I am currently building a 64" extra type plane. I want this plane to have sufficient power to be fully capable. It should weigh no more than 8.5lbs in the air, probably less but we'll see. I've been looking at a magnum 120 4 stroke but I wonder if a thunder tiger 91 4 stroke will do it. I know a magnum 91 4 stroke will hover a 8.25lb plane but it will not pull vertical out of the hover. I want for this plane to pull out of the hover and have responsive torque.
Any input will be appreciated. Do the larger 2 strokes have good torque?

As much as I like magnum engines, I would recommend a saito. The are much more powerful and much lighter in weight. I would recommend a saito 100 or 120. They are very reliable and economic once broken in properly.

This is just my opinion, but I hope it helps.

If you do choose a Saito, go for the 100, not the 120, as it's a lot lighter and will suit an 8.5 lb plane perfectly.

-DC

OR a YS 91FZ (or 110)

Yes. I admit it doctor.

I am at risk, at the moment, of becoming a YS man instead of a Saito man, having run my YS110 a few times now.

-David C.

go for the saito 100 i have a 9 pound extra and it will rocket out of a hover
use a 15x6 APC prop

Thanks for the inputs. sounds like the saito 100 will do it or the ys 91. Best I can tell is a good 3D plane needs torque to pull vertical and "reset" in the hover when you start to roll/fall out. I'm new at this 3D stuff. Are these large 4 strokes tempermental?
The TT pro46 and 36 I use now have got me spoiled I guess because they run perfect everytime. Thanks for the help.

I have found that most 4 strokes (all brands) are less tempermental than the 2 strokes. Once set up, I hardly ever have to touch the needle valves again, even when changing brands of fuel.

I agree. 4strokes have been much less tempermental for me also. Some I have even flown straight out of the box(magnum, saito) without problems. I wouldn't recommend that though.

I have found the bigger powerplants take a little more time to break in, but are still easier to use.

I've mounted them sideways, inverted, up straight with no problems. I even have an airplane were the fuel tank centerline is two inches above the carburator of my inverted saito 100, and no problems whatsoever! :boxing:

My dads Magnum 91 runs good, I was very impressed with it but it will barely hover his 8.5lb plane I built for him. I'll look at the Saito 100. I probably will have to cover the plane and get a good feel of the all up weight before buying the engine. Right now framed up minus the gear it weighs 3.5 lbs. I'd like to be at 7.5lbs without fuel but that may be wishful thinking.