Wayne look under the Titleist club section for drivers Gives all the information on these drivers.
D2 driver is 460 head higher launching and higher spin.
D3 driver 440 head low spin low launch.

917D2 - Distance with forgiveness in a full pear, 460cc profile. Offers more forgiveness, a slightly higher launch and more spin versus the 917D3 driver.
Available Lofts: 8.5°, 9.5°, 10.5°, 12°

917D3 - Distance and Workability
Distance with workability in a traditional, Tour inspired pear, 440cc profile. Offers more workability, a slightly lower launch and less spin versus the 917D2 driver. Available Lofts: 8.5°, 9.5°, 10.5°

For more details about each club, click on clubs above on this site and then click on drivers. Cheers, Chuck

D2 is a little more forgiving, a little bigger, launches a little higher, D3 is more workable, lower spinning. I have the D3 and love it.

D2 is slightly larger and slightly more forgiving while the D3 is slightly smaller and less forgiving but is more workable than the D2. Both are great drivers and if truly considering one by all means see a certified titleist fitter. Best of luck.

See below....and then visit the Clubs/Drivers page for more details.

917D2
DISTANCE WITH FORGIVENESS
Distance with forgiveness in a full pear, 460cc profile. Offers more forgiveness, a slightly higher launch and more spin versus the 917D3 driver.


917D3
DISTANCE AND WORKABILITY
Distance with workability in a traditional, Tour inspired pear, 440cc profile. Offers more workability, a slightly lower launch and less spin versus the 917D2 driver.

Generally, D2 is 460cc, and D3, 440, a little smaller. Generally D2 a little more forgiving, D3 more workable. Spin rates are slightly different too, but you'll see Tour players using both. Test them both, see which works better for your and your game. Although they look the same in a photo there are differences when you see them in person. With some folks they like the look of one better than the other. I had a D2 in the 910, a D3 in the 915 and D2 now in the 917. This worked the best for me, and is the best all around driver (feel, forgiveness, sound, distance) I've had. Had some other brands over the years, that might be a little more forgiving but had to compromise on feel. Maybe one felt good but sounded like crap. No compromises on the 917. But get fit, so it will be dialed in. Doesn't mean you'll be guaranteed to hit everyone long down the middle, but when you don't you'll be sure it's the pilot and not the plane.

D3 driver is a lower cc smaller head, but deeper face. It will spin the ball a little less the ball will be more workable. D2 is the opposite.

Check this:

www.titleist.com/.../drivers

917D2

Distance with forgiveness in a full pear, 460cc profile. Offers more forgiveness, a slightly higher launch and more spin versus the 917D3 driver.

917D3
Distance with workability in a traditional, Tour inspired pear, 440cc profile. Offers more workability, a slightly lower launch and less spin versus the 917D2 driver.