What is the difference between "Marine" and not?

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4fiddyR

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« on: July 31, 2011, 06:59:37 PM »
Hi Everyone,
What is the difference between a regular motor and a "marine" motor?

Also, will an aluminum block have longevity issues as apposed to an iron block in a marine application?

For example what makes this motor a "Marine" motor:

http://www.jegs.com/i/Blueprint+Engines/138/MBP3830CT/10002/-1

Thanks



mobboss

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« Reply #1 on: July 31, 2011, 07:21:53 PM »
funny you should ask!!! well sorta! its a touchy subject. not one i really believe. ok so here you go. marine parts are made to stricker values . my oppion its crap. but ...  as far as aluminum thats tuff i would say no dont do it. there is no coolant to keep the alum protected. your going to get a lot of anwsers here about the marine versus non here!!!! good luck!
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obnoxious001

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« Reply #2 on: July 31, 2011, 08:20:44 PM »
First of all, I would not agree about that Jeg's "marine" engine being ideal for marine use.  Note that it has a cast crank, factory rods and hypereutectic pistons.   I normally would highly recommend forged components.

Marine engines have to be looked at differently than "street" engines for several reasons.  They run under a constant load,, no "coasting" at all,, let off the pedal the the boat stops moving.  Also, they routinely run about twice the rpm of a street vehicle.  My Chevy truck runs about 80 mph at 2500 RPM.  Depending on the particular boat and drive,,  2500 may be barely planing, and constant running RPM of 4000-5000 rpm may not be uncommon.

Due to the above mentioned facts about marine engines, and also the difference in block temperature between a street vehicle with a radiator that runs perhaps 180-200 degrees all the time, and a marine engine that may never reach those temperatures, piston to wall clearance is usually (always in anything I build) increased since the block is cooler(less expansion), and the pistons are hotter(more expansion).  Along with that, engine bearing clearances are typically "looser" for the extended higher rpm running and loads. 

4fiddyR

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« Reply #3 on: July 31, 2011, 08:32:19 PM »
First of all, I would not agree about that Jeg's "marine" engine being ideal for marine use.  Note that it has a cast crank, factory rods and hypereutectic pistons.   I normally would highly recommend forged components.

Marine engines have to be looked at differently than "street" engines for several reasons.  They run under a constant load,, no "coasting" at all,, let off the pedal the the boat stops moving.  Also, they routinely run about twice the rpm of a street vehicle.  My Chevy truck runs about 80 mph at 2500 RPM.  Depending on the particular boat and drive,,  2500 may be barely planing, and constant running RPM of 4000-5000 rpm may not be uncommon.

Due to the above mentioned facts about marine engines, and also the difference in block temperature between a street vehicle with a radiator that runs perhaps 180-200 degrees all the time, and a marine engine that may never reach those temperatures, piston to wall clearance is usually (always in anything I build) increased since the block is cooler(less expansion), and the pistons are hotter(more expansion).  Along with that, engine bearing clearances are typically "looser" for the extended higher rpm running and loads.

Thanks for the tips.  I figured it had something to do with the constant high RPMs. 

I keep seeing 4500 RPM everywhere I look, so that must be the magic number for jet drive boats?

obnoxious001

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« Reply #4 on: August 01, 2011, 01:17:19 AM »
Thanks for the tips.  I figured it had something to do with the constant high RPMs. 

I keep seeing 4500 RPM everywhere I look, so that must be the magic number for jet drive boats?

The larger piston to wall clearance is more based on the freshwater cooling.  Piston manufacturers will normally recommend an additional .001"-.002" for a normally aspirated marine engine.

RPM depends  on horsepower and pump set up. 

Lots of mild BBC engines run around 5000 rpm with a fairly stock pump.  I have built a handful of Comp Jet circle race engines that turn around 6200-6500 with a cut down impeller.

4fiddyR

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« Reply #5 on: August 01, 2011, 07:15:54 AM »
Lots of mild BBC engines run around 5000 rpm with a fairly stock pump.

