Or does the Pport overlap between exhaust and inlet also cause a
pulsation which enhances 'organ pipe' tuned length.

The Pport has less overlap than the bridge ported engine. However, it is more directly connected between intake and exhaust and poor muffling and added back pressure reduces power more so than the same muffler on a street port or bridge port. Two primaries exactly the same length into a collector. And a foot or more of tubing after the collector will really perk things up.  

 

Primaries the same ID as the outlet on the exhaust liners. So, 1 7/8" to 2 1/8" depending.

 

A longer collector gives a broader RPM band. Shorter gives a narrow band. A 2 1/2" to 3" tube to the muffler.

 

Primary length in multiples of about 11" So even 11" is OK for tight spaces. Angles into the collector exactly the same. Or 22 to 24" or, 33" to 36". Shorter for higher RPM power. Longer for lower RPM power. Largest radius turns possible in the space available.

 

Tubes run as far as possible straight out of the port before the first turn.

 

Thick walled stainless if you can, and then wrap with heat tape. Amazing difference in cooling and heat under the hood and against the fire wall. Get it at the hot rod shop. Lace it on with .032 safety wire when finished. You can touch the headers on a running engine.

 

Do not heat wrap mild steel tubing. It will fatigue into a corn flakes like substance and fail dramatically.

 

No data on an airplane muffler at this point. Tracy has been doing testing, but my muffler is way too heavy and too large. At 4" ID and 7" OD and 30" long in stainless. About 28 pounds. We have to be under 103Db at 50 feet. We are usually around 100Db Very loud.

 

I have a conventional muffler I jam into the tail pipe when checking timing and such. The sound is not a pleasant note. I  left my hearing on the USS Forrestal, but it bothers other people so I keep that muffler stuck in it all weekend except for racing.

 

At least two slip joints to avoid stressing the headers. (let the engine move around while the muffler may be mounted nearly solid.

 

The picture is of a slip cuff. Heavy springs are used between the tabs. Safety wire through the spring coils to save the connection and trap the pieces in the event a spring breaks.

 

The Dutch clamp is for producing a rigid connection, in overlapped tubing, not a slip joint.

 

Lynn E. Hanover