Replacing the 80 HP 2.5L Iron Duke with a 140 HP 3.0L Mercruiser Iron Duke

[BenM]

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.

[carnuck]

It's not hard to retrofit

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

Jesse

I

[Prafeston]

Cool stuff in here! I'm researching the Iron Duke right now so I found this thread very helpful!

[captspillane]

Good timing in reminding me about this thread Rafe. I have information to post here soon.

[Prafeston]

Right on! Sounds like a nice upgrade. More horsepower and better mileage than a stock 4.2 I would think!

[captspillane]

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.

[Prafeston]

Very cool. A buddy of mine has a parts car Monza just sitting at his house. I wonder which engine is in it..

[IowaEagle]

This is an interesting upgrade.   I thought most marine engines were reverse rotation, apparently these are not?

[rollguy]

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.

[IowaEagle]

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.

[captspillane]

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.

[carnuck]

Later on boat designers got smart and used a transmission to reverse the prop rotation.

[DownwardFlame]

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?

[carnuck]

totally different engines.

[Creepingmonza]

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 [email protected] 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.