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Author Topic: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke  (Read 32830 times)

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Offline captspillane

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I've decided to replace the Iron Duke in my Kammback with a boat engine. Turns out a 140 HP 3.0L Mercruiser engine is nearly a direct bolt in upgrade to replace the original 2.5L Iron Duke. It may be a better option for some people than a 4.2 swap. It almost sounds too good to be true. I'll post what I've learned so far and the progress I make in this thread. This project car won't be worked on until the end of the summer after I've finished the two SX4's I'm currently assembling.

I learned about this option when trying to figure out what engine was in my Kammback. As soon as I opened the hood I asked, "what's that? It's not an Iron Duke and it's not an AMC 150." The previous owner thought the car was all original. The owner before that had replaced the AMC Iron Duke with a rebuilt unit from a 1977 Chevy Monza. Thankfully the car came with a box full of reciepts that documented what work was done.

I might need to use the intake and exhaust manifold from the 1977 Iron Duke to install the Mercruiser 3.0. I'm going to try, but I'm not sure I can modify the marine version to work. If so that will make it harder for someone else to make the same swap. In my case I have everything I need for a bolt on installation. This is the current engine bay of my Kammback with the 1977 Iron Duke. The most obvious difference is that the carb is on the wrong side and the distributor is in the wrong spot.



« Last Edit: March 25, 2012, 03:09:52 PM by captspillane »
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

rohnk

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Sounds like a neat project. I have to ask though, what is wrong with the current engine? I am assuming that it could not be rebuilt?

Offline captspillane

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What's so great about the Mercruiser engine is the crank. Its the same crank as the "Super Duty" crank that Pontiac offered for race versions of the Fiero. It is obviously heavier and more robust. A Marine engine is designed to operate under full load and at the efficient RPM of the propellor, which is about 4K RPM, for a very long period of time. That's why a heavier crank was necessary. An automotive Iron Duke was designed for fuel efficiency only, so it was lightened and weakened on purpose to have just enough strength.

It’s also one of the most produced engines of all time. The first Iron Duke engines were made in 1977 using the dimensions and characteristics from another earlier Chevy engine. It was marketed as the "Iron Duke" because the Chevy Vega aluminum block engine was a disaster with lots of bad press. Those engines were prone to cylinder thermal expansion issues because of the iron pistons in an aluminum block. They were fixed by sleeving them, but that didn't fix the horrible reputation that engine had. The first engines had a Holley carb and non-cross flow head very similar to the older engine it was based off of. The valve cover gasket pattern, flywheel pattern, and bellhousing pattern was identical to a small block chevy. It even uses a SBC small diameter flywheel.

The 1977 and 1978 Iron Dukes got modified in 1979. The block casting was changed slightly. A new cross-flow head was added, which put the carb on the passenger side. A Rochester carb replaced the Holley. The Distributor was moved to a new location to make room for the intake manifold. The cross flow head is not compatible with the earlier blocks. In 1980 the block casting got changed again to replace the small block Chevy bellhousing pattern with the new 60 degree pattern.

Chevy continued to make the Iron Duke until 1993 with the new bellhousing pattern. They sold the rights and tooling to AMC for the 1979 casting. AMC continued to make the 1979 GM Iron Duke through mid-year 1983 when it got replaced by the AMC 150 four cylinder engine. The Chevy Iron Dukes are one of the most produced engines of all time. It got throttle body injection in 1982 which increased the power output from 80 hp to 90 hp. It jumped to 98 hp with changes to the TBI in later years.

Meanwhile Mercury marine engines decided to start making their own inboard engine. They started with the 1977 Iron Duke block casting. All the accessories bolted to the engine are different, including the oil pan, but there is no difference in the block or head themselves. Marine grade cranks, internal parts, salt resistant freeze plugs, and better gaskets are used throughout.

They initially made a 2.5L. They eventually came out with the Mercruiser 3.0L. This has a 4” bore and 3.6” stroke on a “Super Duty” crank. It’s essentially an Iron Duke stroker. It was offered with different carbs at 120 or 140 HP. Those numbers are painted right on the top of the motor to identify them. They should be identical internally. It is still identical crank flange to accept an automotive flywheel  and external characteristics.

I have seen that my 1977 Monza engine has one bolt slightly off on the passenger side engine mount. Its very minor and the rest of the bolts are in the exact same spot as an AMC Iron Duke. Mine has the hole enlarged by the person who made the swap in 1995. The Mercruiser engine will bolt up to the crossmember engine mounts and transmission of an Iron Duke AMC Eagle with little or no modification whatsoever.

Mercruiser eventually decided to make their own 3.7L midgrade engine. They took their Iron Duke tooling and applied it to an Aluminum block. The head and pistons are identical to a Ford V8. The bellhousing pattern, mounting pattern and outside of the block looks like an Iron Duke and it’s commonly called an Iron Duke. Those had different carbs to make a 160, 170, and 190 HP motor. I initially wanted one of those because they should bolt up just as easily as the Mercruiser 3.0 but I found out that the oil pan is different. I looked up the gasket patterns to confirm. If you use a Mercruiser 3.7 you will have to take the oil pan and cut it to make your own. On the 3.0L engines you simply bolt your Eagle Iron Duke oil pump pickup and oil pan on to replace the funky Marine oil pan. There is also no sign of anyone ever installing a Merc 3.7 in a car before while the 3.0 has been many times, so I’m going to avoid that engine for now.

The 3.0 has had EFI added to it recently. You can buy fuel injected crate engines. Those are to be avoided, however, because they don’t work for automotive applications. The EFI is non-feedback, which means that it works fine for a limited RPM range and that’s it. It doesn’t adapt the fuel mixture to account for different RPM’s and engine load that you see driving. The timing advance is also very limited in comparison to a car distributor.

You might have good results with the Marine carbs IF AND ONLY IF you change the ignition system to have the proper timing advance. Supposedly a Chevy distributor works fine since the Iron Duke cap is a V8 cap with four blank spots where wires would go.

I’m personally going to try to adapt a Howell TBI kit intended for a Jeep 4.2. It should have the right size injectors for this engine since a 4.2 with TBI gets right around 140 HP just as this thing will.

The Mercruiser 3.0 did have changes in production that affect the rear main seal. There are three year ranges. I believe it was 1992 before they changed the seal. All ‘80s boats should have an engine that I can rely on being compatible with my Eagle oil pans.

The Mercruiser 3.0 is in nearly every small inboard boat from 16 to 19 feet long. They are extremely common. They’ve been produced by three companies including GM and are still produced today. That engine and its compatible marine grade Chevy V8s are the industry standard now, so as near as I can tell all the new diesels made by “Merc-Cummins” actually uses the SBC pattern and similar, if not identical, engine mounts as the 3.0 and in turn our AMC Eagles. I’m hoping to find a Marine diesel engine to install in an Eagle one day too.  
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline captspillane

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Sounds like a neat project. I have to ask though, what is wrong with the current engine? I am assuming that it could not be rebuilt?

I've driven most of my life with an Iron Duke SR4. They're great and very practical, but it always left me desperate for more power when I had to slow down every time I went up a hill. 80 HP is not enough for me. Its just not. The 115 hp in a stock 258 is barely enough to appease my appetite. 140 HP is pretty much the least amount I will accept in a car I'm going to keep long term.

