Gentlemen,
I've been flying a profile with a G21-46. The engine doesn't have nearly as much power as some of
my more modern engines, but I love the sound of it.
Using a venturi with the spray bar going through the body of the venturi, how large can I open up the
inside diameter of the venturi without having to use muffler pressure?
I don't care much for the "through the middle" venturi - if it's not already drilled through, i would certainly suggest using the stock arrangement.
Assuming that ship has sailed, I think about .280 is about all I would have much enthusiasm for. And that will likely be marginal, particularly on 5% fuel.
If you want more power, I would look into fuel rather than venturis. The last gasp of the ST46 was David's at the 89 TT, running 15% or 20% Cool Power with some castor added. You definitely need some synthetic to keep everything cleaned out and the ring moving. And don't be afraid to throw nitro at it. 15% for sure, more if necessary. If it starts doing funny ignition things (and ONLY if it starts running funny) you can add shims until it stops. I think this is far better solution and far more reliable way to get power out of it than pushing the venturi to the limits.
And in any case, to get any sort of power out of it, *you need a good ring*. That's about the only thing that matters as far as the engine itself goes. Engines with weak rings will run nice and smooth but be gutless. If you have one of the early really good stock rings, then good, but if not several people still make rings and I would suggest looking into that. I have one of the strongest ST46s that my buddies and I have run across, and it's absolutely bone-stock internally - with an exceptional factory ring. Never even had the head or backplate off.
We all thought that my engine was the so good that we couldn't imagine what else you would want - until we got a 40VF! A really good ST46 is a nice stunt motor but no matter what you do to it, don't expect miracles. And AeroTiger will eat it's lunch as far as stunt performance goes.
See *many* previous posts on the topic of ST46s. I was one of the last holdouts and trying to keep up with the ST60 crowd and then,briefly, with the 40 TP motors, we pretty much had all the tricks figured out. And it boiled down to having a good ring and the right (pretty ordinary) fuel. Without that it didn't matter what you did. Most of the bizarre theories at the time (porkchop cranks, "0065" cranks, hemi-heads, shaving the head fins, etc) were either pointless or detrimental unless for some strange reason you thought you needed to "detune" it.
Brett