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5.0 Engine Swaps for Early Broncos (by Paul Nowak) As the youngest of the early Broncos passes 20 years of age this year more
and more of the origonal motors are getting tired. To breath some life
back into these worthy vehicles, one of the more common swaps among early
Bronco owners is to remove the old 302 or 289 and replace it with a late
model 5.0 HO motor. Many people are also swapping in the EFI electronic
engine control system when swapping over to the new motor. While the EFI
offers certain advantages, many people like to stick with carburation and
the stock Bronco engine accessories for reasons of simplcity and cost.
This article details the swap of an '85 HO Mustang motor into a '77
Bronco. Swaps of other year HO motors into various year Broncos will also
be discussed.
The HO 5.0 Mustang Motor of 1985 - 1993
The '85 HO motor was a big step forward for Ford in a number of areas.
Starting in 1985, the HO motor gained 33 HP to 210 HP over its 177HP
counterpart from 1984. Along the way the '85 motor received a number of
internal enhancements. Beefier internals included: forged pistons, a
roller cam with HD valve springs and rockers, a double roller timing
chain, better flowing heads and beefier connecting rods among other
things. In side by side comparison with a stock '77 Bronco motor, it's
clear that an '85 or later HO motor is beefier just about everywhere you
look.
Among the '85 to '93 motors, there are some important differences. The
main difference is that the '85 was the only motor to come from the
factory with a carb. This motor, in stock form, has a 4bbl alum intake and
a 4bbl holley. This motor is also the only one of the series to come
with Duraspark ignition making the ignition swap a plug-in affair on a
'76 or '77 Bronco. For those keeping a carb, the '85 motor is most
desirable due to the intake and distributor.
Starting in '86 the HO motor came with Ford's excellent EEC-IV digital
engine control system. The '86 motor was a bit of an odd-ball setup
though with high compression and a swirl-type combustion chamber. This
was the lowest rated motor of the series making only 200HP in stock
form. The '87 motor came with new heads (truck heads actually -- similar
to the '85 motor).
With the new heads, some revised pistons and a new calibration in the EEC
computer, the '87 and later motors were rated at 225HP. This number was
really a bit of an over kill on the later motors though as the '89 and
later motors were more like 210-215HP motors even though Ford kept the
published output at the same 225HP. Internally, the '87 to '93 motors were
identical except some time during '92, the forged pistons were replaced
with hyperutetic cast pistons. Also, the cam grind was changed slightly
to reduce noise but this had minimal effect on power ratings (or noise
for that matter).
Although beyond the scope of this article, for those considering swapping
the EFI system along with the motor, the best years for you to get are the
'89 - 92 motor ('88 - '92 in California) because those years came with
mass air sensors and forged pistons. The mass air sensor allows the
computer to adapt to different engine conditions more effectively. Also,
a motor out of an automatic trans mustang is desirable even if your Bronco
has a manual trans. And, if you're swapping in an AOD as well, AODs
starting in 1990 are beefier than earlier versions.
Swapping an '85 HO motor into a '77 Bronco w/ C-4 Automatic
Since for my swap I wanted to retain carburation and the stock Bronco
engine accessories, I decided to focus on the '85 HO motor as the motor
for my swap. After a month of looking, I was able to purchase such a
motor for $475 here in Michigan from a Ford yard. The motor came complete
with pan, intake, distributor (important!) and I took the carb even though
it was not worth squat (the stock carb is a 4bbl holley emissions carb
with very limited adjustability without doing some expensive machining on
it. It's cheaper and better just to go with a Carter/ Edelbrock carb).
Mileage on the motor was claimed to be 70,000 which on these motors is
barely broken in. Pulling the pan when I got it home revealed that the
motor had never been apart and that the bores still had the factory
cross-hatch in them. Along with solid compression, the motor seemed
excellent and later proved to be just that on the road.
To start the swap, I pulled the stock motor. I then took the '77
vibration dampner and the '77 flex plate to my machine shop and asked that
they balanced it for the '85 motor. Since they knew what the balance
specs were for the '85 HO motor, I did not have to provide them with any
other information. Not knowing this in advance, I also brought with me
the vibration dampner off the '85 motor just in case they needed to measure
the imbalance of the '85 part to balance the '77 part. Balancing for
each part was about $45.
