The Iron Duke Resource Site



Welcome to my newly redesigned Fiero 2M4 resource site.  The original site recorded over 12000 visits,  hopefully this one will also prove as useful.
Ira Crummey

A Modest Duke
The Iron Duke is not exactly sunshine and roses as a performance motor.  Here Randy Agee lets us know just how difficult it can be, especially if you must learn the hard way.  Originally written in May of 1994.
Ira Crummey
"I gave up on hopping up Dukes years ago- it was like pissin' in the wind and throwing money down an outhouse hole.  Smart and experienced folks like Jim Sutter at IRM tried to tell me back then, but I had to learn the truth my way and ignored their advice.  I could have saved a bundle of money if I had listened......
there are several rusting self-destructed Dukes in the corral to serve as a lasting reminder."                            Randy Agee

We can debate this until the cows come home..... but unless you go the SD route you ain't gonna make a significant difference in the overall performance of street driven Dukes with add-ons (been there - done that).  If you are successful in cranking out significantly more HP, the lower end will not last much longer.  Experience has taught me (and others) that when you start consistently pushing a Duke over 5,000 rpm it is going to self destruct.  It ain't a matter of "If", it is when.
Do you ever wonder why the early 2.5 turbo kits died off so quickly?  It wasn't the introduction of the V6 - they were a prescription for a broken crank or pitched rod.
Still, there are some things you can do to a Duke to improve performance that are simple, cheap, don't compromise reliability and should be done anyway.  Sadly, they are often overlooked or ignored.  It has been at least 5-6 years since I put this on the list, but it is still valid.  If you have previously done these, GREAT!  If not, try it - you'll like it.  (You will also get better gas mileage)
1.  Replace the fuel filter.  Do this every other oil change or 6,000 miles. Restricted fuel filters lower fuel pressure.  Lower fuel pressure translates to a drop in performance.  This is often overlooked and is true for the 2.8 as well.
2.  If you still have the stock converter, replace it with a new high flow unit.  Gains will be noticeable as the original L4 brick catalyst is very restrictive.
3.  Drop in a K&N air filter - or at least a new paper one.
4.  Pop in a new oxygen sensor

5.  Change to synthetic oil

6.  On 84-86 Dukes, bolt on a performance coil and a new set of lower resistance plug wires.
7.  Install a fresh set of spark plugs - NEVER put Bosch Platinum plugs in a DIS car (87 & 88)  If you have not added a higher voltage coil and wires, close the gap .005 less than specified.  "Trick" plugs (Splitfire, etc.) are OK, but a waste of money as far as performance gains.  A set of new steel electrode AC plugs will do just fine.
8.  Bolt up the dual outlet muffler and pipes from a 85-87 V6.  There are tons in the junk yard for little or noting.  Don't expect a great performance improvement, even if there is one less chamber in the V6 muffler, but it looks and sounds better.
9.  Run maximum allowable air pressure in your tires and avoid those tall fat ones  - especially on the back.  They can change your effective gearing and reduce HP at the point where the rubber meets the road.
10.  Try a 160 or 180 degree thermostat.  It may take longer for the car to go into closed loop but Dukes seem to run better in the 180-200 degree water temp range.  Add a manual fan switch so you can cut it on at will, don't wait for the fan temp switch to do it or the water temp will soar even with a low temp thermostat.
11.  Be sure no calipers are dragging - especially the rear EM brake.
12.  Run a batch of carbon removal and top engine cleaner through (Ed Parks sells this and the stuff really works!).
13.  For quicker off-on throttle response, disconnect and plug the vacuum hose to the EGR valve.  May have to move to mid grade 89 octane gas for this.  Also increases emissions.  Will not give more overall HP - only quicker throttle response.  On a 2.5 the ECM doesn't know this has been done. (Note this may cause emmissions problems. I.C.)
14.  Give the car a wash and wax, clean cars always run better - you know, less wind drag over a slick surface thing.
If you have not done these low cost items, you will be amazed in how much better your Duke will run.  Then, if you gotta learn the hard way (like I did) go ahead and face the wind and pull those bills out of your pocket for your visit to the johnny house...... or you could just donate them to me.
No way (short of the SD-4 - see and click on "Blast  From the Past" for SD 4 articles) will you get the HP gains you want with the other higher cost add on mods for the L4.  Port matching and larger TB's won't hurt - but they won't help much either unless you go the whole nine yards (heads, headers, cam, etc.).
Randy Agee
The Fiero Ranch
Mechanicsville, VA