Twinspark - 964/993 & Motronic

[Magnum]

Morning all

I've managed to pick up a 964 dizzie in anticipation of going twinspark on my 3.2L "rennsport" interpretation, but continuing to use the Motronic (which will be re-chipped). This is a reasonably common modification, and importantly at sensible (to me) cost, although not strictly period looking with the single 12 lead dizzie.

I'm not too concerned about the latter point, however, the issue is that the traditional way of splitting the signal from Motronic ECU to two coils is using the purpose built Andial (in the USA) signal splitter. With Andial no longer operational and these signal splitters NLA, there is much conjecture but few specifics on how this is achieved nowadays.

This seems a very common question over on Pelican and the UK based Impact Bumper forum...…so of course this has Jonny of Classic Retrofit written all over it and I'm appealing to him all over the place .

Have you got such a system or recently done similar, or even know who has had this done, or even got an Andial splitter lying about (that could be looked at) - if so I'd be very grateful for any advice.

Many thanks

[fetuhoe]

You could fit a Canems DRH Performance Motronic ML1.X

This gives you a programmable unit so you don't need the re-chip and will work with the dizzy and associated coil pack.

It is a simple plug in replacement unit.

[Magnum]

Thank you Chris

Excellent advise as always! I've researched this (after seeing your message) and it appears to be an excellent product, however, I was hoping for a simpler solution (such as the Andial splitter) until I at least embark on a full engine rebuild with different pistons, camshafts etc. which lies somewhere in the future.

Any simpler ideas out there?

Many thanks

[smallspeed]

Could you just run it as a single spark set-up for the time being and then update with something like Chris recommended in the future?

[Magnum]

Gosh...

Smallspeeed - I hear you, however, like a small child I want the sweeties, but without paying too much! Based on research there is a lower cost interim solution where I can have twin-spark without stumping up almost 2000 pounds for the programmable ECU, software and mapping sessions.

By the way this is one of those areas that requires levels of cleverness and understanding I don't have, perhaps a degree in automotive electrical engineering might help.....I think I live only in the larger physical items realm, not the electron one!

The confusing part is that even the most "distinguished" experts on the Pelican Board have had heated arguments over the "lower" cost solutions - for instance as to whether splitting the signal from a MSD CDI will work properly with the argument focused on strength of spark etc. There are also other way of achieving this and I've had another "expert" suggest this is easily achieved by using 2 x TP100 ignition modules....whatever that means.

I think perhaps the interim/cost effective solution is the "half way house" - using the simplest, yet efficacy contested (although it seems to work for many), way and upgrading to full programmable ECU at some point in future when the entire engine is re-done.

Ultimately I think this is going to need face-time with a couple of experts and then a decision, however I don't want to be used as a guinea-pig and have extended phaffing. Problem is we're a little thin on the ground with those here in Cape Town......

Decisions.....I'll report back once this is done.

[smallspeed]

For my own interest - does this provide two sparks at the same time, per cylinder? Or is it one then the other?
Not sure whether it creates a "wider" flame front or a "longer" one (like on a rotary engine for example)

[911hillclimber]

Good question.
I thought it was 2 sparks simultaneously fired into the cylinder from the 2 sides of the hemi chamber so a fire front comes from two sides from the plug and meet in the centre so the max force of the explosion is on the piston faster.

[fetuhoe]

The traditional reason for Twin Plug 911 engines is really due to the SOHC design of the engine.

A traditional 'hemi' head such as a Lotus Twin Cam places the plug in the centre of the sphere and the flame propagates radially from this position.

With the off-centre plug of the 911 engine the flame path has to progress across dome of the piston and the early engines had deep combustion chambers and high dome pistons.

This can cause combustion issues and effectively causes incomplete combustion.

The early 906 engines always used a Twin Plug arrangement to avoid this problem and the 901/01 engines had a cam cover tha had locations which demonstrated that the engine was originally planned as a Twin Plug unit.

The original Marelli S121 Distributors fired the upper and lower plugs at the same time.

In simple terms the higher the compression - hence the taller the dome- the greater the benefit of Twin Plugs.

The re-designed combustion chambers of the later 2.2 and subsequent engines reduces the benefits of Twin Plugging unless compression ratios are increased.

I have always wondered why two sparks fired one after another helps to improve power.

If the delay is short then perhaps the second spark helps to stabilise the ignition kernel but if the delay is relatively long then it seems as of the second spark discharges into a plasma of exhaust gas.

I am not sure that I understand how increasing the rate at which the peak cylinder pressure is obtained changes power output.

I can understand how this may effect the torque curve in terms of shape but not the peak levels.

Twin Plugging becomes more important on heavily modified engines but I am not sure if it has much influence on otherwise standard engines.

964 and 993 engines obviously use Twin Plugs but they are relatively high compression and I would tend to believe they are used for emissions control rather then just horsepower gains.

[smallspeed]

The Mazda rotary uses twin plugs fired one after the other due to the changing shape, and the elongated size of the combustion chamber. They use significantly different "temperature" plugs which I guess helps get over the different mixture conditions? I assumed that the Porsche set-up would be two at the same time but thought I'd check first in case I'm missing something overly complicated with the control side of things (ie timing of the sparks relative to each other)

If they're both together, are there two coils or just one? I can't remember from my 964..

[fetuhoe]

Two Coils .

The original Marelli S121 Dizzy had 4 x sets of Contact Breakers and 2 x condensers and were a nightmare to setup.

The 'cam' in the dizzy had 3 x lobes.

It is possible to convert and existing 3.2 Distributor for Twin Plug operation and if you use a single trigger it will work with the Canems Motoronic otherwise an Andial type splitter would still be needed.

[christaylorsound]

I am also after the same answer to Magnum's question, indeed I asked the same question over on IB some time ago and have yet to receive the answer I'm looking for. Two coils are needed, one for each half of the dizzy. Both sparks fire at the same time. The benefits are indeed cleaner more complete combustion which has emissions benefits, but also a single off-centre plug firing the mixture better on one side of the piston tends to drive the piston down the bore slightly off-centre, increasing ring wear on one side of the piston. Biggest benefit is that with a single plug the spark must be timed earlier to ensure complete combustion, meaning some 'negative work' ie. resisting the piston's up stroke is inevitable. Twin sparks allows the spark to be timed later so less 'negative work' is done = more power.
Chris.

[Magnum]

Calling Jonny of Classic Retrofit, come in, come in...…………..You can run, but you can't hide....the people want splitters.....

[smallspeed]

I think either he or tim (impmad2000) are your best bet

I don't know enough about the standard system (ie if its like a BMW ECU / coil / dizzy set-up or if its CDI or whatever) but if its like the BMW system the coil is fired by the ECU grounding. if its similar it might be fairly simple to use that standard "ground" to operate two BIP coil drivers or similar, which could then ground a coil each if the issue is capacity of driving two from one ECU "signal".. Electronic stuff is not my strong suit, so fingers crossed johnny or tim come along soon! :D

[smallspeed]

I assume you've read this thread?..

http://forums.pelicanparts.com/porsche- ... lug-6.html

[fetuhoe]

There is a later thread in 2016 and one of the guys has developed a system which had a target price of $600 to replace the Andial Splitter.

It was supposed to be available from Pelican but has never shown up and doesn't seem to be available.

By the time you have added time you have added the new chip at $350 (?) and the $600 for the splitter you may not be far off buying the Canems unit.