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Discussion Starter #1
I've always been curious about the weight of an M120 for someone who was using it outside of its native W140/R129 chassis. A thread on "motor weights" over on the PeachParts forums shows an M120 coming in at roughly 654lbs as removed from the car (accessories, flex-plate, starter, intake, oil, exhaust manifolds, etc.).

Well today, I was able to weigh my M120 in what I'd consider "long-block" form and it came to 440lbs dry (weighed with the engine stand bracket on, estimate 15lbs). This configuration is as pictured below. That means that in long-block form, the engine sheds 215bs of fat... quite the number! 32% of the engine weight is:

  • Intake
  • ETAs
  • Fan Clutch
  • Water Pump
  • Dual-Pump
  • AC Compressor
  • Exhaust Manifolds
  • Filter Housing
  • Flex-Plate
  • Fan
  • Other things I'm missing
I figure the whole engine, in the configuration I'll be running it in, will weigh about 500lbs even (dry). This will include:

  • Long-Block - 440lbs
  • Lightweight Alternator - 7.2lbs
  • BMW Electric Water Pump - 6.5lbs
  • Hayabusa Individual Throttle Bodies + Plenum - 20lbs
  • Equal-Length 6-2-1 headers - 30lbs
I'm cheating by not counting the starter (as it will be mounted on the transmission I'm using) or a power-steering pump (since I have a manual rack and if the 500lb anchor hinders that, I'll use an EPAS set up out of an MR2).

Not sure if anyone else would find this info useful, but I figured I'd share!
 

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Always interesting. The main reason i bought my car was the engine. Its too bad these sort of engines are expensive to extract the big potential power numbers they have but still excellent power in a lighter chassis.

What are you putting it into?
 

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Discussion Starter #3
I'm hoping for 480-500 at the crank, which is fair for a bone stock 6L engine (with an NA motor you're a slave to displacement). A 6.2L LS3 with mild work (bolt-ons) can do the same, but then you're just another guy with a V8!

My -current- plan is to put it into a 1986 Mazda RX-7 (shell in the pictures). But that is subject to change. I would love to drop it into an Nissan R32 GT-R but even as shells they are getting expensive. RX-8s are a dime a dozen but then I'm messing with emissions equipment that I would, technically, need to keep. I'm going to be building a test platform for it that will also act as a jig for building the headers, so I'll have it running before I know what it's going in (but will have to know what it's going in to design the headers).
 

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Excellent info. I always had a hunch the engine itself does not weight much for what it is, considering the block itself is quite light and the thing has magnesium cam covers.

Looking at the AMG engines one of the first things they do is get rid of that intake manifold. A great design, durable, attractive and fits under the hood on production cars, but given the space alternative designs are called for to help extract power & lessen weight, especially being up so high.

Good luck with the build.
 

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Discussion Starter #5
My thoughts exactly, for an aluminum block without iron sleeves... I didn't understand how it could be so heavy. Now I know it's because of all the stuff hanging off of it!

To put it into perspective; other popular engines that people swap into things (dressed weights, best googling applied):
  • Nissan RB26DETT - i6 - 550 lbs
  • Toyota 2JZ-GTE - i6 - 525 lbs
  • Chevrolet LS1 - v8 - 410 lbs
  • Chevrolet SBC - v8 - 550 lbs
  • Chevrolet BBC - v8 - 650 lbs
  • Mazda 20B-REW - 3 rotor wankel - something stupid... likely heavier than anything listed above...
As for the intake, working without the constraints of the original design envelope is always nice. Though I am pondering picking up a W140 S600 that's clapped out and seeing what I can fit under the hood as far as goodies/updates are concerned. An ETA is just a stepper motor, no reason that stepper can't drive a bank of six ITBs vs one larger butterfly. So an ITB arrangement that fits under the hood and doesn't screw with ASR or throw any dash lights, neat? Maybe even modernize the engine management since there are single boxes that can treat the V12 as a single unit vs two i6.

Oh, if I only had more time in a day, days in a week, weeks in a months, and months in a year!
 

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Just curious about the BMW electric water pump. how does it work?
It's just a motor driving a pump, variable speed, depending on temperature. The motors are known to fail unexpectedly, leaving you stranded. 70 to 80k miles is typical safe life before failure. Expensive at $300 or so. Frankly, I'd rather have a conventional pump that usually gives warning before failure.
 