It seems like most jet boats I see for sale have a big block.  Why is that?  I see a lot of "Olds 455" jet boats on craigslist by comparison say a ford 460 or chevy 454. 

Is a Chevy 454 a good motor for a jet boat?  I had a 350 small block in mind, but I would rather not get it all setup and then wish I had a big block.

I am looking to build a motor myself, it will be my third V8 and I want to make a motor that has a real snappy throttle response that sounds good but is not too loud. 

I won't be racing the boat. It is just an island cruiser that will hopefully gather a crowd.  There are not a lot of wicked boats around here any more because the sheriff tends to ticket speeders and noise.

Thanks again for your help



wizard612

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« Reply #6 on: August 01, 2011, 07:59:18 AM »
Big blocks are preferred because it's easier to get a lot of torque. Also Cubic inches are much easier to get (obviously) with a big block. Guys who have tried small blocks usually regret it.  There use to be a popular V-drive sprint boat class called ERR ( E Racing Runabout )used all small blocks but jet drives needed more grunt to run fast. Olds, Ford, or Chevy? This site will give you any answer you want. Olds are temperamental and need a good doctor to stay healthy, Fords have a growing community, but the record books for jets would lean to Chevy. What ever you do have fun stay safe.

IRRebel

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« Reply #7 on: August 01, 2011, 08:33:09 AM »
The Olds 455, Chevy 454 and Ford 460 are really almost identical in performance in stock form given the same pump, hull, etc. It's when you start hot rodding the engines the differences rear their ugly head.

Chevy is the cheapest to build and add HP to, as parts are everywhere and dirt cheap, and every engine shop in North America probably does 2-3 Chevy engines for any sum of all other engines they do combined. Some will argue because parts break so often the aftermarket floods to cash in on this, or the same for "inferior" parts. I beleive it simply stems from the fact that the smalll block Chevy has been in existance nearly untouched for going on 60 years, and the BBC just benefits from "guilt by association" and nearly the same for 40 years. 

The 460 Ford is popular, and was with the boat builders, because it's so damn strong to begin with, for one, and you can build BIG hp fairly easily and inexpensively while not changing a thing on the bottom end as far as rods, main caps, crank, etc.  In fact, a little birdie told me of a rumour of a dyno pull only engine being built. Stock 2 bolt block, cast crank, twin turbos and hoping for 2000 HP just to prove a point. But it is far more expensive to "Go Big" on this engine vs the Chevy.

The 455 is simply the odd man out in this arena. Probably why you see more of them on CL. BBF and BBC boats command higher prices, and if you notice, at least I do, Pump brand is mentioned early and often if it's  Berk, rarely if at all on a Jacuzzi or Panther.

Ray
"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways totally worn out shouting 'Holy Shit what a ride!"---Crewcheif22 AKA Keith

obnoxious001

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« Reply #8 on: August 01, 2011, 05:54:45 PM »
It seems like most jet boats I see for sale have a big block.  Why is that?  I see a lot of "Olds 455" jet boats on craigslist by comparison say a ford 460 or chevy 454. 

Is a Chevy 454 a good motor for a jet boat?  I had a 350 small block in mind, but I would rather not get it all setup and then wish I had a big block.

I am looking to build a motor myself, it will be my third V8 and I want to make a motor that has a real snappy throttle response that sounds good but is not too loud. 

I won't be racing the boat. It is just an island cruiser that will hopefully gather a crowd.  There are not a lot of wicked boats around here any more because the sheriff tends to ticket speeders and noise.

Thanks again for your help

If you don't have any mounts or accessories for the boat to begin with, you will find that big block Chevy mounts and exhaust are the easiest to find

If you think about a basic, mild performance build that may yield around one horsepower per cubic inch, the logic of going with a 454 big block vs a 350 cubic inch small block is obvious, roughly 100 horsepower difference. 

"Noise" of the engine will be more related to the type of exhaust you run, although variations in displacement and compression will make distinct differences in the sound of the engine.

 


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