Troy,

Angus might have a point.

Using an internal vernier, I have measured the ID of the Hatori and Asano manifolds (both new) at 9.5 mms and 8.0 mms respectively. This means that even as new, the Asano has only 71% of the cross sectional area (CSA) of the Hatori.

However, as you infer, many top F3A pilots (including Naruke San http://www.excite.co.jp/world/englis...=JAEN&wb_dis=2) are using the Asano manifold. I would not expect them to be doing so if it caused a significant reduction in power – at least when new.

I would however expect the Asano to be considerably more prone to the effects of carbon build up than the Hatori. A 1 mm build up of carbon on the walls of each manifold would reduce the diameters of the Hatori and Asano manifolds to 7.5 mms and 6 mms respectively. At this point, the Hatori would have 62% of its original CSA compared to 56 % for the Asano. Perhaps more significantly, with this amount of carbon build up, the Asano would have 64% of the CSA of the Hatori compared to its original 71%. In a nutshell, the smaller the diameter of the manifold, the faster the effects of carbon build up will be seen.

Also, for what its worth, I have had limited success with cleaning hard carbon from the internal walls of a manifold. The sections of the pipe near the inlet and the outlet of the manifold are relatively straightforward, but the area around the inside of the bend - where the build up is likely to be at its worst - is more difficult to get at, even with chemicals and pipe cleaners. Unfortunately, the pressure that can be generated by blowing through the manifold is insufficient to give a reliable feel for the amount of restriction unless the blockage is severe.

On a separate topic, I have now read several posts and have also picked up other independent reports, where users of early production YS 170’s are experiencing problems. Typical of the issues reported are difficulty with maintaining a steady idle and instability at higher revs. I appreciate that the problems being reported may be utterly unrepresentative but I do find it slightly worrying that the problems are being reported by experienced and trustworthy users who have had many hours of trouble free running with 140 and 160 Dingos. I hope it is not the beginning of a trend!?

Regards

Bob