I'm scratch-building a Pitts Special, from Nick Ziroli plans from 1967. The plans don't provide finished weight, but the sketchy instructions that came with them suggest a .45-.60 size two-stroke. (Specifically, those instructions say the prototype carried a .46, and that was "minimally acceptable.") And, remember this was all said in 1967.

The longer wing-span is 53", the shorter is 44", and the fuse is 45" long. Similar sized ARFs on the market generally recommend .60 sized two-strokes or .90 sized four strokes. The airplane is balsa and ply built-up, mostly sheeted with 1/8" balsa, and I'll cover it with some brand of film.

My objective for performance is primarily reliabilty. I'm not looking for a screamer, but I don't want to regret under-powering it. Also, I take some pride in trying to be economical - I'd rather spend less money than more, although I don't want to be foolishly cheap about it. I don't have a strong preference between a 2-stroke or a 4-stroke.

I'm considering the Tower .75 two-stroke. What do you guys think?

Go with a 60 to 75 size engine. I have a Global Tecate Bipe with a TT 46 Pro and it's ok. My Lou Andrews Aeromaster flew great with an OS .61 FSR

The Tower .75 would provide more than enough power....

Magnum .91's weigh about the same as most .60/.75's, and they're on sale right now for $129. I like them so much I have 2 of the newer XLS, and an older ASP(a little heavier). But the XLS .91 with a 16x6 would do nicely. I have it on a 9.5 lb fun fly that will rocket out of a hover.

That size plane begs for the right sound too. Sheldons Hobby recently had Enya .90-4c for less than the same size magnum. Enya engines last a very long time. The Fox .60 was the highest powered .60 2 cycle in a recent M.A.N. shootout. Their .75 uses the same design and weighs no more. (it will be inside a cowl won't it?)

Most 2 strokes put out today have a bit more power than those of 1967. I suspect a .46 would be just fine. The smaller biplanes fly a bit squirely at times and can be a bit challenging to fly. I'd start with a .46 2 stoke and go from there. But weight and wing loading is a major factor in selecting the engine size. I'd suguest weighing your airframe and see what you have to work with. Do you show an wing area?

Biplane: lots of drag for the increased wing surface area. Personally, there is nothing sweeter than a 4 stroke engine in a biplane. If you can fit one, the Saito .91 would be a great lightweight choice for this aircraft.

Those are great suggestions. Thanks!

I'm persuaded by those who say I have to put a 4-stroke in this bipe. What's the best value in a .90 size 4-stroke? Is there any such thing (worth buying) for under $200?

Since power and weight are of concern for this bipe, a used Saito .91 is a good bet or a new Magnum 4c. However, if you need a littlte extra ballast and want the power of a Saito 100 in a .91 package than the TT .91 beats most 4c .91s hands down.

I will second the thoughts of using a 4-stroke. Enya, Thunder Tiger or Saito are all very good choices. Otherwise I would go with a nice 60 size two stroke like the Enya or Thunder Tiger.
I have a Great Planes Sportster Bipe and it is under powered with a 46FX on it, even though it is light, it just has a lot of drag. My Saito 91 will be going in it for next season.
Remember you always have the throttle.

Fuelman

O.K., I'm getting close. I'm looking at a Saito FA-80 or FA-91S. They're only about $10 apart in price, so I should go with the .91, right? Then, is there a better way to buy a new one than directly from Horizon Hobbies? Finally, is there a Pitts-style muffler available for these?