Buy another saito 90R3 and put them in a TopFlite, KMP, or Hangar 9 B-25. The power output of a saito 90R3 is closer to a saito .72, not a .56 as suggested by another poster. If you look at the specs, the motor can turn an apc 13x8 @ 8500 rpm's. The saito .56 cannot do that....its top prop size is a 12x8.

Using a little bit of math here, we can deduce the power output in general terms.
The 170R3 has been stated to be equivalent to a saito 1.20
The 1.20 has 2.2HP
The 170 is comprised of 3 .56 saitos. The .56 puts out .90 HP, so you'd think its doing 2.7HP, but, as a result of the inefficiency of multicylinder engines in model aspect size, you lose some power thus makign it similar to a 1.20
So, simple math:

2.2 ~~?percent
--- x ----------- = 81.48% power output of combine single cylinder outputs on a radial
2.7~~ 100

So, now we look at the saito 30 since the R3 is made of 3 of them
Power of saito .30 is .50 HP x 3 for a radial is 1.5HP
1.5HP x 81.48% gives 1.222HP

Now Horizon basically comfirms that the 90r3 can fly a .60 size radial warbird by stating its "maximum realism for .60 size radial warbirds". This means they have at least flown one .60 size radial warbird with this motor(but at there elevation of about 1000 ft above sea level...keep that part in mind)

It will fly a Hangar 9 Corsair or similar that weighs 8 pounds like has been stated by another poster. This also lends credibilty to the fact its putting out more power then a saito .56 because a saito .56 will NOT fly a .60 size bird without using 30% heli fuel and even then its marginal at best

I have had the 90TS twin and it did put out 1.2HP as advertised. The 90 radial will be about the same, however, in reality, might be doing more like 1.15HP