The E46 BMW 325i, particularly in its Wagon guise, is one of our favorite means of transport. There’s something about the wagon combining performance with utility that makes it fun to drive.

Perhaps the only problem with the M54 2.5L motor was that it always lacked the performance to make it as much fun as it might be. The engine lacks the top-end grunt to make it a real contender on the road, and there wasn’t a BMW 330i Wagon in the US as an alternative. So our goal was to bring this 325i closer to the 235hp E46 330i ZHP, which typically dynoed around 200hp at the wheels.

To achieve this, we decided to see what could be done with a regular 325i and a box of parts. We’d try everything from high-quality lubricants to software, full exhaust, intake and even a supercharger in order to discover what gives the best bang for your hard-earned buck.

Starting with a rare five-speed manual 325i Wagon, we’d run it through the barrage of tests using our Actron 9190 scanner to monitor coolant, ignition timing and intake air temps to ensure consistency throughout each stage.

Vehicle Data

2002 BMW 325i Touring

Engine: M54 2.5-liter inline-six

Transmission: five-speed manual

Mileage: 174500

Dyno: Dynojet 424x

Temp: 64-71°F

Humidity: 32-63%

Test Gear: third

Fuel: 93-octane

Test 1: Baseline

Before we got started, we needed to know where we were starting. So we tested the car on the Dynojet 424x dyno at Modified by KC, our Kansas City center for dyno testing and tuning.

Peak Power: 167.2hp at 6000rpm

Peak Torque: 156.8 lb-ft at 4700rpm

35-95mph dyno acceleration: 6.01sec

6000-6500rpm air-fuel ratio: 12.4-12.2:1

Temperature: 71°F

Humidity: 59%

Test 2: Tune-up

You might be surprised to learn that high quality lubricants can increase power by simply reducing friction. In the past, we typically see 5-8whp and 10 lb-ft peak gains with this “tune-up”, but the wagon had been looked after so the gains were lower. The current owner specifies BMW’s expensive differential fluid (which remains), good synthetic motor oil and iridium plugs.

That said, we picked up a little power with our choice of fluids from Bavarian Autosport and new plugs from sparkplugs.com We definitely recommend a fluid treatment and spark plugs in every vehicle for optimum performance, longevity, and fuel economy.

Parts

  • Lubricants: Liqui Moly Transmission Fluid and 0W-40 synthetic motor oil, Mahle filter, Lubro Moly Engine Flush, Motor Protect
  • Spark plugs: NGK Iridium BKR7EIX
  • Installation time: 2hr
  • MSRP: $225

Peak Wheel Power
167.4hp @ 6000rpm

Peak Wheel Torque
157.8 lb-ft @ 4700rpm

2500-6400rpm Dyno Accel:
5.98sec

6000-6500rpm AFR:
12.5-12.3:1

Max Power Gain
1.5hp @ 6200rpm

Max Torque Gain
2.3 lb-ft @ 3500rpm

Temp:
71˚f

Humidity:
59%

Pros

  • Basic upgrades for most cars
  • Prolonged engine life
  • Easy install

Cons

  • None

Test 3: ECU Flash

The Conforti flash-loader supplied by Turner Motorsport plugs into the OBD2 port in the driver’s-side footwell. The ECU upload is quick and simple.

Back on the dyno we found extra horsepower up top, with the biggest gain from the raised rev limit. Being able to keep the car in gear longer, especially in first and second, produces better acceleration times. A noticeable improvement in throttle response also made the car feel sportier.

Parts

  • Conforti hand-held flash tool
  • Installation time: 10min
  • MSRP: $350

Peak Wheel Power
171.5hp @ 6200rpm

Peak Wheel Torque
160.6 lb-ft @ 4700rpm

2500-6400rpm dyno accel:
5.89sec

6000-7000rpm AFR:
12.3-12.1:1

Max Power Gain
5.4hp @ 6200rpm

Max Torque Gain
11.1 lb-ft @ 2500rpm

Temp:
75˚f

Humidity:
55%

Pros

  • Performance gains
  • Easy install
  • More rpm
  • Better throttle response
Cons
  • None

Test 4: Intake

We love this high-quality carbon fiber air intake but understand not everybody would spend so much, especially on an aging 3 Series. We didn’t expect much of a gain from an intake on the M54 engine but, in order to find out how much power we could get from the motor, we opted for one of the best products available.

The GruppeM intake uses a carbon fiber heat shield that almost encloses the filter to block engine heat, but allows air to be drawn from the front grille. The conical filter itself is a K&N element specially made for the system.

Despite its credentials, we were only able to net 3.7whp. Fortunately, the induction sound above 5000rpm brought a smile to everybody’s face, helping to justify the expense.

The power curve was near identical to the software up to 6400pm, but the dyno acceleration numbers are slightly down. However, the small gains were above 6400rpm where things start to happen.

Parts

  • GruppeM-specific K&N filter, carbon fiber conical heat shield, adapter
  • Installation time: 30min
  • MSRP: $970

Peak Wheel Power
171.6hp @ 6100rpm

Peak Wheel Torque
160.3 lb-ft @ 4700rpm

2500-6400rpm Dyno Accel:
5.94sec

7500-8000rpm AFR:
12.3-12.2:1

Max Power Gain
3.7hp @ 6700rpm

Max Torque Gain
3 lb-ft @ 6700rpm

Temp:
77˚f

Humidity:
59%

Pros

  • Easy install
  • Induction sound

Cons

  • Expensive

Test 5: Exhaust

This full exhaust system from Magnaflow with headers, catalytic converters, X-pipe with resonator and mufflers was a direct replacement for the factory parts.

So whether you’re looking to improve performance or replace rusted parts, this is a good upgrade.

