Auto engine marinization

[brian eiland]

The Dec/Jan 2005 issue of Professional BoatBuilder has a really excellent article on the subject of diesel-electric propusion by Nigel Calder

[Tater]

Alright, I've read through this entire thread and have seen it start off with if auto engines can be used in marine applications to attacking people's knowledge to attacking people countries. Seeing how this thread shows up at the top of the results for a Google search on this issue and I'm sure more people would be interested in hearing about this topic, I believe it behooves us to get back to the topic at hand and really work out the details. I really want to know how much better it might be (if at all) to drop something like a Chevy 350 in place of a Mercruiser equivilent on a 20+ foot small powerboat cruiser.

I'm quite sure the US has more regulations on boat design than other countries, probably to keep marine companies from being blamed for too many accidents. However, I think there's some reasonableness to installing fire/spark suppression systems onto a marine engine. There isn't the realtively free flow of almost constantly moving air throughout a marine engine compartment as there is in an automobile. My question is this:

"Is it possible to alleviate this problem by installing new or used marine alternators/air filters/starters/whatever else onto the auto engine? Is this cost effective or more trouble than its worth and why?"

There is a lot of debate about the durability of a standard automotive engine versus that of a standard marine engine. I'm hesitant to believe anything coming from the manufacturer since they would much rather you spend the extra $$ on a proper marine engine than finding a rebuilt automotive one. My question:

"Is it possible if you chose an engine that was significantly more powerful than the minimum amount of power required to sustain a boat at a reasonable speed AND you geared that engine for a reasonable RPM at wide open throttle AND you chose a properly matched propeller, would that particular engine last a reasonable amount of time" (sorry for the overuse of the word reasonable)

I won't even touch the cooling issue because it seems that can be accomplished using already exsiting closed-system cooling equipment. But, please let me know if I'm wrong.

Thank you
Tater

[Danielsan]

In a general way that is what I thought also. Some people have me made to change my mind and not to do it.
But still, last night I ran into some used BMW850CSI engines rated 450HP >400Nm torque.
Indeed using the Ex(x) certified alternator and starter would be the only thing to change.
I was even more on this because I would use a jetdrive, so thrust bearing, etc wouldn't be neccessary anymore???

Greetz,
Daniel Peeters

One thing not to forget is all the (high) tech ignition system of a good recent engine. But a good engine tuning shop can do the job well.

The answer is YES. Any engine will power the boat. The remaining YESES require YOU to know how to do it, or someone else with the knowledge and ability. If you are still answering YES, you do not need help. All those who have a NO at this time need lots of reading and homework to have a good chance of pulling this off safely. In my personal opinion I would remove every all the fuel system and computer system and ignition system. Replaced by a MARINE carburator of the correct C F M. A MARINE distributor, M S D is a simple 3 wire hook up with a REV LIMITER. The engine is now running reliably, and USCG legaly safe. At this point we start the how long do you want it to LAST in fresh or salt water. Be back. Supper calls!!!!

[woodboat]

On every marine engine I have used there is a lot more than the carb and alternator. That has really beem discussed almost to death. In my case, a small block chevy, the block and crank are different. now I have used a car engine and it out lived the boat. The thing is though I had a proper marine engine as a donor. So I pulled the marine pan, dipstick, valve covers, intake, carb,starter, alternator and entire cooling system and placed on the car engine prior to installing. See you have to control fuel (carb, fuel pump....) then you have to control gases (dipstick, valve covers.....) and also spark(alternator, distributor, starter.......). All this and you typically have a less reliable car version of a power plant. So if you can afford a proper marine engine then install one. If you are looking for a stop gap intil you can afford a proper engine then choose the car version of what you have now to use as a donor. If your looking to due it from scratch I doubt that you will save any money by the time you buy the marine parts and will have a weaker engine when finished. At least this is the way I see it

[gonzo]

Here is one significant difference: top ring gap in automotive engine-.035" top ring gap in marine engine-.080. It accounts for the higher piston dome temperature.