The Iron Duke that is in the car was overbored and professionally rebuilt in 1995. The car has 208K miles, so that engine probably has 60K or less miles. The Holley carb is set ok and idles very well, but it doesn't accelerate smoothly or run well under load. Its probably a timing issue. I'm going to pull it out and stick it in a parts car that  I want to move under its own power. Long term I'll sell or give it away to someone with the patience to use it. I have three other running Iron Dukes with the same fate. I'm planning on driving this Kammback as one of my maiin cars, so it needs more power, a TBI, and a paint job.
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline eaglebeek

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Catspillane...about your exhaust/intake manifolds...inboard and stern drive marine engines have water-cooled/jacketed exhaust manifolds. I'm not sure how they would work in an automotive application. My concern would be if this exhaust manifold would burn out if water wasn't circulating through it.
1984 Eagle Wagon, 258, auto, 2.73 gears, daily driver
1983 Eagle Limited Wagon, parts; sold
2000 Jeep Cherokee, 4.0, auto
2007 Hyundai Accent, radical downsize from minivan, wife's car and she loves it!

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Catspillane, what an interesting story and good research! I think it will bring some of us to a good idea, so a good egg for you!

Anjo
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Offline captspillane

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Catspillane...about your exhaust/intake manifolds...inboard and stern drive marine engines have water-cooled/jacketed exhaust manifolds. I'm not sure how they would work in an automotive application. My concern would be if this exhaust manifold would burn out if water wasn't circulating through it.

The non-cross flow head on the 3.0L is the same head as my 1977 Chevy Monza engine. I'll use that intake and exhaust manifold. I’m also planning on creating my own carb adaptor from scratch to attach a Howell TBI kit intended for a 4.2 where a Holley carb is now. I do know that the 3.0L intake and exhaust ports changed shape slightly around 1992, so I'm sticking with 80's boats.

Indeed it’s possible that the marine carb and manifolds will work just fine. I’ll look at that possibility and post my thoughts here. Even if they did work I wouldn’t use them because I want to retain my current exhaust pipe that I just made.

Unfortunately it’s hard to find 1977 and 1978 Iron Dukes. They're very rare. I know I sure didn't know what a Monza was until I started this research. I'm lucky to already have one in my Kammback. If I wanted to do this to a second Eagle I would try to make a custom intake and exhaust manifold from scratch. I think that the mounting surface and basic shape of the marine intake and exhaust would be a good starting point for someone skilled with a welder to make their own. It might even work as is.

I also have read of people using a small block Chevy cross flow head. Supposedly the bolt pattern is the same but one water jacket needs to be modified. It should be less difficult than installing a 4.0 head on a 4.2. That is supposed to allow for bigger valves for extreme racing engines. Of course the people who make modifications like that also make their own manifolds from scratch as well.   

I found one rebuilt 3.0L, engine only, for $700, one running complete boat for $500, and one 3.0L in need of rebuild for $300. I also found about a dozen other boats and 3.0L engines for sale within two hours of my home. Imagine finding a freshly rebuilt 140 HP Super Duty Pontiac Iron Duke race engine for $700. I can’t imagine finding one at all.


Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline captspillane

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Here is the comparison photo of a regular 151 crank and a Super Duty 181 crank  I got it from. I also included several photos of a 3.0L crate motor, of a Monza from the H-body forum, and my own Kammback.

http://myfiero.oceanmoon.com/how-to/engines/iron-duke-performance-faq














« Last Edit: March 26, 2012, 11:25:15 AM by steveabn8295b »
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline bigdog56e

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 I remember some air compressor company was using the 3.0 engine on trailer mounted air compressors. Might look for a source of GM industrail engines. Chrysler made Air Raid sirens in the '50's with the 354 Industrial Hemi engine, and Ford had a industrial version of the 2.3L four cylinder.
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Offline nwamcsx

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Any update/more info on this swap??


Thanks

Offline carnuck

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I was wondering if they used the SBC pattern 2.5L or the later 60 degree GM pattern in the SX4s.
AMC/Jeep gauges are for amusement only. Any correlation between them and reality is purely coincidental!

Offline captspillane

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Each number is its own entirely different engine casting, each often confused with the others.

1) 1977, 1978 Chevy Monza and all Mercruiser 2.5L and 3.0L engines are SBC with non crossflow heads.

2) 1979 only Chevy cars and 1980-1983.5 AMC cars are all SBC bellhousing pattern with crossflow heads. Distributor hole moved in the casting to allow room for intake on opposite side.

3) 1980 to 1993 Chevy cars and trucks are 60 degree GM pattern.

Notice that a 1983 AMC engine is the same as a 1979 GM engine, but not the same as a 1983 GM engine.

4) Late 1983 and 1984 four cylinder Eagles are a different engine entirely. It's a TBI AMC150 four cylinders with 60 degree bellhousing. I've seen one once and would love to see another in this lifetime.

5) Mercruiser 3.7L engines, rated for 180 and 190 HP, are externally interchangeable with Merc 3.0L engines and often get called "Iron Dukes". Internally nothing is the same. They use Ford pistons and heads instead of Chevy V8 pistons and heads. The AMC oil pan will not match it. The SBC bellhousing and engine mounts should be identical, however.
« Last Edit: March 06, 2013, 02:59:33 PM by captspillane »
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline captspillane

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As for an update to my project status, I recently let the annual inspection expire on my Kammback. It needs a wheel alignment desperately and I'm not willing to align it until all the ball joints have been replaced.

If I need the car on the road in a hurry I'll simply fix and inspect it and keep running the current Monza 2.5L. It was professionally rebuilt in 1995 and should run strong for a long time once I replace the intake gasket.

If I don't need it quickly I'll pull the entire crossmember and engine and continue with this swap. I haven't decided if I'll use the TH400, 700R4, or T5 after the swap. I've got at least one of each already. I'm leaning toward the 700R4 but I'll probably stick with the T5.

I also used my Howell TBI kit in my 1980 Eagle Wagon. I'll need to source another kit or start making my own. I won't install my 3.0L Merc motor without a GM TBI already adapted to it. I'm going for full spark control since the GM HEI distributor is compatible.

I've got a large number of Louver kits to make and a SD33T turbodiesel swap to finish first. It will realistically be a year or two before I pick back up with this project.
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline carnuck

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Each number is its own entirely different engine casting, each often confused with the others.

1) 1977, 1978 Chevy Monza and all Mercruiser 2.5L and 3.0L engines are SBC with non crossflow heads.

2) 1979 only Chevy cars and 1980-1983.5 AMC cars are all SBC bellhousing pattern with crossflow heads. Distributor hole moved in the casting to allow room for intake on opposite side.

3) 1980 to 1993 Chevy cars and trucks are 60 degree GM pattern.

Notice that a 1983 AMC engine is the same as a 1979 GM engine, but not the same as a 1983 GM engine.

4) Late 1983 and 1984 four cylinder Eagles are a different engine entirely. It's a TBI AMC150 four cylinders with 60 degree bellhousing. I've seen one once and would love to see another in this lifetime.

5) Mercruiser 3.7L engines, rated for 180 and 190 HP, are externally interchangeable with Merc 3.0L engines and often get called "Iron Dukes". Internally nothing is the same. They use Ford pistons and heads instead of Chevy V8 pistons and heads. The AMC oil pan will not match it. The SBC bellhousing and engine mounts should be identical, however.

I haven't seen many 4 cyl Eagles and none with the AMC 4 cyl, but that is the same motor used in '84-'86 Cherokees and a few '86 Comanches (then they went to TBI and later to MPFI)

The AMC 4 pattern is also the same as 2.8 Chev 6 and '80 up front wheel drive Caddy, Buick, etc (including the Northstar V8s)
AMC/Jeep gauges are for amusement only. Any correlation between them and reality is purely coincidental!

Offline j2sax

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Althought the AMC 4 was not EFI'd in the Eagle. 

Jesse

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The early AMC 4s used a similar ECM to the AMC 6 that AMC called CEC. It was only programmed slightly differently and used a PWM solenoid instead of the stepper motor on the feedback carb. (As per the TSM.) It was a YFA carb, similar to the old YFs used on the old 232s and 258s.

