M103 2.6 and 3.0L head differences? - PeachParts Mercedes-Benz Forum

ps2cho · #1 03-16-2011, 02:30 PM

Does anybody know if a 3.0L head can be put on a 2.6L block?
Are the valves any different between the two?

I have 20-25% leakdown in each cylinder and I can hear escaping during the leakdown test, just doing some searching in case I find its leaking head-side.
Compression is good -- 175-185 across all 6 cylinders. If I rebuilt the head, would I net any increase in engine efficiency and HP?

duxthe1 · #2 03-16-2011, 08:53 PM

Yes the head will bolt but the 2.6 head has a squish pad and the 3.0 is an open hemispherical chamber. So a 3.0 head on a 2.6 would have a lot less compression. FWIW, there may be a few oddball assemblies out there but AFIK... no dice.

I wouldn't expect much gains from a head rebuild unless yours is in poor shape with excess deposits. Mercedes heads are pretty good castings out of the box but you may be able to get a little more out of it. Most of the work I did to my head was on the chamber side, the ports are hard to improve on.

ps2cho · #3 03-16-2011, 10:23 PM

I wonder if that would aid for future turbo setup? Any idea what it would drop compression to?

duxthe1 · #4 03-17-2011, 12:19 AM

I've often wondered that same thing. I don't kow the numbers but I fear the compression drop would be excessive, even for a turbo.

Hit Man X · #5 03-17-2011, 11:52 AM

Just over 9:1 is fine for turbocharged, it is ALL in the tuning. Keep dropping it and you will lose more and more response off boost.

teezer · #6 03-17-2011, 01:49 PM

worth a shot at trying to compare on paper ~~~ the only number you would need is the combustion chamber volume, which might be available for both the 2.6 & 3.0 somewhere in a technical manual ~~~ already knowing the compression ratio, i would assume by changing the formula around could net the chamber volume

The ratio is calculated by the following formula:

, where

= cylinder bore (diameter)

= piston stroke length

= clearance volume. It is the volume of the combustion chamber (including head gasket). This is the minimum volume of the space at the end of the compression stroke, i.e. when the piston reaches top dead center (TDC). Because of the complex shape of this space, it is usually measured directly rather than calculated.

ps2cho · #7 03-25-2011, 10:56 PM

I cannot seem to find any data to the volume differences between the two heads...

Could we guesstimate it would drop compression to maybe 8.5:1 ?

http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/01-4000.pdf
According to this, am I right in reading that each cylinder also has matching pistons? What would be the implications to using a 3.0L head with the 2.6L bottom end regarding piston changes.

The larger intake valves on the 3.0L head is the most interesting part for me.

duxthe1 · #8 03-26-2011, 01:16 PM

It's been a while since I've had a 2.6 apart but I seem to recall that they had a dished piston to get an acceptable compression with the "tight" head. So you will end up with dished pistons and a low compression head to bolt on the 3.0. Worst of both worlds, so to speak. In addition to losing compression, you also lose the squish that promotes cylinder turbulence. This is from a failing memory and certainly not fact without confirmation, so I could be wrong ....

teezer · #9 03-26-2011, 04:04 PM

to many years since algebra, with only having one unknown (clearance volume) should be able to find that value using previous formula i posted

comp ratio is 9.2:1 on the 300 and 260

bore on 260 is 82.9

bore on 300 is 88.5

stroke on 260 and 300 is 80.25

after finding the clearance volume you can substitute that and see how that effects each engine's compression

Hit Man X · #10 03-28-2011, 09:36 PM

You also may induce shrouding of the bore with too much valve on too little bore or a decrease of port velocity with the larger valve and not enough motor.

What am I saying? Just leave it alone. Again, 9:1 is great for street turbo cars.

gschira · #11 03-28-2011, 11:15 PM

Quote:

Originally Posted by duxthe1

Yes the head will bolt but the 2.6 head has a squish pad and the 3.0 is an open hemispherical chamber. So a 3.0 head on a 2.6 would have a lot less compression. FWIW, there may be a few oddball assemblies out there but AFIK... no dice.

I wouldn't expect much gains from a head rebuild unless yours is in poor shape with excess deposits. Mercedes heads are pretty good castings out of the box but you may be able to get a little more out of it. Most of the work I did to my head was on the chamber side, the ports are hard to improve on.

Just curios--Does anyone have pics of the two different heads and piston tops? Also, what is a squish pad?
Could one of those oddball assemblies be a 2.6 head on a 3.0 engine?