Welcome to my newly
redesigned Fiero 2M4 resource site. The original site recorded over
12000 visits, hopefully this one will also prove as useful.
D.J. Draper's Duke
D.J. Draper outlines the steps he is taking to build a more efficient Iron Duke rather than looking for raw power (which may not be there reliably).
One of the most important things you have to be aware of when trying to improve the performance of the Iron Duke is the well-known fact that it has a weak block. Remember that this engine was designed from the ground up to be as fuel efficient as possible. High performance was never a major design goal of the engine. Therefore, strength and the ability to accommodate higher performance was sacrificed in the name of weight reduction. Low cost was another design goal, so more aggressive steps to increase efficiency such as porting and polishing were overlooked. It is in areas such as these that I believe the performance can be gained; not by pulling more power out of the engine, but rather removing obstructions or restrictions that are consuming the power that the engine already has. I believe that if you are going to be successful, you have to accept the concept of 'power through efficiency'. Any other approach is going to result in a blown engine. I can almost personally guarantee it.
That said, the next most important thought you should keep in mind is that of properly matching all the parts during the rebuild. An engine with a well-matched set of conservative parts will usually provide better results than an engine full of high performance parts that are not matched. Take a good long look at your driving habits and your expectations for this vehicle. If the car has a manual transmission, what RPM ranges do you normally shift at? What gear do you prefer to use when passing people? What speed are you normally driving at when you decide it's time to 'get on it'? Is this a daily commuter or a weekend sportster? Take these thoughts into account before, during and after you start to rebuild the engine.
You also need to be realistic about your expectations. The Iron Duke is a great engine for efficiency and moderate to respectable performance. If you are looking for a truly significant jump in performance, say more that a 25% increase over factory rated HP; this is not your engine. By the time you pull that much HP out of the engine, you will have spent a small fortune and in all likelihood the engine will fail very quickly. This article is for those that have more time and patience than money and just want to have a
reliable, efficient, smooth running little 4-banger that gives them reasonable performance when it is occasionally needed. If you are expecting more, go for a V6 or V8 conversion. The bang to buck ratio will be much better with a conversion approach and they are not as expensive as you might think.
If you are an experienced mechanic and are comfortable with choosing your parts, by all means do so. If you are a little foggy in this area, like myself, seek out the advice of an expert in your area. Most of these people are more than happy to share their knowledge with you, especially when they see that you have already given some thought to how you want the engine to perform and considered how your driving habits have played into your decision. If you don't trust your mechanical skills at all, you can have a local outfit build the engine for you. Just make sure you pick a quality shop to do the work. If you have no fear of spinning wrenches, feel free to ask an expert for guidance on how to best match and assemble the right parts for your needs. They usually don't mind being used as a resource because they know that you will have to have certain machine work (boring, milling, turning, etc.) done somewhere, and if they are helpful, they just might get your business.
The first step to building an engine is to select a camshaft that matches your performance expectations. This one part more than any other will determine the true nature of your new engine. Again, be realistic. If you try to put a full race cam in, you will have to take extreme measures to take advantage of it, by which time your will likely have exceeded the block's capabilities. Once you have chosen the camshaft, you should build the rest of the engine around that. This will affect what type and compression of pistons you use; how you have the head milled and what type of valve springs you will use. It can affect what kind of exhaust system you install and what type of ignition products you buy. Based on the camshaft, you might choose to port and polish the head and intake manifold. You may opt for a three or five angle valve job. Of course, some of this may be a bit overboard, and if you choose a cam that HAS to have all of this, you're probably being a bit aggressive. Again, consider a conversion instead of going overboard.
I was fortunate enough to have an engine designed for roller cams, which made having a new profile ground onto the original cam a viable possibility. Roller cams have far more success than standard tappet cams with longevity after being reground. This was certainly a good thing because there were not many aftermarket options for a new cam at the time. Kams, Inc. in Oklahoma City put a mild RV profile on the cam that adequately matched my driving style. It was certainly streetable; started easily even in winter; had a good mid-range power curve and respectable fuel economy at highway speeds. From there, I chose 9.5:1 compression pistons that would pull a little more power out of the fuel without inducing too much stress on the weak cylinder walls.
I had a great local outfit named Buddy Rice do all of the machine work on the engine. They were the ones that helped me choose parts that would perform well with the camshaft profile I had selected. The block and head were both cleaned. Then, I had the centerline bore reestablished on both the camshaft and crankshaft bores. They also trued up the bores on the connecting rods. They milled the head and performed a 5-angle valve job, and then shimmed the valve springs to match them with the camshaft. The crankshaft journals were also turned, along with the mains that were 'recentered' to match the work done on the block. They looked at the idea of balancing the crankshaft, but ultimately decided against it because of its light weight and the fact that it was already fairly well balanced. While the engine was still at the shop, we carefully looked over all the parts for any signs of wear. Anything that showed any significant wear was replaced. Better to catch the problem now that to find it later after it fails.
With the block and head prepped, I took all the parts home and started putting the engine together. I didn't do anything special while assembling the engine. I just made sure I was liberal with the engine assembly lube. I use this stuff on everything, not just the camshaft. I also made sure that I followed the torque specifications for everything; using several increments up to the final torque for anything over 25 ft/lbs. When working on the engine or suspension, I never tighten anything with an ordinary wrench. I always use a torque wrench to make sure I am not overtorquing something. I also do this to make sure that matching bolts on a part are torqued uniformly to prevent warping.
One note of caution; whenever you are not working on the engine, make certain to but a thick plastic trash bag over the engine and seal it airtight with tape. When I first started the engine, I had no oil pressure at all. After taking it back apart, I found that a wasp had built a mud nest in the oil pump that completely blocked the passageway to the oil filter. Fortunately, the liberal use of the assembly lube saved the engine from damage. The bag will also help protect the engine from dust and humidity.
At the time of this writing, this was the extent of the work done to the engine. Notice that the only higher than stock performance parts are a mild camshaft and slightly higher compression pistons. Everything else was just removing any possible sources of resistance, and making sure that each part could do its job in the best possible environment. The engine already performs extremely well. As time permits, I will port and polish a spare head and intake manifold from another engine. I will install them along with a new exhaust, headers, Holley's Big Bore TBI and a good aftermarket coil.
Some additional notes would be that I removed the restrictor plate underneath the TBI in the intake manifold; I use a cooler thermostat and coolant fan switch; and that I disconnected and capped the vacuum line to the EGR valve. If you choose to do the same, make sure you reconnect the EGR for one day every month and take the car for a long drive. That way, it will work when it is time to get your inspection.
Something else to keep in mind is that I personally would probably never go this far with another Iron Duke. When I started, I did not know about the ease and tiny cost of certain V6 conversions. Also, I was fortunate enough to have a rare engine. This is a 2.5R engine, not the normal 2.5L. GM ran the numbers on it and describes my engine as an '84 Fiero Second Design' engine. They swear it is definitely for the '84 Fiero even though it has roller lifters, which the '84s are not supposed to have. I'm certain this
plays a part in the better performance, and in this case, makes the extra effort worth it. I have a 4 banger that performs very close to many of the V6 Fieros, yet retained the efficiency of the 4 cylinder and did not sacrifice reliability or life in the process. I paid a whopping $200 for the car and spent around $1,000 rebuilding the engine. As long as I take care of it, this little baby will last forever.
D. J. Draper
(2) '84 2M4s