In the interest of furthering renewed interest in Spec3, the series leader and series director put together a constructors guide for those interested in building a car from scratch.
The purpose of this guide is to share useful information related to building a Spec3 race car. This is information everyone needs, and it will sort of act as an addendum to the rules listed on DriveNASA.com.
One of the most economical ways to race a BMW in NASA, Spec3 uses the 1993 to 1995 BMW 325. It’s the most restricted series in NASA in terms of which cars can be used as donors, but donor cars are plentiful. If Spec3 is something that interests you, find out more below, or on the NASA Forums, where there is a longer, more comprehensive version of the one you see here.
Finding the Right Donor Car
A 1993-1995 BMW E36 chassis is required for the NASA class. In addition, any 1992 – 1998 BMW E36 chassis may be used provided that all relevant components (motor, engine wiring harness, transmission, brakes, etc.) are used from a 1993 – 1995 production vehicle. See Rule 9.3.2.2.
The most important thing to consider when sourcing a car is the quality of the shell. Avoid cars that have been in significant collisions because the unibody may be out of alignment. Likewise, avoid cars with significant rust because it may compromise structural components. Rust repairs can be expensive, and the rust may reappear in the future. High mileage drivetrains are often still competitive and high miles should not discourage a potential buyer.
Sedans are legal. Convertibles, 318Ti compacts and wagons are not. There is great debate on coupe versus sedan, but ultimately it comes down to personal preference and the type of clean chassis you can find. The coupe provides larger doors, which aid egress, but the sedan’s rear doors provide access to the back seat area.
There are critical areas to inspect when looking at a potential shell/car:
- Shock towers front and rear: If not reinforced, they can blow out or “mushroom.”
- Rear trailing arm pockets: This can rust out and pose a potentially build-ending safety risk.
Engine
The E36 uses the BMW 2.5-liter single-VANOS inline six cylinder engine known as the BMW M50b25TU. See Rule 6.3.1. and Appendix A.
Engine Management
- Stock Bosch DME, part numbers 0-261-200-413 or 0-261-203-506, with Bimmerworld performance chip, part number 12.536.0003. See Rules Section 9.3.1.7. Stock DMEs without EWS are commonly known as Red Label and Silver Label, which comes with an EWS module.
Transmission
Stock Getrag 250 five-speed transmission stamped with one of the following numbers: 23001221836, 23001222393, 23001434407, 23001221837, 23001222400, or 23001434410. See Rule 9.3.12.1. Automatic to manual swaps are fairly straightforward, and there is a great guide on swapping an E36 automatic to a manual online.
Flywheel/Clutch
As of July 2020, only the stock dual-mass flywheel and unsprung clutch were allowed. However, an exception can be made by contacting the regional series leader and submitting the proper documentation to run a single-mass flywheel conversion because the LUK brank dual-mass flywheels are known to fail.
The Valeo single-mass flywheel conversion has been legal since the 2021 season. They’re available online from FCP Euro.
Intake
Stock air intake with K&N or Green Filter air filter and optional “S3 Air Duct” sold by Bimmerparts.com and available via the Ebay.
Exhaust
You must use the stock exhaust manifold and collector pipes followed by the Spec3 exhaust sold by Mitchum Enterprises in Richmond, VA., which does not have a website. Call (804) 402 1239 or email [email protected]. See Rule 9.3.4.1.
Installation of this exhaust requires you cut the exhaust on your car right after where the two pipes join in a “Y” after the header, before the catalytic converter. This exhaust will then clamp on using exhaust clamps. You may weld any of these portions together.
Suspension
The Spec3 suspension setup is Swift springs and Koni yellow strut inserts on an M3 (1996-1999) strut housing modified to take a strut insert. These are paired with Vorshlag camber plates and 96-99 front lower control arms.
There was a spec Eibach sway bar kit that must be used, but it became no longer available in 2021. H&R offers replacement front and rear bars.
The rear suspension is just a Koni yellow shock and a Swift spring.
Basically they make aftermarket shock inserts that allow you to cut your stock M3 struts and pull the factory shock tube out. Then you slide the aftermarket one in and attach it with a bolt through the bottom.
