In a message dated 5/4/2008 10:48:21 PM Pacific Daylight Time, lendich@= optusnet.com.au writes:

Lynn,

I'm having a discussion off-list with a cha= p who is claiming the need for 2" runners for runways over 10,000 ft and hot= days - in other words lower density situations where Max power is needed&nb= sp;over 10,000 ft. I have suggested he look at velocity rather than size, bu= t I feel he has a mind-set.

What do you think about his concerns for po= wer at altitude, does this add another dimension with PP sizing?
I understand power will be down at altitude= , but don't see how a bigger port compensates for that.

George ( down under)

That would be good if you are always in and out of this particular airp= ort. Short 2" tubes to a turbo intake with about 4 pounds of boost.

You would be down to 55% power or less, without the turbo, so performan= ce is going to be less than sparkling. You might want a bit more wing span a= s well. Altering tube diameters for pest power at 10,000 feet is reduci= ng power at 6,000 where most folks cruise around. With the rotary, you can s= tay at full throttle and take out power by leaning well below peak EGT. = ;

A 12A bridge ported with small diameter runners 11" long has 173.3 HP.=20= It actually uses the stock intake manifold gasket. That was with front EGT i= s 1515 rear is 1491. BSFC is (the devils own) 666. Oil temp 162 degrees. oil= pressure 99.9 pounds and A/F of 12.3. This particular engine was dynode thi= s low to get a good curve going. They are used between 7,500 RPM (218.2 HP)=20= and 9,600 RPM (244.4 HP).

I would calculate the area of each stock port and add about 20% to each= tube diameter to reduce flow drag. Make the tubes about 24" long to the man= ifold. The last 6" to the port I would reduce to match the port exactly. It=20= is most important that the ends of the tube at the manifold look like the be= ll of a trumpet. You are probably looking for best power between 5,000 and 6= ,000 RPM. With your firewall forward built up and mounted on a shaft in pill= ow blocks. A bathroom scale one foot from the centerline of the pillow block= s would give you foot pounds of torque, and the RPM would give you HP. A cou= ple of days of tuning (I bet) would have you over 190 HP.

Lynn E. Hanover

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