[tom kane]

My criteria for DIY Auto Engine Marinization is..
Safety for myself,family and Public is paramount,along with using good engineering practice.
You are legally obliged to comply with local Boating Regulations even though the Regulations may not be up to date or even sensible and anti-competative.
If you can afford what is supposed to be the best of anything,by it and try it.
If you are not satisfied with what is available,try to modify it to suit and or make your own model,and if your model is not legal,try and get it recognised.This is what usually happens anyway.
Some of the best ideas come from people who know nothin about a particular subject,as just about anything can be made to work.

[Tater]

Thank you all for your quick response. I'm starting to believe that it might initially look as if you'll save time/money by using an automotive engine, you're probably much better off just sticking with the original and having it rebuilt. It seems like this would, in the long run, be much less stressful. I suppose if I had an old engine lying around it would make better sense to give it a try....Does anyone concur?

A marine engine is the right way to go.

[Corpus Skipper]

In my case, a small block chevy, the block and crank are different

Sorry Woodie, but I just can't let that one go. I have rebuilt dozens of Chevy 350s, auto, truck, and marine. They're identicle. The marine engines are merely the truck, and or factory high performance engines. They have 4 bolt main bearing caps, found in trucks, Chevelles, Novas, Camaros....., they have forged steel cranks (sometimes), also found in cars/ trucks, and higher output camshafts, high performance/ truck rods, and double roller timing chains. Reverse rotation engines are the exception, having a gear drive rather than a timing chain, so that the distributor/ oil pump turn the right way, and the pistons are hung 180 degrees from norm. The only things that differentiate a "marine" engine from a GM factory truck/ high performance engine are the accessories, as Richard pointed out, and ring gap, as Gonzo said. You could pull a Mercruiser 350 out, swap the carb, ignition, alternator, etc.... on to a 350 from an '85 Silverado, overhaul it, regap the rings, and have the same thing you got from Mercruiser. End of rant.

[woodboat]

I specifically wrote "car"
Additionally it isn't the only thing different. The ring gap thing is huge. The cam is different also. Yes, one could build a truck engine to marine specs but we wouldn't be saving any money so what is the point? Note I have used a true car engine with 300,000 miles in a boat. Wasn't pretty but it worked. It was a tired old 307. I put in some new stuff but the cam bearings were pitiful so oil pressure was pretty low. Again it worked but there really is no point. I did all that work swapping it in and got a tired old motor. Only reason it made sense was it was a tired old 26ft plywood trojan that we cut up two years later. We've been round and round. My assessment still is that the low price point for a small V8 chevy means that swapping in a car engine just isn't worth it.

[woodboat]

I did a quick search. This is from an engine remanufacturer.

Fileman sells engines in 24 states, but does not do any retail business. He only works through dealers and distributors. "There are a lot of marine engine builders in Florida, and a lot of automotive rebuilders who are trying to do marine engines. But many of these people have little or no experience in the marine market and try to sell a passenger car engine as a marine engine for as little as $600. Those kinds of engines won’t hold up because they don’t use marine quality parts.

"Marine applications are very demanding, and there’s no way to build a marine engine inexpensively. You have to use top quality parts. One hundred hours in a boat is roughly the equivalent of 25,000 miles in a car because you’re often at full throttle under constant load." Fileman said he sells a Chevy V8 marine engine for $1,200 to $2,000 with a one-year warranty on engines rated up to 375 hp.

from here http://www.aa1car.com/library/2003/eb60342.htm

[woodboat]

this one mentions thicker castings on the heads as well as cam differences
http://www.asme.org.vt.edu/docs/asmenews78.pdf

[ndias]

Yes Tater, you're right...

many countries many laws, but the sea remains the sea.

With time and if you are a guy who likes to do everything on board, you can get an auto engine and get a new one for your boat and I asure you that is money worth.

best regards

Nuno Dias (Portugal)
I myself did from a grp hull of a lifeboat a gaffrig cuter (www.geocities.com/ntbrd68)

Please do not worry! All those who need to go fast. You will only have to pay more for the same speed. GM is quiet. Not dead.