[QUOTE=gliding_serpent;8488790]I suspect sw could adjust for altitude. What type of dyno ( mustang, dynojet)? I wonder if the altitude factored in.

Certainly a custom chip could be programmed for a specific altitude, but not for a 10,000 ft range of atmospheric conditions. The dyno is a Mustang with additional software and it is equipped with a weather station to factor for current atmospheric conditions.

Indeed, even 100LL has a LOT of lead in it and thats not good for both oxysensors and cats. 100 octane unleaded race gas is a FAR better choice in every way.

There are really too many variables to offer specific numbers, but its substantial and quite noticeable. Twin-plug 3.4's should never use those wedge-dome pistons; the normal double valve relief ones such as Mahle RSR ones are the right ones for those applications since even at 10.5:1, they are safe for pump gas.

Just collecting some good links on 3.4, single vs twin ignition, je vs mahle

Discussion of many topics, including je stepping up quality to mahle with tighter clearances.
Welcome to Rennsport Systems, Porsche Performance Products for the 21st Century

Je vs mahle
http://forums.pelicanparts.com/911-engine-rebuilding-forum/161373-je-pistons-vs-mahle-2.html

Je durability discussion linked to above thread
http://forums.pelicanparts.com/porsche-911-technical-forum/189275-je-piston-longevity.html

The threads you refer to are quite old. I know that JE improved their products in the last couples of years. These are photos from the last series that they made (series 32P). I just received these 3 weeks ago. they are 3.4, 10.5:1. Sorry I don't have a picture of the dome that show the valves relief, but if you need one, I can send you one later this week.

http://forums.pelicanparts.com/uploa...1424105579.jpg

Pretty clean looking. Do they do single plug style 3.4's?

Re JE Pistons... are they more safe to run single plug than the standard Mahle piston designed for CIS?

What is a safe CR to use with single plug using JE pistons on a 3.2SS running on CA 91 octane?

David

JE makes many pistons and you should call them to see if they offer the wedge-dome ones. We mainly use Mahle's.

I wouldn't use more than 9.5:1 on 91 octane so you can maintain reasonable ignition timing.

If I understand your question correctly, yes, they do make a lower compression 9.5:1 piston that can be used with a single plug system

These are their off the shelf regular pistons:
PORSCHE - PORSCHE 911 (Automotive Section) - JE Pistons

I bought the product#274645 as marked under the piston (10.5:1 for my twin plug system.)

As Steve was saying, they make many pistons, and they have different lines available. I even think they can make custom or special order products. You should contact them to have the most accurate information.

I did a bit of research and the JE pistons, plus having your own cylinder bored, was the cheapest way to achieve 3.4L.

Thanks Steve, really appreciate it!

The 3.3 930 has 97mm pistons, and is generally considered to benefit from twin plug - even with a flat piston. It's the diameter that's the problem - but a piston crown doesn't exactly help flamefront propagation either...

Personally, I'd twin-plug the heads while they're off and fit a J & S Safeguard.

If the J&S triggers and retards ignition, then at least your motor is protected from detonation. This gives you time to drill plug holes in a spare set of valve covers and worry about getting an ignition splitter - not to mention getting another ignition map to suit twin-spark...

I have prevented myself from entertaining much thought of twin plugging.

Now that i have a good understanding of increasing displacement, compression ratios, and piston top design for single vs twin plug. I also understand benefits and indications of twin plugging... So now the million dollar question: How is it done? Where does one drill? Is there a machining process i can provide to a local machinist? Buying the kits seems easy... But we have no local shops that do this kind of thing regularly, and sending heads to the us from rural eastern canada does not add up in my mind.

I still can't get past the mental block of overtly modifying the design of the engine from original. Twin plug a 3.2 and is is just no longer the same, even if it is "better."

Not sure what a J+S safeguard is. May research if the machining thing is doable locally. Otherwise, it would be too much work to peak my interest.

The cylinder diameter is part of the problem for sure... But the real problem is the distance the combustion flame has to travel. Had the plug been central, the longest distance the flame would have to travel would be less, even for a much larger cylinder. But the two large central valves per cylinder forces the spark plug off to the side, which is really a suboptimal location for efficient burn. Thus the compression ratio and octane limits without twin plug.

