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Upgrading my 1995 Mercedes W124 diesel to produce 500 BHP

28th July 2021, 13:55 by Chirag Moro

Like the good old Mercedes engine of that time, it was an utterly reliable and mile munching unit. But, because of its power potential, it turned out to be a legendary one as well.

BHPian mayurhuria recently shared this with other enthusiasts.

Potential of OM606 engine

First of all, my apologies for not updating the thread, life was hitting like a single big turbo hits boost (late and hard). Now, OM606 engine from Mercedes first came in the year 1993. Like the good old Mercedes engine of that time, it was an utterly reliable and mile munching unit. But, because of its power potential, it turned out to be a legendary one as well. OM606 in stock form can take a lot of abuse and makes a good amount of power. And often, called as the diesel 2JZ.

It came in turbo and non turbo options. With major internal differences of pistons, connecting rods, camshafts between the two. They are becoming a rare breed now, in India. The N/A ones are rare and the turbo units are even rarer. When I saw the E300d, this particular reason was the major one to convince me.

I had a fixed goal in mind that I want to target 500 BHP no matter what. Now, the issues related to it are since the N/A unit is not as robust as the turbo unit, the internals have to be beefed up to the levels of turbo unit.

Second most reason was since these are IDI units and when they make power, they also become Rolling Coal, which has to be avoided at any cost. So with all this in mind, I had to plan the best route possible.

Beefing up the internals

We had no plans to build this engine as otherwise it would defy the purpose of the build i.e selecting a capable unit ground up. Mind you, the N/A unit is capable of 350 hp which is a fairly good number. But we want to be as close as to my goal. The usual practice is to swap in a turbo unit. But I wanted to retain the originality & legality as much as I can. Another thing, if the N/A 606 are rare here, then turbo 606 are next to impossible here. Importing one was not even worth the efforts. Difference between the two:

So, we decided that instead of going with forged pistons and rods, we imported used OE turbo pistons and rods from Sweden. They were in great shape (expected from the Mercedes parts of that time).

The block is pretty good in both unit and so is crankshaft, so with new rings and new valve seals, polishing, balancing pistons and rods, we made a reliable & capable unit, which would serve a long time.

And we didn’t have to do a lot of changes considering the amount of time, work, efforts on it plus its now an OEM+ unit.

KM CAMS 8000 rpm VALVE Springs

OM606 is a high revving diesel engine with a rev limiter 5500 rpm in stock form. When power output is increased, its a natural practice to raise the rev limiter to usually 6000 rpm (have seen one OM606 in MKIV Supra doing 7500).

Now, the issue with raising the rev limit is valve tends to float at high power levels, so usual practice is to limit fuel when its about to reach 6000 rpm. This means not able to get the real benefit of raising the rpm limit.

Solution:

8000 rpm rated valve springs with undershim from KM Cams.

Yes, we got no plan of going over 6500 rpm to maintain the reliability plus our desired power goals come well within 6000-6200 rpm. But its better to have an overbuilt unit than to worry later on about stuff.

Pinning Intake CAM

This is a very small but major step. When producing high power, there is a high chance of intake cam sprocket spinning and causing engine damage. So pinning it is the best solution.