I have only had 2.8s, but I am looking at a 4 cyl that needs only a head (reportedly). It seems like it would be pretty cheap to go old school and get some type of upgraded head, a header, and and a big intake/carb combo.

What could I expect? Any recommendations on specific units?

I never really thought about it, but 2.5 is not that much off from 2.8 in terms of displacement, and they look easier to work on. Could be a fun project.

I'm no expert but the general consensus is that the 2.5 won't take kindly to mods and after a lot of work, and money you MIGHT get 140 - 160 hp which is pretty weak performance nowadays.

You get a lot more bang for your buck swapping in a mod friendly engine like a 3800 that only a few loyalists will bother to work on the 2.5.

Actually I have an 88 3800 and 4 speed auto already mounted on a Fiero cradle... complete with all accessories, axles, and harness. It just looks like it's over my skill and time level to put it in, so I have been trying to sell it on craigslist.

Maybe I will consider giving it a try after all.

Thanks!

You can easily spend many thousands of dollars on a 'duke for a whole 20 extra HP. And if you try to go much farther than that, you'll soon find out why there arn't many performance 'dukes around. The engine will happily grenade if you go too far beyond the 120 HP mark. It's simply not a performance engine.

I had this grand vision of coming out of auto zone with a cart full of goodies and coming out better than a 2.8. I guess displacement is not always everything

quote Originally posted by Fireball Fiero: I guess displacement is not always everything

Displacement is not everything...

There are plenty of 2.5L engines out there that make decent power...the Iron Duke is not one of them however. The BMW 325i from the same era was making 170 hp with a 2.5L engine.

There's been many, many bright-eyed people who have embarked on a "build up the duke" project. The one thing that we've learned from all of their experiences is that the upper limit for the duke is 120 HP. Anything beyond that leads to broken engine parts in short order...

There's a thread on a 200hp build-up.
Personally, I don't see why everyone knocks the duke so much. Any modern rebuild should get you lots of reliability. In the end, you are paying for half the work of a V8 rebuild...so expect half the power - 140hp isnstead of 280hp.

If I had a duke, I'd do the basics, stoke it to 2.7 or 3.0 liters and do lots of head porting and intake porting. Put on a header and descent exhaust.
There is no reason why a rebuilt duke balanced and using todays materials and tolerances shouldn't be reliable at 140hp.

I'd start with the 87/88 duke and swap in the 91 GA duke. That alone gets you 14hp (110 gross)... The difference - a better intake and head.

On the older Dukes:
Lest we not forget that a 2.5L Duke with a SD head and proper intake and exhaust did 210hp. If the block blows, you can get another one in the junk yard for $10. But like I said before, a proper rebuild (and balancing of the internals) of any block today should yeild ALOT of reliability.
The 2.7L pace car did 232HP...

That being said, I've never owned a 4 cyl Fiero, but I've always contemplated owning one as a second car for the fuel savings...

If you actually take a look at the 'duke, you'll realize that the block, connecting rods, crank, etc etc etc are all paper thin. It's not a question of if the block will blow apart when you get into the area of 140 HP, but when.

I sure hope that 210 HP 'duke had as much of the bottom end replaced as the top end. And at that point, it wouldn't really be a 'duke any more.

[This message has been edited by Jax184 (edited 01-04-2007).]

quote Originally posted by Jax184: If you actually take a look at the 'duke, you'll realize that the block, connecting rods, crank, etc etc etc are all paper thin. It's not a question of if the block will blow apart when you get into the area of 140 HP, but when. I sure hope that 210 HP 'duke had as much of the bottom end replaced as the top end. And at that point, it wouldn't really be a 'duke any more.

Agreed. If you put the most rock hard rotating assembly in the duke, you still have a very weak block that will not hold up long.

quote Originally posted by Fireball Fiero: Actually I have an 88 3800 and 4 speed auto already mounted on a Fiero cradle... complete with all accessories, axles, and harness. It just looks like it's over my skill and time level to put it in, so I have been trying to sell it on craigslist. Maybe I will consider giving it a try after all. Thanks!

