By: Haitham Alhumsi
I’m going to talk about my own car for a bit here… I’ve been in the performance scene for a long time and have helped a lot of people fix, repair and build up their cars from being a stock neglected and abused second hand car into being a gem of a dual purpose daily driver and weekend racer.
One of the things that I’ve learned through experience, is that unless you have the ultimate in tenability on your car, with a control system that is able to compensate for barometric changes, varying load conditions, rapid temperature swings…etc then it is best to get a car that is very close in stock form to your desired power levels and use the minimal number of power modifications required to reach your ultimate power goals.
This path of 20/80 *using the 20% of the modifications that will give you 80% of the results* usually leaves you with a very reliable car, with proven power potential; a car that you don’t need to give your mother a pre-race briefing on how to drive it before she borrows it to go to the grocery store, and a car that you will never be reluctant to take on a long weekend road trip out of town. After all, the point of having an enjoyable car is being able to spend as much time enjoying it, rather than working on it and having it break down. This is especially true on a dual purpose car that spends a lot of time serving you in your battle against the daily grind of school, college or work.
So, in looking a car to buy as my daily driver after college back in 2005, I was looking for a car that was already supercharged (taking away the headache of finding a reliable supercharger kit and an intelligent engine management system that I could rely on). I also wanted a car that had potential to be slightly modified to make it more engaging and that had good handling from the get go.
In doing my research I landed on the 2005 Mercedes C200 Kompressor equipped with the M271 engine. The m271 engine is an impressive factory engine equipped with a lot of things that we usually upgrade on factory supercharged cars. The car utilizes a 4th generation Eaton MP45 supercharger utilizing Teflon coated rotors for higher thermal efficiency and an increased maximum RPM range of 16000 rpms and a peak power capability of 240hp or ~360cfm. Even in a low boost package of 4psi on the C180 and 6psi on the C200, the car is still factory equipped with a front mount air to air intercooler to cool the air charge down. On the intake side, the car is equipped with a generously sized air-box with a cold air duct to the front grill.
The engine itself is equipped with dual variable valve timing on the intake and exhaust cam for optimized power delivery, better emissions. The ignition system is factory fortified with a coil over plug setup but with generic Bosch platinum spark plugs.
As far as tuning goes, the car is equipped with an MAS air flow sensor and a MAP pressure sensor, as well as a transmission slip and wheel spin sensor. The combination of all these sensors is that the factory computer can very accurately distinguish between boost pressure and load by comparing actual acceleration with the acceleration demand. This load sensitive ECU also uses dual knock sensors equipped on the block to detect individual cylinder knock. The result of these factors is an ignition timing optimized for each cylinder based on boost / rpm / load and air flow with individual cylinder timing retard to keep as much timing in the engine as possible for peak power delivery, while retarding timing in the offending cylinder to prevent the engine from detonating itself to pieces in case of a bad fill of gas or a clogged injector..etc
Over all the car is an impressive factory package. However, a 1.8 liter engine in a heavy chassis with 10 factory air bags, fully adjustable front seats, xenon lighting, a sunroof, and other heavy Mercedes amenities leaves the car slightly underpowered and requiring modification.
Below is a list of minimal modifications that have proven power potential as follows:
- Carlsson CK20 kit
- Remus 60mm Catback exhaust system
- Ported factory throttle body
Overdrive Pulley Kit
The Carlsson CK20 pulley kit includes a 15% overdrive crank pulley, and a matching undersized waterpump pulley (to allow the larger crank pulley to fit). The whole kit comes with the proper sized pulley belt.
The 15% overdrive increases boost on the C200 from a factory 6.5 psi to 9.68 psi which is a gain of about 3psi of boost.
In addition the kit includes a cotton gauze high flow air filter that replaces the factory paper cone air filter. The rest of the intake ducting on the car is fairly adequate for power delivery, for example the factory filter has a 3” base that connects to a generously sized 3” MAS housing. This is definitely more than adequate for a 200 hp car as we will see later on.
