MJ, I ran my SF w/pipe for a short while, but I didn't take any tach readings. I can't really do a lot of running on the patio, so I need to take the engine to my field. I cut my header to 6" which is what Macs recommends for this engine. But, I extended it a bit with a longer Aerotrend blue coupler. I'm using the 10cc Long Stroke quiet pipe #1062. Anyway, it really sounded strong with an APC 12x8 and as I tune the length I'm sure it will get better.
I think you 13,300 sounds good. It will probably go up as you shorten the header. However, I think this engine was intended to be propped around 12,000 or so. I'm setting mine up for a 12x8 or 11x10 (they turn about the same) and I hope to get close to 12,000. I'll be very happy with that, if I get it.
BTW, Graves R/C is selling the #1062 long stroke pipe for $52.99. It's the cheapest I've seen anywhere. I got it in two days; great service, IMO:
Macs lists this pipe for $100.95!
I'll post again when I have some numbers. Maybe by next week. Oh, it's going in my Bridi UFO: