enginehistory.org

jjuutinen · Joined: 13 Jul 2003 Posts: 180

Any idea how the Japanese managed to squeeze out more power from a smaller engine than folks at Wright with poorer fuel? Homare´s displacement is about 36 litres vs. R-2600´s 42 litres.

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

A quick search shows 1990hp as the most common figure, and this link seems to indicate that this was only attainable on high-quality fuels. If this site is correct, then R-2600 was about on par with this Nakajima design.
Bear in mind that 1180mm/46in diameter may indicate a shorter stroke (I couldn't find bore/stroke dimensions), allowing higher revs.
This site reckons 3000rpm - not slow for a radial, which might allow greater hp/c.i.

http://www.ne.jp/asahi/airplane/museum/nakajima/nakajima2-e.html

jjuutinen · Joined: 13 Jul 2003 Posts: 180

The Homare had same cylinder dimensions as the Sakae, bore 130 mm, stroke 150 mm. It did at highish rpm. But isn´t the highest rating for the R-2600 (dash-20) 1900 hp, i.e. about 5% lower power with almost 20& greater displacement than that of the Homare.

szielinski · Joined: 13 Jul 2003 Posts: 94 Location: Canberra, Australia

If we assume this the link is correct about the higher grade fuel, we still don't know how high a PN it had. That in itself could explain the difference in power. Then take into account valve timings, intake manifold lengths, valve size, etc, and the differences could easily stack up into several percent.
Let us know if you find out, it's always interesting to hear about other engines.

rinkol · Joined: 13 Jul 2003 Posts: 40

I have a book by the designer, Ryoichi Nakagawa, which was published by SAE some years ago. A rating of 2000 hp with 500 mm boost at 3000 rpm is refered to. This is higher than nearly all other air-cooled engines (I don't think the Sakae exceeded 2,800 rpm). There is also a reference later in the book to the use of methanol-water injection to permit the use of fuel having octane ratings of 89-91 instead of the 100 that the engine was originally designed for. This would have helped as well.

This document seems to indicate that the Homare was not simply an 18 cylinder version of the Sakae. Additional differences included:

- forged steel crankcase
- increased spacing between cylinder rows (220 mm vs 150 mm) to improve cooling and provide additional space for other engine components
- optimized intake system design for more uniform mixture distribution
- improved reduction gear, bearing and lubrication systems

Robert