3.4L max moritz compression ratio calculation help
 

Hi folks,

So I am told that my deck height for my 3.2L to max moritz 3.4L is 1.05mm. Compression ratio is supposed to be 9.8:1 as per Mahle. My heads have not been machined based on appearance (still single plug also), and the engine is using stock 0.25mm shims.

A few useful links...
http://forums.pelicanparts.com/911-engine-rebuilding-forum/767059-deck-height-dome-volume-compression-ratio.html
CR calculator Engine Compression Ratio (CR) Calculator
http://forums.pelicanparts.com/911-engine-rebuilding-forum/792313-measuring-head-volume-ccs-compression-ratio.html#post7863347

- 35.4cc net volume (As per Mahle. The Max Moritz piston dome is 10mm tall). There is a shorter one, 9.3mm tall, with 28.3cc net volume that is for their 3.0 to 3.2 pistons. i just confirmed with mahle. The pistons are in, as are the heads and cam housings. Note: one is the 3.0 to 3.2, the other is the 3.2 to 3.4. There are NOT two versions of the 3.4!!!
- 98mm bore
- 90cc combustion chamber volume (going with factory values)
- 74.4mm stroke (factory)
- 1.05mm deck height (measured)
= 9.98:1 compression ratio

That is a little high for 91 octane. Adding in a 0.5mm shim instead of the 0.25mm shim would give me a 9.71:1 compression ratio. Of interest, plugging in the smaller 28.3cc piston dome volume, you get 9.06:1 compression ratio. I had better figure out which is which. Update, the 35.4cc dome volume is for their 3.4l pistons, as confirmed my Mahle.

Any thoughts on these calculations? I am thinking that cc'ing the heads would be of help, as would determining which piston dome volume is the correct one. Not sure why there are two versions. Finally, finding how many deck heights were measured, and from what piston(s).

Not sure of my compression ratio, but have a 3.0 with 3.2 Max Moritz high compression pistons and 964 cams. The key to get it to run well on 91 octane is ignition timing. Mine runs great at 29 degrees total advance. I hope this is of some assistance.

From my experience with my 3.4 conversion, there are two variations of the Max Moritz pistons. My engine builder initially received a set of high compression Max Moritz pistons (10.5) from the Mahle distributer and they were returned for a set of 9.8 CR pistons. In the end, my compression ratio is 10.0 measured volumetrically and the car runs well on 91 octane.

Do you happen to have a picture of either or both compression variations to show the difference?

Curious why you don't have this in the engine rebuilding forum?

All the big builders hang out there. :cool:

I am putting the brakes on this in attempt to not spread misinformation (??? Really, the internet?). :-D

there are not two versions of the MM 3.4L pistons with 9.8:1 comp ratio like i read in another thread. Rather, one version is the 3.0 to 3.2, and the other is the 3.2 to 3.4 like i have. I am not crazy. Something was lost in translation and reported in another thread. Now the question is which measurement is for each piston?

My heads are on so I can not just measure. I will share when i find out. As i wait till monday to get the answer for mahle, i will take this to the engine building forum.

Mahle confirmed that the max moritz 3.2l to 3.4l, 9.8:1 pistons have the larger 35.4cc dome volume.

Thus, by deduction, it is the 3.0 to 3.2l max moritz pistons that have the smaller 28.3cc piston tops.

I hope this info helps others avoid the misinformation I came across. Check your pistons before instslling thrm to ensure you were not sent the wrong set by mistake.