Max moritz 3.4L 9.8:1 comp ratio pistons - what us the piston top volume and height?

[gliding_serpent]

Max moritz (3.2 to) 3.4L 9.8:1 comp ratio pistons - what is the piston top volume and or height?

Mahle reports 35.4cc/10mm and 28.3cc/9.3mm, but i do not know which is the 3.0 to 3.2L vs 3.2 to 3.4L. See post #9 below for where I got my info.

Edit: As Per Mahle Motorsport, the answer is 35.4cc for the 3.4l pistons!

i would measure mine, but they are installed, and i figured it would be easier to find out online than it is. Will check with mahle monday, but i figured i would try. Thanks for any help.

John

Edit: or... What are the specs for the 3.0 to 3.2l pistons.

[Josh D]

Originally Posted by gliding_serpent

Max moritz (3.2 to) 3.4L 9.8:1 comp ratio pistons - what us the piston top volume and or height?

Mahle reports 35.4cc/10mm and 28.3cc/9.5mm, but i do not know which is thror 3.0 to 3.2 vs 3.2 to 3.4

i would measure mine, but they are installed, and i figured it would be easier to find out online than it is. Will check with mahle monday, but i figured i would try. Thanks for any help.

John

Thanks for doing this. I have a set for the 3.0 to 3.2 conversion and have not found any difinitive answers either. My best conclusion so far is that the MM 98mm pistons for the 3.0 to 3.2 conversion are 9.3:1.

[Trackrash]

You need to measure it yourself to be certain. Look at post #26 here.http://forums.pelicanparts.com/911-engine-rebuilding-forum/875606-3-1-short-stroke-build-66-x-100-a-2.html

[gliding_serpent]

Too late...

[Trackrash]

Not if you haven't installed the cams....

[gliding_serpent]

If the info is not available via the brain trust of the internet, i will await the answer from mahle, and then post back here.

[Trackrash]

There are a number of variables that can affect a compression ratio. If you really want to know your CR, you should do the check.

[gliding_serpent]

Originally Posted by Trackrash

There are a number of variables that can affect a compression ratio. If you really want to know your CR, you should do the check.

My understanding is that the only difference in my engine is the reseating of the valves, and the pistons. We have a deck height of 1.05 average. Calculations (assuming 90cc head) are about 10:1 vs 9:1 based on the two dome volumes above.

But you are right.

[gliding_serpent]

Here is where I got some of my info that raised my question of the true dome volume for these pistons. Sadly, EBS, who supplied my pistons, had no more in stock to give me measurements, and his Mahle rep was gone for the weekend. They wil be getting back to me early next week. I also emailed Mahle, to see what they say.

Originally Posted by billb123

I am rebuilding my '85 911 3.2 to a 3.4L.

The much bigger question i have is about my compression ratio. I'm using Mahle P&Cs, 98mm bore, "Max Moritz"style pistons. This setup is supposed to yield a 9.8:1 CR. Trouble is, some of the published numbers don't seem to add up.

One view: Mahle says the dome volume is 28.4ml. With 98mm bore, 74.4mm stroke, 1.25mm deck height, 90cc head the CR is 8.89:1 - Way Off.

Alternate: Mahle says the dome height is 9.3mm, which is consistent with my measurement. I "cc'd" the dome volume by positioning the piston in a cylinder so the top is even with the top of the cylinder, used a burette with windex to measure the remaining volume to net out the volume of the cylinder dome. I get 33.1ml for dome - very different dome volume, but the CR is looking better. That dome combined with the same assumptions as above for other dimensions yields a CR of 9.47:1. Better but not 9.8. If I used a 1mm deck height, i get 9.7:1. I know my volume measurements aren't perfect, but it seems more consistent with 9.8:1.

Looking at his measured dome height volumes, it would appear that the larger of the two dome volumes (35.4cc) correlates to the 3.2 to 3.4L MM pistons. However his measurements also point to the 9.3mm dome height, which Mahle says should correspond to a 28.3cc dome volume (see email from Mahle below).

Here is a supposed word for word response from an email inquiry to Mahle. Mind you, I have posed questions to Bilstein about shocks and got a rep who gave me bad info. After calling them on it an re-inquiring, I got the correct info. Numbers are only as good as the data given.

Originally Posted by Tie Rod

I was wondering if there was any new information as I am traveling down this exact path. To add to the discussion, I emailed Mahle and was told there were two different piston made from the 98P11 forging. Here is the reply I received.

"There were two similar pistons with the wedge style dome made from the 98P11 forging. The Max Moritz piston dome is 10mm tall, with 35.4cc net volume. There is a shorter one, 9.3mm tall, with 28.3cc net volume."

I interpret the above response as Mahle referring to both of their MAx Moritz piston styles... the 3.0 to 3.2L option, and the 3.2L to 3.4L option.

Interestingly, my forging number seems a bit different. Presumably just a different production run.

[pooder]

FYI:
This piston is from the set that was used in my 3.2 to 3.4 conversion. It is listed as 9.8 CR, with my final CR measured at 10.0 due to head work.



Peter

[Josh D]

Here's pictures of my 98mm 3.0 to 3.2 pistons. If you look at the short side of the dome, it's clear that it is shorter than the short side of the 3.2 to 3.4 pistons you have. That's a pretty good indication the 3.4 pistons are the ones with the greater dome volume and higher compression.





My best guess would be that the 3.4 had the higher 9.8:1 ratio due to the Motronic having spark control in it's mapping and could handle the higher comp ratio. The lower 9.3:1 3.0 to 3.2 where originally developed for the low compression (8.5:1) big port Euro spec engines that didn't have spark control, but had a richer tuned CIS. It could only handle a modest increase in comp ratio without spark control when ran on premium fuel and an adjustment of the CIS to run a bit richer. That's my guess anyway.

I'll be curious what info you get from Mahle.

[gliding_serpent]

JoshD, thanks for those photos!!! You basically answered my question then. Makes sense, and it means my comp ratio should be near bang on! I will await word from mahle before anouncing it to the world.

Thanks again!

[Josh D]

I'm still not convinced of the 28.3 cc dome volume of the 3.2l 98mm piston. That's essentially the same dome volume and comp ratio as the stock 8.5:1 95mm piston. Everything I've read or seen advertised says 9.3:1 or 9.8:1.

[gliding_serpent]

What makes me scratch my head is that billb123 measured 9.3mm for the height of his 3.4L piston tops. Makes me wonder about the accuracy of the info that supposedly came from mahle. Again, I was given bad info from Bilstein once. Mahle does produce a million different pistons.

My attempts to get info from Mahle have been stalled as the only part number I had was the one from the top of the piston, which they reject, resulting in them telling me they can not answer my question (via email). Hopefully Don from EBS has better luck with his Mahle rep.

[gliding_serpent]

So here is the response from Mahle. They gave me the run around at first, saying i needed to give them a parts number... Which i did, each time. Here is their response:

"Called Motorsports for you this morning & confirmed part # & specifications for you. Compression height is 32.8mm. & volume is 35.4cc & this is based on the 3.2 to 3.4 application. The actual part # is PP98-013"

So my compression ratio is spot on!!

[Tie Rod]

What is the piston pin diameter for the 3.0 to 3.2 conversion set?

[gliding_serpent]

No idea. Sorry

[Josh D]

Originally Posted by Tie Rod

What is the piston pin diameter for the 3.0 to 3.2 conversion set?

22mm