M113K Build Guide: Making Real, Repeatable Power in an E55, CLS55, SL55 or S55

The M113K is one of the great bargains in performance. A hand-built 5.4-liter supercharged V8 that made 469 to 510 horsepower from the factory, in a car you can now buy for the price of a used Camry. Here is how to build one properly — what actually makes power, what makes that power repeatable, and where most builds go wrong.

What you are working with

The M113K is a 5.4L three-valve V8 with a screw-type supercharger driven off the crank through an electromagnetic clutch, fed by an air-to-water charge cooler. It went into the E55 (W211), CLS55 (C219), SL55 (R230), S55 (W220), CL55 (C215), and G55 (W463), backed by the 722.6 five-speed automatic.

Two things define this engine as a platform:

1. The bottom end is genuinely strong. Forged crank, solid rods, and a block that tolerates far more boost than it left with. People make serious power on stock internals.
2. The charge cooling system is the bottleneck. Not the heads, not the blower, not the fuel system at first. Heat. We will come back to this because it is the whole ballgame.

Factory boost is modest. There is a lot of room in this supercharger before you are asking it to do anything unreasonable.

The truth nobody tells you first: heat is the enemy

Every M113K owner learns this the same way. You make one pull and the car feels like a rocket. You make a second pull and it is slightly slower. Third pull, slower still. By the fourth you wonder if something broke.

Nothing broke. Your intake air temps climbed, and the ECU pulled timing to protect the engine.

Here is the mechanism. The supercharger compresses air, which heats it. That heat gets dumped into a closed coolant loop that runs to a small heat exchanger up front. On a single pull the system handles it fine. On repeated pulls, the coolant in that loop soaks up heat faster than the little front-mount exchanger can shed it. Charge temps rise, the tune pulls timing to avoid knock, and power falls off a cliff.

This is why two identically modified E55s can trap wildly different numbers. One of them manages heat and one does not. If you take away one thing from this guide, take this: on an M113K, cooling is a power mod. It is not a supporting mod, it is not maintenance, it is the difference between a car that makes 550 whp once and a car that makes 550 whp every single time.

Step one: pulley and tune

The supercharger pulley is the single highest-value modification on this platform. Smaller pulley, faster blower speed, more boost, more power. Combined with a proper tune it is the biggest jump per dollar you will ever make on this car.

Your options, roughly in order of aggressiveness:

• 83mm clutched pulley — the conservative step, and the right call if your factory clutched pulley is failing and you want a fresh unit with a modest bump rather than a big one.
• 76mm clutched pulley — the sweet spot for a street car. Meaningful boost increase, still friendly to the stock supporting hardware, retains the clutch.
• 70mm clutched pulley — aggressive. Do not run this without the supporting mods below, particularly fueling and cooling. This is where the car starts asking for the rest of the build.
• Clutch delete pulley — fixed drive, no electromagnetic clutch to slip or fail. Built for higher-boost setups where clutch slip under load becomes a real problem.

Clutched vs clutch delete — which one

The factory clutch lets the blower disengage at light load, which helps fuel economy and reduces wear. It is also a wear item, and under high boost it can slip — and a slipping clutch means boost you paid for that never reached the engine. If you are building a street car and want to keep factory manners, stay clutched. If you are chasing a number and you want every bit of blower speed reaching the rotors consistently, delete it. There is no wrong answer, just different priorities.

While you are in there: the OEM Nachi supercharger pulley bearing is cheap insurance. It is a known wear item and replacing it during a pulley swap costs you nothing in extra labor.

Belt grip matters more than you think

Small pulleys spin faster and demand more from the belt. Belt slip is invisible — no light, no code — and it silently costs you boost, especially when things get hot. Upgraded idlers improve belt wrap and grip:

• Mini idler pulley — M113K
• 54mm smooth mini idler pulley — M113 / M113K

None of the above means anything without the ECU tune. The stock calibration does not know you changed the pulley and will not take advantage of it. Tune with the hardware, not after you have driven on it for six months.

Step two: let it breathe

The factory intake is restrictive once you are pushing more air. A 3-inch aluminum intake kit opens the inlet side and is a straightforward bolt-on that pairs naturally with a pulley step.

Headers: shorty vs mid-length, and how to actually choose

The factory exhaust manifolds are cast log-style pieces built for packaging and quietness, not flow. Headers are a real gain on this platform — but which style you want depends entirely on what kind of car you are building. This is the question we get most, so here is the straight answer.

Shorty / log-style headers

M113K shorty log-style headers are a direct replacement for the factory manifolds. They keep everything in the stock location, which means:

• Simplest install by a wide margin — least labor, fewest surprises
• Retains factory catalytic converter positioning
• No exhaust fabrication, no sensor relocation headaches
• Solid, honest gains without turning the project into a weekend-eater

Choose shorties if: you are building a clean street car, you want to keep the car emissions-equipment intact, you value install simplicity, or you are running a mild-to-moderate pulley setup where the exhaust is not yet the limiting factor.

Mid-length headers

Mid-length performance headers for E55 / SL55 / CLS55 use longer primary tubes, which improves exhaust scavenging — the exhaust pulses do more work helping to clear the cylinder. In practice that shows up as stronger midrange and top-end pull.