I think all the 151s used a Rochester Varajet either with or without a PWM solenoid and C4 feedback, which is a totally unrelated system. The Varjet used a progressive secondary design like a Weber 32/36 DGEV.
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Offline carnuck

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It's not hard to retrofit
Althought the AMC 4 was not EFI'd in the Eagle. 

Jesse
I
AMC/Jeep gauges are for amusement only. Any correlation between them and reality is purely coincidental!

Offline Prafeston

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #17 on: December 04, 2013, 07:37:18 PM »
Cool stuff in here! I'm researching the Iron Duke right now so I found this thread very helpful!
1983 AMC Eagle SX/4 - Penny

Offline captspillane

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #18 on: December 05, 2013, 06:17:04 PM »
Good timing in reminding me about this thread Rafe. I have information to post here soon.
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline Prafeston

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #19 on: December 05, 2013, 06:49:18 PM »
Right on! Sounds like a nice upgrade. More horsepower and better mileage than a stock 4.2 I would think!
1983 AMC Eagle SX/4 - Penny

Offline captspillane

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #20 on: December 05, 2013, 11:03:00 PM »
It also solves some major headaches about the crossflow head design. People often comment about how wide open the Eagle Iron Duke engine bay is and assume it must be easy to work on. It's a nightmare! Everything is crammed into one little corner! The engine bay in my Kammback with the non-crossflow head is wide open and everything is accessible the way it should be. That is reason enough for the upgrade.

I posted on the Monza forum a few month's back and someone did have the parts I wanted. It took a long time to close the deal but a box full of Monza parts is on its way this week. I actually own two sets of the rare automotive manifolds from a '77 Monza now. The freshly rebuilt Monza engine will stay in my roadworthy Kammback while I do this upgrade to my second Kammback. In my garage right now I've got two 3.0L and one 2.5L Mercruiser motors and a pair of stock Eagle Iron Duke's for comparison and tear down pictures. It's coming together steadily but slowly.
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline Prafeston

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #21 on: December 05, 2013, 11:06:52 PM »
Very cool. A buddy of mine has a parts car Monza just sitting at his house. I wonder which engine is in it..
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Offline IowaEagle

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #22 on: December 06, 2013, 08:46:24 AM »
This is an interesting upgrade.   I thought most marine engines were reverse rotation, apparently these are not?
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Offline rollguy

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #23 on: December 06, 2013, 12:10:14 PM »
This is an interesting upgrade.   I thought most marine engines were reverse rotation, apparently these are not?
I believe reverse rotation engines were only needed when 2 engines were used together.  My brother had a friend in Washington that had a commercial fishing boat.  It had 2- Chevy V8 engines, one standard rotation, the other reverse.  The reverse rotation engine had 5 things different- water pump, cam, distributor, starter, and alternator.  When these items went bad, the cost was 3 or 4 times that of it's standard rotation counterpart (marine only).  Everything on the standard rotation engine was normal automotive stuff.
1980 Eagle Turbodiesel Wagon (only 2 known to exist as of 2008)- 7-7-2011 Flight to it's new nest @ Rambler Ranch
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Offline IowaEagle

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #24 on: December 06, 2013, 12:24:17 PM »
Thanks Rich.  That makes a lot of sense.  Just like GM fuel pumps being cheap for a Chevy, but the same pump was four times the cost when bought for a Allis Chalmers tractor.
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Not a Jeep.  Not a Car.  Its an AMC Eagle!

1982 Eagle SX/4 Sport;
1980 Concord DL;
1970 Ambassador 2 Dr HT, SST
2002 Hyundai Santa Fe;
2008 Jeep Patriot Sport - Freedom Drive II

Offline captspillane

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #25 on: December 07, 2013, 01:16:25 PM »
For the Iron Dukes the biggest difference between marine duty and automotive duty is the distributor. It has a limited range of operation because the propellor dictates a very narrow range of RPM and a steady operating power. The Mercruiser carbs also would not work well in a car because they're not designed for driving in traffic, just steady on. In this case the marine dizzy gets chucked in the trash and an automotive one put back in its place. They are externally identical.

