By: Dave Homstad
7220 Upper 164th St.
Rosemount, MN 55068
(952) 432-3596
E-mail: DHomstad@charter.net
Goal: install a 1962 394 (345 HP) Olds engine into a 1956 Olds Super 88 Holiday Coupe, while retaining as much original appearance of the 56 324 (240 HP) as possible. Reuse the original 56 throttle linkage, transmission linkage, transmission hoses and lines, ignition coil, electrical and spark plug wiring and brackets, vacuum lines, radiator hoses, power steering pump, fan and spacer, water pump pulley, and air cleaner. The 62 394 was the last year for the early style water pump housing that looks the same as the 56. If the 56 Hydramatic is retained, then the 56 drive shaft and all the transmission linkage can remain and does not have to be reinvented. The 62 "Slim Jim" transmission did not have a good reputation anyway!
Why?: I was lucky enough to obtain a rebuilt 394 with only a few thousand miles on it for only $200! My original 324 had noisy lifters and got only 300 miles per quart of oil. The cost of a 324 rebuild would probably approach $3000. Parts for the 394 are a little easier to find. The weight to horsepower (advertised) ratio of a 394 in a 56 is close to a 442.
A 1969 442 Holiday Coupe is 3650 lbs/ 325 HP = 11.2 lbs/HP. A 1956 Super 88 Holiday Coupe is 3891 lbs/345 HP = 11.3 lbs/HP. A 1956 88 Coupe is 3758 lbs/345 HP = 10.9 lbs/HP.
A. Engine preparation:
1. To use the original 56 wiring and temperature idiot light sending unit, replace the 394 throttle linkage stand at the rear of the LH head with the one from the 56 that has the temperature sender in it. Replace the 394 temperature sender at the front of the intake manifold with a brass plug from a hardware/plumbing store. This fitting location could also be used for an under-dash temperature gauge sending unit or an auxillary cooling fan switch.
2. To use the 56 upper radiator hose, install the 56 thermostat housing on the 394. A new thermostat is recommended.
3. The 62 394 has ribbed valve covers. Earlier 394 (and later 371?) valve covers were smooth, more like the 56. Use these and the "Oldsmobile Rocket" decal created for the 56 and earlier valve covers.
4. Paint the engine Oldsmobile green.
5. The LH 394 dual exhaust manifold that exits at the rear will not work because of the master brake cylinder and linkages. Use the LH single exhaust manifold that exits down between cylinders 1 and 3, same location as the 56.
6. The RH exhaust manifold on the 394 is no problem, but it is a tight fit to the frame. For dual exhaust, the manifold front opening cover plate from the 56 will also fit the 394. For added clearance to the frame, grind off any protrusion of the cover plate that extends wider than the manifold.
7. The front motor mount bolt spacing on the 56 and 394 blocks is different. Use the 62 (61-64, P/N 579129) motor mount. The bolt spacing to the frame holes is the same.
B. Flexplate and transmission:
1. The 394 engine crankshaft is externally balanced with the flywheel, as a matched set indexed to the crankshaft. The 56 324 is internally balanced on the crankshaft. To use the 56 Hydramatic, the balance value must be transferred from the 394 flywheel to the 56 flexplate. There is room for 1/8 inch thick metal plates to be welded to the torus side of the flex plate. Compare the 56 flex plate and 56 flywheel/ring gear together for available locations for placement of added weights. A racing shop can do this balancing process. The 394 has one of the crankshaft bolts for mounting the flywheel slightly offset for crankshaft/flywheel alignment. The 56 flexplate holes are evenly spaced. Select and mark one flexplate hole to be slotted slightly until it aligns with the 394 offset crank hole. When balanced, these 2 offset holes must be used as the same index point. If this balance transfer is not done, and depending upon the amount of balance correction necessary, significant engine vibration can result. A 57 flexplate may work even better, with a complete circle design.
2. Because the 394 flywheel is thicker than the flexplate, the 394 flywheel mounting bolts to the crank are longer. Use the 56 flexplate bolts, or the 394 bolts will stick through too far and may hit the block web.
3. The 394 has a slightly smaller diameter ring gear than the 56 324. The 394 block had a small radius added to the casting where the horizontal web at the bottom of the block meets the outer sides of the block extension, and some material added to the horizontal web. This extra material will cause an interference fit between the block and ring gear teeth! Grind this excess material away until at least 1/4 inch of clearance to the block is present with the flexplate and ring gear (on front half of the torus) mounted.
4. Replace the torus cover seal O-ring and front shaft seal (a.k.a. front housing oil seal) while the transmission is out. Also replace the rear oil seal.
