I am looking to buy an asp 4 stroke engine, But i am not sure what size to go with. I want something that will be close in power to the fx or tt pro 46. I am not looking for top end speed but more pulling power. How does a 65 4stroke compare to the 46 2 strokes? Is there a basic rule to follow to get and equilvant 4 stroke to a 2 stroke? i saw on a site that the magnum 46 2 stroke has better top end speed but the 4 stroke 52 has better pulling power or vertical. I thought about getting the asp 80 4 stroke but if it going to weight a ton more than the 46 2 stroke and produce a alot more power then i dont really want that. I am looking to put it on a 5 to 6lbs plane and want to get good vertical performance and hovering with it and enough power to pull out of a hover. I chose asp because the price is so much better. I heard that they are also made in the magnum factory also.

I can't give you a scientific answer but I can tell you my experience with motor substitution. I have a low wing monoplane with a 60" symmetrical wing, about the first step up from a high wing trainer. I started with the recommended 0.46 two stroke OS LA engine. The plane flew ok if you just wanted to fly around but it didn't have enough power for vertical manuevers like humpty bumps and big loops. I put in an OS 72 4 stroke and the plane is now a lot of fun to fly. The bigger prop pulls the plane well on vertical lines giving me more room and time to do stuff like humpty-bumps. Loops can now be much larger. The engine is heavier but I had to put in nose weight anyway when I had the lighter two stroke on it. With the tricycle landing gear, the 12 inch prop has about an inch clearance to the runway. I used to run a 10 inch prop with the old engine.

A few more comments. OS 72 4 stroke manual says to use 11x9 or 11x10 prop with engine but these props are not commonly available in hobby shop so I went to a 12 inch prop. I think its a 12 x 8. It works but I trim the grass if I make a hard landing. My plane doesn't have enough rudder to hover.

Hey Grant, If your flying a 6lb plane and want to hover with pull out power and vertical I go with a good 4 stroke with large diameter prop and low pitch a O.S. 70 at 24oz or a Magnum 91 at 23.3 oz you can always throttle back and My choice would be the Magnum 91 I have two and they are great and you cant beat the warranty be leave me you cant

On the man. the YS-63 has more power than an OS-70 or Saito-65 but the Saito 72 has tons of power and is lighter than the 65-

etc, etc.

The Magnum 52 4 stroke does not have more power than the 2 stroke 46 period>.

The Magnum 91 is light and they are surprisingly good engines! As are ASP- (same thing..)

Good luck,
james

If you want to hover a 6 lbs. plane, get a YS 63, Saito 91, Magnum 91, or OS 91 four stroke. However, the Saito 72 might be able to do the job for being light. As stated above, you want an engine that can swing a large diameter, low pitch prop. If you use the Saito 72 to spin an APC 14x5 prop at 9300 rpm, then according to Thrust Calculator, this combo would give you 9.97 lbs of static thrust.

Hey tcastner -

I think my OS 70 Surpass (1) weighs in at about 20.6 oz with pipe and muffler. Makes it about 3-4 oz heavier than a Saito 72 and 2-3 oz lighter than that Magnum 91.

GoMike

Grant;
To try to answer your initial question.... the rule of thumb in trying to equate a 2 stroke to a 4 stroke is you size 1 up from the 2 stroke! for a 45 2s look in the 60-75 4s, 60 2s is 90-100 4s, and 90 2s is 120 4s. This is a rule if you want equal power. Of course most of us want more power....
Now for power vs size, the YS-63 will give you the same power as most 90 4 strokes. So there's alot of bang for the buck there. If you are just starting in 4 strokes you might want to get an OS. They are very user friendly for first timers. Saito's and Magnums take a little more breakin time and tlc. While the YS, you just have to be a little more meticulous in your setup.
Good luck and remember to just have fun!

Thanks guys for the quick responses. I found a TT F91 s 4 stroke for a good price. Are these good quality engines like the the TT 2 strokes?