This information details a V6 conversion performed on a 1985 Toyota
SR5 Extra Cab 4x4 truck in late 1991. The truck was originally
equipped with a multi-point fuel injected 2.4 liter four cylinder
backed by a five speed transmission and the two speed transfer case
(2.29:1 low range). Axle gears in the truck are 4.88:1 and the
truck has approximately 4" of suspension lift. The engine swapped
in is a 1988 Chevy 4.3 liter throttle-body injected (TBI) and the
transmission chosen is a late model GM 700R4 4 speed automatic with
30% overdrive. Fourth gear engine speed is about 2500 RPM at 65 mph
using 32" tires.
A view of the engine as
it sits in the truck.
ENGINES
A 1988 engine was used that could provide both TBI and a single,
serpentine fan belt for the engine and all its accessories. The 4.3
liter GM engine provides 165 hp and about 205 ft. lbs. of torque.
It uses the same block design as the small block Chevy less two
cylinders. Pistons, rods, bearings, etc. are all interchangeable.
It also uses roller lifters. The only flaw in this engine is a
slight imbalance condition at about 1200 rpm. About 1992 or 1993
Chevy revised this engine by adding a crank driven counter-balance
to completely eliminate this slight vibration. The 3.8 liter Buick
engine is often used in Toyota conversions. There are many parts
available for the Buick motor and it is a bit smaller and lighter
than the Chevy V6. However, the Buick has a worse vibration problem
and tends to run a bit on the hot side. There is also a Turbo
version of the Buick engine, but is best avoided for any
application where the truck will have slow or limited cooling air
flow.
The small block Chevy V8 is about 4-5" longer than the V6 and
weighs about 80-100 lbs. more. The V8 can be used in a conversion
but will require firewall modifications due to the added length and
the rear mounted distributor. Installing the V8 may also require
that the front grill sheetmetal area be modified and the radiator
relocated forward somewhat. A stiffer front suspension is also
required with a V8 conversion. Any of the above engines will fit
well between the Toyota frame rails and should allow use of a
regular air cleaner under the stock hood. The one exception is the
Turbo conversion which will require a 2-3" body lift in order to
clear the air intake components. All conversions need a 3" or more
suspension lift in order to have oil pan clearance and retain
adequate front suspension travel on a live axle truck. The 1985 and
up 5 speed transmissions are supposedly quite strong and able to
withstand sane amounts of V6 and V8 power provided a sturdy
aftermarket clutch is used. However, rebuild cost for a blown 5
speed transmission is high. Toyota transfer cases are bullet proof
and will easily withstand V8 power applications. The Toyota axle
shafts are very strong and strength-wise lie somewhere between a
Dana 44 and Dana 60.
The weakest links in the front axle are the
Birfield joints of the stub axles. One risks grenading these when
getting lots of air while running large, high traction tires and
then slamming the front end to the ground. The weak link in the
rear drivetrain is usually the driveshaft U-joints. These can also
be destroyed by violently slamming a truck to the ground while
under high power. The only time strength is of real concern in the
differential is when 5:1 or greater gears are run. At this point,
the number of pinion gear teeth is reduced significantly and
ring/pinion strength suffers. Overall, the Toyota drivetrain is
very strong and reliable, and can withstand V8 power easily, if not
abused. In general, an engine can be legally swapped into a vehicle
if the engine is the same year as the truck, or newer, and all
stock engine emissions gear is retained. However, swap laws do vary
from state to state.
MOTOR MOUNTS
The stock motor mounts were removed from the truck frame and custom
motor mounts for the new engine were fabricated from 2" x 3" x
3/16" box tubing. These mate to the stock GM rubber engine mounts
and were welded to the truck frame. A single bolt on each side
secures the two mount halves together. An out-board stabilizer was
also constructed of steel and uses a urethane bushing to prevent
the engine from torqueing excessively. An alternative to the above
method is to use bolt-in aftermarket mounts or make custom mounts
and use aftermarket urethane mating mounts. The urethane would
provide a firmer engine mount and remain more stable during hard
acceleration.
