And since the higher power engines are emissions certified at all probable load and speed states, then emissions certification becomes very simple. It's very easy for them to program power or torque limits. But, you can bet that they have very accurate models built into the ECM that know how much throttle opening results in what torque and power output of the engine. I don't know if the Yamaha uses torque demand, desired airflow, cylinder airmass, or other basis for control. It looks like Yamaha switched to DBW in about 2005. In a modern drive-by-wire system, the throttle body is modelled in the ECM such that it is known what the airflow is for any given manifold pressure (MAP), baro pressure, and throttle angle. And as others have mentioned, retarding spark timing adversely affects emissions, fuel economy, and EGT which is especially important on a marine engine. Either way, this likely only accounts for 5-10 hp, not 50 or 100. I have some data that 2 deg of spark timing is really only worth about 2% power change or less, depending strongly on how far off from MBT you are. So, if the octane is 2 numbers higher, then the higher power motors might see 2 deg more spark timing. On the spark timing, the published rule of thumb is that each octane number allows about 1 degree more timing before knock. Since the compression is the same, then the differing octane requirements must be due to different spark timing (more significant effect) or cam timing (less significant effect). The lower power versions allow 87 octane but the higher power require 89. I'm afraid we can't get anything from the torque and rpm ratings.Īll of them are 10.3/1 compression. Torque peaks are between 35 rpm, not necessarily correlated to power rating.

The torque numbers are even more non-intuitive, as the 225 makes the least and the 300 makes the most but the 200 is in the middle. Ironically, the 200 peaks at 6000 rpm and the 300 is at 5500. Now that we are sure we're talking about the 4.2 liter 4-stroke v6.and IF it's true that the powerheads are identical (this can be verified using parts diagrams).then we can gather some additional data and apply what we know about engine calibration to figure what's most likely changed.Ī quick search of the CARB database reveals that all of them from 200 to 300 hp peak between 50 rpm.

Ecu flash for yamaha outboard