Has anyone tried turbocharging a 5.0 L or 5.7 L Merc engine in this
group? I know that it used to be done back in the 70's but I can't
find any info about any current set-ups. From what I can find it
seems like it might be advantageous by allowing you to run a better
pitch prop for higher top end speed and reduced RPMs for cruising
which seem like it would be good for efficiency and engine life. I
don't think it would drop your low end that much because the
compression on stock marine engines is close to 9:1 and you can
probably run 10PSI of boost on 8.5:1 engines. Any thoughts or
comments? I am more familiar with turbo applications on cars so I
might be missing something. Thanks for the help!

I think your missing the fact of turbo lag.
On top end you would probably gain about 4" of pitch (600 rpms or so).
On the hole shot that would kill you since you don't have the power at 600
to 1000 rpms to turn that big a prop.
Now, a torque shift would work but the power on top end would tear the
gears/springs out of it. Plus it is not the most efficient for top end
which is what your looking for.

Racers use them but they are not looking at hole shot but rather sustained
high end speed.

--
Tony
My boats and autos - http://t.thomas.home.mchsi.com



"Hemicuda" wrote in message
om...
Has anyone tried turbocharging a 5.0 L or 5.7 L Merc engine in this
group? I know that it used to be done back in the 70's but I can't
find any info about any current set-ups. From what I can find it
seems like it might be advantageous by allowing you to run a better
pitch prop for higher top end speed and reduced RPMs for cruising
which seem like it would be good for efficiency and engine life. I
don't think it would drop your low end that much because the
compression on stock marine engines is close to 9:1 and you can
probably run 10PSI of boost on 8.5:1 engines. Any thoughts or
comments? I am more familiar with turbo applications on cars so I
might be missing something. Thanks for the help!

It's quite common to turbocharge Grand National ski race boats. Usually
two of 'em.

b.

Forgot to mention. Try taking a look at Hot Boat Magazine. Past issues
would have examples of turbocharging V8's as well as many of their ads.

They also have a competent Technical Editor dept. that could probably point
you in the direction of companies that could help.

b.

wrote:

: Forgot to mention. Try taking a look at Hot Boat Magazine. Past issues
: would have examples of turbocharging V8's as well as many of their ads.

Ack!

That should have been "Powerboat Magazine".

www.powerboatmagazine.com

good for efficiency and engine life.

From what I've read in automotive repair histories, the
turbocharged engines require more maintenance.

J K

You're far better off with a blower. Turbos have a lag problem as another
poster pointed out. There is the prop issue because you'll have to run a
really
high pitch for when the turbo kicks in which will make it a dog out of the
hole. You also have to deal with a water cooled exhaust system.
And heat issues. A 144 or 177 blower will give you the same boost without
any of these problems.

"Hemicuda" wrote in message
om...
Has anyone tried turbocharging a 5.0 L or 5.7 L Merc engine in this
group? I know that it used to be done back in the 70's but I can't
find any info about any current set-ups. From what I can find it
seems like it might be advantageous by allowing you to run a better
pitch prop for higher top end speed and reduced RPMs for cruising
which seem like it would be good for efficiency and engine life. I
don't think it would drop your low end that much because the
compression on stock marine engines is close to 9:1 and you can
probably run 10PSI of boost on 8.5:1 engines. Any thoughts or
comments? I am more familiar with turbo applications on cars so I
might be missing something. Thanks for the help!

"J K" wrote in message
. 201...
good for efficiency and engine life.

From what I've read in automotive repair histories, the
turbocharged engines require more maintenance.

J K
Turbo-charging allows an engine to pack in move air and fuel, making the
engine develop the same power as a much higher displacement naturally
aspirated engine.The energy normally wasted in the exhaust is use to pump
the incoming charge above normal atmosphere pressure. If you have more air,
you can burn more fuel. The nice thing about a turbo as compared to a blower
is that the amount of boost is related to the exhaust temperature, and this
is related to the amount of fuel you are burning. In practical terms, it
runs when you need it. The bottom line is that you can make a 300 cubic inch
engine deliver the same power as a 450 cubic inch engine under full
throttle, and run as efficiently as the 300 cubic inch engine when running
at lower power settings.