The beauty of the MAx Moritz piston top design is that it essentially attempts to reshape the combustion chamber to make the single plug in effect more central. Does it make a huge difference? No, but one could argue it allows an increase of 0.3:1 compression (allowing you to go from 9.5:1 to 9.8:1 on single plug and the same octane). Better than a kick in the pants. I don't have hard numbers to back that up, but armchair logic tells me that I am sure people with far more experience and knowledge of such things probably already tried to push those limits, and the 9.8:1 was the best they could do. Physics always wins.

JE does make custom wedge domed pistons for our cars. But you will need to pay a premium (~1400$ for a set) and provide a piston with the wedge design to copy. Other shops have already gotten them to produce such custom pistons (Max Moritz copies), likely in batches that they sell out of their own shops. I think EBS is one. I suspect most shops want you to buy through them, so will not share their "custom" design, and JE protects their customers. Can't blame them. I had a thread about generating a group design/order, but it did not take traction.

964 cams
 

I read with interest advice related to conversion from a 3.2 to 3.4 ...
I drive an 87 Carrera already with a 100 cell cat and a free flow 1 in 1 out Monty muffler & a 91 oct. Steve Wong chip fitting this set up.
I am aware of the max moritz P&C requirement but I fail to identify BY PRODUCT # from our host the 964 cams required to complete the set up...
Can someone help in identifying it for me?

964 cams are from the '89-'94 ( I think) engines and can be bought new and used or have your existing cam reground to this profile.

Here is the pelican page that lists them:

1992 Porsche 911 Carrera 2 Coupe - Camshafts & Timing Chains - Page 1

GS, just twin plug it!!!!! This would allow you to stay at 3.2 and run higher compression :-)

This bits and pieces do show up here once in a while quite reasonably priced. The hard part to find is the Andial Splitter.

3.2 to 3.4
 

Thanks but no thanks...my interest is in increasing capacity of the engine with compression below 10....(98mm & 98.1 comp & 964 cams, SW chip)...it is a more expensive option but it is a clean and proven one.
my car has 82,000 miles on it, it runs great but one day it will require an overhaul and I am preparing for it theoretically...knowledge is free.

Many machine shops that have done this more than once have built jigs, and it's pretty much a no-brainer for them.

At least 3 guys on this board have done this themselves. Thought I had more.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/584651-twin-plugging-using-14mm-plugs.html
http://forums.pelicanparts.com/911-engine-rebuilding-forum/171111-twin-plug-diy-2.html


Sorry. Twin-plugging is "modifying", but slapping on a big-bore kit isn't? :D

This is true; JE has made custom pistons to our specification for many years which they are bound not share with anyone and I know many other engine builders who do the same,. :)

For street engines where longevity is THE most important aspect of a rebuild or suite of modifications, we prefer Mahles.


Wellll,.....I'd kindly disagree. :) Porsche used twin-ignition on almost every air-cooled race engine from 1955 to 1998, except where rules specifically forbade it. Twin-plugging a 3.2 (or any other such motor) doesn't change anything but its appearance due to the distributor and 6 additional plug wires.

JMHO,..but from an appearance POV, using coil packs for twin-ignition DOES detract from the original configuration and I don't find them attractive at all. We use COP ignitions where aftermarket Engine Management is installed or an RSR-type distributor which does look period.

All that said, if its something you just don't like, then your best option is to either simply leave the engine factory original or install a set of the MM 98mm pistons since its more or less invisible.

It's probably the simplest, least intrusive way to add a Bosch knock sensor and 20th-century knock detection/adaptive detonation control to older cars with distributors or Motronics.

J&S Electronics SafeGuard Indivdual Cylinder Knock Control

Piggybacks into the ignition circuit, listens for knock and doesn't do squat if it doesn't need to. If it hears detonation, it backs off the cylinder that's knocking - but it's always trying to advance the timing again, e.g. when it doesn't hear detonation anymore.

This is potentially great for ignition curves that are a little marginal on sketchy gas and heavy load on a hot day - but fine 99.9% of the rest of the time... No need to give up the throttle response when you don't have to...

You could either run as much advance as you want, and use the Safeguard to keep the motor on the ragged edge, or simply use it to provide protection against a tank of bad fuel or a clogged injector.

I know I was very grateful I had one fitted to my (then) CIS 930 when the distributor plate stuck fully-advanced, giving me something like 25 more degrees of timing than I wanted below 3500 RPM and lighting the J&S up like a christmas tree if I used any throttle at all...

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/611409-my-j-s-safeguard-paid-itself-last-week.html