Experience with Mahle high compression 3.2 -> 3.4L kits?
 

Hi guys,

I am currently planning out the rebuild of my 220k kms 3.2 engine, with worn valve guides and a broken head stud. Unfortunately it's the low compression 217 HP cat version, even though it's a Euro car.

I'm still running the numbers on rebuilding mostly stock but with Euro 10.3:1 pistons, vs. upgrading to 98mm "while I'm in there". If I do that Mahle offers the 98mm 10.1:1 Max & Moritz kit (Mahle PS98-010) that maxes out what you can do with single plug and Motronic, but "while I'm in there" they also have a 11.0:1 kit that allows you to run bigger cams and has a shape optimized for twin plug (PS98-017).

Does anybody have experience with these kits, and is it worth the extra cost of going 3.4L M&M single plug (approx. $1500 extra vs. just a set of pistons) or 3.4L high compression twin plug (another $1500 or so on top with head work, Steve Wong DME mod + splitter + used 964 dizzy)?

Thanks for your input!

Cheers,
Lukas

You can also rebore your old cylinders and then pick any piston you want.
It’s best to look at the engine as a system and build from the bottom up.

That's true and it's something I have also considered, but if I factor in the value of the core cylinders, shipping + return, etc the bore and replate only saves a few hundred $.

Given that quite a few people have had with problems with cylinder roughness vs. ring seating after replating and the different expansion rates of the alloys used in aftermarket pistons vs. Mahle cylinders leading to some piston (slap) noise, I am wondering if a new Mahle piston in a (new/used) Mahle cylinder might be worth the extra cost for piece of mind and longevity?

I think the engine start noises with JE Pistons are a thing of the past with updated 4032 & latest JE design

I installed a set of 3.4 Mahles in my nephews 911. They have been flawless from the get go. I have 98 mm JEs in mine and oil consumption is more than the Malhe but still well within acceptable limits. The JE pistons use a much thinner oil control rings and I suspect that is the reason for higher consumption. In summary, both are good.

Just as long as you prep all surfaces of the mahle motorsport rings , this is your best bet .
The rings tend to have burs on them .

Ian

Thinking about this as well. What is the power difference 3.2 vs 3.4? Roughly?

All other things being equal, the increase from 95mm to 98mm bore results in a 6,4% increase in displacement - 3164ccm vs. 3367ccm - so should add about 15 HP to a 231 Euro 3.2


Thanks for the tip Ian. I'm a bit surprised given the price of Mahle parts but have heard this from other sources as well, the pistons definitely should be removed from the cylinders, disassembled, cleaned meticulously, measured etc.

Did you have to gap the rings as well, or were they within spec?


Thanks for the feedback, that is good to hear. Might be worth an extra grand or so for long term piece of mind, not a big difference given the overall cost and time effort of rebuilding one of these engines.

Did you go with the standard Motronic 10.1 compression kit, or the higher 11.0 one?


Yes that should definitely help vs. their older 2618 pistons, but most pros seem to think that Mahle still has an edge in terms of longevity with their special super secret alloys that perfectly match the cylinders.

Interesting read here!
http://forums.pelicanparts.com/911-engine-rebuilding-forum/979564-mahle-vs-je.html

quote "Did you have to gap the rings as well, or were they within spec?"
The rings were gaped properly , the mfg burrs were a problem.
Take a cotton ball and dress around each ring , it sticks to burrs .

Ian

And I presume once you find a burr you gently get rid of it with something like 600 grit sandpaper in some fine oil?

D

Play the game first and see if you can find a burr, once you find a few , I just prep all the
lower rings , top ring not so much , just check and knock off the sharp edges from the gapping process


Ian

I’m trying to figure this out while I have the entire motor torn apart and at the machine shop. Not sure if there is a better all around option than 98mm P&C 9.81 compression ratio and 964 cam SW chip. Is an added knock safety sensor still needed? CP or JE pistons?

A bit old now but lots of good info:
https://forums.pelicanparts.com/porsche-911-technical-forum/851793-3-2-3-4-must-you-go-twin-plug-3.html

Stubble- I just did the upsizing from 3.0L to 3.2L and kept my CIS- a bit different from your concept. But, based upon that, I recommend doing the following:

1. Call William Knight to learn his experiences with such projects. He knows what works and what doesn't work.
2. Suggest spending the $4K and getting the Mahle 98mm piston & cylinder KIT made for your project, if William agrees.
3. William will recommend best cam for your application.
4. Prepare to be impressed.

That's the best recommendation I can give you.

Ok. Great. Thank you.
I have called EBS. With core exchange 98 mm cylinders $1470 JE pistons $1450
Supertec has a 97mm for around $3700
964 cam. Either webcam or having mine grind down. I can get a deal with a barely used webcam for $600
But I’ll check with William.
Thanks

Just FYI you can get a brand new 98mm Mahle cylinder plus piston kit for a couple of hundred $ more, if you look online. Anf then you can still sell your 95 cylinders as cores.

If you e got a link for that let see it. I don’t see anything under $4600

Stubble- I just sent you a PM. That should get you started. I seem to recall William mentioning in another thread that this upsizing from 3.2L to 3.4L has a couple challenges in order to reach its full potential. But William knows the tricks and will steer you towards the best path for your application. Don't be surprised if he recommends a different cam than you are considering; Suggest waiting to discuss with him prior to buying anything. Please report back when you determine your direction. Thanks