Front Control Arms
BMW part numbers 31-12-2-228-461, 31-12-2-228-462, and 31-12-9-069- 035 from the 1996-99 BMW M3. See Rule 3.8.2.
These are sometimes hard to find. Note that the 96-99 M3 arms are different from the 95 M and 92-99 non-M arms. The M3 arms use a centered bushing while the other arms must use an offset bushing to have the same geometry, and they are not allowed. Pick up a used set of 96-99 M3 arms and press in new ball joints.
You must run the Lemforder E30 M3 ball joints part No. 31121126254. They are heat treated. Other models are not heat treated and prone to breakage. The inner ball joint is Lemforder part No. 31121126253.
Front Struts
You must use BMW part numbers 31-31-2-228-007 and 31-31-2-228-008 from the 1996 – 99 BMW M3 modified with Koni front strut inserts, part number 8641-1342S3. See Rules 9.3.8.4.1 and 9.3.8.4.3. There’s a video on YouTube on how to modify the strut.
Rear Suspension
Stock M3 upper and lower ball joints, part No. 33-32-1-140-345, and stock rear trailing arm bushings, part No. 33-32-6-770-817. Rear trailing-arm bushing shim limiters are highly recommended. See Rule 9.3.8.15. One thing to note is that the non-M cars have a bushing for the rear lower outer control arm connection to the trailing arm. It is legal and recommended to upgrade this to the M3 bearing, which is used on the rear upper outer trailing arm connection.
It is highly recommended you weld in the rear trailing-arm bushing pocket reinforcement plates to prevent failure.
Subframe bushings can be poly, Delrin, or any other non-metallic material but you must also weld in the reinforcement plates if you do that. The inner bushings on the upper and lower control arms are usually fine to leave alone, but not a bad idea to replace if everything is out anyway. It is recommended to replace your diff bushings while you are in there and upgrade to the larger front differential bolt.
Rear Shocks
Koni part number 8240-1115S3. See Rule 9.3.8.3.1. Stock rear shock mounts, part number 33-52-6-754-096. See Rule 9.3.8.12.
Springs
Swift Race Springs, front and rear, part “NASA Spec3.” See Rule 9.3.8.7.1.
Contact RRT Racing in Sterling, Va.
Remember to install all the plastic spring retainers or the springs may fall out.
Wheels
Wheels for wet weather shall be either 15 inches by 7 inches, with a minimum weight of 15.5 pounds. Dry-weather wheels must be 17 inches by no more than 8.5 inches with a minimum weight of 16.5 pounds, and can be any brand, unless otherwise specified in these regulations. All wheels on the vehicle must be of the equivalent size.
The recommended “optimal” size is 17 x 8.5 ET40 with 15mm front spacer and either 15 or 12 in the rear. The Spec3 Facebook page has a guide to wheel spacers.
Tires
Toyo Proxes RR in size 235/40/17 (dry), or 225/50/15 Toyo RA-1 (wet). See Rule 9.3.9.1.
Brakes
Stock non-M calipers and rotors with Hawk DTC-60 front pads, part number NBS3F or HB136G.690, and Hawk DTC-60 rear pads, part number NBS3R or HB227G.630. See Rule 9.3.10.1. These can be found at Andrew-Racing as well. The stock caliper brackets can be upgraded using the same part from a Z3.
Differential
The 3:15:1 ratio limited slip differentials were standard on OBD1 cold-weather package cars. See Rules 9.3.11.1, 9.3.11.2, and Appendix A.
Differential Bushings
May be upgraded with aftermarket bushings, including metallic. See Rule 9.3.11.4.
It is a common mod to drill the front diff bushing and install a larger bolt. E36s are known for snapping the stock size bolt under hard acceleration.
Rear Subframe Bushings
May be upgraded with non-metallic aftermarket bushings. See Rule 9.3.8.9.1.
