trying to decide on P&C for single plug
 

My original pistons are Alusil and have some damage on the piston heads due to floating valves.

I have no desire to go with a twin-plug setup, so I need help in deciding on the best P&C setup.

Any suggestions on what I need to get?

(FYI... I've read Wayne's books, and unfortunately there is some contradiction written in his Engine Rebuilding book)

Can I go with 98mm 3.4, even though Wayne's book says 98mm needs dual plug? Can I go with the Euro spec P&C, even though Wayne's book says compression above 10:1 needs dual plug?

I'd rather not stay at 3.2 if I can find something better. Now's the time to upgrade while the engine is getting rebuilt.

(Everytime I research more, I'm just more confused and start doubting I'd make the right choice)

The Max Moritz style piston is designed for a single plug, the dome shape is a wedge, compared to the traditional dome which would split the cylinder and can block spark propagation.

Since yours is a 3.2. you can bore out your cylinders to 98mm and have them replanted fairly inexpensively.

I was thinking this as well.. but would have to get new cylinders... not using mine due to Alusil.
However... I came across a page on Patrick Motorsports site that sells the Max Moritz style 3.2 to 3.4 but they claim it is a 11:1 compression. That seems too high for a single plug setup.

Onche you plate nikisil on the alucil cylinders you have what you need at98mm
Bruce

You use your cylinders as cores. There are a few places that can bore them out to 98mm, and replate them with Nikasil.

I would give EBS Racing a call, I know they do it, and can probably sell you the pistons.

You're fine going to 98mm just don't go high compression, that when you need the twin plug. I ran a single plug 3.4 with JE 9.5:1 pistons for several years.

I rebuilt my engine to 3.4 with Max Moritz style pistons. I shipped the cylinders to EBS and they had them bored and replated. They also supplied the Mahle Max Moritz pistons (9.8:1 CR), single plug. Great set up here in Michigan, though we have 93 octane gas. Steve Wong did the chip to match everything. Been running flawlessly for over 3 years now.

Just curious... but does anyone make a 3.2 to 3.4 piston that isn't a Max Moritz style?

As far I can find... since 3.4 isn't a factory size option, it seems ALL the pistons have the Max Moritz style cut to them.

The bigger question is... are JE and Mahle pistons identical in measurements?
Meaning... is there a determined standard on what makes a piston a Max Moritz style??

I looked at EBS Racing and it looks like they use JE pistons. I had planned on buying Mahle pistons, only because I'm familiar with that brand.
What makes JE pistons better than Mahle?

Some info here - looks like JE do a single plug piston:

http://forums.pelicanparts.com/porsche-911-technical-forum/852111-want-je-forged-3-2-3-4-max-mortiz-style-pistons.html

Maybe use the search facility for a JE v Mahle discussion:

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

There are these.... https://www.fvd.net/us-en/10010303304/mahle-30-liter-32-liter-rsr-piston-and-cylinder-set-1031-98-mm-big-bore-for-911-30-l-cis.html

Yeah, I have 98mm Mahle RSR pistons. They have a traditional dome with valve pockets.

http://forums.pelicanparts.com/uploa...1069134036.jpg

So does this piston provide a higher compression? I saw an RSR style design for a 3.4, but the compression was something like 11.3:1 which seemed really high for a 98mm piston.

The RSR style I saw had a slight concave center
http://forums.pelicanparts.com/uploa...1535950328.JPG

you need to start with what octane of gas you have and want to use.
last thing you want to do is have to retard timing because of fuel.

I don't remember the exact advertised compression, but I remember it was pretty high, but a factor in the compression ratio of the volume of the combustion chamber. It measured at 9.8:1 with my 3.0/late SC heads. My engine is twin plugged though, so not a concern.

For comparison:
Wossner Pistons, Huntington Beach CA

trakrat - since the single spark plug in your 3.2 is off center (dictated by valve placement), you need a wedge-style piston to facilitate flame propogation from the single plug across the wider 98mm 3.4 piston width. Regardless of whether it's referred to as a "max moritz" etc., assuring that the piston's designed to work with a single, off-center plug is key.

Although I recognize that you have no desire to go with a twinplug setup, I presume that you're going to need to have machine work done to your heads (valve guides, etc.) -- I'd strongly suggest at least inquiring into the cost of drilling the heads for a second plug (and capping the tapped holes). That way, if your build does have detonation issues, etc., you could convert to twinplug without disassembling the engine to have the heads tapped. Keep in mind that the 3.2 motronic system lacks a knock sensor and that by changing the design of the engine, you're introducing the potential for knock.

100 octane... or the equivalent of 100 octane.

so if detonation could be an issue... could I go with an aftermarket ignition system to allow for a hotter spark plug to be installed and used?

so WHAT is considered high compression then?

I'm told that anything above 10:1 compression needs twin plug... if so.. then did Porsche twin plug their Euro spec cars from the factory to support the 10.3:1 compression that their factory spec P&C?

I was planning on buying the Mahle 3.4 P&C set... but then I noticed the weight of the 3.4 is heaver than the 3.2... which made me wonder if I would be gaining anything worth the price of going to 3.4

When I sent my heads to EBS in the way-back, the cost was not prohibitive. Don't remember exactly, but not a back breaker financially.

Just talking. I had a cylinder head sensor port machined into my #6 cylinder. I think it was $60, 1997 money.

trakrat ---

1) more detonation clarification -- believe the key here (and I'm not an expert) is preventing preignition of the fuel, which is exacerbated by the longer path the spark-ignited fuel needs to travel in a wider, larger displacement cylinder. Hotter spark may help a bit, but what you're fighting (and what twinplugging will most effectively fight) is spontaneous ignition of the fuel at the far side of the cylinder before the sparkplug-ignited fuel lights it off -- spontaneous ignition at/before the piston reaches tdc is BAD.

