2.9 L 4 cyl in a Fiero?

My boat uses a GM 4 cyl 2.9 L engine. This engine appears to be identical to the 2.5 Iron Duke, and was actually used for many years in export market Chevys to South America.
I wonder if this engine can be used in place of a 4 cyl Fiero engine. Internally the 2.9 is a marine block, with stronger internal components.
It has a bigger bore and stroke, so its unlikely its components would actually fit into a 2.5L block.

The starter motor is located on the same side as the exhaust manifold.

It is designed to operate at full throttle, 140 hp @4500 rpm, all day long. Therefore, it should hold up to a few good modifications.

Has this type of conversion been done before?

People in 4 cyl class racing use them all the time. It's identical to an iron duke block in every way except it's cast thicker. You can bore out a 2.5 to a 2.9 but it's not reccomended because the automotive block is too thin and can crack under heat.

The starter is on the correct side. You'll have to switch to a non-marine carb, or use stock Fiero TBI.

People in 4 cyl class racing use them all the time. It's identical to an iron duke block in every way except it's cast thicker. You can bore out a 2.5 to a 2.9 but it's not reccomended because the automotive block is too thin and can crack under heat.

The starter is on the correct side. You'll have to switch to a non-marine carb, or use stock Fiero TBI.
Thank you for the reply. Now, I am very familiar with the 2.8 V6, having built a few myself. Does the 2.9 have any more performance potential than a v6, when modified?

In general, the more cylinders, the better the engine will hold up under high performance demands. In a 4 cylinder engine, each cylinder contributes 25% of the total power. In a v6 it's less then 17%. So if you have two 500 hp (just a random number) engines, one 4 and one 6, the 4 is likely to blow up first, as there is 8% more strain on each component, be it piston pin, rod bearing, or what have you.

On the other hand, your 4 is a marine engine, and therfore it's built to take more abuse then an automotive engine. It's really a toss up, but If it were me, I'd build the 4. People would belive a V6 could push big hp, but most will think there's no way a 4 would do it. (without the help of n2o, turbocharging and a BIG wallet) You could win a ton of bets - and maybe pink slips too - with that motor :)

Good approach! Thank you for the advice.

I think I can clear up a few things.

First, GM made until recently, (2) different 4 bangers for boat and industrial applications. comparing them to the PONTIAC Iron Dukes, The specs are;

2.5L, (153 c.i.) 3.875 bore, 3.25 stroke. Chevy II from 1962, boat, and industrial applications. The head had intake and exhaust manifolds on the same side. Bellhousing is a Chevy V8 bolt pattern.

3.0L, (181 c.i.) 4.0" bore, 3.6" stroke. Boat, and industrial applications. The head had intake and exhaust manifolds on the same side. Bellhousing is a Chevy V8 bolt pattern.

2.5L, (151 c.i.) 4.0" bore, 3.0" stroke. This is the Pontiac "Iron Duke" released in 77 - 78. This used pistons and connecting rods from the PONTIAC 301 V8. (half of 301 = 150.5 inches. Get it?) The head had intake and exhaust manifolds on the same side. Bellhousing is a Chevy V8 bolt pattern.

2.5L, All FWD and Fieros. (151 c.i.) 4.0" bore, 3.0" stroke. This is also the Pontiac "Iron Duke". This used pistons and connecting rods from the PONTIAC 301. The longer 301 rods connecting rods reduced stress on the crank, improved power, and made the engine much smoother at low rpm, without the engine lugging, even at 1000 rpm. (Did you ever TRY to drive a Ford 2.3L with stick, BELOW 2000 rpm? It can't be done!)

The block and crank were lightened not only to reduce weight, but to IMPROVE acceleration. Reducing the stroke reduced the stress on the crank, allowing it to be lightened considerably. A new head design featured the "cross flow" design, with intake and exhaust manifolds on opposite sides of the head.

The flywheel was reduced in diameter and weight, and a new smaller bellhousing bolt pattern was made.

The water pump location was changed from being in the front of the block, to mounting to the side of the block, This and a redesigned single piece rear crankshaft seal made the motor much shorter, so it could be mounted sideways in FWD cars and Fieros.

