The OS 91's and Saito 91's as well as the Magnum and Thunder Tigers are all very simular engines and as to which one is best would cause some debate on here. You should buy the one you get the best deal on or the one you first come accross. The Saito 100 is a good user friendly, higher power, alternative if hoovering is your game. It is more powerful than all the others but about the same as the Y-S 91 in power.

The Y-S 91 is more powerful, heavy, and cost more than the other engines with the exception of the Saito 100. Although a new one generally runs extremely well, they can have trouble and due to their complexity, can be a real problem to get to run correctly unless you are very good at engines.

It is cheaper to just buy a stand alone pump for one of the above engines (with the exception of the Y-S) from Perry if you decide in the future that you may need one. The OS pump is nice but it costs a lot and they will obsolete it before you know it and then you will have to buy a stand alone pump anyway. Pumps are a added complexity that often cause as many problems as they cure. There are also demand regulators avaiable that help keep the fuel delivery from the pump constant. It is usually best to pick a plane design that has the tank positioned to where there is no need for a pump.

Any current R/C fuel tank should be fine for the above engines. The above mentioned 4 cycle engines do not produce anymore tank pressure than the two cycle engines do.

The question of bursting tanks refers to the Y-S engines (both 2 cycle and 4 cycle). They use ported crankcase pressure with a check valve to build up a lot of tank pressure. however, I havn't had any trouble with just using a standard Dubro tank with them. But you should relieve the pressure after use. Don't press your luck.

You can hoover with either 2 cycle or 4 cycle engines. It's just that we've been in a transition period to four cycles in recent years and everyone talks about them all the time.

The best things in life are simple!

good luck,

Jim