2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

[ZmOz]

Re: 2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

My '74 150hp inline 6 only got around 2mpg on my 16' Glastron. Then last August when I was breaking in my new 140hp powerhead I found around 6mpg! It literally took all day to empty my 12 gallon tank...I could do that in an hour with the 150!

 

[andrewkafp]

Re: 2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

This is good reading.. Lot's of good tech points raised. Think I might stick to the small 50 for the time being though

 

[Clams Canino]

Re: 2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

I big inlines love to cruise at 4000. Prop it to break 5000 - but cruise it at 4000.<br /><br />-W

 

[phatmanmike]

Re: 2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

my inline ran its best right around 3800 - 4200. i got about 3/4 throttle and it was on plane fully and smoothly, and it gave such a dramatic difference in MPG than WOT. <br /><br />some smart tabs or similar will give extrordinary results. <br /><br />try a link and sync to get the motor in its best tune.<br /><br />make sure the bottom of the boat is clean and smooth. less drag the better.<br /><br />you dont have a spare jack plate hanging around do you? less motor in the water , the less drag you have.

 

[ST]

Re: 2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

myoutboards,<br />thanks for your suggestions! Yes, I'll do the clams' "link and sync" procedures if test won't show any improvement. Btw; you previously suggested to remove the hydrofoil, which I did, now you're suggesting a "smart tab"?<br /><br /> I understand those tabs and foils would lift the back side up somewhat when planing; but doesn't this action also requires more energy: thus increasing fuel consumption?

 

[MercFan]

Re: 2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

I'm also confused with the talk of smart tabs, hydro foils and jack plates.<br /><br />I had 2 huge wings mounted above the prop. Removed them and gained about 7mph. It looks like they could've worked well if my engine wasn't mounted too low in the water. But with them running "in" the water they just a huge drag.

 

[ST]

Re: 2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

Hi Mercfan,<br />Was your "huge wings" look like this?<br /><br />

<br /><br />Wow, I'll be please if I could gain 7mph without the hydrofoil. I'll go test my boat in about 2 weeks...

 

[phatmanmike]

Re: 2.7 MPG on Inline 6 - 90hp 1982 Merc. Is this normal?

most hydrofoils are junk. there are a few that are ok, but most are just selling ploys! if you think youll "fix" your planning problems and get faster for just 25 dollars, think again!<br /><br />trim tabs work in a completely diff way. better way. they dont drag under water behind the boat. they work at every rpm and at every mph.<br /><br />do a search for SMART TABS.... everything they say is 110% true. i have them on all of my boats(that run)