The original header pipes were so crimped, it’s hard to see how gas gets through at all. This made us optimistic for big gains, especially since the stock cats were gone as well.

After our dyno testing, we found about 7whp: not bad, but a little less than expected. Given its price, the exhaust doesn’t offer a big bang for the buck, but again shows the M54 simply doesn’t have much to give.

We also noticed the fuel map was richer by almost a full point. We imagine that fitting software specific to a full exhaust system could lean the mixture, improving power delivery and fuel economy.

As a word of warning, removal of the factory system is hampered by the fat cats that block access to the header bolts, requiring the motor to be lifted slightly.

Fortuantely, the best part is the sound. Give it full throttle and it emits a deep, intoxicating tunes of an inline-six. In fact, after a highway fly-past, the exhaust note is almost intimidating. Yet it’s refined when cruising, and the tips are a subtle improvement over stock.

Lastly, it should be noted there was a 39 lb weight loss over the factory exhaust.

Parts

  • Magnaflow headers, catalytic converters, X-pipe with resonator, mufflers
  • Installation time: 6hr
  • MSRP: $2200

Peak Wheel Power
174.9hp @ 6100rpm

Peak Wheel Torque
162.2 lb-ft @ 4800rpm

2500-6400rpm Dyno Accel:
5.84sec

7500-8000rpm AFR:
11.4:1

Max Power Gain
6hp @ 3100rpm

Max Torque Gain
10.1 lb-ft @ 3100rpm

Temp:
77˚f

Humidity:
63%

Pros

  • Good fit, sound
  • Throttle response
  • No resonance

Cons

  • Expensive
  • Stock cats tough to remove
  • May effect emissions legality

Test 6: Supercharger

Before installing the G-Power SK Basic supercharger kit, the GruppeM intake and Conforti software were removed.

We did test the kit with the Conforti tune but the ignition timing was too much for the boost, causing knock with our 93-octane.

With the stock software, the car gave its best performance. But as is common with centrifugal superchargers, there was a 12 lb-ft parasitic loss from pulley drag below 3000rpm. You’d only feel it pulling away, at light cruising, or when towing.

If there is anything to deter you from this kit, it’s the installation. It’s not a DIY kit for the average wrencher, and should only be attempted by a qualified professional. Even then it can take around 16 hours to complete. Part of the problem is removing the intake manifold, which is a real pain and we had to rely on Modified by KC to complete.

Other than that, you’ll enjoy the extra 50whp on tap (that includes the full Magnaflow exhaust and tune-up lubricants, plugs, etc). And if that weren’t enough, while the intake noise was gone, a turbo-like whistle from the ASA blower replaced it, making you repeatedly dip into part-throttle to hear it. The high-speed impeller was also responsible for the unusually fat torque curve.

Since there was no intercooler, we monitored intake temps on the dyno but only saw about 20˚ over stock, thanks to the relatively low 4.8psi boost pressure.

G-Power also offers an “RS” kit with a CNC intake manifold, intercooling and more boost that releases about 20whp.

Parts

  • G-Power SK Basic kit with ASA supercharger, brackets and mounting hardware
  • Installation time: 16hrs
  • MSRP: $3300

Peak Wheel Power
224.3hp @ 6300rpm

Peak Wheel Torque
190 lb-ft @ 5400rpm

2500-6400rpm Dyno Accel:
5.11sec

7500-8000rpm AFR:
13.3-13.4:1

Max Power Gain
50.9hp @ 6370rpm

Max Torque Gain
44.7 lb-ft @ 6350rpm

Temp:
69˚f

Humidity:
62%

Pros

  • Good fit, sound
  • Value
  • No software needed

Cons

  • Fitting time
  • Low-end power loss

Conclusion

The normally aspirated upgrades we fitted gained a total of 10whp at 6400rpm and 14 lb-ft at 2800rpm. This was noticeable on the road but unspectacular.

Of course, the gains compare to the stock rev limiter, negating the comparison above 6400rpm, where we found an extra 4whp with the intake alone.

Also, custom software should counteract the rich mixture from the exhaust, gaining more power.

As it stood, with its intake and exhaust noise, improved response, more rpm and extra grunt, the car was more fun to drive but it cost a few grand to get there.

For similar money (but higher install costs), the G-Power SK Basic kit produced five times more power when combined with the Magnaflow exhaust – its low-end response negating the supercharger’s parasitic losses.

When compared to stock, the supercharger and full exhaust contributed 59whp at 6350rpm and 49 lb-ft of torque.

The SK Basic kit added to the fun factor and surpassed our 330i performance goals.

Thankfully, the clutch is holding up and the 325i Touring is gobs more fun. It’s become a sleeper, especially when the car catapults forward from 4000rpm.

SOURCE
GruppeM USA
8120 Monticello Ave
Skokie
IL  60076
888-360-5590
www.gruppemusa.com
MagnaFlow Exhaust
www.magnaflow.com
G-Power
230 Northgate St. #810
Lake Forest
IL  60045
888-360-5590
www.hpmx.com
Bavarian Autosport
275 Constitution Ave.
Portsmouth
NH  03801
800-535-2002
www.bavauto.com
Bridgestone
535 Marriott Drive
Nashville
TN  37214
615-937-1000
www.bridgestone.com
Actron
15825 Industrial Pkwy.
Cleveland
OH  44135
800-228-7667
www.actron.com
TSW
14462 Astronautics Lane
Huntington Beach
CA  92651
800-479-9723
www.tsw.com
Sparkplugs.com (Monarch Products)
30500 Garbani Rd.
Menifee
CA  92584
951-672-8501
www.sparkplugs.com
Turner Motorsport (TMS)
Amesbury
MA
www.turnermotorsport.com
Modified By KC
6138 Merriam Drive
Merriam
KS  66203
913-432-8468
mkcperformance.com
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