ALthough the overall dimensions of ALL the above motors are roughly the same, there is little interchangeablity between components. Putting the boat motor in a Fiero would be a major challenge.


As to the number of cylinders making power, The winning-est engine in history has got to be the Meyer-Drake-Offenhauser. It was a FOUR BANGER ! Designed in the 30's, It won more races at Indy. But in the late 70's, fuel restrictions did it in. It started with about 200 cubic inches. Over it's history, rules were changed to reduce power by downsizing it, and finally it was down to (I recall) about 96 cubic inches. But even then, they were producing OVER 1000 HP for qualifying!!!!!

So the number of cylinders is only one minor factor of many, in determining the performance level of any engine.

We have road raced Fieros with the Iron Duke. We ran the engine at high rpms for many hours on the stock motor, without any engine failures.

I hear people say the crank is weak, (and it has no real counter- weights), but honestly, I've never seen one fail. Now there were a lot of CONNECTING ROD FAILURES in 84-85, but those were due to a manufacturing problem with the rods, and people not checking their oil, with the (then) 3 quart oil spec. (Pontiac's biggest mistake on the Fiero.)

This engine has excellent specs (bore, stroke, valve size, port design) which all say this engine has potential. The intake and tubular exhaust manifolds are excellent. (Headers for the street are a waste of money and time). All this motor needs to wake it up is a good CAMSHAFT, and metal timing gears.

For what it's worth,

fIEROWISEGUY

The Chevrolet designed 151ci, 153ci & 181ci Mercruiser L4's were the inspiration for Pontiac's "Iron Duke" - the question was can it be put in a Fiero, and yes, it can. Since it shares the bell housing pattern with the small block v8, all that's need is a V8archie adapter. The motor mounts may be a little wonky but that's easily fixed with a little inspiration, an angle grinder, a handfull of steel plate and a welder.

Building up a 2.5L works, but it's BORING. Tossing in a mercruiser is the kind of stuff that makes the project unique and fun. GO FOR IT.

As far as the number of cylinders goes, it doesn't matter if you have 1 hp or 1000hp, the more cylinders the engine has the less strain there is on the individual components because the work is divided evenly between them. Four people can build a house, but if you have 8 people they'll be 50% less tired when they're done.

Besides, regardless of what engine it is, 1000 hp is only good for one thing, going straight forward really fast, usually on the 2 rear wheels. Wake me when it's over.

Ragtop, I'm not dissin' you.

But your first posting said the boat motor and the Duke were "similar in every way". All I was pointing out, is that they are not, which you confirmed when you said to get a V8 Archie adapter. This is NOT a straight forward swap.

Even the distributors and ignition controls are different, and in a different location. How are you going to get the boat distributor to work with the Fiero CPU? The lectronics are completely different. There is some major work here.

I assume you would want to use the Fiero TBI instead of a carburator. So, now you have to design an adapter plate to mount it to the boat manifold.

What about a flywheel? Boats don't have clutches.

If yo are going to do all that, then why put in the boat motor when you could go for a V6 or 8 in the first place?

As to boring, that's up to the individual. But ANY engine swap is not for the faint of heart. I've done my share, and you constantly come up with PROBLEMS, during and after the swap.

A good kit helps, but there are always problems that crop up, and takes some of the fun out of just DRIVING the car. (overheating, leaks, electrical issues, etc. )

A lot of people start such things, get discouraged and frustrated it takes so long, then finally give up.

I'm just saying that a cam is a much easier change to make and have the same results as the boat motor swap. And you can do it in a weekend!

For what it's worth,

fIEROWISEGUY

No dissing assumed here. :)

You're right, I wasn't thinking when I said "in every way" so I deserve 1,000 lashes with a wet noodle on that one. :(

As far as clutches go, early chevettes and t-1000's used a lighter duty 181 that shared the same crankshaft bolt pattern.

I did forget about the EST distributor - it could fit though, I've simply never tried. If it was me, I'd just use a carb.

Engine swapping has it's headaches, yes, but no more then your average engine modifications. Even something as simple as changing a cam could lead to accidentally setting the timing gears a hair off, causing bent valve and cracked pistons just by cranking the motor over.

I agree the iron duke is one of the best 4 cylinder engines ever. I still think a mercrusier block would have twice the potential though.

Can we agree to disagree?