This question maybe belongs in engines,but I'm in the middle of building so here goes.How do I decide how big of an engine to use? If I can not use what I have then I am going to need to sell something or try and get another one buy the boss haha.I"m building another LT-40 with some mods so it will be a little heavier so I would like to use something bigger any help?

Saito .56 should move it along rather well. I run my LT-40 woith an OS .46 FX and 11X4 prop. Under propped, yes, but man can it pull!

AN 11X5 may be better.

Sounds like Iwill have to go shopping again.I only have a
satio 91 that is'nt doing anthing right now.I have a MDS 40 in my other LT and a MDS 68 in my 4*60.

Elwood could not have said it better. The OS.46 FX has PLENTY of power for a little extra weight. My choice would be the .56 Saito. (I love the 4 strokes)!! I had a .46 FX and still have the .56 Saito .. both are great engines!!! ..lownslo

Thanx for the help,I started this hobby years ago(and I mean years) in control line and then on up.It still gets a little cofusing,I was sitting here looking at the planes I have,being the GP Tiger Moth,LT-40 and the 4*60 and they are all pretty much the same size heck the wings between the * and LT look like they can be switched. so how is engine size rerally figured out? short answer will work haha