a few things about the factory MB V12 M120 engine- they are totally choked with emissions, and ASR traction control ! I've been tweaking a '94 coupe for nearly 3 years....let me share this: pull the ASR module, tape off the 4 or 5 pins controlling the ASR, then you will get full power of the engine to the tires. otherwise the anti-slip regulation limits power to about 1/2 of rear wheel HP the engine actually has. 400HP becomes 200HP. pull the block the dual EGR valves, disable the air pump, delete the cat converters, and delete the muffler. let the resonator in place, it will act as a somewhat louder muffler, actually ends up sounding quite good. not too loud, just right. obtain (2) mass airflow sensors MAF's from 300SL/320SL 6-cylinder cars. they are identical but slightly richer. the V12 MAF's are tuned to 13.9/14:1 a/f ratio. the 6-cyl MAF's will idle at 13.5-13.6 a/f ratio. it gives a richer idle to start from, and richer across the rpm band. obtain 1991-1992 EURO spec LH modules, and EGAS module. they are richer, have a high top end speed limiter, and higher rev limiter. by Euro spec I mean cars sold in Europe. they have a different part number. put (2) K&N air filters in the factory airboxes. they are worth about 120cfm each more flow per K&N testing. (their numbers, not mine). RETAIN the factory ram air snorkels through the front radiator support, for cold air/ram induction ! scan the system, replace any defective MAF, IAT, O2, CAM, CRANK, etc. sensors on engine, there are 2 of each. I also had to change both ignition coils on my car. 1996-up has 8 coils, coil on plug. they are known to go bad. scan the car, look at burn time, if it's high, replace them. if your car has dual distributors, replace both caps/rotors. mine were SHOT. the gaps between cap/rotor are critical ! use only factory MB caps/rotors- the aftermarket ones have wider gaps, and run like a worn out cap/rotor ! only use PREMIUM fuel. 93 octane minimum. pull the round resistors out of both ignition modules, located on inner fenders. that will give maximum spark advance. don't worry the knock sensors will eliminate any spark knock. use 10-30 synthetic oil, less friction, more HP, better protection, runs cooler. check the car for bad wiring- these are known to have biodegradable harnesses to MAF's that deteriorate prematurely, I had to rewire mine. get an AGM or Gel battery for trunk ! regular acid wash batteries create a lot of hydrogen/acid gas fumes ! group 49 at Rock Auto $180 shipped to your door with discount code. change the idler pulley, and tensioner pulley- they seize and take out the drive belt ! these cars accelerate better from the first kickdown point in the gas pedal, rather than all the way down into downshift mode at the second kickdown point in gas pedal, when it hits the downshift switch, if so equipped. the second detent keeps the car in lower gears 1-2 too long and is detrimental to acceleration. do NOT remove the factory airboxes ! I tried 2 K&N open element cone filters, they will flow more air at idle/part throttle, driving the a/f mixture and Lambda duty cycle higher to enrich the mixture, and give somewhat better part throttle response around town, but above 50-60mph, they are inferior to the factory airboxes- the latter is a resonant pressure wave box with insulated interior, and is far superior for power above 60MPH. some have reported as much as a 10% HP loss at higher rpm when removing the airboxes ! keep the factory intake runner setup. it's been carefully designed to match the pulses of the crossram intake, cylinder heads for pressure wave utilization at a specific rpm range, matching the camshaft design. if you remove the airboxes, you lose intake runner volume, and the tuned ram effect/cold air induction, keep in mind the entire intake tract from inlet snorkel, to back of intake valves, is one long velocity stack and port at WOT, only it's laying down horizontally. a lot of money, time, manpower, hours, expertise went into designing it- let it there. make sure the engine temp sensors at front of waterneck/thermostat housing, are all working properly. there are many of them ! I changed them all. also had to change both fuel pumps, filter, they were shot. (no fuel pressure when I got car). and changed regulator for good measure. GOOD LUCK ! let me know how you make out with that car !
