Mill's Perrfomance Guide

This page tries to summarize the possibilities of performance mods for BMW M50/52 S50/52 engines (most of it also applies to any other fuel injection engine).

Mod	effect	comment / description	Price / Supplier	Rating	hp gain	link
Replacement air filter	Better air flow	cheap, minor effect, filter doesn't have to be replaced anymore	30-40$ (K&N)	**	1-2	af1
air filter /air box C A I (cold air intake)	Better air flow	Better than replacement filter, more throaty and aggressive sound, heat shield recommended, at some places not street legal (too loud)	80$ (K&N)	***	~3	af2 af3
intake manifold	Better air flow	only for the restricted M52 engines recommended, M50 engines already have a very good flowing intake manifold	? $Schrick	**	~8 (m52)	im1
Individual throttle system	Better air flow	as in BMW M-cars (M1, M5, M3 E30/ E36euro), claims 30 hp increase over stock	3000 $ (Bekkers, Axiom)	****	20-30	itb1 itb2
Wider diameter throttle body	Better air flow			*	0-3
Bigger air mass/flow meter (HFM, heat film meter)	Better air flow		500$ Dinan	*	0-5
Head work	Better air flow	enlarge intake openings, polish ports	expensive	**	5-10
Turbo charger	Forced induction, more air	Kinetic energy of the exhaust drives a compressor, which deliveres fresh air to the motor. Normally combined with an intercooler, which cools down the compressed and warm air. Cold air is important to avoid engine knocking with hi-compression engines. Boosts from low rpm range to the red line. Normally compression has to be decreased in order to compensate for the extra pressure coming from the turbo. Expensive, bur effective!	From 6000$ up (Active autoworks)	*****	depends on boost, up to +150 hp	tc1
Super charger or compressor	Forced induction, more air	similar to a turbo charger, but the turbine is driven by the engines crank shaft. Boost is proportional to engine rpm. Boosts from about 4000 rpm to red line. Less effective than turbo, but also less expensive	Dinan, Turner, ERT, G-Power	****	depends on boost, up to +100 hp	sc1 sc2
Aftermarket muffler	Free flow exhaust	Improves sound & look, minor hp gain (0-5 hp), Stock M3 muffler is very well flowing (but heavy) and '95 model bolts directly on 325's	SuperSprint. Remus, Sebring, BMW M3, Borla	*	0-8	xh1 xh2
headers	Free flow exhaust	Good hp increase (10-15 hp)	800$ SuperSprint	***	~10
Remove ör bypass cat	Free flow exhaust	Adds 5 hp, not street legal	SuperSprint	*	~5
Performance chip	injection	increases torque and horsepower by changing the injection timing maps. This is probably the most cost effective mod. Up to 10% performance increse for about 300 $, if you have already mods like cold air intake, cams etc. you need a custom chip which is optimized for your setup	250-400$ Jim C, Dinan, Active Autowerks, Superchips, Racing Dynamic	****	5-15	ch1 ch2
Larger injectors	injection	if the stock injector reach their maximum mass injection rate, then a replacement with larger injectors may make sense. This normally the case if a super charger or turbo is installed.	TMS	*	?
Cams	Valve timing	timing of inlet and outlet valves can be changed by installing different cams, 10-15 hp increase possible, stiffer springs necessary for higher redline	Schrick or M3 cams	***	10-15	cm1
Head work	Higher compression	Higher compression leads to higher temperature and pressure during combustion and this will produce more power.		**
Flywheel	Reduce dynamic mass	quicker throttle response of your engine, improves acceleration		*	-.-
Racing pistons	Reduce dynamic mass, higher compression	quicker throttle response of your engine, improves acceleration, most often combined with larger bore or higher compression	Mahle, (Alpina)	***	hp gains with higher redline or higher compression
Light weight rods	Reduce dynamic mass			*
Exchange motor	Bigger displacement	325 to 328, M3 3.0, M3 3.2, Alpina … 328 to M3 3.0, M3 3.2, Alpina, BMW 535 (6-cyl) engine M3 to 3.5 Hartge	Big $$$! Hartge, Alpina, ACScnitzer, BMW, Bekker, Axiom	*****	depends on motor
Engine conversion	Bigger displacement	Exchange crankshaft will give you more stroke (325 w/ 325 tds or 328 crankshaft) larger bore stroker	BMW Hartge	****	depends on motor
Lower car	Better aerodynamics, better handling	Exchange springs with stiffer ones, looks good (especially with big rims) and improves handling	700$, Eibach, H&R	**	may increase top speed, no hp gains
Aerodynamic parts	Better aerodynamics	M3-mirrors (minor effect), looks good	500$, BMW, ACSchnitzer, Hamann...	*	-.-
Front spoiler	Better stability @ hi speed	increase pressure on front wheels for improved top speed stability, looks good	400$ .	*	-.-
Rear wing	Better stability @ hi speed, cornering	increase pressure on rear wheels for improved high speed cornering, big rear wings are not everybody'd taste		*	-.-
Underdrive pulley	Reduce parasitic power losses	Reduces power losses coming from A/C, power steering etc.	ERT	**	5-10

* minor or no improvement, do it if you race or if you have too much money or if you interested in the side effects (better looks, sound or handling)

*** "you can feel the difference" improvement, if your budget allows it, then do it

stage 1: install K&N air filter or cone w/ heat shield, performance chip and if you like the sound and looks add a aftermarket exhaust (DTM tips look awesome)

stage 2: lower your car, buy 17" rims with good tires, do all the fast looking goodies you like or if your car already looks good go to stage 3

stage 3: now your car probably looks faster than it is, so it's time for the real mods:

buy a turbo kit or a euro M3-engine (321 hp), if you can afford it and join the out-of-competition bimmer dudes club and laugh at all those people fiddling around with wanna-be mods.

you don't have the $$$ for a turbo and have to do all the small steps: get the headers, get the cams ...,get the crank shaft, get the individual throttle kit and turn your car into a "M-car", do some decent head work, with all these mods it should be possible to get 240-260 hp out of a M50TU engine and you probably spent more money than it costed to buy a M3, but it was fun ;-)). And to be honest, if you had the M3 with 321 hp, you would bolt on all the mods anyway...so what the heck.

Feel free to send me your comments, additions and other modification possibilties