The om606 and the Holset HE351

This past week I received an Instagram message from a team doing a build for the Hunting for Horsepower event in Idaho. One of their sponsors sent them an HX30 and told them that they would be good up to 600hp. While that is a generous contribution, I would worry about putting that compressor housing through the car’s sheet metal if I were to push enough boost through it to make that kind of power.

From personal experience, I can attest that being new to Mercedes diesel builds is tough. There is so much information out there, it is hard to discern who is speaking from experience and who is reiterating someone else’s opinion. That is why I see the dynocar as being crucial to all of us. It won’t be laboratory quality data but it will provide real world performance gains on a specific control, or upgraded component. The problem is the dynocar is still a work in progress at this time.

So let’s talk about some basic things I have learned about the om606. Five hundred horsepower is a threshold for the om606. Out of the box, the engine is strong and very capable but once you go over that point things can change. The intake cam gear is pressed on so you should drill a set screw between the cam and the gear so it cannot slip. Some people do the same on the crank because you are screwed if the woodruff key gives way. At 500hp and a lot of boost, valve springs are recommended to prevent float. Go much beyond 500hp and rods are recommended. Pistons should be fine. So, over 500hp it gets expensive and unless you are competing with the car, it’s hard for me to advise you to spend that money on upgrades (image that, a vendor telling you to not spend your money).

So what about the 400-500hp range? Let’s dig in and take a look at what it should take to get us in the ball park. Please keep in mind that there are so many variables that it isn’t realistic to think that I can give you an exact combination in a blog for your engine. Considering attributes such as wear, drivetrain loss across various combinations, altitude, temperature, intercooler efficiency, and even dyno setups can have a big effect on outcome. We will focus on the big items and look at the HE351 and a 7.5MM pump to get us to our goal.


Without the fuel, don’t bother! There are two routes to go: Mechanical or EDC.

EDC: If one is not swapping the drivetrain into another car, EDC makes sense because everything is tied to the ECU, including your transmission. The transmission controller relies on throttle position sensor, boost, etc, or at least the aftermarket controllers do. I do not have an EDC setup but my understanding is that going that route, one will need a 4bar MAF and an ECU tune to reap the benefit. For the ECU tune, it’s not like tuning up an LS. There are only a couple guys I know of that do it and they are in the UK. Expect to have to send them your ECU or work out a swap with an immobilizer hack. If you swap, make sure you understand the impact of local emission testing. We sell (exchange) Dieselmeken built 7.5MM pumps

Mechanical: Mechanical pumps we can upgrade in a couple weeks of receiving your core. If doing a swap, this is by far the easiest method of getting fuel to your monster. I tend to buy om603 cores with a tag of 6030701001 because they are the most common 603 pump I come across.

A guideline on fuel level for horsepower is:

  • 200cc = 700hp
  • 180cc 600hp
  • 160cc 500 hp
  • 140cc 400hp
  • 120cc 300hp
  • 100cc 200hp



When I built my car, I didn’t have the luxury of spending $1-2k on a turbo so I went (and continue) to go with Holset. Holset turbos are proven as they are the turbo on Cummins and an incredible value. Currently I run a Holset HX40 Super pushing 40 PSI. When it kicks in it is awesome but the lag is horrible - bigger is not always better for turbos! I would NOT run a knock off turbo that hard without a turbo blanket and expect serious damage if it grenades!

Here comes the detailed part I usually dread. Try to stay with me and go easy on me in the comments - I know every conceivable parameter isnt accounted for and easy numbers were used!


  • Austin, TX is 489’ above sea level and the National Weather Service shows pressure readings from 29.84 to 29.93 over the last week. Sea level is 29.92 Hg (14.7 PSI) so we will just move forward with 14.7 in our calculations
  • Mass flow (old rule of thumb): need 10 lbs/min air per 100 horse power goal
  • I will use 15% power loss from engine to rear wheels
  • Target horsepower (engine) = wheel horsepower * (1 + power loss) or target horsepower = 400 * 1.15 = 460 hp
  • Based on an engine hp goal of 460hp, I need a mass flow of 46+ lb/min air.
  • Use 5500 RPM as peak
  • I am not worried about absolute theoretical values – our cars are not perfect or theoretical. There are so many variables that could be considered like inlet temperature and turbo efficiency. Too much to get in to.

