So we have heard a lot about the poundage on Mongolian and English bows, but how much poundage did the Japanese bows have? Did the Japanese have the 180lb range that the English and Mongolians did, or where they more in the 60lb range?

I'm not aware of any specific unambiguous quantitative details. "Heroic" bows are described as requiring unusual strength to draw or to string. There are descriptions of bows as "two-man", "three-man", "five-man", where this is the number of men required to string it. "Two-man" appears to be the standard.

There are also descriptions of arrows shot from strong bows piercing armour.

So compared to Chinese (plenty of literary sources, with quantitative draw weights), Turkish and Indian (plenty of surviving bows), and English (plenty of surviving bows if we count the Mary Rose bows) archery, we lack good direct data.

For indirect data, Japanese military archery was centred on armour penetration. From literary sources, armour penetration was valued, and powerful bows were valued. From the design of the bows and the arrows used, the main goal was high-energy arrows, to the point where accuracy and speed are sacrificed.

I'd expect the typical Japanese war bow to be about 100-110lb at full draw (which is much longer than 28"!), like typical Chinese, Central Asian, Turkish, and Indian bows. One could/would find more powerful bows in the hands of some archers, but much more powerful would be unusual.

180lb is plausible for the most powerful bows.

What sources do we have for armor piercing being a desired quality?

First, descriptions of the heroes in the epics.

E.g., from Tale of the Heike: “Do you then consider me a mighty archer?” asked Sanemori with a scornful smile. “I can only draw an arrow thirteen handbreadths long. In the eastern provinces there are any number of warriors who can do so. There is one famed archer who never draws a shaft less than fifteen handbreadths long. So mighty is his bow that four or five ordinary men must pull together to bend it [to string it?]. When he shoots, his arrow can easily pierce two or three suits of armor at once."

Second, some military writing: “For shooting an enemy on the battlefield, one needs, moreover, to practice shooting at a distance of seven or eight ken [approximately 15m] to be able to penetrate his armor. But in tōshiya [a form of sport archery], by sending an arrow light as a hemp stalk a distance of sixty-six ken, how can one hope to pierce armor?” (a 17th century complaint about the sportification of archery, quoted in G. C. Hurst III, Armed Martial Arts of Japan: Swordsmanship and
Archery, New Haven, Yale University Press, 1998.)

Apart from literary sources, the standard war arrows, togari-ya, had armour-piercing heads.

http://www.archerylibrary.com/articles/outing/yumi/ ive found this attributation here
"Every time his bowstring twanged an enemy fell."

SO it was said of Yoritomi, the ablest Shogun and greatest ruler that ever lived in Japan—he who founded the dual system of government by making himself the first dictator, with his seat of government at Kamakura, while the Mikado was maintained a ceremonious, dignified, but unapproachable captive at Kioto.

This important event in the history of the Japanese was the outcome of a great battle fought in 1185, when Yoritomi, the leader of the powerful Minamoto family, overthrew the Taira. It was a naval battle between great high-pooped junks, loaded to the water's edge with warriors. But, strangely enough, it was a naval battle that owed its victory, if we can believe the chronicler, to the prowess of the bow and arrow.

The iron bolts shot from the longbows of the Minamoto archers are said to have gone crashing through the planking of the Taira junks, scuttling them as effectually as the more modern rifle-ball. As the riddled hulls sank, they left the brave warriors, swimming in a bloody sea, easy targets for the showers of relentless arrows of the Minamoto.

So that makes it clear that powerful armor piercing bows were required, the next question is (since the seem to be measured in men needed to string them) how powerful would that be in pounds? I don't see how you could have a 2 man bow or an 11 man bow since the archer himself (I am assuming) would have to string the bow by himself. The only way that makes sense to me is if they are using the term Odyssey style, where it would take many *normal* men to string Odysseus's bow. However that's more of a mythical type term, rather than an actual unit of measurement.

Also William, that source you cited doesn't look very credible, as I don't see what primary resources he is citing, and seems to be very much of the old Victorian notions which I deeply mistrust.

I would be surprised if that was as literal as means 5 people, whatever weight the bow is 2 people as described above is plenty. There are ways for one person to string a 100lb + horsebow.

Ya, sounds like the man system is just a legendary thing rather than an actual measurement.