2) compression -- octane is a measure of a fuel's ability to resist knock/preignition. Euro engines have higher compression because european gas formulations generally have a higher available maximum octane level than the US (requiring lower compression to avoid knock/preignition)

3) weight -- unclear why this is an issue. A 3.4 liter engine will provide room for more fuel/air to collect in each cylinder, resulting in a bigger explosion pushing the piston down (and therefore more power / torque). Component weight may come into play in some manner, but the justification for a bigger engine is a bigger "bang."

Unfortunately Bob... the heads are on their way back to me after getting everything done to them.
Besides that... adding all the costs to setup a twin plug (new distributor, etc...) makes things get expensive quickly.

It's not that I "won't" go to a twin plug... its just that I'm not ready. I've only driven the car for about 4 months before I had to rebuild the engine... and once that's done.. I'll ne to rebuild the suspension... and fix rust... etc...

I figure, since I'm rebuilding the engine and have to buy a new set of P&C... I thought I'd go with something slightly better than what the car came with.
But maybe that's not an option? It seems that if I don't get twin plug... then I should admit defeat and face the reality that I should just buy another set of factory 3.2 P&Cs?

Call EBS racing and see if they can source you the 98mm Mahle Max-Moritz style pistons you need. They can machine your stock cylinders to fit.

emcon5 -- good advice -- seems the key here is to go with a proven, middle of the road, setup and there are plenty of single plug 3.4l engines out there. Go with what others have successfully used in the past and don't try to "reinvent the wheel" -- Trackrat, also keep in mind that once done, you'll need to get a chip mapped to provide proper afr to your now bigger/thirstier engine

Agree.

Would be cool to have that as a hip pocket option down the line with the machine work already done.

Do call EBS and just yak with them. I like the 3.4 option. Don knows his stuff. Jon is the boss but I don't think he works the phones like in the way back.

trakrat -- if you're committed to running 100 octane gas all the time, you should have zero issue going with eurospec pistons (or much higher compression 3.4 pistons than would ordinarily be run on a car running on pump gas) -- 100 octane has much higher anti-knock properties than 93 octane pump gas.

I echo Bob Knotak's suggestion of discussing this with somebody knowledgeable about this particular issue -- somehow missed your comment about your being dedicated to running this motor on 100 octane gas exclusively

i see you referring to what Porsche did. they did not do things based on 100 octane fuel.
no one has considered the fuel you plan to use so I don't think much of the advise has been helpful.

100 octane opens the door for you.

start with fuel as I said,
figure out engine size, CR and cam based on the fuel.
with 100 octane you might be better of with a 3.2, higher CR and a cam that will work with it.

Big Bore Pistons
 

When I built the 3.3SS for my SC, I used a set of Mahle 100mm pistons. They were supposed to be 10.1:1 but wound up closer to 10l8:1, probably due to the heads being cut one or more times. These pistons have a nice, low, hemispherical dome that is less likely to block the flame travel. I am using twin plug ignition, but if you stayed under about 10:1 premium pump gas should work ok. Some pictures:

http://forums.pelicanparts.com/uploa...1536151553.jpg
http://forums.pelicanparts.com/uploa...1536151577.jpghttp://forums.pelicanparts.com/uploa...1536151652.jpghttp://forums.pelicanparts.com/uploa...1536151731.jpg

Twin Plug ignition..........
 

I used the Electromotive XDi twin plug, crank fire system. It not only is completely adjustable for timing, but eliminates the distributor completely. No expensive distributor caps or rotors to buy come tune up time! A tune up on my twin plug engine consists of an oil change, filters and 12 spark plugs! Plus, deleting the dizzy really cleans up the engine clutter! Cost for the system was about $1300.

Engine running with no distributor!
http://forums.pelicanparts.com/uploa...1536152443.jpg

I raced a single plug 10.5:1 3.4 with JE pistons, on 100 octane fuel, for several years. I also raced a 3.2 with the same fuel and comp ratio. My street SC is a 3.2ss with 9.5:1 compression and runs on 91 octane, also single plug. Both engines were built by Supertec. We've got another Carrera based single plug race engine with over 11:1 and it runs 110 octane. So in my experience those are about the limits for single plug: 91 octane - 9.5:1 or lower, 100 octane - 10.5:1 or lower, more than 10.5:1 and you'll need 110 octane and/or twin plug. A good engine builder can provide more info I'm sure, but that's my experience.

Just send your heads to "cgarr" for twin plug. You won't regret it.

You don't have to add the 2nd ignition right away, and can add later. You'll sleep better at night!

Detonation sucks!!!!

agree -- even though they're in transit back from being machined, better to incur the (relatively minimal) expense of having the heads ready for twin plug IF needed then to disassemble the top end to pull the heads post-rebuild.

Wonder what the "over/under" would be mileage-wise between the premium paid for 100 octane gas and the additional expense necessary to twinplug and run pump gas?

Well I talked with EBS Racing to see what option I have... and apparently quite a few when talking about custom JE pistons.

I need to get my heads in to do some measuring to get back with Don @ EBS racing to see what would work best.

10.0:1 Mahle 98mm single plug pistons are available - you’d need to decide on the single v twinplug though. They’d be single plug for sure in UK.

https://www.*****************/fu/prod137451/Piston-engine-set-Porsche-911-CARRERA-32L-to-34L--1984---1989--Motronic-inj---98mm-/