Need an engine for a 77" Weeks solution X and a 119" Piper Pawnee PA-25 and looking for help, 3W, DA etc.

Thanks

Ron

DA

ZDZ.

Best power at lower rpm using stock exhaust is 3w. Pretty much always will be unless some designs make big changes. Weight is a factor since 3w engines typically weigh more.

3w is typically more sensitive when tuning and weights more......Da is easy to tune and weights less ,of course DA's customer service is second to none.

Agreed, DA is easier to use. 3w's just require a little bit of knowledge.... The sacrifices one must make[8D]

Customer service is a great thing. I usually never think about it unless I've crashed an engine

MVVS80
In my tests I achieved tons of power on a RE3 Tuned pipe, and very good power using a very small volume reduced (shortened) TD75. This shows that the engine is flexible, and responds to different muffler systems well.

What's the numbers on that MVVS 80, Pe?

I got 7000 slowly rising to 7100, which equals about 11.0 hp.
You can read my full test data [link=http://www.prme.nl/forum/viewtopic.php?t=213]here.[/link]

Depending on the exhaust setup and tuning - the results will go all over the place .
What do you want the engine to do?
produce max power ?
That's it?
Then opt for a small short pipe and a smaller prop and a increased intake timing :different reeds on a reed setup or retimed intake port on a rotary.
The ZDZSuper 80 a rotary setup really works on a long pipe and a big prop- The results are very linear over the entire speed band (rpm)
However if I flew wide open throttle all the time -as some do -I would have shorted the pipe and reduced the prop load a bit and gone for max TOP END only.
OR if I was a race - - I would have recarved the intake opend th carb size as much as practical and let er shriek - The converted weed eater engines do this nicely using NO reeds or intake valving .
Once you get the flow going - at the best speed for th porting - Most of these engines were designed to run WOT and typically at 9-10 thou -hour after hour.
For my own use ' NWAS.
When I was deep into pattern engine setups -year back using glow engines I tried the various combs - which really are no different in results than seen on gasoline setups .
The 11" tuning on a .61 on a 11x7" prop produces wild speed at fullthrottle but really a pain to fly as controlled power was non exiztant .
So when you ask "most power?"
qualify the desired results .

Dick,
I ditto that 100%. Power alone is not the criterium. Itis the power at which rpm, and the power band needed that is part of your setup decisions.
In my every day experience with pilot friends, this is one very tough piece of knowledge to grasp for the other guy. All those variables that made my head spin when I started out tuning engines, and slowly bye the bye became part of the "natural" feel for the engine at hand. The follow the leader symdrom is what yu see everywhere. Mr. Q- so and so uses this, so THAT is what I am gonna use! Without knowing all the slight differences that play such important roles.
It is he who knows how to combine the few means he has access to, that is the most successful if he has the ability to make do.

I prefer a nice and linear throttle myself and not max power. I was experimenting with them Macs tuned pipes on my ZDZ 120. My home built header were built long enough so they could be cut down. They produced the excact same power and throttle response of the cowl mufflers. Never did cut them, but I bought a set of headers that go with cannister mufflers. They are half the length of my other headers and produced an 700 or so RPM gain. Flew two flights like that but went back to the cowl muffs because the midrange was really soggy. Them flights were the first and second of a brand new plane, and I didn't feel like experitmenting until the plane is dialed in. I've had the engine for a while now on another plane and only flown it with the cowl mufflers. The vertical was tremendous with the Macs, but like you told me before Dick, they are not the quietest pipe(s) out there!