I have a duke in an 88, complete with the almost impossible to trace down stumble and the stalling when the a/c is on. Crappy power in a nice car--it's the car that's getting the 4.9 and the 4t60e. Putting any money into a 'duke is money down a rathole.

There's a reason some of us call it the 'dooky' engine. It's better suited to running a tractor (or even a boat's inboard-outboard drive) than a car. No I don't hate the duke, but GM had the quad 4 available and should have used it.

If you can afford it, Loyde is the 3800 guru and he's located in Dallas. I don't know if he does mentoring on conversions, but you could trailer the whole lot over to him for the necessary work. Here's his URL http://fastfieros.com/

[This message has been edited by Brian Lamberts (edited 01-04-2007).]

quote Originally posted by Brian Lamberts: I have a duke in an 88, complete with the almost impossible to trace down stumble and the stalling when the a/c is on. Crappy power in a nice car--it's the car that's getting the 4.9 and the 4t60e. Putting any money into a 'duke is money down a rathole. There's a reason some of us call it the 'dooky' engine. It's better suited to running a tractor (or even a boat's inboard-outboard drive) than a car. No I don't hate the duke, but GM had the quad 4 available and should have used it. If you can afford it, Loyde is the 3800 guru and he's located in Dallas. I don't know if he does mentoring on conversions, but you could trailer the whole lot over to him for the necessary work. Here's his URL http://fastfieros.com/

first off, if your getting rid of an 88 duke, I wouldn't mind getting the crank on that from you.

I will have to go look up the website again but there was a very nice site that explained all the things you can, and cant do to a duke. If I remember correctly, I think the 84-87 dukes are rated to handle up to 150 hp (of course if you run at the limit of the rating you are going to shorten the life of the engine a bit) and the 88 duke is rated up to 180 hp. What seems to kill these engines is that people who make them "performance dukes" run up the revs much higher than they can handle.

If your engine needs new heads, the most beneficial thing seems to be porting to intake and exhaust. Then, if you want, you can go for the holley throttle body or even if you can find one the holley intake manifold. I haven't read much of anything about exhaust mods helping much. I think that the stock manifold is sufficient for most applications.

So if you want to mod a duke, I would suggest the 88 which had a stronger crank (hense why I would like to get my hands on Brian Lamberts), or put the 88 crank into what ever block you are running and then port out the heads and give it a general tune up. If you want a stronger block to work off of the 91-93 (i think) s-10 blocks were stronger than the fiero ones. you can go from there. I'll edit when I find the website that I am trying to remember this information from and you can verify it there.

edit: here we go, an excellent source of information http://ironduke7.tripod.com/IronDuke.htm
some more here: http://www.dukemods.50megs.com/PAGE1.html
and a source of different performance cams: http://www.amotion.com/p4.html#10

[This message has been edited by 86fierofun (edited 01-04-2007).]

I on the other hand would suggest avoiding the '88. The '88 has the internal combination ballancing system/oil pump. These seem to commonly fail around 80,000 miles or so, causing the engine to lose all oil pressure. Followed of course by the loss of a connecting rod or two, and if you're unlucky, the car due to the resulting engine fire.
If you're utterly devoted to building a performance duke without using a super duty block, you'll want to get one out of a '93 or so S-10 and modify it to fit in the Fiero.

using the 88 crank does not necessatate using the 88 oil pump. use a pre 88 cam and oil pump.

the duke is weak pile of cr#p .its also heavy.and even stock dukes with zero mods to this day are still breaking connecting rods .the duke was redesigned with a different block crank and rods to make it cheaper , not better ,for the old X cars .thats the engine we got stuck with .the mercruiser motor is based on the original duke and is a very good motor .but the crank wont fit in the fiero motor and the bell housing has a different pattern .the super duty block is a different casting ,different crank and uses SBC rods .it shares the same bore centres and whatever else they needed to keep it classed as a stock block motor for classification purposes.the first year IMSA GTU sd motors put out 300 hp at 8000 rpm.this engine was never used in a production car. 0 -60 in 4 sec . 1/4 mile 12.3 sec @ 112 mph .dont compare the duke to a super duty . source :car and driver magazine june 1985 .i saved all my old mags that had fiero articles .the rest i threw out.

quote Originally posted by 86fierofun: first off, if your getting rid of an 88 duke, I wouldn't mind getting the crank on that from you.