Transmission kits, external seals only or complete overhaul:
FATSCO: 800-524-0485
Northwest Transmission Parts: 800-327-1955
5. Because the 56 Hydramatic starter ring gear is a different diameter and has different size teeth, it is necessary to use the 56 starter and the 56 cast lower bell housing. It may be possible to use the 62 lower bell housing or the 62 starter with the 56 starter drive gear, I just knew the 56 parts (ring gear, lower bell housing, starter) would work with the 56 transmission and didn't have time to investigate.
6. The original 56 starter is designed for a smaller engine than the 394, so it cranks a little slower than normal. I retrofitted a late model racing starter that has about 50% more torque for faster starts. It comes with a special mounting flange and gear to fit the old Oldsmobiles. This came from Hi-Test Racing at pittmant@mindspring.com or lakad@awtobahagi.com This starter comes with shims that go between the starter motor and the mounting flange. It is important to measure the distance from the starter mounting surface of the lower bell housing and the face of the ring gear and add the right number of shims to assure there is clearance between the starter gear and the ring gear when the starter is disengaged. Mine took 2 shims. Too many shims will result in insufficient gear engagement. Due to the relocation of the starter electrical terminals from the top of the old to the bottom of the new starter, a longer starter cable is required. The original battery cable is 34 inches long. A new cable about 40 or 42 inches is perfect.
C. Engine compartment:
The 56 power steering gear box has a small housing and hoses on top that may interfere with the 394 LH exhaust manifold. The 59 and later steering gear boxes do not have this small housing and are a much more reliable design (not prone to rapid wear and excessive play). I installed one from a 70 442. The newer box fits the frame mounting holes and can use the 56 mounting bolts. But the nose is longer and the frame must be dented in (heat red hot and dent in with a sledge hammer; move the fuel line mounted under the frame for this operation) or notched where it curves around the front of the box's nose. The input shaft is shorter on the newer box, so a 5/8 inch spacer must be fabricated to mate with the flex coupling on the steering column shaft. Other boxes may need a different thickness spacer. The overall thickness of the adapter may also vary depending upon the variables of the body and frame and steering box and steering column. Measure the actual gap between the flanges of the new box and the old column before having it made. The function of the adapter is to ensure that the pins from the box engage with the slots of the column flange. This is for safety so if the flex joint fails, the car can still be steered. The pins may also take the stress of the flex joint when there is a lot of force from the box. It may also be possible to loosen the steering column bolts and slide it down to take up the space. Use a 56 power steering pitman arm (a non-PS pitman arm will not fit the shaft), it fits right on the pitman shaft of the newer box. The design of an Olds non-power steering box is much different and did not include a flex joint, so there is no flange at the end of the column to mate with the new box. You will need to use a 56 Olds PS column. The newer box has different hose fittings. If reusing the original 56 pump, use the 59 - 63 88-98 power steering hoses. Mike Fusick (860-623-1589) has new hose sets.
D. Engine installation:
1. For the LH exhaust manifold to clear the upper control arm, it is necessary to place a 1.0 inch thick spacer block under the front motor mount. New bolts (grade 8 are recommended) from the frame to the motor mount need to be 1.0 inch longer. It may also be necessary to grind away a little material from the LH upper control arm flange at the rear upper inner bushing area. Lower motor in place to check clearance and potential contact points between the front corner of the manifold and the control arm.
2. The 56 rear motor mounts (54-56, LH P/N 759263, RH P/N 759264) fit the 394. Do not tighten any of the motor mount bolts until all have been loosely installed. New motor mounts are recommended. These are occasionally found at swap meets or on eBay.
E. Miscellaneous:
1. The 394 oil dipstick tube is relocated to between the starter and the block, causing interference with the solenoid on the original 56 starter. Slot the mounting holes in the solenoid flange about 1/8 inch to reposition the solenoid farther away from the engine block.
2. Use the 62 generator mounting brackets and generator. The 56 generator mounting location on the RH exhaust manifold is not present on the 394. Also, the 64 (and 63?) had an alternator with different brackets, if desired.
3. The 56 power steering pump mounting bracket needs a small amount of material removed where it contacts an intake manifold bolt head. The pump will align with the 56 pulley. Only 2 bolts may be used to mount the pump bracket, but this will be fine since the belt pulls the pump down.
4. The exhaust pipe flange bolt pattern is the same on the 56 and 394. Unfortunately, the bolt hole pattern has been rotated 90 degrees. The exhaust pipe flange needs to be cut off, rotated, and re-welded. New pipe sections bent to fit are recommended.