Usually the main reason "marine duty" is so expensive is not for rust control or fire prevention, it is because of the duty cycle. A Marine engine is put under full load and left there the entire time you're using it. In this case with the Merc Iron dukes it only cost a couple dollars more for the corrosive moisture and salt resistant plugs on the side of the motor but it cost over a thousand dollars more from the factory for the "Super Duty" cranks they had.
« Last Edit: December 07, 2013, 01:18:15 PM by captspillane »
Currently Inspected and Insured as of Jan 2013:
-1985 Eagle Station Wagon 258 T5 Stickshift
-1980 Eagle Station Wagon 258 Auto Fuel-injected with GM TBI

Minor Repairs Underway:
-1982 Eagle SX4 258 T5
-1981 Kammback 2.5L Iron Duke T5

Restoration Efforts Near Completion:
-1982 SX4- 401 NV3550
-1983 SX4- 4.5 MPI NSG370 (6 Speed)

Restoration Efforts Underway:
-1985 SW- 4.0 MPI AX15
-1982 SX4- 4.0 AW4
-1981 SX4- SD33T NV4500 (Turbodiesel 5 speed)

Future Rescue Efforts- '85 Maroon SW, '87 Limited SW, '84 Limited SW, '87 4 door Sedan, '81 2 door Sedan, '88 White SW, '77 4 door Hornet, '74 2 door Hornet, '79 Spirit AMX, '81 Kammback.

RIP- Red '81 SX4, '84 4dr Sedan, '84 SW, '81 SW, '80 Spirit, '83 SW, '83 4dr Sedan

Offline carnuck

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #26 on: December 11, 2013, 06:21:15 PM »
Later on boat designers got smart and used a transmission to reverse the prop rotation.
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Offline DownwardFlame

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I've been doing a lot of research on the iron duke as I am considering buying a 4 cyl sx4. I have found that the cross flow head is rather poor flowing and tends to crap out at 4500 rpm and has very thin runner walls that only allow for very minimal porting. In the cyl head thread I think I read that the AMC 150 head out performed it. My question is will the 150 head bolt on to the 151 block?
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Offline carnuck

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totally different engines.
AMC/Jeep gauges are for amusement only. Any correlation between them and reality is purely coincidental!

Offline Creepingmonza

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I have a 1980 Chevy monza with a 151 iron Duke and want to swap for the mercruiser 3.0.I'd like detailed info on this swap and it can be sent to creeper0629@gmail.com.my 151 is pushing maby 70-76 hp and brand new was 82.this merc is the same block with a stroker kit and will double my hp without me haveing to mod my while front end,and weight should be the same.it is converted for Marine use so I'll need help converting back to automotive use.

Offline Creepingmonza

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #30 on: September 06, 2015, 08:47:15 AM »
I gota ask,to clarify, do you have a monza or just the motor? Pm me on this please

Offline vangremlin

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Re: Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke
« Reply #31 on: September 07, 2015, 11:24:01 PM »
I gota ask,to clarify, do you have a monza or just the motor? Pm me on this please

captspillane seems to be the only one that is knowledgeable on this and he has not been on the site for several months.  Try to PM or email him directly for best results.  Good luck!
1981 Kammback 258 - "Pepe"
1980 Coupe 258 - "Ginger
1972 Gremlin X 304
1978 Gremlin 4 cyl 121 - sold
1964 TBird 390 - sold

Offline tb30570

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here is some swap info from the Fiero forum that might be useful:

http://www.fiero.nl/forum/Archives/Archive-000001/HTML/20120111-2-093668.html

here is some information on a crankshaft swap:

http://www.fiero.nl/forum/Forum1/HTML/093573.html

 

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