Didn't know it was special. The engine swap won't happen until late March--that's the earliest I can get a smog test for the next 12 months of registration & and I want the registration to be as fresh as possible so that I have 12 mo. to work out the details with the smog lab at the DMV.

When the dooky comes out, I'll let you have the crank for about $25 (to pull it from the engine and cover getting it boxed up, etc.) plus whatever for the shipping. If you think this is something you'd like, lock it in with me with a return pm. We can take care of details later. . .

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DONNER PARTY FIEROS

Selling quality used Fiero Parts since 1846

pm sent

The 2.5L engine used in the Fiero is NOT the only block used for the "Iron Duke" earlier production versions of the engine are stronger.
There are performance parts to build up a duke (not counting the SD4 version)
The problem is the FWD version (also called the "Tech IV" ) of the "Duke" was shaved and trimmed down for economy reasons. The engine will break with drastic mods due to weaker/lighter parts used. But grab a block from the late 70's Monza/Sunbird/Skyhawk/Firenza and you can build one up to about the 200 hp range and it will hold together just fine.
Of course you could always hunt and track down SD4 parts and really build up a "Duke".

http://www.pawinc.com has many, many, performance parts for the 2.5L Iron Duke.

Best off the shelf part for value is 120 feet of chain.
Keeps your boat in place really nice once attached to a duke.

quote Originally posted by Oreif: . But grab a block from the late 70's Monza/Sunbird/Skyhawk/Firenza and you can build one up to about the 200 hp range and it will hold together just fine.

Let's see replace the block, the heads, the crank, the rods and pistons and then after all that you got 200 hp... same as a 4.9 out of the box. I don't see the point.

Some people just want a 4cyl with the same as an out of the box V8, I am not sure if theres even a gas mileage difference between the 2 after you have built one up that much... I personally have a duke with a holley big bore TB and intake manifold and I am selling it, it just doesnt have the punch I want... and I guess the difference in power availability from the difference in displacement between a 2.5 Duke and a 2.8 V6 is just that one is a V block... better for the revs and power combo, you may not have as much torque as the inline but I am not sure on that one, its been a long night...

I like this thread, it gives you lots of views on the options out there for all

and I just bought an 87 with a duke in it so I could use the body and it died on the previous owner at 89k miles I think it was a later 87 and died to the oiling problems and I plan on using it for a baja style go-kart made from the wrecked gt just chopping off the bent front parts of the frame and a lot of Fab-work suspension wise and I think that a stock duke would be enough power/torque for go karting in the dirt and fields

just my .02$$

[This message has been edited by jack_ink (edited 01-05-2007).]

This is basically the jist of it...

120hp on a stock bottom end is fairly attainable with a replacement camshaft, worked head, intake, exhaust.

Here is some information from Ira Crummey:

http://ironduke7.tripod.com/dukefaq.htm
That aside, it's REALLY not that hard to get sick power from a duke. All you need is a Chevy S-10 crank, or a Lunati performance crank. You'll also want stronger connecting rods, and there are a whole host of connecting rods that will fit.

Once you've got both of those, and a set of good pistons, you can basically dump a ridiculous amount of boost in there. With good cyl head bolts, you can go nuts with the Duke. It's probably the most basic, simple, and raw 4 cyl motor you'll ever see aside from a flat-head. There's nothing inherently bad about it's design, it's an extremely simple design. The block is not "weak", so, assuming you're willing to spend some money on the internals, you can get as much power as you want.

The cyl head in the duke is soooo friggin easy to remove too...

If you want more compression with stock components, just deck the head... you won't run into any fitment issues like you will with the V6.


However, the argument is whether or not all this work is worth the hassle.

If you have the chance to get a 4 cyl Fiero for cheap that just needs a cyl head (this is VERY common), then I say get it. A remanufactured cyl head will cost you around $300 bucks. Assuming the mileage isn't TOO bad on the car (as in, worn rings), you can get a bit more power than stock by just decking the head.