Reinforcements
Reinforcement of the following components is highly recommended but not required:
Chassis
Rear sway bar pick-up points, front subframe motor mounts, rear lower control arms, rear trailing arm pockets, and rear subframe attachment points, BMW part numbers 41-00-2-256-495, 41-00-2-256-496, 41-11-2-256-497, and 41-11-2-256-498. See Rule 9.3.8.11
Shock Towers
Front shock tower, part number 31-31-2-489-795, and rear shock tower, part number 51-71-8-413-359. See Rule 9.3.8.13
Bracing
Front X-brace, part number 51-71-8-410-212, and any bolt-in front and rear shock tower braces. See Rules 9.3.8.14 and 9.3.8.10
Building Tips
Heater Core Delete
To get down to the class weight, most Spec3 drivers delete their heater core, though it is not required. This has the added benefit of removing hot coolant from the passenger compartment, simplifying the cooling system greatly, and clearing up space under the dash.
A block off plate must be installed on the rear of the head and a heater core firewall block off panel also must be added.
Water Temperature Sensor
In the diagram above, there are three ports on the intake side of the head. The farthest to the rear of the engine is a coolant passage that gets blocked off when doing a heater core delete. This nipple can be removed and replaced with a water temp probe. Most likely, you will need an adapter to thread into the head, which will then accept the water temperature probe.
Kill Switch Wiring
Per the CCR, every race car must have a kill switch. This switch must not only disconnect power from the battery when turned off, but it must also disable the car and turn the engine off. The only exception here are items like electric fire suppression, radios, cool suits, etc. This switch should be placed in a place easily reached while you are strapped in your seat, and also by emergency workers from outside the vehicle. Purchase a high-quality switch because you don’t want this part failing in the middle of a race, or 5 minutes before the flag drops! The photo above shows a common way to hook up a six-pole switch on an E36. A two-or four-pole switch will not work.
Achieving Minimum Weight
The following most likely will need to be done to a prepped car to reach race weight:
- Wire harness thinning.
- Polycarbonate rear side windows. Windscreen and rear glass must remain stock.
- Heater core removal.
- Door gutting.
- Lightweight battery.
- AC and cruise control delete.
- Interior stripping.
- Sound deadening removal.
Sound Deadening Removal
There are two popular options for removing sound deadening. You can heat the sound deadening with a heat gun and scrape it up, then use a solvent to clean up the adhesive. You also can use dry ice to freeze the sound deadening, then chisel it up. This method is much cleaner.
Defrost/Defogging
It is suggested that you install something like the Bimmerworld defrost kit, or install a blower motor to blow air from the transmission tunnel to the windshield to use as a defroster. At any rate, you should invest in some Rain-X defogger spray or dish soap to coat the windshield with.
M3 Control Arms vs Non-M Control Arms
A lot of online vendors will list the non-M part as fitting the M3 and pair it with an offset bushing. This is not the arm you should use for Spec3. The easiest way to tell the arms apart is that the M3 arm has the outer ball joint centered in line with the control arm where the non-M — and 95 M3 — arm has the ball joint offset and this creates a little “dog leg” bend.
Cooling System
The Achilles heel of most BMW engines is the cooling system. Early M5/X engines came with a plastic composite water pump impeller that would come apart and let the engine over heat. These engines do not tolerate high water temps — 260-plus-degrees Fahrenheit — and will quickly warp or crack the head.
It is suggested to upgrade to a performance water pump with a metal impeller such as a Stewart unit, along with a metal thermostat housing and an aluminum radiator such as a CSF or Mishimoto. Some racers elect to run a lower-temperature thermostat as well.
It is imperative that you have at least the factory radiator ducting — top, sides, and undertray — to ensure adequate air flow through the radiator. The next step to upgrade beyond that is an undertray with an integrated radiator baffle, such as the Motion Motorsport unit, or a dedicated radiator duct such as the Kinematic Speed Radiator Duct kit.
Brake Cooling
This topic is up for debate, but the general consensus is that running at least the factory brake ducting is recommended if you are a front runner in the class. The Hawk DTC-60s operate fine and do not fade or drop off unless you are pushing the car 10/10s in a hot summer event. Expect to replace your rotors every three to five events due to cracking. Some racers elect to run dedicated brake ducting systems and results are unclear. Brake pad temperatures will be kept lower, which basically eliminates brake fade, but at the potential cost of cracking rotors more often.
