What are my options for a light muffler to use on a LA 25? Looking to use muffler pressure. Are the Big Art mufflers very light, an can I use muffler pressure on them?
Ay yi yi! The "new" version 25LA with the *stock* parts exactly as it comes out of the box makes for a remarkable effective stunt engine system, far better than most people have ever had since CL was invented in about 1937. Every single "improvement" people have tried on this engine (and it's logical predecessor the 20FP) has made it work much worse.
Big Art mufflers are top notch but as far as I know they are not tuned the same way that the stock E2030 muffler is. Chip mufflers are not tuned at all and will certainly degrade the run quality compared to the stock unit - far more degradation than the weight saved will make up.
The stock system should use muffler pressure from the existing pressure tap into tank set up with a suction vent.
The stock venturi is the same as a 20/25FP, ~.257, which I expect is really 6.6mm. With the *stock* spraybar/"nozzle" and the *stock* muffler set up per the instructions, with a 9-4 or 10-4 APC, this works perfectly. If you replace the spraybar with an ST-type, it will remove about 30% of the power which will make it very difficult to use with a 4" pitch prop. And since you have to drill out the case to get it to fit, you can't easily go back to the superior stock arrangement.
I very strongly urge you to *use everything stock straight out of the box* and I have never seen any modification or alternate parts make it run better for stunt. At least, if you absolutely must experiment with alternative parts, don't do anything that will prevent you from putting it back the way it came out of the box, screws, muffler, venturi, spraybar, etc. because that's where you will end up at the end of the experiment.
Brett