RE: what to use black or red muffler
Hi,
Thanks for writing.....
17,500 on a 8.8x9 prop is just about right for a SJ-50 engine.
Yes, you can use the black racing muffler on the .50 engine.
However....
Same target rpm is important - you want a prop selection that allows the engine to easily get to 19K ground peak rpm or better. Then back off 800 or so rpm for flight.
Question though.....
Do you have a sport .40 ? (CAPS or SEMPRA racing engine?) Those were supplied with the SS sport racing (red) muffler.
Or is it one of the 428 engines with a carb added?
(Dub sells the 428 racing engines with an added carb quite often - but it is the race engine, not the sport engine)
Easy way to tell typically..... look at the liner. The racing engines are almost all AAC (aluminum liner). The sport engines are ABC (brass liner)
Based on the prop and rpm, it sounds like you have the 428 .40 engine with a carb added on - thus the black muffler.
That engine would have no problem turning the 8.8x9 or 8.8x8.75 prop up to and over 19k.
The SJ-50 sport engine is lower timed less rpm but a bit more torque and a great deal more user-friendly. Expect to run LESS prop to get it to turn up with the black muffler. Typically an 8.8x8.5 is a good bet.
Hitting the rpm is important or the engine will not needle properly and may overheat
Bob