Maybe I'm looking at a different spec sheet or different year model
but.....

On Mon, 12 Mar 07, "Shaun Van Poecke" wrote:
the 15 and the 9.9 seem to share a common block, but with a
different carb and prop? they have exactly the same weight (50kg),

I'm seeing a heavier 15hp than 9.9hp (granted, I'm looking at specs on
short shafts).

same
displacement (323cm3),

I'm seeing 362cc for the 15hp, and 323cc for the 9.9hp

same compression (9.19:1),

9.3:1 for 15hp, and 9.19:1 for 9.9hp

different gear ration
(2.92 for the 9.9, 2.08 for the 15).

Yep

but different RPM ranges. 5000-6000 for 15hp and 4500-5500 for the
9.9hp.

is the 15 just a 9.9 with a different carb?

My guess...... no.

are they just as reliable as the
9.9?

My guess.... yes.

Im guessing they wouldnt have as much usable thrust as the 9.9 with
its bigger prop, but probably a higher top speed?

Depends.... (see my multiple choice post).

thanks for any and all info,

Good questions. Glad you asked.

BTW, here are the spec sheets I'm looking at:
http://www.yamaha-motor.com/outboard...s/4/specs.aspx
http://www.yamaha-motor.com/outboard...s/5/specs.aspx

Rick