5. The 56 Hydramatic dipstick tube upper support brace does not align with the 394 exhaust manifold bolts. Fabricate a strap, wrap it around the tube and bolt it tight. Bolt the other end to a manifold nut. The old bracket may be removed if desired, however, it is not very visible.
6. The flexible rubber Hydramatic oil cooling hoses from the transmission to the metal lines on the frame are 55+ years old, and are brittle. Mine did not leak until they were flexed slightly during uncoupling for transmission removal. Replacement is highly recommended. Find new ones at a swap meet if possible. An alternate is to use new brass fittings with hose nipples to replace both hose ends. Use high pressure transmission oil hose (not gasoline hose!) and hose clamps. Mike Fusick (860-623-1589) has new hose sets.
F. Carburetor:
1. The 56 carb will fit the 394, but it's smaller CFM rating will reduce power output.
2. The 62 carb is a much better choice and is correctly calibrated to the engine. In order to make the 56 transmission linkage work properly, it is necessary to use the complicated factory bellcrank assembly bolted to the left rear side of the 56 carb. This fits on the 62 carb, but it pushes the throttle shaft lever instead of pulling as the 62 bellcrank does. The 62 carb throttle shaft lever is designed to be pulled back from above the throttle shaft axis of rotation. The 56 linkage is designed to push forward below the axis. The direction of rotation is the same for both: clockwise. I fabricated a simple adapter plate that bolts to the 62 carb throttle lever (above the axis) at the linkage connection hole, and extends down to the equivalent location of the hole in the 56 throttle lever (below the axis). Works perfect with the 56 bellcrank.
3. The vacuum fitting for power brakes and wipers on the back of the 56 carb throttle body can be transferred to the 62 carb.
G. Final assembly:
1. Install the original 56 throttle linkage, transmission linkage, transmission hoses and lines, vacuum lines, ignition coil and bracket (suggest a new hotter coil), electrical and spark plug wiring, radiator hoses, power steering pump, water pump pulley, and fan and spacer. A new metal fuel pump to carb fuel line will be needed.
2. Route the spark plug wires using the 56 spark plug wire guide brackets: RH, LH, and center. Some of the 56 intake manifold bolts are necessary for the bracket mounting studs. The mounting holes on the feet of the center wire bracket need to be slightly slotted for the wider width of the intake manifold.
3. The 62 394 has a draft tube for crankcase ventilation in the middle of the RH valve cover. The 56 is at the back of the block at a hole not present on the 394. I added an aftermarket spacer with a PCV port under the carb (a common item required on California cars), and a hose from the valve cover hole through a PCV valve to the carb spacer. (A later Rochester may have a PCV port.) Another hose from the oil filler tube cap to a fitting on the back of the aircleaner. If an earlier smooth valve cover is used, a PCV fitting will have to be added. This creates a sealed and improved crankcase ventilation system. If a 394 is to be rebuilt, a breather hole could be added to the back of the block to use the 56 fitting.
4. Even with the 1.0 inch spacer under the front motor mount and a ½ inch spacer under the carb, the 56 aircleaner will fit under the hood, barely. Use the 56 carb air cleaner stud. I removed the very dirty under hood blanket. Verify clearance before closing the hood. This aircleaner can be converted into a paper element by removing the oilbath element, un-crimping the internal lid from the oilbath element, and installing a suitable paper element under the internal lid. A nut may be needed to hold down the internal lid, or some spacers that will hold down the internal lid when the outer cover shell is installed. The corrugated surface of the lower base section can be sealed to the paper element with RTV.
5. Cooling with the original 56 radiator may be a problem. I have seen the "hot" light come on a few times on hot days, but have not boiled over yet. The easiest solution is an auxillary fan in front of the radiator, with a control switch mounted in the unused front mounted temp sender hole in the intake manifold.
H. Modern improvements
Ross Automotive has come up with some nice improvements for these old Olds Rockets. For the 1949 - 1964 Olds V8, they have the following parts available. Contact Tony Lombardi, 330-544-6615, lgrt02@yahoo.com
1. Aluminum head, hardened valve seats and unleaded valves, greatly improved flow.
2. Rocker arm assembly: roller tip and adjustments for pushrods.
3. Improved head gasket.
4. Transmission filter with spin-on filter.
5. Transmission adapter for use with TH350 and TH400.
6. Solid lifters, .921 dia.
7. High torque modern mini starter with adapter.
8. Intake manifold: modern high-rise single 4 bbl single plane.
Drawings available:
1. Steering shaft spacer for newer gearboxes.
2. Carb linkage adapter.
3. Front engine mount spacer block.