I did this to a 1984 Fiero 2m4 SE that I used to own. The Fiero's duke is REALLY designed for LOW LOW end torque, like... right off the line. It seems to die around 3,500 rpms. After doing nothing more than a simple top-end rebuild (kept the stock cam, gears, etc), I was able to get the 84 to break the tires loose just by stomping on the gas (Th-125c Automatic with 3.08:1 final drive). I used to not be able to do that with my stock V6 87 automatic at the time.

------------------
Todd,
2006 Pontiac Solstice
2004 Volkswagen Beetle Convertible (Wife's Car)
2002 Ford Crown Victoria LX
1987 Pontiac Fiero SE / V6 (3.2) 5-Speed
1984 Porsche 944 5-Speed
1981 Pontiac TransAm (Olds 455BB)
1973 Volkswagen Type-2 Transporter

quote Originally posted by 82-T/A [At Work]: However, the argument is whether or not all this work is worth the hassle.

Exactly, and that's a value judgement. We might as well argue which is the best color for a Fiero. In my humble opinion, it is waaay too much work to replace nearly every component of the engine and still end up with something less than 200 hp. If you want performance, there are waaaay too many other choices. The 4.9 was just one example.

If you have a running duke in your car and you like it... more power to you. (I have one in my car and it mostly runs) But if I wanted more power building up the duke would be my last choice.

quote Originally posted by jscott1: Exactly, and that's a value judgement. We might as well argue which is the best color for a Fiero. In my humble opinion, it is waaay too much work to replace nearly every component of the engine and still end up with something less than 200 hp. If you want performance, there are waaaay too many other choices. The 4.9 was just one example. If you have a running duke in your car and you like it... more power to you. (I have one in my car and it mostly runs) But if I wanted more power building up the duke would be my last choice.

A VERY simple upgrade to the Duke, could be a Gen-1 3.4 V6/60 that's carbureted.


It's VERY, VERY simple...

The engine will bolt right up to the cradle using standard V6 Fiero motor mounts. It will bolt up to ANY transmission you happen to have in there currently bolted to your duke.

Assuming you have a GOOD, used motor...

All you need to order is:

1 - Edelbrock 2.8-3.4 V6/60 Intake Manifold with the 4-bbl adaptor plate
2 - MSD multiple spark discharge distributor (or you can get a good cheap used GM vacuum advance distributor)
3 - Holley 390cfm Carburetor
4 - Adjustable Fuel Pressure Regulator


You'll need some miscellaneous V6 Fiero parts like the oil pressure sending unit / tube, the V6 coolant pipes and hoses, a newer temperature sensor, exhaust manifolds and Y-pipe, and that's it.

I mean, it's really that easy.

It'll be carbureted, and of course you'll want to have it tuned properly, but there really isn't much to it.

It's really kind of sad... but you'll have MORE power in that stock 3.4 V6/60 than most people do who rebuild a 3.4 into a Fiero to look stock (my plan).

I mean, what... you're looking at around 170-175hp and over 200 in torque???


That's like a low 15 second vehicle for... lets see, under $1000 bucks?

That depends on what you can get the motor for... but there is a place near me that sells RUNNING 3.4 V6/60s out of Camaros / Firebirds for around $250-500 bucks.

Then, you need to source some cooling tubes, used exhaust manifolds, the Y-pipe, and a few other various pieces (get them from Ed Parks) (couple hundred), a used distributor or a new one from MSD... and there you go. What's better is that you DON'T have to worry about computer control. Not that it's bad, but if you already have a 4 cyl, why bother swapping in all the MPFI stuff from the V6 Fiero if you're going to get less horsepower, stock for stock...

Awesome upgrade.

------------------
Todd,
2006 Pontiac Solstice
2004 Volkswagen Beetle Convertible (Wife's Car)
2002 Ford Crown Victoria LX
1987 Pontiac Fiero SE / V6 (3.2) 5-Speed
1984 Porsche 944 5-Speed
1981 Pontiac TransAm (Olds 455BB)
1973 Volkswagen Type-2 Transporter

quote Originally posted by 82-T/A [At Work]: That aside, it's REALLY not that hard to get sick power from a duke. All you need is a Chevy S-10 crank, or a Lunati performance crank. You'll also want stronger connecting rods, and there are a whole host of connecting rods that will fit. Once you've got both of those, and a set of good pistons, you can basically dump a ridiculous amount of boost in there. With good cyl head bolts, you can go nuts with the Duke. It's probably the most basic, simple, and raw 4 cyl motor you'll ever see aside from a flat-head. There's nothing inherently bad about it's design, it's an extremely simple design. The block is not "weak", so, assuming you're willing to spend some money on the internals, you can get as much power as you want.

