Top Speed Issues

[Nick Hughes]

I appreciate the altitude explanation. We had 10 on the boat yesterday, light chop and hit about 40. My brother thought we were doing 60, it was fast. Im fine with everything Im experiencing, I just wanted to make sure I didn't have a problem if I'm only hitting 7000 RPMs. I saw a few other threads about 2015 models topping out at 7000 and they thought they had issues. From what Im reading, i do not. Im surprised the ECM can limit RPMs by 10%. I wouldnt think a car under the same conditions would limit the top end RPMs by 10%, but I get it, these aren't cars.

 

[Gym]

I appreciate the altitude explanation. We had 10 on the boat yesterday, light chop and hit about 40. My brother thought we were doing 60, it was fast. Im fine with everything Im experiencing, I just wanted to make sure I didn't have a problem if I'm only hitting 7000 RPMs. I saw a few other threads about 2015 models topping out at 7000 and they thought they had issues. From what Im reading, i do not. Im surprised the ECM can limit RPMs by 10%. I wouldnt think a car under the same conditions would limit the top end RPMs by 10%, but I get it, these aren't cars.

I could be wrong but I believe the ECM is metering the fuel flow based on the air/oxygen available to burn. I still think if you get a chance to operate your boat at a sea level location you will see higher rpms and higher speed. 40 mph with 10 people on board is pretty good though.

 

[Mainah]

@Nick Hughes You may want to check your throttle adjustments on the side walls of the engine bay. I had to adjust mine to get full rpm. The adjustment procedure is in the the manual and is easy. What that adjustment does is ensure that the combination accelerator and throttle position sensor (APS/TPS) can output as much of the reference voltage to the computer and throttle body as the APS/TPS (this is a dual analog potentiometer) will allow.

1300ft elevation will have an impact. Not sure that is enough to require throttle body spacers but that may be an option and others have done that. Still it would seem to me that 1300 should not make that big a difference but I am a sea level guy.

For those interested the ECU only controls fuel delivery in the air fuel equation on the 1.8l. Air is determined by the cable actuated APS/TPS which sends a analog voltage signal to the throttle body directly as well as a seperate voltage signal to the computer so it knoes how much the throttle body is open. So with properly adjusted cables at WOT the throttle body is max open but max fuel may not be being delivered depending on the amount of oxygen in the available air (with O2 sensor) or the is not enough oxygen for complete fuel burn (no O2 sensor) even with max fuel and air being delivered.

 

[Nick Hughes]

@Mainah Your explanation may explain this. When I have the throttles at about 80-90% Im at 7000 RPMs. So moving them the last 10-20% to WOT results in no additional RPMs. So that could mean i need to adjust or it could be fuel delivery is cut off because of not enough oxygen. Getting to sea level isnt really an option for me. I will be going to Put-In-Bay (Lake Erie) in September, but even there is only ~600 above sea level. Next summer may. I will look into the throttle spacers as well.

 

[Nick Hughes]

Also, what is different with the California version? Can "it" be "removed"?

 

[Mainah]

Short answer is no it can't be removed. CARB model adds catalytic converter (increased back pressure is most of what cuts down the hp) and O2 sensor. Removal would be very difficult because of the ecus programming and expected O2 sensor values.

 

[Speedling]

Remove cats, remove 02 (or use a gauge and see what you are running at) find a trashed ski ecu and swap.

 

[Gym]

1300ft elevation will have an impact. Not sure that is enough to require throttle body spacers but that may be an option and others have done that. Still it would seem to me that 1300 should not make that big a difference but I am a sea level guy.

I don't discount your suggestions but as I explained earlier his boat is not operating at 1300 feet but almost double that at only 70 degrees. Most of us boat in warmer temps so if @Nick Hughes is boating in 80 degree weather his boat is actually operating at 3200 feet above sea level which will definately have an effect on engine output. The computer in a car or boat will lean the fuel to match the oxygen deprived air resulting in less horse power. The humidity level will effect this even more. Before you rip your boat apart and your hair out, try a sea level run on a reasonably cool dry day with a light load. That will give you a quicker, cheeper answer.

 

[Nick Hughes]

Unfortunately, 500 feet above sea level is as low as i can find in ohio. And thats the nasty ohio river.

 

[Mainah]

@Speedling Interesting thought. If one were to remove the cat and O2 sensor and replace with a straight pipe then all one would have to do is send the proper signal through the O2 wires to the existing ECU. I can think of a couple of ways to do that. Do you happen to know if a 100% duty cycle dc voltage matching a normal 14.7 to 1 equilibrium voltage output of of about half a volt dc sent through the O2 sensor wires would cause havoc with the ECU or would the duty cycle of the O2 sensor need to be matched?
Obviously this would void the warranty so I am not about to try this but curious if you know of a case where the ECU was fooled in this fashion without damaging it or causing other than normal engine running or errors codes?

 

[Speedling]

@Speedling Interesting thought. If one were to remove the cat and O2 sensor and replace with a straight pipe then all one would have to do is send the proper signal through the O2 wires to the existing ECU. I can think of a couple of ways to do that. Do you happen to know if a 100% duty cycle dc voltage matching a normal 14.7 to 1 equilibrium voltage output of of about half a volt dc sent through the O2 sensor wires would cause havoc with the ECU or would the duty cycle of the O2 sensor need to be matched?
Obviously this would void the warranty so I am not about to try this but curious if you know of a case where the ECU was fooled in this fashion without damaging it or causing other than normal engine running or errors codes?

It is a little trickier than that. Depends on the 02 sensor. Wide band or narrow band.

Of course, not seeing the engine i don't know how they attach the cat. It could probably be drilled out easily enough and leave the 02. Or, i know on my mustang they had plug ins that eliminated the 02 somehow.
http://www.americanmuscle.com/stmilel.html

 

[Noko]

I think I'd try the ECU reflash that @swatski was doing before I'd mess with removing the catalytic converters. But I think overall its not worth messing with a Carb boat to get maybe a few more rpms and a few mph, not at least on my AR. We all feel the need for speed but running at WOT probably is about 5-10% of the range you are normally running at.

 

[Gym]

Unfortunately, 500 feet above sea level is as low as i can find in ohio. And thats the nasty ohio river.

Ok @Nick Hughes you're officially invited to Boston.

 

[Gym]

@Speedling ...............
Obviously this would void the warranty so I am not about to try this but curious if you know of a case where the ECU was fooled in this fashion without damaging it or causing other than normal engine running or errors codes?

I think Volkswagen has the answer to that one.