The second modification on this list is a complete catback exhaust system from Remus comprising a 60mm midpipe and axleback to replace the factory exhaust system. On 2005+ cars equipped with a second undercar catalytic converter, the midpipe also eliminates the second cat converter promising another 3 to 5hp of gains on top of the Remus Dyno.
They dynograph resolution makes it slightly difficult to see but we can see about a 3hp gain at 2000 rpms, about 5hp at 4250 and a peak gain of 7 wheel horsepower at 5800 rpms.
Ported Throttle Body
The last modification on our list is a ported factory throttle body which was developed by a community member rather than a known brand like Carlsson or Remus. The factory throttle body has an inner lip that hinders air flow and a very large actuator arm that impedes the airflow. This modification machines away the protruding lip and smoothens the throttle body inlet. The throttle arm is further machined to reduce its profile increasing the overall bore area of the throttle body.
This modification shows great top end gains (above 4500 rpms which is after the computer switches over from a conservative and emissions friendly 14.7:1 air fuel ratio to a more power efficient 12:1 air fuel ratio and advanced timing). The gains are a nice 5hp @5000 rpms and 10hp @ 6200.
A good companion modification for this mod is upgrading the throttle inlet elbow. On my car I used an HKS 60mm elbow and some 60mm silicone hoses. This eliminates the ‘kink’ in the intake system right before the throttle body.
The only modification I would add to this list of my own is a set of 1-step colder iridium spark plugs. You can see here (barely) the factory Bosch platinum plug on the left with the long spark tip and ground strap, vs the 1 step colder iridium spark plug by Greddy NGK with a more recessed tip and shorter ground strap. A note to anyone attempting the install, you need a low profile spark plug socket with a 6” or so extension to be able to reach into the M271 spark plug wells and replace your plugs. Also seen here is the nice coloration of the Bosch factory plug, the base circle is a little black and rich, but overall the ground strap and the porcelain insulator have a tan coloration which shows a good mixture, slightly on the richer side of things. The ground strap also shows conservative factory timing.
Now one thing that is not true about power modifications is that the combination of a 40hp pulley kit with a 7hp exhaust and a 10hp throttle body does not mean that our 163hp car ends up with 220hp because we have to take into account which rpms those power gains were made at…
So I threw all of these numbers into an excel sheet to give you an illustration of what to expect with the final combination of these power adders:
As you can see here our final power output is 215hp @ 6000 rpms rather than 220 hp. As you add more and more mods people similarly tend to overestimate their final power expectations. Adding up your rpm specific power increases based on real world dynos is a better way to get a closer estimate to what the overall power will be and where you will make it.
The combination we have here is very ‘top end’ biased where we only have 17hp worth of gain at 4000 rpms which grows nicely to a 60hp peak gain at redline. Part of this might be the limitation of the factory ECU keeping fuel and timing conservative before 4000 rpms so I think there is more to be gained here with tuning.
Now for how much this affects our acceleration, although we have a peak gain of 32% power, our average gain is much less since the power is very biased towards the top end of the rev range. The average power gain is 22% and so the expected reduction in acceleration times is 1.8 seconds going from a mediocre 9.8 0-60mph to a more friendly 8.0 0-60mph. What’s nicer than these numbers show is that car performs better in passing and highway pulls now with the increased top end and is overall more nimble considering its weight.
The power calculator
Last thing I want to do here is a 3 way compare between what the car was equipped with stock, what we have modified on it, and what the results are from our power calculator software for this application (going from 165hp @ 5500 to 215hp @ 6000 rpms)
|Intake||3” Paper filter with cold air duct||3” high flow air filter with factory cold air duct||70mm (2.75” intake system)||Yes|
|Exhaust||60mm ‘sport package’ cat-back exhaust with second under car cat.||60mm aftermarket exhaust with eliminated 2nd cat, with straight through resonated midpipe and a freer flowing Remus end muffler.||2.28” (57mm) cat-back exhaust system||Yes|
|Throttle body bore||58mm outer diameter||58mm ported||55.5mm (inner diameter)
|Spark plugs||Factory||1 step colder||1 step colder||Yes|
|Boost Pressure||6.5psi||9.4psi||9 psi is estimated as the requirement for producing 215hp @6000 rpms||Yes|
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