ROAD TEST: MBE 4000 ENGINE
Add another color to the rainbow. We’ve already got red ones, yellow ones, and blue, green, and black ones – now, add silver to the mix. The Mercedes-Benz MBE 4000 is here and it’s here to stay. Launched at the Mid-America Trucking Show in March 2000 and first delivered in November of that year, it was developed specifically for Freightliner but has a rather European personality. It's part of the Detroit Diesel family.The MBE 4000 got a bit of a leg up on the market at its introduction as it didn’t have to comply with the EPA’s October 2002 emissions deadline. According to the so-called ‘consent decree’ in 1998, domestic engine makers reluctantly agreed to push the ’04 emissions requirements ahead 14 months. They had to have ’04- compliant engines on the street by October 2002, but since the MBE 4000 wasn’t here in 1998, it wasn’t included in the agreement, meaning it didn’t have to comply until January 2004.
That gave DaimlerChrysler (parent company to both Freightliner and Mercedes-Benz) a significant financial advantage over North American engine makers – around $8000 per engine, in fact. That price break, coupled with the uncertainty surrounding the introduction of the first EGR models, drove the first sales.
Strike while the iron is hot, they say, and strike is what Freightliner did. In early 2003, J.B. Hunt placed a 2100-truck order with Freightliner, and a large chunk of the deal included MBE 4000 power.
Say what you want about how the engine made it to our shores, it’s a solid performer, and destined to become as much a player in the North American market as the traditional brands. And even with the price spread all but eliminated, the MBE 4000 really holds its own in the 12.8-liter category.
In Canadian terms, ratings of 350 to 450 hp may seem a little light, but given how much of our market serves customers in the lower 48, it’s a shoe-in. Even in the heavier tridem class, a 450-hp power plant isn’t out of the question. But a B-train or a quad? Better leave those to the MBE 4000’s bigger brother, the Detroit Diesel Series 60. The lower-output 350- to 410-hp engines are better suited for vocational applications like single dumps and mixers, utility trucks, etc.
And if you’re worried that the smaller, lighter block can’t handle the hills, my recent trip on B.C.’s Highway 3 from Abbotsford to Castlegar proves it’s up to a Canadian challenge. Up and down the hills, the MBE 4000 got the job done, and at a respectable 6.95 mpg, it’s hard to find something to complain about.
The Nuts and Bolts
This engine has several things going for it. It’s an in-line six with a 12.8-liter displacement, tipping the scales (dry) at 2117 lb — 153 lb lighter than its 12.5-liter yellow rival – and 360 lb lighter than the heaviest of the 12-liter blocks. While the yellow one can squeeze out an additional 75 hp and 200 lb ft of torque, the MBE 4000 produces up to 600 hp worth of whoa power with its optional turbobrake – and that really counts in the hills.
It’s got six individual cylinder heads with four valves per cylinder grouped around a centrally located six-hole injector tip. The engine’s individually controlled unit injectors are managed by one of two electronic control units – the other handles all the other engine monitoring and control functions. The net result, Detroit Diesel
says, is better control of the injection event, better engine aspiration, and better fuel economy.
It’s got a high compression ratio of 17.75:1, making cold starts a snap. As mentioned, 2004 meant the MBE 4000 had to be EPA-compliant. It uses a cooled EGR system, controlled by a mechanically simple reed-valve arrangement in the EGR loop and a modulated EGR valve. As well, engineers have isolated the intake manifold from the head and the block to reduce noise, while a specially designed gear-driven oil pump and air compressor contribute to the quiet operation of the engine.
But the really interesting element of the MBE 4000 is its retarding capability. Standard equipment on an MBE 4000 engine includes a constant-throttle-valve compression brake and an exhaust brake. The constant throttle valve is a
hydraulically activated, dedicated fifth valve in the cylinder head that opens at the top of the compression stroke, venting the compressed air into the exhaust manifold prior to the downstroke. Unlike the Jacobs compression brake, the MBE 4000 does not use the exhaust valves – just the constant throttle valve.
The exhaust brake is a flap valve located in the exhaust pipe immediately downstream of the turbo outlet. When closed, it creates backpressure in the engine, contributing to the braking effort. These two work in tandem, generating 433 braking horsepower. But here’s where it gets interesting. Add the MBE 4000-exclusive optional turbobrake, and this 450-hp engine produces a whopping 600 braking horsepower, giving drivers an unheard of degree of control on long grades from an engine of this displacement.
