You strut sounds too low to me can you post a pic with the boat sideways on ?,.Strut depth might need to try level with sponsons or just below not sure how deep yours are but the boat needs to be riding on the prop not the sponsons.
Pipe length will depend on motor if its stock your not far away,mine was a full mod at 11 1/2" .You will need to experiment with it and see where is best for your setup.
Mart
Heres a thread might be of interest
http://www.rcuniverse.com/forum/m_83...tm.htm#8360535
some more
http://www.rcuniverse.com/forum/m_63..._1/key_/tm.htm
http://www.rcuniverse.com/forum/m_4900779/tm.htm