Auto vs Marine

Big D · Post by **Big D** » Sun May 09, 2010 9:54 pm

I was reading a thread on another forum about the differences between auto and marine engines if any. It's almost like there's this thing going on between auto and marine mechanics. The entries were from a few years ago but an interesting read all the same. I liked your entry at the end Prowlersfish.

I know how the members of that forum think on this subject, but am new to this forum and was wondering what the take on the subject is from our members? Or am I just opening up a [Stripermann2, insert your can of worms pic here]!!!

Most of us know about the obvious differences, still some would never interchange the two, while others don't think it really matters. Where do you fit in and why?

captainmaniac · Post by **captainmaniac** » Sun May 09, 2010 10:22 pm

A boat (or at least, most of the ones owned by members of this forum) weighs at least 4x what a car weighs.

A boat is always pushing against water, while cars only push against air (much easier).

To plane, a boat needs to not only push against water, but to use enough power to climb on top of it.

A marine engine works much harder than a car engine - think of a car, towing a 10,000 pound trailer, up a hill, constantly..... that's what your marine engine is doing. An engine and parts designed to deal with 'highway' driving, or sitting still and idling at stop lights, just don't cut it for marine use.

Aside from all that is the spark / ignition proof requirements for marine parts. If a car leaks fuel, it drips on the ground and fumes quickly dissipate. Whatever leaks a marine engine or fuel system may have, the raw fuel or fumes remain in the bilge area until evacuated by bilge pump and blower... until then, any spark of any kind may well kill someone.

An auto mechanic may tell you there is no difference... but that just means they don't have a f*ing clue what they are talking about.

Rodman · Post by **Rodman** » Sun May 09, 2010 11:02 pm

captainmaniac wrote: An auto mechanic may tell you there is no difference... but that just means they don't have a f*ing clue what they are talking about.

Ill second that motion.

turtlem1969 · Post by **turtlem1969** » Mon May 10, 2010 9:23 am

I have replaced "marine" engines with "auto" engines, after switching out carbs, starters, fuel pumps, alternators, etc, and only saved a few dollars doing it that way and not noticed any real difference in the performance.

Tuck · Post by **Tuck** » Mon May 10, 2010 9:38 am

captainmaniac wrote:An auto mechanic may tell you there is no difference... but that just means they don't have a f*ing clue what they are talking about.

roflmao! i love it. i think i'll make that my quote of the day.

ready123 · Post by **ready123** » Mon May 10, 2010 4:52 pm

One of the biggest reasons for me is the heavier duty main bearings... I can't think of any auto usage that puts the load on an engine that a boat motor gets.... certainly not with a regular car transmission.
I wonder how well dragsters would do with stock auto engines?

mr elevman · Post by **mr elevman** » Mon May 10, 2010 5:29 pm

marine moters are made to live thair life in the worst enviroment salt water salt air water in the fuel and wot for extended pirerds of time

chauzer · Post by **chauzer** » Mon May 10, 2010 5:38 pm

most gas marine engines are 4 bolt mains and the heads are different (water jackets). at least from what I've seen in the 10,000 marine and truck engines I've worked on. had one individual tell me that all gas marine engines are stainless roller interior! unless you have the newer pci 6.0 liter engines or have put roller cam and lifters in, they are hydraulic. go diesel and no more worries! just ask Paul! i had a '79 Chevy mud truck with a mildly built 350 that would hold 11,000 r.p.m and not float a valve. i beat that truck for 5 years with no engine issues.

prowlersfish · Post by **prowlersfish** » Mon May 10, 2010 6:33 pm

Many of the late 350 (5.7) where roller lifters , and the roller lifters on the 5.7 and 6.0 where hydraulic of course. I don't think you find difrent water jackits in the heads between marine or car or truck , infact I know you won't .

Stripermann2 · Post by **Stripermann2** » Mon May 10, 2010 7:03 pm

prowlersfish wrote:Many of the late 350 (5.7) where roller lifters , and the roller lifters on the 5.7 and 6.0 where hydraulic of course. I don't think you find difrent water jackits in the heads between marine or car or truck , infact I know you won't .

Cooling passages in the heads are the same indeed...no difference.

chauzer · Post by **chauzer** » Tue May 11, 2010 12:08 pm

the water jackets in the head are larger to allow better cooling of exhaust. maybe its different in a closed cooling system but in a raw water cooling system they are bigger. the late model 5.3, 6.0 and 8.1 are roller interior right from the factory. i don't want to start a pi**ing match here, but a guy can't build a set of brodix aluminum truck heads and put them on a marine engine. the exhaust temps would be through the roof!

prowlersfish · Post by **prowlersfish** » Tue May 11, 2010 1:14 pm

All 4.8 5.3 and 6.0 Chevy's are roller cam engines , many late 5.0 and 5.7 are also . all these were of course hydraulic/roller lifters. The head casting on the old small and big block is the same car or marine. Made of cast iron ( yes they had some HPerf alum)

the new type small block (4.8-6.0 and up ) used alum. heads I don't think you will find any of these raw water cooled .

Racing heads/brodix aluminum heads and there castings are something else and really irrelevant to this . as they are after markit not OEM

chauzer · Post by **chauzer** » Tue May 11, 2010 2:26 pm

if auto and marine heads were interchangeable, there should be no reason you couldn't build a set of high perf heads and put them on. they aren't so you can't. in a closed cooling system on a boat, a.k.a. heat exchangers, water jacket size may be the same as autos. but, on a cooling system that draws its water straight from what its floating on and sends it through the block and heads, the jackets are bigger.
example: start your boat engine, let it run for 10 minutes, then grab the exhaust manifold. warm. but not hot. do the same with your car. i would be willing to bet its hot or at least uncomfortably warm.
several years ago i rebuilt the engines out of a f36. they were GM 350's. the bottom end is the same as a truck engine (4 bolt mains). the heads however,are marine heads which i found out have larger jackets and exhaust ports.

prowlersfish · Post by **prowlersfish** » Tue May 11, 2010 8:03 pm

Do you think maybe the exhaust manifold on a boat is cooler because it has water or coolant flowing through it and and your car manifold has no coolant in it ?

Now the exhaust manifold is completely different from a car to a boat

the heads are the same fresh or salt water cooled .car truck or boat same casting . we are talking about stock heads not some off the wall racing head

wowzer52 · Post by **wowzer52** » Sun May 16, 2010 11:24 am

An auto mechanic friend of mine replaced his twin engines with car engines in a 35ft Chris Craft and they lasted three months with regular use. Even though he used all the marine accessories the engines could not handle the stress of marine use.