Preface

First and foremost this is a rebuild of a classic E21, due to the limited number of cars built the original engine block will be maintained along with other components that make the car a john player special. With that in mind, my goal is to coax an extra 50hp (and the torque that follows) from the motor fit an eaton MP90 supercharger driven by the rebuilt motor to produce an extra 100-150hp, rebuild the suspension, transmission and differential, then restore the bodywork to its former glory. The purpose of the build has changed slightly, rather than returning it to road use, we will also participate in a few road sprint events along with the odd track day, so you can see where a few changes to the build sheet have occured. 

The Engine:

The Bottom End

Starting with the original 1981 2.3L M20 block, the bottom end will be bored and stroked to take the motor out to 2.6L, Independant 45mm throttle bodies fitted with the whole lot being controlled by a Microtech LT12s.

Block: 1981 M20 (2.3L) Block with 80mm bore, hot tanked, rebored 40 thou (1mm) over, decked and resurfaced with mains line bored due to fitment of a new crankshaft.

Crankshaft: 1996 Bmw E36 328i (2.8L) crankshaft from an M52, linished and balanced.

Connecting Rods: Eagle H Beam forged steel Carrillo PRO-H forged steel with ARP bolts.

Pistons: Custom JE, 11.4:1 comp ratio, Custom JE, 9.5:1 comp ratio based off original 323i piston, modified with a raised crown and valve reliefs.

Flywheel: Standard 2.3L (13lbs stock), machined and lightened to 9lbs.

Hardware: Ishihara-Johnson crank scraper, ARP main bolts, ARP Head stud kit, new oil pump, waterpump and other associated hardware.

The Cylinder Head

Due to the bore size of the block and due to the high cost of the 325i heads, it was decided early on to stick with the smaller chamber 323i heads and try to get it flowing as best as possible.

The later model "731" heads come with larger ports than the standard "200" heads, some testing done by marquis-rex displays the difference between the 3 types of M20 cylinder head and is well worth a read.

Casting: 1985 M20 323i "731" head from an E30.

Valves: Osvat (made in italy), +2mm, 42mm Inlet, 36mm Exhaust, back cut to remove excess material and improve flow.

Camshaft: Catcams 293', 12.4mm valve lift, 3.85mm lift @ TDC, 108' LSA.

Rocker Arms: Pure Performance Motorsport, billet rocker arms.

Springs: Schrick dual valve springs and retainers.

Hardware: Replacement rocker shafts and locks.

Work: Hot tank, crack test and resurface head.

New guides, stainless steel valve seats, clean up the ports, light polish inlet port, heavily polished exhaust ports, port match manifolds.

Work out the bowl areas working on the short side transition, blend the area from seat bottom.

Remove material around guide area, smooth and shape the area around the guide into the port.

Clean up combustion chamber to reduce shrouding, 3 angle valve job to finish.

Extras

Entire bottom end from vibration dampener (balancer) to flywheel assembled and balanced by precise engine reconditioners. A great deal of weight has been removed from the bottom end of the motor which requires balancing in order to reduce engine vibration and increase throttle response.

The Bolt Ons:

Supercharger

5th Generation Eaton MP90 supercharger,  1" drive snout.

Manifolds

Toyota 4AGE "Black Top" throttle bodies (6) with cast alloy inlet manifold supplied and manufactured by Rowland Manifolds in South Africa. Exhaust manifold custom made stainless steel, tubed design, port matched.

Exhaust

JPS cars originally came with a full length, stainless steel split twin system utilising larger diameter pipe (1.75") and mufflers (2.25") compared to a standard 323i. We have stayed true to the design of the original system, however we have removed the centre resonator but kept the original 1.75" diameter pipe. This is due to the reduced backpressure now the resonator has been removed, an increase in pipe size see's a large reduction in torque and throttle response as gas velocities drop.

Clutch

Clutchnet 6 puck sprung clutch plate with upgraded pressure plate.

Transmission

Rebuilt getrag 245/6 transmission, brass shift forks, updated syncro design getrag 265 transmission from a 635csi, using the M20 belhousing from an E28 528e. 

Differential

ZF 3.91:1 BMW E21 LSD, standard differential comes with a 25% lockup, rebuilt with new bearings, replacement clutches and modified ramp angles incorporating a 50% lockup.

Brakes:

Front

Massive Brakes E21 race kit.

Rotors: Wilwood HD 300x32mm

Calipers: Wilwood Forged Superlite 4 piston

Hats: Massive Brakes

Pad: Wilwood "E" Compound

Extras: Supplied caliper brackets and mounting hardware, braided brake lines.

Rear

Rotors: Standard replacement DBA rotors

Calipers: E30 323i

Pads: Mintex 1144 Compound.

Extras: Braided brake lines.

Fluid: Castrol 5.1 brake fluid.

Steering and Suspension:

Steering: Rebuilt steering rack fitted with 2.5 ratio quick rack supplied by jason (Jason_323i)

Front

Shocks: Bilstein motorsport struts, rebuilt and revalves to suit 420lbs front springs.

Springs: Custom 420lbs progressive, 45mm drop

Strut Tops: Kmac solid adjustible top mounts.

Swaybars: Standard 323i item, whiteline additional 17mm bar (bolts to standard item).

Strut Brace: Modified Whiteline E30 brace (new mounting plates).

Hardware: Superpro polyurethane bushes.

Extras: Alpina style frame rail support. Replacement ball joints. Stitch (10mm per inch) welded seams and sills, reinforced chassis with gusset panels and bracing to strut towers.

Rear

Shocks: Bilstein motorsport shocks, rebuilt and revalved to suit 325lbs rear springs.

Springs: Custom 325lbs, 40mm drop.

Swaybars: Whiteline 18mm.

Hardware: Custom poured subframe bushes, Superpro polyurethane bushes.

Extras: Modified subframe for camber/toe adjustments.

Body/Interior/Appearence:

8 point weld in cage

BBS RA 15x7" wheels, restored and repaired, gold centres with polished lip.

Motorsport front and rear spoilers.

Repair bodywork, lead filled panels and seams.

Respray 2 pack Schwarz (black), original gold pinstripes.

Restored original Recaro interior with gold stitching.