Hi!
I want to find better valve springs for my om606 build, but i found hard to find any info about them on the net. SO:

Brought some springs for testing from various sources and tested them with drill press and ordinary scales at install height 34mm. Here are my results. It might help somebody...

-Om606 spring. Color code Yellow - White. It was removed from my om606 engine. Install rate 24Kg.
-Om606 spring. Color code Purple - Blue. It was found in my om606 (somebody replaced it), i'm not sure about the code, but purple-blue springs should have 6110530220. Install rate 24Kg.
-6110530120 Color code Yellow. This one was bought from local supplier according to mercedes manual and it says it fits to all w210 cdi models, including 3.2cdi. Install rate 17Kg.
-3.2cdi spring. Color code White - Yellow. Bought complete 3.2cdi head in salvage yard, and it's the one from that head. Install rate 27Kg.
-??? Color code Purple - Yellow - White. Found this spring in mercedes salvage yard. It fits to om606 head, but i don't know the model it came from nor the code. Maybe somebody knows what puprle- yellow-white color code means? Install rate 38Kg.
-6110530120 org. Color code Purple - Green - White This one was bought from MB Dealer according to mercedes manual and it says it fits to all w210 cdi models, and it`s intake spring. Install rate 17Kg.
-6110530220 Color code Purple - Blue This one was bought from MB Dealer according to mercedes manual and it says it fits to all w210 cdi models, and it`s exhaust spring. Install rate 28Kg.

I Will search for more springs and update you if i will find something interesting. The Purple - Yellow - White spring looks amazing with 38Kg install rate. Its even better then KM Cams springs which are at 34Kg Install rate as their website says.

Are you trying to rev the om606 past 5000 rpm?

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CENSORED due to not family friendly words

FYI, higher tension does not automatically mean higher RPM capability. You need to think about resonance of the spring, pounding (hardness) of the valve face/seat and coil binding at high rpm.