I went out on a cross country from Everett, Washington to Walla Walla and back the
last few days. Cruising at WOT at 11, 500 feet I had a MAP of 19-20 and was making
about 140 mph true rpm was around 6200 with a catto 3 blade 74 x 88 pitch. I need
some aerodynamic cleanup on my cooling scoop, something I intend to work on this
winter. But I think that I'm probably only making about 150 hp or so- not bad, but
not what I could make. I think that the NA 13BREW with four ports and 9.1/1
compression would not be a match for a 13 b with p ports and 9.7/1 compression. I'm
thinking that I might be building such and engine for an engine swap in the future.

Oh, and by the way, it was a great day for flying.

Brian Trubee

Build another engine with a p-port Brian. It will really help up high.
A 4 port will never match a p-port. A good 4 port manifold is hard to make as well.
I assume you have a 2.17:1 gear box.

Paul Lamar

No, I've got a 2.85/1 gearbox. I'll fly with the present engine,but I'm thinking
about building a P-port for installation in the future. I was burning 8.2 gph on my
flight the other day, for an AIS of around 145 mph at 11,500 msl.

Brian Trubee


That's good. A p-port works better with a 2.85.

You might be able to make your current manifold a bit better.
Make the runners adjustable length and make the runners the same diameter
all along their length. If necessary put the bells in the plenum.
Also a ram cold air scoop. Do away with 90 degree the down pipe.

What is the ID of the throttle body?

You could also try a smaller diameter prop to get the RPM's up.
74" is a bit much IMHO. 70" would be about right. Check with CATTO.
The tips are 80% of the drag. Looks like you are over prop'ed. Sand the tips down
until they are really thin.

Paul Lamar
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