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Why did I choose
to go with the 3.4 DOHC? Well, I am 19, money is in short
supply. Between the 3800 Series II Supercharged, 4.9 PFI, 3.4
DOHC, It was a tough decision. But in the end, I knew I wanted a
motor that is unique. I took a look at the web site,
www.car-part.com, to price out a motor. I found several 3.4 DOHC�s
in my area all priced at about $800, so I picked the best one
out of those, the 1996 motor. Within a few days the motor was in
front of my house, just as I was dreaming it would one day be.
And so the decision was finalized. Immediately I bought a timing
belt and put it on, I checked a few things out, opened the cam
carrier covers to look at the cams. All looked good. Project 3.4
DOHC is a go. This motor swap was only my second one, and was
destined to go into my 85 2m4.
The car is in
somewhat rough shape, but that�s OK since it is the car to
experiment with. Originally the 2m4�s old 2.5 was ready to
throw a rod, and was so bad I had to tow it home. Total cost for
the car $0, not a bad place to start. The first motor I put into
it was the 1989 Pontiac Grand Prix LE 3.1L. The donor car was
totaled, when a pickup truck T-boned right into the passenger
door. Total cost for donor car $0, Now you know why I put that
engine in. The final cost was about $400, which included the
$200 I spent to replace all the brakes with Beretta calipers,
pads and rotors, on all fours. When I did the swap I put in the
whole driveline, including the 4T60 transmission. After about 5
months and 8,000 happy miles I decided to retire the tired
engine and slipping transmission, which had 133,000 miles
already.
The 3.4 DOHC is
basically the same engine as the 3.1 was, just slightly bigger
pistons, and a pair of heads that flow like no other. Just so
you know, The 3.4 pushrod, and the 3.4 DOHC, share very little
other then the basic layout of the block. The crank may be the
same, as well as the rods, but not much past that point. The
heads are definitely not interchangeable. Anyway, when my 3.4
DOHC was delivered, it came with a clipped wiring harness, no
alternator, and no A/C compressor. I had to buy an alternator
($130.00) but the AC compressor on the 3.1 fit perfectly, and
with a little shaving of the compressor manifold, the stock 85
Fiero hoses fit right on. As for the wiring, I decided that the
best route to go was to take the 3.1 wiring harness, and adapt
it to the DOHC, since the Fiero was already wired for that
harness. Some lengthening and shortening of wires was necessary,
but in the end it worked out ok. I added a map sensor, and
eliminated the Mass air, as well as disconnected the crank
position sensor, and the cam position sensor. For the computer I
originally planned to learn how to re-program the computer and
just tune it myself. When the time came, I had to have this car
on the road, so I spent $100 and bought a 93 3.4 DOHC computer
with the chip. I didn�t know this, but figured it out soon
enough, but the computer plugged right in, not one wire had to
be moved. The engine runs "OK". The final total cost
so far is about $1500 not including the first motor swap, or the
brakes.
The decision on
what transmission to use was a tough one, I had the 125C all
ready to go, and the cradle was already modified to fit the
4T60, so I could have used either. But, since the 4T60 was
slipping and needed a rebuild, I figured I�d just throw it in
with the 125C. Either way, I was going to have to make it so a
TV cable would hook up to the throttle. The transmission didn�t
last long at all. The first time on the throttle, it slipped
going into third. I wasn�t near floored. Then a few days
later, and just the second full throttle run, 2nd went. so all I
had was first, and a slipping third. I rebuilt another 125C for
it with racing clutches and the whole 9 yards, It still blew the
transmission in short order. But it still drives; I just have to
go real easy on it when it shifts from first to third.
About the
performance, I was fairly impressed with the amount of power it
has, Its not punchy or very responsive at low RPM, but if you
were to floor it from a standstill, you�ll smoke the tires.
The 3.1 performed about the same at the bottom, just the 3.1
seemed more punchy and responsive at low RPM. As the engine hits
around 3K, it begins to come out of hibernation, by 4K its at
about its peak, and holds it well past 5K, but begins to loose
its thrill above 5,800 RPM up to the 6500 rev limiter. If you
ask me, the engine needs a 2 stage intake system. Gas mileage so
far for me has been Horrible, to pathetic. Something isn�t
right for sure, 12-15 MPG. It also pings a lot even on 94, but I�m
sure that has a lot to do with it being so far out of tune. I
just drive it real easy.
Maintenance,
you wouldn�t believe how easy this motor is to maintain in a
Fiero compared to how hard it is in the car it comes from (96
Grand Prix GTP). You may have paid your mechanic $1,000 and lost
the car for a week just to change the timing belt every
30-60,000 miles. In the Fiero, it can be done in about an hour,
It isn�t that hard, and no, the engine does not have to come
out. Best bet in any case, when you get the motor, CHANGE THE
BELT while its still out of the car. Another thing you may
have heard about, the spark plugs. Anyone who says its really
hard, or thinks you may need to drop the cradle, hasn't really
worked on this install. Its easier then the stock Fiero V6 by
FAR. and if you have a pre 96 DOHC, its even easier. On the
91-95 engines, The spark plugs in the rear are accessible
without removing the intake plenum. On the 96 you have to remove
it, but still isn�t much of a challenge. The front 3 plugs,
are a little more difficult. I suggest you remove your dogbone
or engine supports so that the engine is free to move around.
Using a bar clamp (preferably quick clamp) you can pull the
engine away from the firewall, then you just remove the decklid,
from the hinge bolts on the decklid. Be sure to scribe alignment
marks before your remove the decklid though. With this done, you
should be able to pull the wires out and change the plugs. See?
not so bad.
Reliability:
Personally I have had a few problems, nothing too serious
though. Other then blowing up 3, yes 3, 125C Automatic
transmissions, I have blown 2 heater cores. I guess the pressure
surge in the water when the engine hits 6500 RPM is enough to
blow it. I have yet to be left stranded, so reliability has been
pretty good.
Author:
Matt AKA
Fierobsessed |
