410 Sport Sedan 8.1 Horizon performance question

[Ruger_Fan]

Hello everyone I'm wondering if anyone has specific experience with a 410 Sport Sedan with 8.1's to provide some baseline data for me to compare to. I've seen numbers suggesting 17-18 knots for best cruise and 26 knots WOT. With fuel burn around 1.5 gallons per mile. I'm finding 18 knots feels solid and smooth but I'm only getting. .39 Nautical Miles Per Gallon which seems excessive even for this behemoth and half what it was speed at.... Engines run great. I have recently installed Fox engine gateways and have included the outputs while running 4k rpms.
Loving the boat but don't hate money so if I'm wasting a bunch I'd love to sort that out early on.

Screenshot_20210703-071318_Fox Marine.jpg

Screenshot_20210703-071355_Fox Marine.jpg

[km1125]

Not specifically addressing your question, but a couple things jump out at me on those printouts. Oil temperature at 32F?? Must just be a default value and it doesn't actually measure temperature. Air intake temps seem pretty high for a high RPM. Probably normal for a hot engine compartment and low speeds but I'd think at 4,000 RPM you'd be sucking in a whole lot of fresh air from the outside and that temp would be closer to the ambient outdoor air temp (maybe plus a couple degrees).

Also curious that the spark advance is only showing at 1 degree. At 4000 and a heavy load you should have closer to 25 degrees total advance. I wonder that what 1 degree is indicating?

[Viper]

Ya there's a few questionable numbers for sure but it's not unexpected with 3rd party software. Maybe some calibrating is in order if that's doable with that system. I'd say the air temp is fine though, they'll generate a lot of heat, and while you may be taking in a lot of outside air at that speed, she's also ingesting most of it but all the while emitting more and more heat in the process. A simple IR temp gun will confirm some of the temp readings. Always good to have one on board.

Can't help you with the fuel burn, speed etc., hopefully a member with the same application will chime in with some numbers for you to compare with.

[bud37]

To be honest, your data doesn't seem far off to me....I don't think your boat will get much better at that rpm. How is the bottom and running gear ...if they are fouled it will slow you down and use more fuel so keep it clean to maximize.

What was the speed at that rpm/data point ?

That is a fair bit of HP you have and that means more fuel at higher rpms.

[Ruger_Fan]

Source of the post To be honest, your data doesn't seem far off to me....I don't think your boat will get much better at that rpm. How is the bottom and running gear ...if they are fouled it will slow you down and use more fuel so keep it clean to maximize.

What was the speed at that rpm/data point ?

That is a fair bit of HP you have and that means more fuel at higher rpms.

I was pulling right at 20mph at 4000rpm's burning approx 50 gph. fresh bottom paint and gear is all "clear" bottom is pretty smooth for a 20 year old boat with ablative paint no big areas chipped off or large amounts of "catches".

[Ruger_Fan]

Source of the post Not specifically addressing your question, but a couple things jump out at me on those printouts. Oil temperature at 32F?? Must just be a default value and it doesn't actually measure temperature. Air intake temps seem pretty high for a high RPM. Probably normal for a hot engine compartment and low speeds but I'd think at 4,000 RPM you'd be sucking in a whole lot of fresh air from the outside and that temp would be closer to the ambient outdoor air temp (maybe plus a couple degrees).

Also curious that the spark advance is only showing at 1 degree. At 4000 and a heavy load you should have closer to 25 degrees total advance. I wonder that what 1 degree is indicating?

Ya that motor must not have an oil temp sender feeding into the computer so the FOX unit just shows a canned value.

[Ruger_Fan]

Source of the post Not specifically addressing your question, but a couple things jump out at me on those printouts. Oil temperature at 32F?? Must just be a default value and it doesn't actually measure temperature. Air intake temps seem pretty high for a high RPM. Probably normal for a hot engine compartment and low speeds but I'd think at 4,000 RPM you'd be sucking in a whole lot of fresh air from the outside and that temp would be closer to the ambient outdoor air temp (maybe plus a couple degrees).

Also curious that the spark advance is only showing at 1 degree. At 4000 and a heavy load you should have closer to 25 degrees total advance. I wonder that what 1 degree is indicating?

I've got a mechanic coming to look at it with me tomorrow as i ended up finding "burn through" on one of my exhaust hoses (Starboard). I'm guessing impellers need replacement as i bought the boat recently and have found zero maint was being done by previous owners. It never got hot but i suspect not enough water was flowing to cool the exhaust.