Fuel Injection and Altitude with Direct Drive ski boat

Do I need to change the prop on my fuel injected ski boat when I run it in big bear (7000+ feet)?
Boat starts, runs, and sounds fine but after being warmed up, if I mash on the throttle, it really doesn't do much from half way to full way (throttle).
P.S. it is a Lexus VT300I V8 Engine.

Thanks,

Brendan

So it speeds up but just not fast enough for u?

If that's the case, Less pitch on the prop will help since you lost some power with the altitude change.

dont know anything about your setup, but do you have o2 sensors that monitor the exhaust gases and adjust the fuel accordingly or is it a preset fuel curve? If it's preset you might need to have that adjusted for the altitude. Just throwing it out there

braindead said:

So it speeds up but just not fast enough for u?

Click to expand...

No, the acceleration stops at about half throttle. Anything after half throttle does nothing.

More noticeable above 3000' you lose about 3% every 1000' above sea level!

The EFI will keep the motor running properly but you are going to lose a noticeable amount of power with altitude.

I am trying to figure out if it is a preset O2 sensor setup. If it is, sounds like my solution is to reprop with a smaller pitched prop.
This is my first FI motor and it fires right up without issue and runs fine. The other issue is that I have never run it at sea level (ie. river) to see the difference.

probablecause said:

Do I need to change the prop on my fuel injected ski boat when I run it in big bear (7000+ feet)?
Boat starts, runs, and sounds fine but after being warmed up, if I mash on the throttle, it really doesn't do much from half way to full way (throttle).
P.S. it is a Lexus VT300I V8 Engine.

Thanks,

Brendan

Click to expand...

If it's a feedback system, you don't need to do anything, if it's a preset curve (programmed map) then it needs to be setup for higher altitude.

Both systems will have about 20-25% loss of power at that altitude, changing the prop will be necessary to get more performance out of it.

probablecause said:

I am trying to figure out if it is a preset O2 sensor setup. If it is, sounds like my solution is to reprop with a smaller pitched prop.
This is my first FI motor and it fires right up without issue and runs fine. The other issue is that I have never run it at sea level (ie. river) to see the difference.

Click to expand...

If it has active 02 sensors it's most likely a feedback system, just change the prop.

If the builder/tuner had to install the sensor to "tune" it, it needs to be redone for it to be optimal at that altitude.

Either way a prop change will help.

SBMech said:

If it's a feedback system, you don't need to do anything, if it's a preset curve (programmed map) then it needs to be setup for higher altitude.

Both systems will have about 20-25% loss of power at that altitude, changing the prop will be necessary to get more performance out of it.

Click to expand...

Not completely true. Even an EFI in "open loop" will change the fuel delivered based upon where the MAP sensor indicates. The boat will be down on power as stated by other posts but it will adjust even if the system is in open loop. A closed loop system (02's active) will still be on another line in the fuel map as a result of less atmospheric pressure.

Bottom line change your prop when you're at altitude.

Every smartass is thinking it so might as well say it...

Did you try a different prop?

I boat at 5280, change your prop, call ACME or OJ they can recommend the right prop. Or put a supercharger on it!

braindead said:

Every smartass is thinking it so might as well say it...

Did you try a different prop?

Click to expand...

:thumbsup Not yet. Boat is in Big Bear and I am in OC. Have to check which prop is on it. Mfg lists 3 different types for my 2000 X22:


Propeller,13x13,RH,4Blade,1"Shaft,99E21,E22,X22
Propeller,13x13,LH,3-Blade,1"Shaft,E21,E22,X22
Propeller,13x13,LH,4-Blade,1"Shaft,E21,E22,X22

I am hoping the prop is marked so I know which one I have.