Calling any 2.5L Iron Duke experts

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g-man

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Topic: Calling any 2.5L Iron Duke experts
Posted: Jun/30/2015 at 7:20pm

I don't know where this is suppose to get posted, so I'm sticking it in the 6 cylinder section.

I need help on this guys.

I need to replace the exhaust manifold on the Iron Puke in my '80 Spirit.

I have considered using a header, for improved exhaust flow, but 2 things are stopping that idea.

1. It needs to stay smog legal for as long as this engine is in the car (so I need the stove pipe).

2. Eventually I will be replacing this motor with a V-8 (once the Puke needs rebuilding) possibly an Indy block (at which time I won't be needing to worry about smog anymore).

So my question is; does anyone know if the below pictured manifold will work in my '80 Spirit 2.5 w 4-speed?

The first picture is the manifold I want to use: listed as fitting an '85 - '93 GM CHEVY S10 S15 SONOMA JIMMY BLAZER 151 2.5 EXHAUST MANIFOLD Part# EN1267

The manifold that is on the engine looks just like this one below. Except the stove pipe is a little different, but it looks like that will bolt over with a little adjustment.

It looks to me like the bolt pattern is the same. But I'm not 100% certain.

I am also a little worried if I am going to have a fitment problem with the head pipe flange being too cose to the slave cylinder.

If it is a little too close, maybe this could be cut and welded a little to change the down angle??

Does anyone have any clue about this?

g-man

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Posted: Jul/01/2015 at 1:14am

Might be better off to ask this stuff on a Pontiac forum. It's a Pontiac engine. There just aren't that many AMC guys out there with the 2.5L. Not many sold and not many exist still.

Maybe somebody will pipe up, but personally I know squat about that engine other than most people hate it, including the Pontiac guys.

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Posted: Jul/02/2015 at 6:36am

Easy way to figure out bolt pattern is to get gaskets for both. Auto parts store might pull them and compare for you without buying. Of course if the part number for the gaskets is the same.... you can check that on RockAuto.

The only issue is clearance at the bottom. If you have clearance for the extended outlet on the S-10 manifold it should fit, you'll just have to re-do the head pipe as it needs to be shorter. There doesn't seem to be any difference in the two manifolds except that extended outlet. If you have good exhaust pipes up front you're better off to get the one that's made for the car.

Or do you have a cast iron exhaust manifold? The tubular models don't usually flow any better, but they do save some weight.

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Posted: Jul/02/2015 at 7:09am

Mating surface of manifold to block should be the same.
I would go with the replacement you have identified and make the trip to the muffler shop to fab a replacement.

Put an ad in the WANTED section here, you might find someone who did a conversion and has one available.

I had the "duke" in my 81 Spirit and it did not have enough power to get out of its own way. I loved the car but the low performance never equated to fuel savings. My folks had a Concord I6 and it had better fuel mileage and could pull a hill without losing speed.

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Posted: Jul/02/2015 at 8:14am

I would look for 4-cylinder S-10s or old GM H-bodies at PickNPull and get the proper replacement manifold. I can't see how a header would help you much with that engine. I had an 80 Spirit with the Duke here on the central coast and I rebuilt the engine and kept it smog legal, but I don't have yes or no answer to your question. Joe

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Posted: Jul/02/2015 at 11:14am

There are a ton of performance parts available for those engines thanks to the GM crowd, and I mean serious performance stuff.

A "header" should not interfere with emissions as long as you do have the stove pipe to provide pre-heated air (although that's as much driveability in some cases as emissions)

My biggest concern would be - after does it fit the engine - how will it work in an AMC chassis? How about clearance and the head-pipe fitment? I know you can have a new pipe made to mate with any manifold or header arrangement - I'm thinking of same clearing mounts, cross member, etc.

They are easy enough engines to work on, when they are all apart - otherwise the manifold arrangement is a pain, as is tuning the darned things......... at least in Spirit and Eagle cars.

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Posted: Jul/02/2015 at 11:21am

The O.P. Is in California and very few if any performance modifications are CARB legal. I bought the book about modifying my duke and researched the racing head etc. when I was overhauling my Sprit and through Internet searches I found that most of that hardware is not commonly available any more. The engine was a major reason I sold the Spirit although I did enjoy solving the problems with the Varijet carb and getting it running well. Joe

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Posted: Jul/02/2015 at 9:44pm

OK, I had an iron Duke in an 1981 Spirit with a four speed. Nothing but problems. Yes you can get a lot of high performance parts for the iron duke. In the end the only stock parts you keep are the valve cover and the oil pan. Every thing else is replaced. Save your self time and money and go straight for the AMC engine. You be well ahead of the game that way. LRDaum

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Posted: Jul/04/2015 at 1:50am

FSJunkie wrote:

Might be better off to ask this stuff on a Pontiac forum. It's a Pontiac engine. There just aren't that many AMC guys out there with the 2.5L. Not many sold and not many exist still.

Maybe somebody will pipe up, but personally I know squat about that engine other than most people hate it, including the Pontiac guys.