After digging the pilot bearing out of the crank of the '85 motor, I was
ready to install the flex plate and vibration dampner. The flex plate
bolted right up. After putting a new seal in the timing cover, the
vibration dampner slid right in and I bolted that down. Prior to this, I
could have taken the timing cover off the '77 motor and used it on the
'85 motor. I did not do this because I didn't want have to reseal the
cover. What I lost by not doing this was that the timing marks on the
'85 cover had to be cut off to allow the '77 vibration dampner to fit.
Since I had a solution for setting the timing without the factory marks,
I was not worried. Also, the stock bronco fuel pump works with either
timing cover.
Next I cleaned the oil pan and bottom of the block and installed the
Bronco oil pan. One difference in the '77 vs. the '85 block is that the
'85 block is drilled for an oil dip stick along the drivers side. With
the stock bronco exhaust manifolds installed this hole is blocked by the
maniflold so I just plugged the hole with some JB weld and a metal insert
and used the stock Bronco dip stick that comes attached to the pan.
After test fitting all the engine accessories while on the engine stand, I
was ready to install the motor. Installation had one problem. The '85
and later heads have a air injection port along the back of the head for
EGR. Since the Bronco is pretty tight along the fire wall, this air
fitting on the driver's side head was hitting the fire wall. Since I
suspected this was a common problem, I called around to see how other's
dealt with this problem and found that some bashed in the fire wall the
required 1/4" while others pulled the engine mounts and slid the engine
into place before reattaching the mounts. Since I didn't need the air
injection, I pulled the fittings, and ground down the driver's side
fitting before flipping them both around and reinstalling them so they
blocked the holes. A better solution would have been to tap and seal the
holes with short bolts.
The install proceeded smoothly from there. The trans bolted right up, the
engine accessories when on smoothly and the distributor plugged right into
the stock '77 duraspark connector. I was up and running in no time. If
you use an '86 or later motor and you want to go carb and duraspark, you
will still need to get an '85 distributor for the HO (Mustang) motor as
this is the only year distributor that has duraspark AND the special cam
gear that mates to the roller cam. Earlier distributors will not have the
correct cam gear and later distributors are EFI -- non HO distributors
will not have the cam gear either.
After a bit of trial and error, I went with an Edelbrock 600 CFM carb. If
I were to do it again I would get the same carb but the Carter version to
save a few dollars. This carb proved extremely tunable to I went and got
the $30 Carter Street and Strip kit from Jegs. This gave me a tray of
different jets and needles to swap into the carb. Using a spread sheet to
compare all the different combinations possible with the kit, I was able
to dial in the motor to a fine degree with this kit and the drivability
was excellent.
Also, I had to get a "Ford kickdown linkage" from Edelbrock for about $14
to hook up my kick down rod. With this carb and intake, the aircleaner
sits at almost the exact same height as stock making hood mods unecessary.
Another option is to just go with the stock Bronco intake and carb. This
works well too and is probably a better setup for off camber situations
like rock crawling but be ready to rejet. Also, the Carter/Edelbrock
comes with offroad floats but I don't know how they compare to the stock
carb when leaned over.
On the Road
The swap was a big success. With the smallish stock bronco tires, I was
able to light the rears just by stepping on the gas. When I later swapped
to 31" tires, I had much better speed on the highway and the high reving
ability of the HO motor allowed me to run as fast as I dared. Just to
test I ran one 10 mile stretch of smooth desolate highway at an 86 mph
average. I did this by timing it since the Bronco speedo was useless at
these speeds. On this same trip I averaged 16mpg -- mostly highway.
Things that hindered the engine I think were exhaust. Using the Bronco
exhaust manifolds and narrow single pipe had to limit power. Also, the
motor is not a huge torque monster so a wide ratio C-4 gear set would
have helped or an AOD swap with the wide ratio AOD gear set would have
been a big improvement.
Swaps for Other Year Broncos and Manual Trans Broncos
The main difference if you were to do this swap on a '75 or earlier Bronco
would only be one thing: ignition. You would either need to upgrade your
truck to duraspark (recommended) or swap the internals in the '85 HO
distributor for the earlier points type distributor internals -- I'm not
clear on issues associated with swapping distributor internals. You
could also go aftermarket of course.
For manual trans broncos, the late model blocks do not have a provision
for attachement of the clutch arm quadrant. The block can be modified to
accept the Bronco parts but I am not familiar with what is needed for
this swap. Good luck. |
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