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Supercharged Bluebird
By Glenn Littlefford

Photo Album/ Tech Article

Australia

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Glenn's Supercharged Bluebird Wagon

I have been playing around with these Datsun motors for years. Although I also own a 350 Monaro, I just love the little datsuns.

The beauty of the Datsun is parts interchangeably. Using the right combination of standard datsun parts can build a potent little motor.

The motor is a L18.
Crankshaft is a double counterweight version. I avoid using the single weight cranks.
The flywheel is off a L24 six cylinder motor, much lighter than the standard unit and accepts the larger diameter clutch plate and pressure plate, which is off a 720 four wheel drive. Gearbox is the standard 5 speed. Oil pump is modified by drilling a 1/4 inch hole near the 3/8 hole at the top of the pump, where it mates with the timing cover, I'll have to take a photo to explain this, but it increases oil pressure at low RPM, important for a blown motor due to the extra torque below 2000rpm.

I use L16 conrods as they are 2.9mm longer than the L18 rods. This improves the rod ratio from 1.66 to 1.7, giving more bottom end torque. The standard datsun piston has a 2.9mm deep dish in the top. So by fitting L16 conrods and machining the piston flat, you end up with a zero deck height, flat top piston bottom end, than has a better rod ratio than the L20B (1.68). Pistons are 60 thou oversize, however I have taken these motors to 140 thou over and used toyota pistons. They must have a thick bore.

The head is a A87. Inlet ports are simply ported to L20B head size ports. Exhaust ports are heaverly modified and now flow 80% of the inlet port. The standard datsun has a very poor exhaust port compared to its inlet port. The problem with the exhaust port is the gentle taper from small to large port area just after the port turns behind the valve. Trick here is to make the exhaust port shorter! But I'll keep this little trick to myself. Port flow improves heaps and as a bonus you get anti-reversion. The combustion chamber is reshaped around the spark plug and smoothed.
I kept with the standard valves, but cleaned them up. As the cam is a standard unit I used standard valve springs, no sense in wasting power pushing heavy springs down when it doesn't need them and the motor wont be revved above 6000. The rockers are ground flat where they are wiped by the cam. By flattening and polishing this wipe pad, the valves are opened and closed quicker, without changing duration or lift. In effect a slightly larger cam. Its an old Ford 2L trick.

I originally had a couple of 2inch SU carbies off a Rover fitted to the motor to run it in. This little motor ended up VERY torquey, I was surprised and pleased.

The supercharger was purchased from Adelaide Jap Weckers, give these guys a
plug for me will you, they were very helpful. The supercharger is from a Toyota GZ motor (I think). It is a roots type with a built in sump with its own dip stick, teflon rotors and an electric clutch, and uses a multi-V type belt drive.
To drive the blower I found a waterpump pulley from a late model Corolla, and with a bit of machining fitted it to the front of the crank shaft. This drives the blower via a serpentine belt and idler pulley. A DCOE 42 carbie is mounted on the blower with a home made adapter plate and linkages. Outlet of the blower is fed into a standard L20B inlet manifold with another home made adapter.

Mounting the blower proved to be a pain. The car is air conditioned and up here in Mackay you need it, so I had to mount the blower above the air-con compressor. With a supercharged motor you need to make the distance from carby to motor as short as possible. You cant use a blow through setup like a turbo motor as a blower will stall the motor when the throttle is closed, or bend the throttle plates, or pop a hose, whatever, it will break something!! That boost pressure has to go somewhere and you will need a bloody great popoff valve to get rid of all that air! A turbo will simply stall or slow down, but the blower is driven by the crankshaft.
To get the blower as close as possible to the motor I had to move the dizzy. I looked into a angle drive, then a toothed belt drive, ended up using a direct drive off the front of the cam shaft. I had a lump of aluminum welded on the front of the tappet cover, then with the help of Ross Torrisi of Torrissi's Garage, made a boring bar that uses the Datsun cam towers to center itself. We bored a hole in the tappet cover to suit a sigma dizzy. The tappet cover was also doweled to the head so it would align perfectly. I had to use a sigma dizzy as the cam shaft spins in the opposite direction to the normal dizzy drive, so a datsun dizzy would retard as rev's increased, where the sigma unit is designed to spin the other way.

The dizzy was shortened, then a 19mm socket fitted to the drive shaft. Once
installed, this socket fits over the cam sprocket bolt and drives the dizzy. I removed the guts of the dizzy and machined a new breaker plate to take a standard datsun twin point assembly. The points are angled 10 degrees apart, and the second set of points is used when the boost pressure reaches 3 pounds as sensed with a pressure switch (out of a washing machine!! $2 from the local junk yard and is even adjustable), effectively retarding the timing by 10 degrees. The points switch a Ford ign module and coil.

Exhaust manifold is standard, flowing into a 2 inch system.

The setup works like this -

Normal driving, blower off.
The blower free spins due the the air passing through it, this gives a very slight lag in the throttle response. Car drives ok, economy is good.

Blower on.
A switch on the gear stick (I was thinking of Mad Max when I fitted it) engages the blower. Response is instant, no turbo lag here! Total boost pressure is 5 pounds at full throttle, even as low as 1500 RPM !!!! Boost pressure remains constant through rev range. Motor is VERY bloody torquey and doesn't ping at all, even with 9.5:1 compression, fuel economy is bloody terrible!

I haven't raced the car at out local drag strip yet, but from past experience I feel the car would do a low 15, high 14 second pass, but the top end speed would be high as it goes very hard in the top gears.

One problem is the carbie behaves differently when blower is on. Running this setup is like bolting a carbie onto a 2L motor, tuning it, and then expecting it to run on a 3L motor, just doesn't work. One solution would be to remove the clutch setup on the blower, and mount a smaller pulley. This way the blower is on all the time and it will be easier to tune the carb, plus giving more boost.