FSJunkie: You're actually sorta right on that point. I didn't know squat about the Iron Duke before I picked up this Spirit (I didn't want to know either).

But since this is what I'm stuck with, I need to do what I can with what I have now.

What knowledge that I have of this motor now, is from going over to an S-10 forum, and lurking through their Iron Duke tech section.

farna wrote:

Easy way to figure out bolt pattern is to get gaskets for both. Auto parts store might pull them and compare for you without buying. Of course if the part number for the gaskets is the same.... you can check that on RockAuto.

The only issue is clearance at the bottom. If you have clearance for the extended outlet on the S-10 manifold it should fit, you'll just have to re-do the head pipe as it needs to be shorter. There doesn't seem to be any difference in the two manifolds except that extended outlet. If you have good exhaust pipes up front you're better off to get the one that's made for the car.

Or do you have a cast iron exhaust manifold? The tubular models don't usually flow any better, but they do save some weight.

Frank: That was an excellent idea about comparing the manifold gaskets (DUH...why didn't that dawn on me.)

I have what I believe to be a cast iron manifold now, and if I'm going to need to replace that, I might as well try for an improvement as the existing manifold is too restrictive.

The exhaust on the car now after the manifold, is all aftermarket and much improved over stock.

gtoman_us wrote:

Mating surface of manifold to block should be the same.

I would go with the replacement you have identified and make the trip to the muffler shop to fab a replacement.

Put an ad in the WANTED section here, you might find someone who did a conversion and has one available.

I had the "duke" in my 81 Spirit and it did not have enough power to get out of its own way. I loved the car but the low performance never equated to fuel savings. My folks had a Concord I6 and it had better fuel mileage and could pull a hill without losing speed.

gtoman: You're right about the power output on this thing.

I've done some improvements, and it is tuned to the Nth degree. But it really has to be flogged to get out of it's own way. (I like to say that the motor is so boring that it yawns when you step on the gas.

However I have been slightly surprised to document the mileage at 25MPG average.

pacerman wrote:

I would look for 4-cylinder S-10s or old GM H-bodies at PickNPull and get the proper replacement manifold. I can't see how a header would help you much with that engine. I had an 80 Spirit with the Duke here on the central coast and I rebuilt the engine and kept it smog legal, but I don't have yes or no answer to your question. Joe

pacerman wrote:

The O.P. Is in California and very few if any performance modifications are CARB legal. I bought the book about modifying my duke and researched the racing head etc. when I was overhauling my Sprit and through Internet searches I found that most of that hardware is not commonly available any more. The engine was a major reason I sold the Spirit although I did enjoy solving the problems with the Varijet carb and getting it running well. Joe

Joe: Actually I think a header would help a bit, the stock exhaust system is so restrictive, I figure anything would help, I know the exhaust that I plumbed up helped quite a bit. As I'm sure you probably recall there is no AIR injection system on this motor, making a header a much simpler proposition for smog purposes.

Hoever, I just can't see paying the expense for a header for this car, when my plan is to put a V-8 into it once this motor expires.

Same with modifying the other parts of the motor. Although as I said, except for the current exhaust leak, I have it running very well indeed.

billd wrote:

There are a ton of performance parts available for those engines thanks to the GM crowd, and I mean serious performance stuff.

A "header" should not interfere with emissions as long as you do have the stove pipe to provide pre-heated air (although that's as much driveability in some cases as emissions)

My biggest concern would be - after does it fit the engine - how will it work in an AMC chassis? How about clearance and the head-pipe fitment? I know you can have a new pipe made to mate with any manifold or header arrangement - I'm thinking of same clearing mounts, cross member, etc.

They are easy enough engines to work on, when they are all apart - otherwise the manifold arrangement is a pain, as is tuning the darned things......... at least in Spirit and Eagle cars.

Bill: The replacement manifold that I'm looking at is more like a "free flow manifold" than a header. Because of smog laws, we are required to have the stove pipe out here, and I should be able to re-use the old one with a little modification.

There is a chance I might need to cut that replacement manifold to modify the outlet slightly for clearance ( I would rather not, but if neccessary...Oh well)!

[QUOTE=mramc]OK, I had an iron Duke in an 1981 Spirit with a four speed. Nothing but problems. Yes you can get a lot of high performance parts for the iron duke. In the end the only stock parts you keep are the valve cover and the oil pan. Every thing else is replaced. Save your self time and money and go straight for the AMC engine. You be well ahead of the game that way. LRDaum

Larry: I cannot argue with your logic sir.

I just want to keep this motor running as strong as I can while I still have it in the car.

It is currently my daily driver, but eventually will only be a "fun" car (auto-crosser), at which time it will be recieving an AMC V-8 and preferably an aluminum block ,at that, for better weght bias.

When I first found it, I didn't really want it because of the Iron Duke.

But it had only 42,000 miles so I picked it up for just $500.

It also had a 4-speed (it's saving grace) I wouldn't even have bothered with it if if it had an auto tranny!

Thanks for all input guys,

g-man

Edited by g-man - Jul/04/2015 at 3:03am

AMC only daily driver

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