a few things about the factory MB V12 M120 engine- they are totally choked with emissions, and ASR traction control ! I've been tweaking a '94 coupe for nearly 3 years....let me share this:
pull the ASR module, tape off the 4 or 5 pins controlling the ASR, then you will get full power of the engine to the tires. otherwise the anti-slip regulation limits power to about 1/2 of rear wheel HP the engine actually has. 400HP becomes 200HP.
pull the block the dual EGR valves, disable the air pump, delete the cat converters, and delete the muffler. let the resonator in place, it will act as a somewhat louder muffler, actually ends up sounding quite good. not too loud, just right. obtain (2) mass airflow sensors MAF's from 300SL/320SL 6-cylinder cars. they are identical but slightly richer. the V12 MAF's are tuned to 13.9/14:1 a/f ratio. the 6-cyl MAF's will idle at 13.5-13.6 a/f ratio. it gives a richer idle to start from, and richer across the rpm band.
obtain 1991-1992 EURO spec LH modules, and EGAS module. they are richer, have a high top end speed limiter, and higher rev limiter. by Euro spec I mean cars sold in Europe. they have a different part number.
put (2) K&N air filters in the factory airboxes. they are worth about 120cfm each more flow per K&N testing. (their numbers, not mine). RETAIN the factory ram air snorkels through the front radiator support, for cold air/ram induction ! scan the system, replace any defective MAF, IAT, O2, CAM, CRANK, etc. sensors on engine, there are 2 of each. I also had to change both ignition coils on my car. 1996-up has 8 coils, coil on plug. they are known to go bad. scan the car, look at burn time, if it's high, replace them. if your car has dual distributors, replace both caps/rotors. mine were SHOT. the gaps between cap/rotor are critical ! use only factory MB caps/rotors- the aftermarket ones have wider gaps, and run like a worn out cap/rotor !
only use PREMIUM fuel. 93 octane minimum.
pull the round resistors out of both ignition modules, located on inner fenders. that will give maximum spark advance. don't worry the knock sensors will eliminate any spark knock.
use 10-30 synthetic oil, less friction, more HP, better protection, runs cooler.
check the car for bad wiring- these are known to have biodegradable harnesses to MAF's that deteriorate prematurely, I had to rewire mine.
get an AGM or Gel battery for trunk ! regular acid wash batteries create a lot of hydrogen/acid gas fumes ! group 49 at Rock Auto $180 shipped to your door with discount code.
change the idler pulley, and tensioner pulley- they seize and take out the drive belt !
these cars accelerate better from the first kickdown point in the gas pedal, rather than all the way down into downshift mode at the second kickdown point in gas pedal, when it hits the downshift switch, if so equipped. the second detent keeps the car in lower gears 1-2 too long and is detrimental to acceleration.
do NOT remove the factory airboxes ! I tried 2 K&N open element cone filters, they will flow more air at idle/part throttle, driving the a/f mixture and Lambda duty cycle higher to enrich the mixture, and give somewhat better part throttle response around town, but above 50-60mph, they are inferior to the factory airboxes- the latter is a resonant pressure wave box with insulated interior, and is far superior for power above 60MPH. some have reported as much as a 10% HP loss at higher rpm when removing the airboxes ! keep the factory intake runner setup. it's been carefully designed to match the pulses of the crossram intake, cylinder heads for pressure wave utilization at a specific rpm range, matching the camshaft design. if you remove the airboxes, you lose intake runner volume, and the tuned ram effect/cold air induction, keep in mind the entire intake tract from inlet snorkel, to back of intake valves, is one long velocity stack and port at WOT, only it's laying down horizontally. a lot of money, time, manpower, hours, expertise went into designing it- let it there.
make sure the engine temp sensors at front of waterneck/thermostat housing, are all working properly. there are many of them ! I changed them all. also had to change both fuel pumps, filter, they were shot. (no fuel pressure when I got car). and changed regulator for good measure. GOOD LUCK ! let me know how you make out with that car !