hmmm..looks like C55 pistons aren't too tough after all.
Your car runs 7* at WOT? Then I guess the C55 I'm working on wasn't so bad after all.
As for the MAP sensor, keep in mind that it reads in atmospheric pressure ( you must subtract 14.5psi to the number it gives you ). Depends where you have yours hooked up, it might not see boost ( if it's plugged into the throttle body area for example ).


I searched around with these part numbers and couldn't find any pictures. However, judging from the prices of those bad boys, I would imaging you're probably not buying new. You could probably find a used engine for that kind of money!
Rods: 113 030 04 20
Pistons: 113 030 43 17
Last edited by 91RS; Oct 31, 2012 at 10:00 PM.
Regardless, I'm getting used rods and pistons from an E55.

I figured used was the way you were going once I priced new stuff. Only $7000! Do you have any plans to do any head work while they're off? Like port and polishing?
I figured used was the way you were going once I priced new stuff. Only $7000! Do you have any plans to do any head work while they're off? Like port and polishing?
Today I got my friends C55 engine torn apart and to my surprise, cylinder #8 ( which gave a 97psi compression number ) was completely intact. So now I'm really curious...EVERYTHING looks good even though I checked it multiple times, all the rest of the pistons had good compression except #8.
What the engine DID have was HUGE amounts of carbon build up...to the point of insanity. I'm guessing my valves are probably not sealing or something but I haven't checked that yet, time to call it quits for today.
The Best of Mercedes & AMG
The reason why the car was giving low compression number apparently was caused by simple wear and tear. Top ring gap was .500+mm and 2nd ring gave me .600+mm. OEM specs are anywhere between .250-.400mm and the new rings I bought were within that range.
Second, I installed the E55 pistons and rods and to my surprise, the engine would not turn 360* without locking it's self...OMG!! Thank God I only install two pistons when this happened. The bottom of the piston was touching the crankshaft. Upon comparing the C55 pistons to the E55 pistons, I found out that what seems to be balance pads that they have on the bottom where the wrist pin goes in is smaller on the C55 then it is on the E55. 1mm smaller to be exact. So....I grinded the E55 balance pad ( I think this is what it's called ) 1mm and checked again....GOLD! I also balanced the pistons to within 3 grams ( oem ones were off by 6 grams ).
Little by little...I'm getting there.
1 = 170
2 = 170
3 = 173
4 = 175
5 = 165
6 = 145
7 = 171
8 = 97
cyl 6 seems weak ( engine has 105k miles and ran nitrous before the supercharger ). Cyl 8 is toast however. Car ran fine though even after the damage. It's always number 8 isn't it.
Keep in mind, AF ratio was high 10's and timing was a ridiculously low 7-9* with 0* of timing retard due to knock up until 3rd gear where it would sometimes retard 1-2* or so in small bursts which isn't bad at all. I guess the engine was just tired.
Cyl number 8 doesnt get proper fuel delivery on our cars... also on all 55k motors its the same. if you get a fuel like loop it'll fix cyl 8....
as far as 6 goes, im not sure....
I'd say its more driver error than parts.
In my case with flowed heads, no catalysts,longtube headers etc etc.
i´ve got with my 2.2 litre kleemann kompressor at 3500rpm 0.55bar of boost.(8psi)
This with a 67mm pulley.(2.64")
Dynosession booked to the late April.







