Jetting at altitude...

[bolivas]

I am in Tahoe all summer, and this is my third summer on this boat and had 5 summers on the 09. It's common to lose about 1,000rpm off the top end due to elevation.

Here's some stats I notice: I only get 6200-6300 out of the engines at the lake. 35MPH seems a bit slow, but as I can get up to the low-mis 40s. One thing to pay attention to is the weight you have in the boat as well as the wind and waves as all three will affect your top speed dramatically. For example, I had 5 people in the boat on Saturday and she was doing about 25MPH at about 5800rpm. on July 4th with 12 people in the boat, it took 6000rpm and about 2-3 minutes before she climbed up on a plane and she would only do about 13mph.

Compare that when I had the boat down at Nacimiento at the beginning of the season (or even up at Shasta) and she will turn 7000+ and top out close to 50 mph.

These normally aspirated engines will struggle a bit to breathe up at the lake.

For those who rep itch for altitude, how does it affect lower elevation performance?

I have the high altitude impellers (normal altitude for our use is 5K' and up) and when dropping down in elevation you have to keep an eye on the tach. I can reach 8K RPM's at about 3/4-7/8 throttle (depending on how low we go). WOT will over rev and eventually cause damage.

 

[Tahoe CAL]

OK - Posting in the event that this helps anyone else down the line:

I'm wasn't sure the difference between the SAT1800FLR and SAT1800FRB models of my boat - or which one I have ( the boat is 200 miles away right now). That said, I know that I have the 4 star California emissions and the S E-Series. Long story short looks like both ribbons are model 6BH-1444B-00-00. With that information - Rich at RIVA was able to steer me to the RIVA Yamaha 08-12 1.8 NA Intake Manifold Upgrade Kit. Side note - the reason that California models didn't change to the smaller manifold size along with the other "49" models is that the other emissions modifications compensated. So they kept the larger manifold size (or something like that). So, I have them on order -- along with the power filter kit: RIVA VXR/VXS FX HO POWER FILTER KIT 2012-19. Hoping to get them installed in the next two weeks or so. Will post an update on performance.

Appreciate the help!

Colby

 

[JDRacing]

Was up at Tahoe early last month. With two adults we saw 40 mph at about 6800-6900 rpm, and with six adults we saw 36-37 mph at about 6500-6600 rpm on a 65 degree calm morning. At sea level, on a 55 degree morning, with 1 person, I saw 51 mph at 7700 rpm. Our boat is bone stock. I think you're right in the ballpark for a stock boat.

 

[swatski]

Even at Lake Powell, which is ~4,000ft(?) performance takes a beating, we were doing about 40 at 7,000-7,100 rpm WOT.

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