I find your summary of the Iron Duke humorous, at best. Unless you consider "a ridiculous amount of boost" to be 4-5 psi. The block is, in fact, weak, and is by any standard, today's, or those set when it was manufactured. The head is extremely poor flowing and prone to cracking. And "good cyl head bolts" is hardly the key to performance with any engine, and especially not the Duke. Not when you have a paper thin deck surface already. Look in my Turbo SD thread for some pictures and actual mic'ed measurements of a stock Duke block.

A crank, rods, and pistons don't fix the rest of the engine automatically.

Nate

------------------

My Web page | The Turbo Super Duty Build.
You know that little voice that says it can't be done? I duct-taped mine's mouth shut and pushed it down a flight of stairs.

quote Originally posted by jscott1: Let's see replace the block, the heads, the crank, the rods and pistons and then after all that you got 200 hp... same as a 4.9 out of the box. I don't see the point.

The point is the title of the thread is:

"What's the best you can from a 2.5 with offshelf parts?"

Not "are there cheap engine swaps to get to 200hp?"

A swap is generally the way to get more power, But some folks prefer to see what power they can get from factory engines that were in thier car.

He wants to stay with the 2.5L for the fun of it. It is an easy engine to build and work on. It may not be the best motor for drag racing, but for someone who wants to enjoy building his own engine and getting more power out of it, It can be a decent project.

I keep looking fo a 4-cly stick shift Fiero at a cheap price so I can pull the motor, build a 2.5L up for a little more power and use it as a daily driver. With the right aftermarket parts it would be fun to drive, very reliable, and easy to maintain. If I want to go fast, I have a V-8 Fiero for that.

[This message has been edited by Oreif (edited 01-05-2007).]

quote Originally posted by Oreif: The point is the title of the thread is: "What's the best you can from a 2.5 with offshelf parts?" Not "are there cheap engine swaps to get to 200hp?"

fair enough, but maybe I made my point too subtle...After you have replaced the block, heads, rods, and pistons, how much of the original duke is left? Unless you have money to burn I just can't see any point to doing it.

I admit there is some challenge to taking the engine to a higher level of power, but I think some of the younger crowd may mistake the duke for a modern engine where you can double the power with free mods and a new tune on the chip. That's not going to happen with a 2.5.

So I think the topic has been covered, as to what the best is you can do from a 2.5 with off the self parts.

If anyone is dying to rebuild a 4 cyl 5 speed, I have one in my yard with a rod knock that I occasionally think about rebuilding then I wake up and come to my senses.

quote Originally posted by jscott1: fair enough, but maybe I made my point too subtle...After you have replaced the block, heads, rods, and pistons, how much of the original duke is left? Unless you have money to burn I just can't see any point to doing it. I admit there is some challenge to taking the engine to a higher level of power, but I think some of the younger crowd may mistake the duke for a modern engine where you can double the power with free mods and a new tune on the chip. That's not going to happen with a 2.5. So I think the topic has been covered, as to what the best is you can do from a 2.5 with off the self parts. If anyone is dying to rebuild a 4 cyl 5 speed, I have one in my yard with a rod knock that I occasionally think about rebuilding then I wake up and come to my senses.

well, he said he had to redue the top end. If he ports it and does a couple of other small mods to it he can get a decent power gain for the duke. the site by the Ira guy is a good place to go to get ideas for a simple performance boost. If you want to rebuild an engine, than yea, there are a lot of trade offs to think about.

All you need to do to really understand why the duke is horsepower proof is to take the lower end apart on one with 50,000 miles or so on it. Look at the wear patterns on the bearings and you'll be amazed...