The turbobrake uses a sliding ring inside the turbocharger (not at all the same principal as the Cummins/Holset variable-geometry turbocharger) to redirect the full exhaust flow against the turbine blades, increasing the turbo speed and air mass flow on the intake side of the turbo. This jams a lot more air into the cylinder during the intake stroke than normal, dramatically increasing the effectiveness of the compression braking effect. The exhaust brake is disabled when the turbobrake is in operation.
When the turbobrake is operating, intake manifold pressure increases dramatically, and drivers will notice the engine temperature rising to fan-on level. MBE 4000 product engineer Steffan Maier says this is simply the heat generated by compressing great volumes of air.
“In effect, we’re turning kinetic energy, created by the motion of the truck, into heat energy by using the truck’s momentum to drive the big air compressor that doubles as an engine,” he says.
And as a significant aside, the turbobrake is virtually silent. All you hear is a whistle, meaning you can use it with impunity in areas that prohibit the use of engine brakes due to noise restrictions. Maybe they should build an engine-brake sound-effect generator into the truck’s stereo system so you’ll know it’s on.
The Seat of the Pants
Dealers report many positive responses from drivers, and my 1300-km trip has me agreeing with them. The best way to describe the MBE 4000 is that it feels like a bigger engine than it is. Output of 450 hp and 1550 lb ft of torque are nothing to sneeze at, nor is it spectacular by today’s standards. But nearly seven miles per gallon through the Rockies definitely is. The secret is in the power curves.
When I said earlier that this engine has a European personality, I was referring to the power curves. Most North American engines used to have a torque curve with
a pronounced peak, somewhere close to 1100 or 1200 rpm. That's changing, but it means as you let the engine speed drift down in a pull, you’re getting progressively more pulling power thanks to the torque output. You can feel the difference between say, 1600 rpm and 1200. There’s more grunt the lower you go, so you sense the torque output of the engine increasing. That’s fine.
The MBE 4000, on the other hand, has a very flat torque curve. It’s producing 1550 lb ft of torque from 1400 rpm right down to 1000 rpm. From the drivers seat, it feels like there’s more power under the pedal, and since North Americans prefer to think in terms of horsepower, the impression is that there’s more horses under the hood because you don’t feel the output of the engine changing as the engine speed drops.
Going up through the gears from a start, the impression is similar. It reaches peak torque at 1000 rpm, making for some solid feeling acceleration after a gear change. As long as you keep the rpm between 1000 and 1400, you’re right smack dab in the sweet spot of the power band. Clearly it’s more than a spot, and that range where the engine pulls the best also happens to be where the best fuel economy is. Win, win.
And that’s the way many European engines are set up. Their speed is limited to 90 km/h over there, or even less, so they want pulling power at that speed and some in reserve for the hills. You’d hardly notice a modest freeway type hill in this country because the full engine output is there as you hit the hill, and it stays with you as long as you don’t drop below 1000 rpm. That’s pure driveability.
The result is less shifting (a less expensive and lighter 10-speed gearbox would suit this motor well), quick but not excited throttle response from the high-output turbocharger, solid acceleration, and excellent hill-climbing capacity. But you know what? In my humble opinion, getting stopped is far more important than getting going, and its turbobrake set my mind at ease on even the Rossland Hill near Castlegar, B.C.
I came down that one at 40 km/h in third or fourth gear – I can’t recall – engine at 2200-2400 rpm, turbo brake on full – mostly – with no brake applications, save for the red light in downtown Rossland. The manual in the truck said the engine produces 550 brake hp at 2300 rpm, and can deliver 600 hp at 2500. I was a bit reluctant to take the engine that high, but the driver’s manual suggested it was
If you’re still looking for some reason not to spec an MBE 4000 in your next truck, consider the following:
The MBE 4000 runs up to 25,000 miles between oil changes with standard CH-4 oil, 50,000 miles between fuel-filter changes, and its three-belt accessory drive
arrangement means longer life for each belt due to lower loads. As well, each belt has an automatic tensioning system that prevents them from loosening over time.
Need more? It’s less expensive, still, than its in-house Detroit alternative — $1540 less, according to Ron Andrews, director of marketing for Freightliner of Vancouver – the chap who made all the arrangements for this test drive. He says even the turbobrake carries less of an upcharge than an optional compression brake on the Series 60 – about $400 less.
So, if the horsepower and torque ratings suit your needs – and virtually any crossborder operator would be well served by this engine – it’ll cost you less to buy and less to operate. It’ll save you money in aintenance, and it feels like a bigger engine than it really is. Bottom line is, it gets the job done and it saves you money. What’s not to like?