Mass Flow Information

  • 1.Naturally aspirated CFM (displacement * .5 * target RPM/1728) = 183ci*.5*5500/1728 = 291.23 CFM
  • 2.CFM w/density considered and 75% volumetric efficiency

Density Ratio: The entire formula is CFM * VE * DR * .069, where VE=volumetric efficiency and DR= density ratio. We will use 85% as the efficiency. Let’s plug in what we know:

291.23 * .75 * DR * .069 = 46

15.07 * DR = 46

DR = 3.05

CFM w/turbo = CFM w/VE * DR = 218.4 * 3.05 = 666 CFM or 45.96 lbs/min

Compressor Map

Unfortunately I don’t have a compressor map for the exact HE351w I sell. This HE351CW is the closest one I could find from

Mass Flow – Working Backwards

1.Pressure Ratio = (14.7+boost)/14.7 – At sea level

2.Looking at the compressor map I would aim for a 2.7 PR to be in the center of the map. Notice the lines don’t match up with the lb/min numbers … that makes it difficult

2.7 = (14.7+boost)/14.7

39.69 = 14.7 + boost

25 PSI (absolute) or 25+14.7 (gauge) = boost at sea level

Turbo Summary

  • Does it look like the HE351 will make 400hp on an engine with that displacement? Yes
  • Not the right compressor map but hopefully close
  • Our calculations put us in the middle of the compressor map which is ideal. We can add more pressure (boost) if needed to dramatically change the outcome
  • No consideration for major factors like air temperature, turbo characteristics or intercooler characteristics. Check out for a turbo calculator
  • Using the not too fast calculator to get 460 hp (rear wheel goal) you need about 38PSI which is a PR of 3.62 and 50lb/min of air. Pretty close to what we have calculated
  • Playing with the calculator it looks like it would be good to about 545hp … things will break before this though!

Not too fast calculator


If you haven’t already looked at the om606 manifold, it has a triangular-shaped flange with a 1.5” hole (or something close to that). As I see it, there are 3 options here:

  • 1.You could build (or buy) an adapter to go to a T3 flange. This will most likely become a restriction though.
  • 2.Buy a complete manifold
  • 3.Build an entire manifold from scratch: If building an entire manifold yourself, the ovals will probably give you trouble but its doable.


All Holsets I carry have a 78.83mm exhaust v-band flange, therefore I would recommend a 3” exhaust. There is no direct bolt on flange though so you will need to be creative. Some people modify the back housing of the turbo and weld a standard vband on, or you can have a ring cut to the right size and weld it on the exhaust pipe utilizing the correct holset vband


If your injectors spray fine, then there isn’t anything you need to do. One common thing is to increase pop pressure (shim) to 150 bar but I noticed no difference other than a lighter wallet when I did my injectors.


Regardless of vehicle a cold air intake/box with unrestricted flow should always be the goal.


A lot of the intercooler decision is dictated by budget and space available. Water to air will usually cost more and one will have to deal with a lot of plumbing but they can be more compact. I would definitely recommend upgrading the intercooler to the largest one you could fit. Check out this link:

My summary of Suggested Modifications

  • Pump: 7.5MM pump @ 140-150cc
  • ECU: Contact me for a referral
  • Air: Cold air intake if you can, regardless make sure the engine can get enough air.
  • Catch can: don’t suck your PCV oil vapor into your turbo and intercooler
  • Turbo: HE351 or HX35. If you don’t care about lag, go a bit bigger but you will lose the race if you are waiting for boost and your opponent has a 2 second head start.
  • Boost: Get something like a turbosmart boost tee or a boost controller to increase the boost. I would stay under 45PSI unless you have the upgrades to the springs, cam gear, and rods.
  • Injectors: Have the injectors tested for spray pattern and pop pressure – I would not modify pop pressure at this horsepower level
  • Exhaust: 3” exhaust
  • Make sure your cooling squared away with a decent intercooler. 

Hopefully I covered everything


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