fed from the same single bypass and the flow had to do a 180 across sharp louvers so it wasn't enough charge to do anything significant.

In the Como 40 they made a baffled piston with the perry ports on the exhaust side of the baffle. This version made good power but the mileage was dismal as allot of raw fuel went out the exhaust.

After that SuperTigre came out with actual shcnuerle porting where each port has it's own transfer passage.

MM  

[Brett Buck]

SuperTigre 35bb eliminated the baffle on the piston and angled the transfer port severly up. Of course with the same port timing this dramtically cuts down on port area. To get some of that area back, they added small ports on both sides of the main port that were angled to the back of the cylinder. It didn't really work because the perry ports were too small, they were fed from the same single bypass and the flow had to do a 180 across sharp louvers so it wasn't enough charge to do anything significant.

In the Como 40 they made a baffled piston with the perry ports on the exhaust side of the baffle. This version made good power but the mileage was dismal as allot of raw fuel went out the exhaust.

After that SuperTigre came out with actual shcnuerle porting where each port has it's own transfer passage.

  HB made PDP engines as well. They were incredibly heavy, but the PDP was much more powerful than the "not PDP" version. In this one, they had a baffled piston and two little (1/16x1/4" or so) PDP ports just in front of the baffle, on both ends.  Mine was a 40, it would easily swing a 12-6 rev-up at acceptably speeds in a 4-stroke, at least as powerful as an ST46.

    I never got as far as looking into the fuel economy, it was just too heavy to use in a stunt plane, but I presume it wasn't very efficient due to the effect you mention. I started looking into getting the accursed ST60, fortunately before I pursued that, Hunt showed us all the right way to go.

     Brett

[Steve Helmick]

The last of the ST .60bb's were Perry Ported...dished head fins..."K model", I think they called them. At least some of the stunt tuners blocked the Perry Ports...Big Jim for one...to improve the fuel economy, I reckon.  Steve

[M Spencer]

Filched From :

Academy of Model Aeronautics
https://www.modelaircraft.org ›

John Perry

" John Perry was born in Rhode Island in 1920. He moved away from home as a youth of 15 to New York. By age 17, he already owned his own machine shop. "

" In 1969, he developed the Perry Carburetor, which provided better idling power than other carburetors on the market. His hobby business was soaring after introducing this to his product line, selling more than 2 million! He also introduced other modeling products including the Perry Pump, the Perry Pump Carburetor, and Perry Directional Porting (DPD) for cross-flow scavenged engines. "

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" The last of the ST .60bb's were Perry Ported...dished head fins..."K model", I think they called them. "

Right . these are the " Three Window " type . Last of the " Four Window " had em too .

The ' windows ' being each individual hole , the bridges to stop the ring falling in , or out , ? , dividing the cylinder ports into windows . Most people called them .
The baffled piston Como 40 & 51 are a development of the old ' G - 40 , 46 , 51 ' around 1980 ( Indy Super Tigre ) and similar to the ' V ' 60 in that theyre all
' 3 window ' and have the same appearing concave finned cylinder head . 



So these Como are P.D.P. , too .