I am preparing to rebuild the engine in my CLK320. While doing the valve job I would like to open up the exhaust by machining the heads to accept larger valves. Through my research I have determined that the M112 (3.2L) and M113 (4.3L) use the same exhaust valve. The other M113 engines (5.0L and 5.5L) use a different part number.

Questions: 1) What are the sizes of the valves?, 2) What are the lengths of the valves?, 3) Valve stem diameters?, 4) Has anyone swapped larger valves into their M113/M112?, 5) what is the piston valve relief size?

I figure that if I cannot use the 5.5L valves, I may be able to find some tuliped aftermarket valves/retainers that will work.

Thanks!

Bump

From my corvette work you are doing the right thing to bring air into the engine for more power.

Based on your question you are in the right details.

Just some suggestions.

If the heads are the same for the larger valves as you currently use you have a good chance. Valve seats are hardened/frozen and pressed into the head in most cases. Opening up the valve area means either replacing the hardened inserts or staying within the limitations of existing seats.

The additional air will result in a change to the fuel mixture and in many cases it is better to re flash the ECM to get max performance you pay for in the valve change.

If this hasn't been done before prepare for lots of experimenting to get fuel/air correct for mpg and power. I assume that you will also consider the MAF size for airflow and the exhaust size/type for exhaust gas removal. The total system will give you what you desire.


Given all the detailed engineering to get it defined for mpg/emissions/power I probably would not do the mod unless there were replacement heads with the valves correctly 3 point machined for the installation. But that is just my thoughts. If you do make the mod be sure to post and let others know how it works out.