• More power than shorties, particularly higher in the rev range
• More involved install — more time on the lift, tighter clearances
• You will likely want an O2 sensor extension harness, since the sensor location moves further down
• More heat in the engine bay, which loops right back to the heat conversation

Choose mid-lengths if: you have already stepped the pulley and addressed cooling, you are chasing a number, and you are willing to pay for it in install labor.

The honest ranking

On a positive-displacement supercharged engine, exhaust restriction matters — but it matters less than boost and charge temperature. If your budget is limited, spend it in this order: pulley and tune first, cooling second, headers third. Headers on a heat-soaked car just make a heat-soaked car slightly louder.

A note on emissions: keep your factory catalytic converters. Check your local and state requirements before making exhaust changes — rules vary considerably by jurisdiction.

Step three: cooling, or how to make the same power on pull five as pull one

This is the section that separates a fast M113K from a car that is fast once. Work through it in this order.

1. Intercooler circuit pump

The factory pump moves a limited amount of coolant through the charge cooling loop. More flow means more heat carried away from the charge cooler per second. The Bosch 010 high-flow intercooler pump is the standard upgrade on this platform and the best dollar-per-degree improvement available. If you only do one cooling mod, do this one.

The Superflo cooling pump is another option in the same role.

2. More coolant volume and more heat rejection

More fluid in the loop means more thermal mass to absorb heat before temps spike, and more surface area up front means faster heat rejection. Both directly extend how many hard pulls you get before the tune starts pulling timing.

3. Ice tank — the track and drag answer

For consecutive runs, nothing beats dropping the temperature of the coolant itself. The 3.5-liter trunk ice tank with Rule 2000 pump lets you fill with ice and water before a run, which collapses charge temps and gives you consistent, repeatable timing.

This is a purpose-built tool. On a street car it is overkill. At a track day or the drag strip where you are making run after run, it is the single most effective thing on this list.

4. E85

Ethanol has a much higher latent heat of vaporization than gasoline, which means it cools the intake charge as it evaporates — a genuine chemical intercooler. Add its knock resistance and you can run more timing safely. The E85 flex-fuel conversion kit gets you there with a flex sensor so the tune adapts to whatever blend is in the tank.

Be aware E85 requires roughly 30 percent more fuel volume, so plan your injectors and pump accordingly.

Step four: fueling

The factory injectors run out of headroom around the point most pulley-and-tune builds land. Push past that on stock injectors and you go lean, which on a supercharged engine is how expensive things happen.

• 550cc injectors — covers most pulley, intake, headers, and tune builds on pump gas. The sensible step for a strong street car.
• 630cc injectors — for higher boost and for anyone running E85, where the extra volume requirement makes the larger injector mandatory rather than optional.

Do not forget the pump. Injectors can only deliver what the fuel system supplies, and a stock pump becomes the limit on a big build. Confirm your fuel pressure holds under full load before you trust a tune.

Step five: getting the power to the ground

You can build 600 wheel horsepower and still get beaten by a well-sorted car making less, because none of it reaches the pavement.

The transmission

The 722.6 is calibrated from the factory for smoothness, which means soft, unhurried shifts where the clutches slip briefly during the change. Add torque and that slip becomes wear and heat. The fix is a Street Valve Body v2 paired with 722.6 Blue Top shift solenoids — firmer, faster shifts that get the clutches locked instead of slipping. We wrote a separate guide on this because it deserves one.

The differential

The factory differential struggles to put M113K torque down, especially out of a corner or on anything less than perfect pavement. A Wavetrac limited slip differential keeps both rear wheels working instead of lighting one up.

And the boring stuff

More power deserves better stopping. Stainless braided brake lines for the E55 W211 firm up the pedal and are one of the cheapest meaningful upgrades on the car.

Three build recipes

The reliable street car

83mm or 76mm clutched pulley, ECU tune, 3-inch intake, Bosch 010 pump, shorty headers, fresh supercharger pulley bearing, idler upgrade.

Fast, drivable, holds up to daily use, does not demand a rebuild of the supporting systems. This is where most owners should start and many should stop.

The serious street car

76mm or 70mm pulley, tune, mid-length headers, O2 extension harness, 550cc injectors, upgraded intercooler pump plus additional cooling capacity, Street Valve Body v2 and Blue Top solenoids, Wavetrac LSD, braided brake lines.

This is a genuinely quick car that will still start every morning and drive to work.

Max effort

Clutch delete pulley, aggressive tune, mid-length headers, 630cc injectors, E85 flex-fuel conversion, full cooling package including the ice tank for run days, upgraded fuel pump, valve body and solenoids, Wavetrac LSD.

Now the supporting systems are the build, and the engine is along for the ride. That is the correct order.

How to know your build is actually working

Log your data. Specifically: intake air temperature, timing, and fuel trims. If your IATs climb steeply across consecutive pulls and timing gets pulled, you have a cooling problem, not a power problem — and no pulley will fix it. If your trims run lean at the top, you have a fuel delivery problem and you should stop making pulls until it is sorted.

The owners with the fastest, most consistent M113Ks are not the ones with the most parts. They are the ones who fixed the heat.

Building one? Talk to us first

Tell us the car, the goal, and the budget, and we will tell you honestly what order to do things in — including when the answer is that you do not need the part you were about to buy.

Contact BenzUnited Parts about your M113K build →

Always confirm fitment against your VIN before ordering. Power figures vary substantially with fuel quality, ambient conditions, tune, and the condition of the individual engine. Retain factory catalytic converters and verify local and state emissions requirements before making exhaust modifications.