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Discussion Starter #8
Just curious about the BMW electric water pump. how does it work?
As mentioned above, it's DC motor driving an impeller. There are a few different sizes depending on the car it's from, and you can send it a PWM signal to control it's speed (has an SSR built into it). There's a company that makes a standalone controller (https://www.tecomotive.com/en/products/tinycwa.html) but my ECU will control it so I'll be good there.

They are considered a wear item and should be replaced every 60,000 miles/100,000 km. Not really much more expensive of a part than an M120 water pump and probably no more difficult to replace (don't need to remove the radiator to do the job).
 

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Thank you for the reply, learning about all that electrical stuff as we speak, thats a cool way around a part that is known to fail. Do you think it takes less of a parasitic loss as a side effect?
 

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Thank you for the reply, learning about all that electrical stuff as we speak, thats a cool way around a part that is known to fail. Do you think it takes less of a parasitic loss as a side effect?
The conventional pump on an M120 is less prone to failure catastrophically than the BMW electric pump. I've got a 530xi with 75000 miles that I won't drive anywhere but locally until I change the pump because when it quits, it's flatbed time. It's typically the motor that fails, not the pump. On some BMWs it's a real bitch to change. Fortunately on mine, there's a little more room. An independent shop quoted $1200 to do the job. Parts kit (pump, thermostat, bolts (aluminum one-use bolts, gaskets, coolant) is around $350.
 

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Discussion Starter #11
Thank you for the reply, learning about all that electrical stuff as we speak, thats a cool way around a part that is known to fail. Do you think it takes less of a parasitic loss as a side effect?
Probably not in the effective range of the pump; but one advantage is that an electric pump will not cavitate at higher RPM. A mechanical pump is only efficient up to a certain point, after which you're running the pump faster than it can effectively pump the fluid. The electric pump will maintain optimal flow independent of engine RPM.

The conventional pump on an M120 is less prone to failure catastrophically than the BMW electric pump. I've got a 530xi with 75000 miles that I won't drive anywhere but locally until I change the pump because when it quits, it's flatbed time. It's typically the motor that fails, not the pump. On some BMWs it's a real bitch to change. Fortunately on mine, there's a little more room. An independent shop quoted $1200 to do the job. Parts kit (pump, thermostat, bolts (aluminum one-use bolts, gaskets, coolant) is around $350.
What's T-stat/water pump job cost on the S600? I'm a DIY-er so I don't really factor in marked up book rates, but they are important to note for some.
I have a 328xi with 140,000km (87,000 miles) and have a water pump/t-stat/OFHG on the shelf to swap out ASAP; thankfully I'm always with CAA distance of my shop!
 

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S600 pumps range from around $150 to 250. They make up a pretty good portion of the cooling and thermostat setup on the front of the engine, so replacing them with electric would require that to be taken into consideration. They also incorporate the separate mechanical fan bearing.
 

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Discussion Starter #14
S600 pumps range from around $150 to 250. They make up a pretty good portion of the cooling and thermostat setup on the front of the engine, so replacing them with electric would require that to be taken into consideration. They also incorporate the separate mechanical fan bearing.
Already taken into consideration. I will be running electric fan(s) as well as making adapters to suit removal of the water pump and thermostat housings.

EDIT: I should note that this engine wont be in an S600 anymore.
 

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Discussion Starter #15
does it take a load off the engine similarly to how people install electric fans and remove their A/C? like one less thing for the engine to power right?
Well, energy is required to do anything. Whether that energy comes from a belt driving a water pump, or a belt driving a more powerful alternator to meet the demand of an electric water pump, the power has to still be generated by the engine. As such, I'd be surprised if there was much gain (if any) in power if you are running both systems with the same flow rates/pressures.

In the case of the air conditioning; I don't understand the logic behind people doing this since the A/C compressor freewheels when it is not needed. Now, removing A/C for weight savings, that I can understand (if you're chasing the final 20-30lbs in weight reduction).
 

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Yeah its shame M120 was limited to the W140 for obtainable cars, the engine wants to do things the chassis doesn't want to do. I always thought the E class would be a nice candidate expect for working on it, or even a replace the BMW V12 from on a 7 series to make the ultimate luxury sport limo.
 

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Yeah its shame M120 was limited to the W140 for obtainable cars, the engine wants to do things the chassis doesn't want to do. I always thought the E class would be a nice candidate expect for working on it, or even a replace the BMW V12 from on a 7 series to make the ultimate luxury sport limo.
R129?
 
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