Originally Posted by
aspeed
We used to break them in with no pipe so it would not get too hot. I think that nowadays the plan is to break them in at the operating temps, but well on the rich side. That CS was nasty tight. Not even heat would do much there. It is good now, just a manufacturing "defect" The CS is more of a kit motor that you have to fit yourself. I am sure the Profi is much closer to being right. The pipes on the F2A stuff sometimes have adjustable outlet sizes that screw in. I think 4.__ mm is about average for them. Quite small really, as the F2D is more like 6mm, which is down from the older 8mm.
Both the .049 and .061 had real nice fits, a wee pinch up top, and lit up fine on the first runs. I'll assume the same on the speed - for the price I am not expecting an engine kit, nor do I believe it is one. Beautifully made.
Yup, 4mm on my Profi F2A - I was advised that for extended runs or 10% fuel, to open it up a little to scavenge more heat. It does not have stinger inserts. The small outlet diameter on a resonant exhaust doesn't surprise me, nor does a more open outlet on a non-piped engine where scavenging is the goal.
I would have bench run the F2A by now but I can't put it in a regular mount, I'll make an Al plate for it sometime soon. The airframe arrives today or Monday, then I gotta get my butt in gear on the rework.
Open pipe to avoid heat buildup makes all the sense in the world - the F3 speed guys do this all the time. But I was also told that - regards the current good speed engines - in most cases you just go out and fly 'em.