In automotive applications, the throttle lag means that the engine may take
a little longer to come to full power, and you have to use a "waste gate" to
prevent the turbo from stalling when you close the throttle quickly - like
in a gear shift. In most boating application these performance issues are
simply not an issue.

Properly maintained and used, a turbo is a very long life item. There is one
moving part - a single shaft with turbine and compressor fans. A turbo spins
a very high speeds - 60 to 80 thousand RPM is not uncommon. The bearings are
simple oil film in most cases. The oil provides both lubrication and
cooling. The cooling thing can be very important because the turbine is
driven by the exhaust. These bearings are the failure mechanism in
automotive application. These bearings have to get oil when the engine
starts up. In some engines the pressure builds rather slowly on startup. If
the engine is revved before the turbo is properly lubricated, a bearing
failure is in the cards. Another popular source of failure is during
shutdown. Frequently, the driver will roar up to a stop and shut the engine
off without letting the turbo bleed off the heat in the cooling oil. The
heat soaks through the housing; the oil left in the turbo breaks down and
cokes up the bearings. Sooner or later the one moving part of the turbo
quits moving because the bearings are gummed up.

Another common problem with turbos - if you build a big fire in a little
furnace, the little furnace burns up. An engine has to be build to withstand
the power developed during boost. A little known fact is that the old Dodge
slant six was originally built as a race engine. Richard Petty wanted and
engine built for turbo charging. If you look at one of these, you will
notice that the intake and exhaust all come together with a turbo would be
mounted. The other salient features was a very long stroke to extract all
the power generated, and *very* heavy main bearings. When there were using
in a naturally aspirated engine, they were not working very hard. The racing
rules of the day required that a certain number of the engines had to be in
productions automobiles to be allowed on the racetrack. The American public
got a great deal out of this - these engines have a well deserved reputation
as being unbreakable - they would keep running when they sounded like a
shaken fruit jar full of marbles. These engines are still being run in
industrial application like Lull lifts. The only reason they are not used in
automobiles today is that the design could not be tamed to burn fuel without
polluting. Rats.

Mark Browne

So from what I can summarize from the above posts are that the turbo
will probably work great while cruising and at top end but will be a
dog coming out of the hole. This is a dumb question but I thought
that at slower speeds boats require less horsepower to move them
through the water. As the speed increases so does the power
requirement for a certain hull design. Is this true? If so it
appears that the low end lack of boost shouldn't kill me. Or am I
totally of base? The other thing I was thinking of was to put smaller
turbos on the engine to reduce lag but sacrifice top end boost.
Marine engines rarely go over 5,000 RPM so I could probably go with a
smallish turbine housing with a waste gate that will bring on boost
quickly and then dump the excess exhaust gas at higher speeds. I know
the heat will be a problem but I think that is manageable but I don't
want to take forever to get up on plane. Has anyone seen or ridden in
a gasoline turbo'd boat and seen how bad the hole shot was? The
reason I want to stay away from a blower is that although it will
boost power I think it will hurt the fuel efficiency. Also blowers
tend to be expensive and I can score a pair of T3 Turbos from old T
birds which would fit a 5.0 or 5.7L fairly well for cheap at a junk
yard and fabricate a set-up. Thanks for all the help and I
appreciate any more thoughts or info you could pass on!

I think the "dog coming out of the hole" comment was based on putting a
bigger prop on it to take advantage of the increased top end. But without
that power down low then the it would be overpropped until the turbo kicked
in.

wrote in message
...
Hemicuda wrote:
: So from what I can summarize from the above posts are that the turbo
: will probably work great while cruising and at top end but will be a
: dog coming out of the hole. This is a dumb question but I thought

It wouldn't be a "dog coming out of the hole". It'd act mostlyl like a
naturally aspirated engine.