Wheel Studs
It is highly recommended that you convert the wheel lug bolts to wheel studs. Only use a high quality kit such as the race studs from Bimmerworld and replace them every one or two seasons.
Fuel Pumps
With the 25-plus-year-old fuel pump in your car, you may experience fuel starve in long right-hand turns when below a third of a tank. There are a few legal options to remedy this.
Some people have found that simply replacing their pump with a new one allows them to run down below a quarter tank without issue. Your results may vary.
The better option is to run two white-top pumps and plumb the return from the rail into the return on the driver-side pump, then send the feed from the driver side pump to the passenger side return, then have the passenger side feed the fuel rail like normal. The Bimmerworld kit does exactly this.
Oil Pump Nut
The oil pump nut on these engines can get loose when the engine is turned backwards due to a spin on track. This problem is made worse by the lack of a tensioner on the oil pump chain. The slack creates an impacting motion on the sprocket which can work the nut loose. The fix for this is to safety wire the oil pump nut to the sprocket.
Oil Pan Baffle
It is suggested to run a baffled oil pan and also overfill by 1-2 quarts to avoid oil starvation during sustained later Gs.
Engine Harness Diagram
The following is not 100% accurate, but should assist in figuring out what goes where if you did not label them during disassembly
Rear Control Arm Reinforcements
It is recommended that the rear control arms have a reinforcement plate welded on.
Setup and Maintenance
The following are the alignment specs listed on the BimmerForums.
Front
Camber: -3.5 to -4.0 deg per side
Toe: 0 degrees
Rear
Camber: -1.8 to -2.2 deg per side
Toe: 0 to 0.10 total toe in (should be 1/8″ total toe-in)
Brake Pedal Feel
The E36 is known for subpar pedal feel at times. The easiest fix is to bleed your brakes at least every other event and try to keep fresh brake pads on the car. If your pedal feels vague and squishy, it’s likely your pads are worn. Replacing the brake pads will bring back a surprising amount of pedal feel.
A lot of racers also install solid brass caliper bushings to normalize pad wear and reduce the taper of the pad material. These must be cleaned and lubricated every event.
Body Panels
Coupes and convertibles share body panels except for the trunk. Sedans do not share body parts with the coupe or convertible except for the front and rear bumpers. Body panels from 92-99 models will all fit, however, the nose panel and bumper are different on 92-95 and 96-99 models. The E36 318ti is a sedan from the a pillar forward, so hood and fenders will swap to a sedan.
Engine
The general consensus is that a healthy, strong, front-running motor can be had with a simple head rebuild and leaving the bottom end alone. You can mill the head .03 mm before needing a thicker head gasket. If you mill beyond .03 mm, there is a thicker head gasket made by Victor Reinz that will make up the milled material and restore your compression ratio to factory spec. The more you mill without making up the space, the higher your compression ratio will be and your cam timing may eventually be slightly off.
Hot tanking the head, lapping and grinding the valves, and refreshing the Vanos will net a strong motor, assuming the bottom end is fine. E36 engines have been known before to have valve retainers crack and cause a valve to drop due to age or high revs. It is wise to replace all the retainers and springs, but most do not. If you have a noisy engine when hot, it may be worthwhile to replace the lifters as well when you rebuild the head. One thing to note is that BMW upgraded the spring retainers after 1995 to a hardened steel part, so any engine with the original spring retainers will have the weaker pieces and any retainers purchased new will be the stronger versions.
Oil Filter Housing Welch Plug O-Ring
The oil filter housing went through various revisions. Some units have press-fit plugs while others have threaded plugs. If your housing has threading plugs, they use an O-ring to seal and this can start to leak. You can buy replacements on the McMaster Carr website.
Getting Started
Join the Spec3 Facebook group will be a big help in seeking tech advice and help with problems you might encounter during the build. You also should read the full Constructor’s Guide on the NASA Forums. This feature is — believe it or not — and abbreviated version of the full guide.
Excellent!