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Let's stir the pot

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matches909

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« on: November 17, 2014, 01:05:47 AM »
Ok here it goes, can someone please explain to me when building a boat engine why is it so different than building a car engine.  This comes from many people's theories I'm looking for answers that people can actually prove not just opinions.  Any response would be great.  I'm about to build another motor and kinda want to know if I'm building it wrong or not.
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JARVIS

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« Reply #1 on: November 17, 2014, 01:16:25 AM »
 >:D  this oughtta be good......
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« Reply #2 on: November 17, 2014, 01:22:48 AM »
X2 , I'm waitin to talk a bunch of sh!t!   :beer: :beer: >:D
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« Reply #3 on: November 17, 2014, 02:05:55 AM »
I heard a good one this weekend.  “Experience comes from opinions and opinions are formed by experience.”

One thing I have learned is to pick ONE expert who’s opinion you value and listen to only that person.  If you pick and choose from different opinions, you will usually end up with a lot of mix-matched useless parts.
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

Flusher

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« Reply #4 on: November 17, 2014, 02:08:51 AM »
Ok here it goes, can someone please explain to me when building a boat engine why is it so different than building a car engine.  This comes from many people's theories I'm looking for answers that people can actually prove not just opinions.  Any response would be great.  I'm about to build another motor and kinda want to know if I'm building it wrong or not.

Are you thinking clearances or cam, compression, and airflow?
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

matches909

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« Reply #5 on: November 17, 2014, 02:10:53 AM »
I hear tons of talk about clearances that have to be different than a engine that is being installed in a car
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aquaholic72

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« Reply #6 on: November 17, 2014, 02:50:19 AM »
Well I'll throw it out, I build all my engines to live, street cars drag cars and now my first boat, the right parts with honesty to ur machinest about what ur doing, and It will be fine .. I beet the shit out of my flatty, and it's built no different then my fury, outside of my cam selection...
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« Reply #7 on: November 17, 2014, 03:15:47 AM »
Oh ya, I forgot! Stop building fords buddy!  :banghead:
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lifted250

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« Reply #8 on: November 17, 2014, 07:10:17 AM »
I be learn to build the boat motor with extra. Clearance cuz it turning 4500 to 5000 rpm on a good day in ur car u only hit that on a down shift so I always blueprint the bottom end of all my motors due to u will always be turning high rpm but that's just me


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« Reply #9 on: November 17, 2014, 09:15:23 AM »
read this:

http://www.enginebuildermag.com/2013/03/bearing-clearances/

boat motors are almost always used high rpm in varying temperature conditions.  cars and other race applications might always see constant temperatures and mild rpms, thus tighter tolerances. 

GT Jets

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« Reply #10 on: November 18, 2014, 08:10:37 AM »
Ok here it goes, can someone please explain to me when building a boat engine why is it so different than building a car engine.  This comes from many people's theories I'm looking for answers that people can actually prove not just opinions.  Any response would be great.  I'm about to build another motor and kinda want to know if I'm building it wrong or not.

Not going to get too deep here.. Maybe if a debate ensues...

No opinion, but in IMHO it's all theory, no matter who writes it...

First off, just to get it out of the way, if you have to ask, you're building it wrong. This process should be very calculated.


A "marine engine" is too general. I am going to say that all of these comments need to have the stipulation that we are talking Jet Boat specific engines, though much of this applies to both propellers and jets, we are talking jets...

The meat and potatoes is pretty simple; A marine engine typically (not always) runs an open cooling system. Meaning that the water makes a single pass and dumps back out into the lake. This simply cannot be accomplished on an automotive type engine.

The water we typically use is about 100+ degrees cooler than that of an automotive dealio.... Basically stated this means that we need a very small percentage of the water flow to that of a car motor.

This is the basis of why the piston to cylinder wall clearances need to be modified. In basic terms, the pistons are still seeing temperatures similar to the car motor, but the block is much cooler, leading to a lack of thermal expansion on the iron side.

This will (in a very limited fashion) carry over to the crankshaft clearances. Though not nearly to the extreme of the piston/wall....

The sustained RPM and loads we see you would be hard pressed to find in other land lubber applications, some may see the RPM, but more often than not, for shorter periods of time and under a small percentage of the engine load. (way less torque requirement than a jet produces).
That being said, it requires a major developmental change in how we get the air/fuel into the engine, typically by increasing the air flow capability of the intake and carburetor, much larger camshaft than you would put in a car at the same RPM, bigger valves, more advanced cam timing etc.

Put that all together and the exhaust system needs to be able to carry that same amount of flow...

The high RPM combined with a lack of any real oil control as far as foaming and windage, short of a dry sump, you will normally want to run a higher weight oil, this will require a little more bearing clearances as well... Not a lot, just enough to sustain a good pressure and still be able to use that higher viscosity, the oil temps are normally pretty high as well, the thicker weight oil comes into play there as well.

The oil clearances being increased and the oil moving within the engine, combined with the potentially cold areas in the engine block and heads requires oil return modifications within the engines heads and block, some engine types more than others. This gets the oil back to the pan quicker and with less drama, but that added flow will still require more pan real estate and volume to keep a good steady flow of blood to the extremities. The added capacity also buys time as far as oil temp, the bigger that oil charge and the farther away you can keep it form the spinning internals, the less foam and in turn the less oil heat... This one gets missed a lot. Gets back to why I always say that a ten quart pan does not necessarily hold ten quarts....

As for virtually everything else, you are dealing with raw, untreated water, this typically requires some changes in what you could use in that Camaro;

Brass Freeze Plugs, a virtual must
Marine or Cometic head gaskets recommended
Closed engine compartments in a boat has it's own set of challenges. i.e carburetor, fuel pump, alternator, starter, distributor and other spark inducing items need to be "Marine" rated by the SAE system.


I hope this helps... Or at least starts the conversation with your builder... Or starts a debate... It's quiet as heck in here lately.... Winter sucks.


GT
« Last Edit: November 18, 2014, 09:00:47 AM by GT Jets »
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

GT Jets

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« Reply #11 on: November 18, 2014, 09:10:47 AM »
I heard a good one this weekend.  “Experience comes from opinions and opinions are formed by experience.”

One thing I have learned is to pick ONE expert who’s opinion you value and listen to only that person.  If you pick and choose from different opinions, you will usually end up with a lot of mix-matched useless parts.


One of my personal favorites is "Well, I can tell you what DON'T work. So I guess we can expand from that"...  Wile E. Coyote

GT


  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:
Ray

 


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