For those of you that own any type of car that operates off of the M52B25 2.5L Flat6 engine...
The first and foremost upgrade
you should perform before anything else is the intake system. A highly restrictive dual-layer cotton box filtration setup is configured with an already moderately restrictive intake runner manifold. Replace the stock system with either a high-brand Dinan or similar make, or create your own. Because there isn\'t much room to get a pipe down under to the wheel-well area, creating a true cold air intake may prove challenging. Therefore, the easiest route would be to purchase or create a heatshield, as the stock system sucks air from a pocket near the front of the engine bay, which brings in cooler air from the front, especially when travelling at high speeds. What\'s important about the intake system is not so much how many horses you\'re going to gain, but rather the free-ability of air movement on the intake side. I\'ve noticed on many 323\'s/325\'s, that with the stock intake system, the car has terrible throttle response, and the car struggles to reach redline, even in first gear...The second upgrade
(and considered the most effective for the 323i/323iS models) would be the upgrade of the exhaust system. The 325-type models & above all came with a dual pipe system that offered moderate exhaust flow, but left good room for improvement. The 323 models operated off the same 2.5L Flat6 engine, but utilized a single midpipe section, which created enormous restrictions in the exhaust. The muffler and cat converter were also compacted with more material to offer more sound-deadening, to those who liked extremely quiet driving experiences. Therefore, first, replace the midpipe with one off of an M3 of the same body-type, get a high performance aftermarket part, or create your own. Some people go as far as taking off the entire exhaust system after the headers, and they create their own true dual exhaust piping, and the whole works. The M52B25 is rated at somewhere around 175 bhp average, and is capable of producing much much more. The 323\'s, because of their extremely restrictive exhaust system, are rated at 168 bhp, and by upgrading at least the midpipe section, you\'re supposed to gain almost 20 hp to the wheels (ontop of the intake system).
By now, you\'re probably sitting right about 180 to 195 bhp, and you\'re car is getting to where it should\'ve been out of the factory. But now, because these basic mods give you only small gains, its time to get into a bit more serious talk...The third mod
you should think about doing is replacing the intake runner manifold with one off of an M50 S52 engine (Euro or E36 M3, engine code M50). The intake manifold runners are larger, and the entire matchup to the intake ports to the engine flow much better. This mod increases top end power dramatically. In my own car, the feeling is like a turbocharger boosting @ 8psi... it kicks in right around 4000 RPM, and throws your car to redline extremely fast. Rumors have it that you lose a bit of low-end torque, but to me, I don\'t notice any loss (in fact, I notice some increase). To take off this manifold, you\'re going to need a standard set of metric wrenches or a wrench kit. Don\'t forget to grab a spare intake manifold gasket just in case (its good practice to replace the old one with a new one anyway, you don\'t want a siezed engine).
Fourth, you should think about replacing those stock headers. Now this mod takes some extensive work. I would recommend you get yourself a pair of rhino ramps if you want to get this done the easiest and cheapest way. If you have a service pit or hydraulic lift, ignore me completely!
Once you get the ramps, simply get your vehicle\'s front wheels up on them, and make sure to use wheel stops on the back two. Get underneath the car, and you\'ll see the headers, with a crossmember in the way, along with many hoses and various pieces of car equipment. The idea here is to take off your midpipe, and move that out of the way, and then take off the header screws that attach to the block. Don\'t take out the screws one by one, but rather loosen each one, and keep them in, until all of them are loose. Once they are loose, take each one out one by one.. you\'re going to have to use a lot of tugging to get these manifolds off, the gaskets have basically welded themselves to the block from engine heat, to keep from leaking. I find it best to take a small crowbar or thick flathead and pry the header in all locations, slowly, until it pops off. The loosened screws will help prevent a header landing on your face while you do this, by holding the header up there just long enough to get it outta there!
I recommend purchasing professionally-crafted true length headers, they add 15 to 25 horses after proper fitment and break-in. As with all major parts, make sure to attach new exhaust gaskets when you put on the new headers!
Now we\'re gunna get into the infamous underdrive pulley upgrade
... tons and tons of off-brand and eBay powerseller companies claim to sell excellent underdrive pulley systems for the M52B25 engine. I\'ve seen some do decent, but some of them have caused disastrous problems. First and formost, some cranks made by these off-branders are lightweight, but cheap, aluminum grade material. They rust and crack EASILY. Once they crack, because these pulleys move at such high RPM, and lots of pressure is being put forth onto them, they will snap off, causing permanent engine damage if in use. Furthermore, the kit come with underdriving the actual crank, which is NOT recommended for this particular engine. It puts too much stress on the crank, and again, can cause permanent engine damage. Purchase these definitely from a reputable company. I believe Dinan Sports creates a package specifically for the 2.5L version..
At this point, it should be okay for you to get into more serious internal work. Purchase the Chilton repair & service manual for your particular car\'s make and year, and go to the crankshaft section. Yes, this is all about taking off the engine\'s cover, and ripping out that crank!! The M52B25 is basically a destroked version of the 2.8L Flat6 of the same make
(E36, respectively)... if you take out your 2.5L crank and swap it from the M52B28 engine, you\'re car will displace at 2.8L respectively. I can\'t go into details for this, because writing up a crankshaft change can get pretty crazy! Therefore, read the Chilton manual, it should provide the information you need!
Lastly, suspension is a major thing about the E36 chassis especially, and upgrading a few things will help put down that hard-earned horsepower to the wheels, and ultimately to the ground, helping your car propel itself to faster speeds.
Make sure to purchase sturdy strut bars for your front strut towers, and the rear
. Also, you may want to purchase the X-bar which is contained in many Z roadsters and convertibles, which attaches to the underside of the engine bay, and helps increase grip and handling, especially at turns and corners.
If you are serious about suspension, purchase Eibach springs and bushings performance kit, and of course, brembo big brakes and calipers
, to help your car stop faster, and prepare to do some dieting. Take out the two rear seats (if you own the coupe version, or if you don\'t care about losing two awesome back seats in a sedan), and hollow out the backside. You can line it with foam, carpeting, or make your custom stereo/subwoofer box setup in the back, add a crazy LCD panel to map your air/fuel and your spark timings, etc., but I would insert a rollcage
back there. Not only are you going to lose ~100 lbs of weight, but you\'ll gain extreme sturdiness with the rollcage.
Flop on an LSD from an M3
of similar body style and hopefully, year, and you\'ll have a naturally-aspirated M52B25 that will rip through gears to 100mph in very fast times. Beating out any of the newer mustangs that have light to moderate modifications shouldn\'t be a problem... camaros of the same situation, not too much either. They may get you off the line, because of their massive torque buildup at low-end, and their gear timing, but once you grab a hold of 2nd and 3rd gear, you should pass them, or make an extreme comeback!
I\'ve gotten all these mods done on a 1998 E36 323, plus had taken out the air condition, air bag system, and climate control/radio instruments, and had a 12 second 0-60 time, which is really nice for an N/A...
I\'ll post up a thread later about how to add a forced induction system with relatively little difficulty, as compared to installing an FI kit. Should be good times, any questions, strongly welcome!
edited on 7/27/2008 8:46:11 PM