Ok, so I was in the pick and pull today and I was speaking with the owner about poking around and hoping to get lucky with finding an SD4. He then brought me right out to a Mercruiser L4 Rated at 170 HP but the tag states it red lines at 4200-4500 rpm instead of the 7200 SD4. He being a race car driver himself with crew and all thought it was an SD4 and I thought I was about the luckiest guy alive when he said he would sell it for $140.
after a little researching this evening, it seems the 181, 170 HP rated L4 Mercruiser is a 3.7L
It has a much larger dbl barrel carb with additional unidentified small adapter plates and what is most certainly the SD4 Intake seen here http://www.kansasracingprod...oducts/Features.html
The Block seemed much thicker and beefier that my 87 L4 DIS. The water passages were different than the stock duke for sure as there was no T stat housing but couldn't see if the water pump passage was there or not. There was a log style exhaust manifold that had what looked a lot like a Turbo flange / mount ? ( whatever you call it) sticking off the top. I am still in the process of researching the engine to the fullest but I placed a deposit on it today to lock it in if it is worth my while. I didn't get a good look at the head however if the SD4 intake is attached to it, I am sure it's bored appropriately. The Valve cover also has the aluminum grooved style like the SD4 but without the SD4 stamp on it. The starter was on the same side as the 2.5 L4 but in a higher position more even with the exhaust ports. It had a GM bolt pattern with additional holes drilled for additional bell housing patterns that I don't recognize.

I was hoping someone might be able to shine some light on the subject. I know absolutely nothing about the design of boat engines but I am aware that boat engines are cooled differently.
I know there was some talk about the 3.0 crank and some other mods to the Duke in the "Super Dukie" thread but it was all very inconclusive and the person toying with it either hit a brick wall or lost interest and stopped posting. Maybe KurtAKX could offer some input since you seem to be the Duke man from what I have read in my limited time here. Some of my primary questions are:

1) Can the block be altered for Fiero use?
2) can the crank be used for Fiero use and / would I want to use it? I have yet to come across any hard specs on the engine and applications.
3) As much info on the head as can be mustered.
4) Anything else you might be able to tell me about the Merc engine and compatibility with the standard 2.5

I have an understanding with a very good machinist and retired builder for machining parts for me to spec at material cost and I've done a lot of home improvement and developing his future home and building his new workshop so retrofitting wouldn't hinder my application possibilities. Thanks a lot in advance!

[This message has been edited by katore8105 (edited 07-19-2010).]

I believe that a good amount of modification would be needed to mount this engine in a Fiero. Check the mount points-are they the same? Might be different.
The check the crankshaft flange. Will it accept a Fiero flywheel or flexplate? Don't believe that it will. There are probably solutions to these issues but how much work and how much money it will take to get the swap done may place you in a situation where a different swap might be more economical.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Inboard marine engines are often modified stock engines produced by various auto manufacturers. Most of the ancillaries are different than automotive. My experience with a 4.3 inboard was that the block was identical to the GM 4.3. Everything inside the engine was identical except the camshaft. It was designed to run under load at all times, since a boat stays under load to keep speed and plane. The manifolds were similar to the log style, but that was so that the cooling water taken in from the outdrive could be dumped out the exhaust, helping to keep down the heat in the engine compartment.

The engine used the standard crankshaft bolt pattern for the flywheel, the same crank pulley and the same water pump as the truck engine. I've only dealt 1 4-cylinder marine engine and except for the bolt-on goodies, it looked identical to the GM 2.5's on the outside.

If you know what year the engine is, you can cross reference it with a comparable year automotive engine for specs. That's what I did when I replaced my 4.3 inboard. Instead of a $3000 marine block, I got a $900 Chevy truck block and installed my marine cam and replaced the metal freeze plugs with brass plugs.

quote Originally posted by fierofool: Inboard marine engines are often modified stock engines produced by various auto manufacturers. Most of the ancillaries are different than automotive. My experience with a 4.3 inboard was that the block was identical to the GM 4.3. Everything inside the engine was identical except the camshaft. It was designed to run under load at all times, since a boat stays under load to keep speed and plane. The manifolds were similar to the log style, but that was so that the cooling water taken in from the outdrive could be dumped out the exhaust, helping to keep down the heat in the engine compartment. The engine used the standard crankshaft bolt pattern for the flywheel, the same crank pulley and the same water pump as the truck engine. I've only dealt 1 4-cylinder marine engine and except for the bolt-on goodies, it looked identical to the GM 2.5's on the outside. If you know what year the engine is, you can cross reference it with a comparable year automotive engine for specs. That's what I did when I replaced my 4.3 inboard. Instead of a $3000 marine block, I got a $900 Chevy truck block and installed my marine cam and replaced the metal freeze plugs with brass plugs.

Thank you both for your replies. I am going to go back tomorrow to get some pictures and measurements to cross reference. I saved a part number today but once again, I am having a hard time locating any information with it. As for the "taking the goodies out" I was figuring I would be going more that route than modifying the whole block but ultimately I need to further identify the block for certain before I can make any major decisions. I'm basically looking at this as a fun project but with no high expectations. If nothing else, a learning opportunity. $140 is not expensive and even worse case scenario if I were to sell off some of the good parts in the chance I never did anything with it, I would make my money back on some of the parts I have confirmed to be sought after.

I am going to have to pull part and cast numbers however to try and narrow down the year but I'm fairly sure it's from an 85/86.
I will get more hard numbers and observations posted tomorrow after I get back to it. Thanks!

For $140 you can not really go wrong. I would buy it in a heartbeat and get it home and then start researching from the angle of not if it will work, but what will it take to work.

quote Originally posted by fieroguru: For $140 you can not really go wrong. I would buy it in a heartbeat and get it home and then start researching from the angle of not if it will work, but what will it take to work.

Yeah, that's kind of what I was thinking. I'm going there this morning to seal the deal. I will have some pictures up later today. You know when people say "sleep on it" well, I did and every time I awoke through the night, this engine was the only thought going through my head lol. Thanks!

[This message has been edited by katore8105 (edited 07-18-2010).]

IIRC, the Mercruiser 3.0 181 engine is a NON crossflow headed duke, that has a SBC bellhousing and SBC (1 Piece seal) crank flange. 181 cubic inches is 3.0 not 3.7.

By non crossflow head, I mean that the intake and exhaust manifold are on the same side of the head, not on opposite sides like the dukes that we know. I do believe that you can change the head for a crossflow or, ideally, a Super Duty head, which is also crossflow.

So the basics of the mounting are the same as a small block, adaptor plate, flywheel...

Adapting the Mercruiser guts to a Fiero duke or S10 Block isn't exactly straight forward:
https://www.fiero.nl/forum/Forum2/HTML/095328.html

And This one discusses the the swap of the whole engine too.
https://www.fiero.nl/forum/Forum2/HTML/105044.html

If its the 3.7, it's half a Ford V8.

Nothing in common with the original iron duke (the 153, which was 2/3 of a straight 6 Chevy), the Mercury Marine 2.5/3.0 (which have the later Pontiac geometry), or the Fiero Iron Duke (151)

Thanks guys. I found some more information as well and have a PM that I am going to post later to further clear it up along with the pics I took. I didn't get the engine. I did however get an SD4 intake that will compliment my Hooker header after I find a larger bore TB.
Hey Kurtakx, how is the fuel economy on your 3.0 crank set up? Also, did you ever find a way to adapt an M62 to it?

Conclusion and pics for future search results coming soon.