TRANSMISSION
The transmission is a late model GM 700R4 4 speed automatic that
provides 3.08:1 first gear and 0.70:1 fourth gear ratios. It is
built with manual 3rd and 4th gear lockup. To tune the shift points
to the particular gear ratio/tire size, a TH350 governor cluster
was used along with a TH400 governor gear. A stock TV cable was
used to connect the transmission to the engine TBI unit. A B&M
Megashifter 4 speed floor shifter was mounted to a custom recessed
floor mount plate which was in turn screwed down to the floor of
the cab. A cable connects the shifter to the transmission and a
neutral safety switch was wired in to prevent the starter from
engaging in any position except Park or Neutral. The transmission
was mated to the stock transfer case using an Advance Adapters
transmission output shaft and case adapter. Fluid lines were run to
a cooler in the new radiator and then to an additional cooler
mounted behind the grill. A dip stick, tube, inspection cover, and
TV cable came from a Chevy S-10 were used.
TRANSFER CASE
The original Toyota transfer case was used along with the original
cross- member. The cross-member was left in the stock location,
however, the transfer case was relocated approximately 1 3/4"
rearward. (The transfer case does not have to be relocated if a
TH350 transmission is used in this configuration.) A custom
cross-member extension was fabricated from 6" x 2" steel channel
and was welded to the cross-member. The transfer case was then
bolted to this extension piece. The floor of the truck cab was cut
out to accommodate the repositioning of the transfer case shift
lever. The floor plate was modified to fit the new hole in the cab
floor. The speedometer cable remained at the stock location in the
transfer case.
DRIVESHAFTS
Relocation of the transfer case required that the rear driveshaft
be shortened about 1 1/2". Use of the 700R4 transmission required a
new driveshaft made of smaller diameter tubing in order to provide
clearance between the driveshaft and transmission pan. (The 700R4
does not have a corner notched pan like the TH350 transmission.) A
custom driveshaft was fabricated using a GM type CV joint coupled
to a GM/Toyota conversion yoke at the transfer case and the
original Toyota yoke at the axle end. Tubing size is 1.25" O.D. x
0.120" wall.
EXHAUST
Factory tubular exhaust manifolds from a 1985 full-size Chevy truck
were modified to clear the truck frame rails. This involved
removing the end flanges and lengthening the tubing sections before
reattaching the flanges further down past the frame rails. A Y-pipe
was fabricated to join the two sides and a single 2 1/2" turbo
muffler added. Also, the pipe boss needed for the EFI oxygen sensor
was removed from the original V6 Y-pipe and welded into one leg of
the new exhaust.
COOLING
An Advance Adapters V8 radiator was used in the stock location
using the stock mount holes and bolts. (This radiator hangs low on
the truck requiring a steel guard for protection. A guard was made
from 3" x 3" x 1/4" angle to protect the lower portion of the
radiator.) This radiator is expensive, but is a quality copper
radiator that drops right in and provides excellent cooling
capacity. Almost any other radiator will require cutting of the
front cowl sheetmetal and the fabrication of custom mounts. The
lower radiator hose is a shortened stock Chevy S-10 hose and the
upper hose is a standard part #71428 (application unknown). The
original Toyota radiator cap and overflow setup is used on the new
radiator. A 17" reverse direction (due to serpentine belt drive)
flex fan is used inside a mid '80s Ford Thunderbird 302 fan shroud.
In a typical GM application, hot water for the heater core is taken
from a tube located at the passenger side rear of the engine. Once
the water circulates through the heater core it is replaced in the
system via a tube connection at the radiator. For this application,
water for the heater core is taken from the water outlet on the
intake manifold (the water outlet used is similar to V6 stock but
has a 3/4" pipe outlet on one side). Water from the heater core is
returned to the cooling system via the tube on the rear of the
engine. A 195 degree thermostat is used.
