Now that gas prices have our attention, it would make sense to convert my
1989 5.7L Alpha One Mercruiser I/O from carburetor to throttle body injection.
A few years ago, when it was marginally economic, I remember ads in several
boating magazines for throttle body conversion kits (remove the carburetor
and bolt in the TBI). I can't find them anymore, even with Google. Does
anyone know if these are still available and where I can get one?

On 2008-06-22 22:23:55 -0400, "Bob999" u44405@uwe said:

Now that gas prices have our attention, it would make sense to convert my
1989 5.7L Alpha One Mercruiser I/O from carburetor to throttle body injection.
A few years ago, when it was marginally economic, I remember ads in several
boating magazines for throttle body conversion kits (remove the carburetor
and bolt in the TBI). I can't find them anymore, even with Google. Does
anyone know if these are still available and where I can get one?

I'm a fan of throttle body injection, but if it's marginal, you might
investigate something a dockmate said *drastically* improved his
consumption: Switching to higher gearing and larger props.

Wish I could remember more, but in the sailboat world, a similar change
just about doubled economy.

(My recollection is that it was a 30% improvement, but that sounds high
for a planing boat. Still, a new prop alone can give 10%, so maybe
that's not so farfetched.)

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

On Mon, 23 Jun 2008 02:23:55 GMT, "Bob999" u44405@uwe wrote:

Now that gas prices have our attention, it would make sense to convert my
1989 5.7L Alpha One Mercruiser I/O from carburetor to throttle body injection.
A few years ago, when it was marginally economic, I remember ads in several
boating magazines for throttle body conversion kits (remove the carburetor
and bolt in the TBI). I can't find them anymore, even with Google. Does
anyone know if these are still available and where I can get one?

Frankly I do not think it's economical on a 19 year old engine. The
kits that I remember were well over $1K plus installation effort and
incidentals. You'd be lucky to save 10% on fuel costs so your pay
back is somewhere over 500 hours of engine operation.

I assure you that a TBI will NOT out perform a properly set up carb in
either performance or economy. That may be possible to some degree in a car,
but not in a marine environment. The big difference between a fuel injection
system and a carb is the FI delivers to the engine what it needs and a carb
delivers what the engine wants. This can make a huge difference in a car
with continually changing loads and engine speed, but not in a boat that is
under constant, continuous load. In that role, a carb will perform every bit
as well. Don't waste your money and yes, Holly sells TBI's, Direct Port
Injection systems as well as their management computers, sensors and tuning
software, but you are better off converting to diesel.
Steve


"Bob999" u44405@uwe wrote in message news:861526204129d@uwe...
Now that gas prices have our attention, it would make sense to convert my
1989 5.7L Alpha One Mercruiser I/O from carburetor to throttle body
injection.
A few years ago, when it was marginally economic, I remember ads in
several
boating magazines for throttle body conversion kits (remove the carburetor
and bolt in the TBI). I can't find them anymore, even with Google. Does
anyone know if these are still available and where I can get one?

Jere Lull wrote:
Now that gas prices have our attention, it would make sense to convert my
1989 5.7L Alpha One Mercruiser I/O from carburetor to throttle body injection.
A few years ago, when it was marginally economic, I remember ads in several
boating magazines for throttle body conversion kits (remove the carburetor
and bolt in the TBI). I can't find them anymore, even with Google. Does
anyone know if these are still available and where I can get one?

I'm a fan of throttle body injection, but if it's marginal, you might
investigate something a dockmate said *drastically* improved his
consumption: Switching to higher gearing and larger props.

Wish I could remember more, but in the sailboat world, a similar change
just about doubled economy.

From the other commentators, it appears that monkeying with the fuel system
is a non-starter. But the props I've reviewed were a tradeoff between
diameter and pitch (higher pitch/smaller diameter). Do you have to do both
at the same time? Like if I buy a new, higher geared lower unit does it come
with a larger diameter prop?
(My recollection is that it was a 30% improvement, but that sounds high
for a planing boat. Still, a new prop alone can give 10%, so maybe
that's not so farfetched.)


--
Message posted via BoatKB.com
http://www.boatkb.com/Uwe/Forums.aspx/cruising/200806/1

On 2008-06-26 17:52:24 -0400, "Bob999 via BoatKB.com" u44405@uwe said:

Jere Lull wrote:
you might investigate something a dockmate said *drastically* improved
his consumption: Switching to higher gearing and larger props.

Wish I could remember more, but in the sailboat world, a similar change
just about doubled economy.

From the other commentators, it appears that monkeying with the fuel
system is a non-starter. But the props I've reviewed were a tradeoff
between diameter and pitch (higher pitch/smaller diameter). Do you
have to do both at the same time? Like if I buy a new, higher geared
lower unit does it come with a larger diameter prop?

Oh, lower unit.... I don't know those beasties much at all. But am
fairly certain he had twin I/Os. My recollection was that he changed
the gearing in the existing transmissions, then added larger props. I
could be wrong, but I'd say to go that route if at all possible. An
all-new unit represents quite a few gallons of fuel, even these days.

My personal opinion, remembering that I travel at less than hull speed,
is to fit the largest diameter prop possible, then find the pitch that
just allows you to max out in normal conditions. The shop doing the
work will either know how to calculate the proper dimensions and/or
they'll let you swap props if they guess wrong.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

"Jere Lull" wrote

My personal opinion, remembering that I travel at less than hull speed, is
to fit the largest diameter prop possible, then find the pitch that just
allows you to max out in normal conditions.

Generally good advice but, if any kids are going to try this at home, they
should be aware that "largest diameter possible" means with an absolute
minimum tip clearance of 10% of the diameter. That will still be noisy,
the thump of the tip vortex hitting the hull each time a blade passes would
be pretty annoying in a powerboat but perhaps tolerable in a seldom run
auxilliary. If you want a smoother installation, try to get closer to 15%.
20% is not uncommon in powerboats where smooth running is important.

--
Roger Long

On 2008-06-27 05:20:16 -0400, "Roger Long" said:

"Jere Lull" wrote

My personal opinion, remembering that I travel at less than hull speed, is
to fit the largest diameter prop possible, then find the pitch that just
allows you to max out in normal conditions.

Generally good advice but, if any kids are going to try this at home, they
should be aware that "largest diameter possible" means with an absolute
minimum tip clearance of 10% of the diameter. That will still be noisy,
the thump of the tip vortex hitting the hull each time a blade passes would
be pretty annoying in a powerboat but perhaps tolerable in a seldom run
auxilliary. If you want a smoother installation, try to get closer to 15%.
20% is not uncommon in powerboats where smooth running is important.

Oh, agreement. I've just known that for so long I forgot to mention it.

I expect he'll have to consult a professional, who also will know that.

--
Jere Lull
Xan-à-Deux -- Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/