Exoscientist Robert Clark has calculated a two stage three core Spacex rocket with the proposed Spacex methane fueled Rocket Engine would enable 536 tons of payload in a single launch. Each core has 5 raptor engines for a total of 15 raptor engines.
A June 2014 talk by Tom Mueller, the head of rocket engine development at SpaceX, provided more specific engine performance target specifications indicating 6,900 kN (705 tonnes-force) of sea-level thrust, 8,200 kN (840 tonnes-force) of vacuum thrust, and a specific impulse of 380 seconds.
The Spacex Falcon heavy has three cores and has nine engines on each core as seen in this picture from the Spacex.com site. Having five engines per core would show about three engines in profile on each core.
In April 2014, SpaceX completed the requisite upgrades and maintenance to the Stennis test stand to prepare for testing of Raptor components, and expected to begin tests at the facility prior to the end of May 2014.