FUEL SYSTEM
The original Toyota high pressure electric fuel pump was left in
the gas tank and a second in-line Walbro electric fuel pump was
added slightly ahead of the gas tank. The old Toyota fuel pump is
not energized but can be used as a backup pump if necessary.
Electric power for the fuel pump is supplied via the engine
harness. A large canister type fuel filter was spliced in-line and
mounted to the firewall in the engine compartment.
CHARGING SYSTEM
The GM alternator (internally regulated) that came with the new
engine was used and was spliced into part of the original Toyota
wiring, A new 8 gauge wire was run from the B+ terminal of the
alternator directly to the positive battery post. The case of the
alternator was grounded using the original black Toyota wire.
Terminal 1 and 2 on the alternator were tied to the white (+) and
yellow (charge) wires in the Toyota harness.
POWER STEERING
The GM power steering pump (integral fluid reservoir) that came
with the new engine was used along with the original Toyota power
steering box. The GM high pressure hose was used by shortening the
steel end at the steering box, replacing the tubing flare nut with
one from the original Toyota hose, and reflaring the tube end. The
low pressure hoses were simply hose clamped and the original grill
mounted fluid cooler was retained. GM power steering fluid is used
in the system.
ENGINE SENSOR WIRING
A Howell Engine Developments TBI engine harness was used to utilize
all the engine sensors and cleanly integrate the new engine into
the power system of the truck. This harness retains full function
of the GM engine computer and easily mates it to all of the engine
sensors, but also allows deletion of the Vehicle Speed Sensor
functions and transmissions functions.
STARTER/IGNITION WIRING
The original Toyota V+ battery cable was connected to the starter
on the new engine. The ignition switched solenoid line on the truck
cannot sink sufficient current to reliably engage the GM starter
solenoid. It was necessary to tie the solenoid line to a relay and
provide a switched V+ line directly from the battery. Voltage is
supplied to the GM coil via the original Toyota harness wire. The
new coil was also spliced into the original tachometer wire to
display rpm on the factory tachometer. The tachometer was modified
to correctly display the V6 rpm by adding a calibrated resistive
shunt to the analog tachometer meter. The check engine light wire
from the new engine was spliced into the original harness and works
with the original in-dash light.
THROTTLE LINKAGE
The original Toyota throttle cable is used and a custom attachment
was made to mate the cable to the TBI unit. It was possible to
retain the function of the original cruise control because the
controller receives it's speed signal from the speedometer.
AIR CONDITIONING
The GM compressor that came with the new engine was used along with
all other original Toyota air conditioning components, The Toyota
and GM hose ends were mated using various tube fittings and crimp
connections. This was done at an AC specialty shop. A GM compressor
electrical connector was spliced onto the Toyota AC electrical
lines.
GAUGES
The original Toyota temperature sender was threaded into the
passenger side head of the V6 allowing the stock gauge to monitor
temperature. The original Toyota oil pressure sender was added to
the V6 (original location) using a Downey supplied adapter. The
stock gauge is used to monitor oil pressure. An aftermarket vacuum
gauge was connected to one of the intake vacuum lines of the TBI
unit. The stock voltage gauge was retained unchanged. The stock
Toyota tachometer was modified and used also.
GENERAL INFO
The engine conversion took place over several weeks and, as in any
such swap, there were a few bugs that had to be ironed out. As of
August 1996, the truck had 175,000 miles on it and 62,000 miles on
the conversion. The engine and drivetrain has performed very well
and provides a significant increase in the driveability of the
truck, both on and off highway. The truck generally runs cool and
mileage varies from about 16-17 around town up to as much as 20-21
on the highway, with the truck now running 33" BFG Mud Terrains. In
the last six years, the truck has overheated twice, but was quickly
shut down as soon as the guage needle went into the red. When
summer temps here in Phoenix near 115 degrees, the truck cannot sit
idle with the air conditioning on for more than a few minutes. The
temp will slowly rise unless the truck starts moving again or the
air conditioning is turned off.