12 Oil Supply and Return
1.6L and early 1.8L engines have a preexisting location for the oil supply. It is located on the driver side of the block near the dipstick port. The correct size fitting to match up to it is a M10 x 1.5. Based on previous issues locating a correct fitting, you'll want to source a M10 x 1.5 to -4
AN fitting. -3AN adapters are nearly impossible to find. You'll plain have better luck source -4AN lines and fittings and save yourself a roadblock. Stainless Steel lines must be used for the oil feed.
1.8L engine that do not have feed bung need to either tee off the pressure sender on the opposite side of the block (next to the oil filter) or use a sandwich plate on the oil filter with a port for a fitting.
1.6/1.8 OEM Feed port
T-ed off oil sender
Also determine whether or not your turbo will require a restrictor on the line as well. Some turbo have a built in restrictor and others tend to need a .060" restrictor fitting just before the turbo.
The return line is simple; Drill and tap your pan. Although the 1.6 block has an oil return port next to the oil filter using it may make your life easier, but in the long run it can make you rip out your hair. The oil outlet should be plumbed to the oil pan above the oil level. Since the oil drain is gravity fed, it is important that the oil outlet points downward, and that the drain tube does not become horizontal or go “uphill” at any point. If it does chances are you'll run into oil burning problems. Added to fact that you have about 5' of return line you'll have to source and route.
The procedure for drilling and tapping the pan is rather straight-forward and well covered in the turbo Miata community. A 1/2" NPT to 5/8" Slip on fitting is typically used when using a high temperature silicone return hose. Or a 1/2" NPT to -10AN fitting would be used if using stainless steel lines.
tapped Oil Return Location
Careful, oil pickup is directly behind the location.