Once you've seen it with your own eyes you'll understand why trying to push more power through that engine isn't a long-term solution.

quote Originally posted by Whuffo: All you need to do to really understand why the duke is horsepower proof is to take the lower end apart on one with 50,000 miles or so on it. Look at the wear patterns on the bearings and you'll be amazed... Once you've seen it with your own eyes you'll understand why trying to push more power through that engine isn't a long-term solution.

I have, and mine has 160k on it.

Are you looking for this Duke to be a daily driver? If so rebuild it in the stock form. In its stock form it is a fairly dependable engine if not abused and properly maintained.
It is also relatively cheap to rebuild as stock. The engine pictured was fine as a daily driver untill I let it overheat, breaking a piston ring in number four and cracking the head.
Having a limited "toy budget" I am only rebuilding this engine for short term use. I'm spending all the spare change on the chassis and body this winter, drive the Duke when the body and chassis are finished, then start collecting all of those more expensive parts for a Northstar on an '88 cradle.
I couldn't resist posting pics.

Duke block ready for reassembly with a matched set of used pistons. Cheap!

Bottom end, weak, weak, weak!

Used head I purchased and had refurbished. With valve job, about $130 invested in this head.

Since I'm working outside on the car I spend the colder, rainy days inside working on the engine.

My daily beater is a Toyota, "takes a licking and keeps on ticking".

In summary, don't count on a dependable daily driver with a modified Duke. Your money is better spent on some other engine if you're looking for more horsepower.

Wow, the guy that suggested I sign up for this forum said I would find all kinds of helpful info, and man was he right. I'm still on the fence over whether to try the 4cyl. I would likely be a daily driver, I was just wondering what kind a extra oomph you could get from one. From what I've read read, maybe not too much without getting into the danger zone. But I like that comment about it being made more for low end power, I am not too into high reving even on the V6, I put 200k on one with "less than optimal" (bordering on negligent) maintenance diligence, but the mechanics tell me driving habits are half the battle.

In the case of the car I am looking at, the head was reportedly just removed because the car was being parted out and everything was still in working order. I will probably go have a more thorough look this weekend. Thanks for all the info, if I get it I will likely have more questions!

Sawzall, an arc welder, apiece of pipe, and a swager. If you have those, you can take off that catalytic converter without a single problem.
I got mine taken off and I felt a very noticible performance gain and it pulls all the way to 4500 RPM

quote I find your summary of the Iron Duke humorous, at best. Unless you consider "a ridiculous amount of boost" to be 4-5 psi. The block is, in fact, weak, and is by any standard, today's, or those set when it was manufactured. The head is extremely poor flowing and prone to cracking. And "good cyl head bolts" is hardly the key to performance with any engine, and especially not the Duke. Not when you have a paper thin deck surface already. Look in my Turbo SD thread for some pictures and actual mic'ed measurements of a stock Duke block. A crank, rods, and pistons don't fix the rest of the engine automatically. Nate

The Duke head isnt prone to cracking. Mine has gone through two dozen overhats (one all the way to 300) and two coolant freezings. No telling how much other punishment the previous three owners put, but the guy I bought it from overheated it bad enough to pour out smoke.

The engine is destined to come out of my 84, but it wont be from a cracked head, friend.

[This message has been edited by AP2k (edited 01-07-2007).]

quote Originally posted by AP2k: Sawzall, an arc welder, apiece of pipe, and a swager. If you have those, you can take off that catalytic converter without a single problem. I got mine taken off and I felt a very noticible performance gain and it pulls all the way to 4500 RPM

If Austin has the same emissions inspection standards as we have here in the DFW area it probably won't pass without a Cat. I had to change the Cat on one to get it to pass

quote Originally posted by Fireball Fiero: But I like that comment about it being made more for low end power, I am not too into high reving even on the V6, I put 200k on one with "less than optimal" (bordering on negligent) maintenance diligence, but the mechanics tell me driving habits are half the battle.

Low end power is a relative term. I've gotten into many debates about how the low end torque of the duke is equal to if not greater than the 2.8 V6. And in a very narrow power band that is true. But you dont stay in that power band very long and by the time you get much above 25 mph the fun is over. The 4:10 gears extend it a little but not much.