Raceservice4u Twin plug systems
Twin plug systems were used on many flat 6 Porsche
race engines.
Examples are 917, 906, 904/6, 911 R, 911 2.5 S/T, RSR 2.8 and 3.0, 914/6, 935 etc.
Experts recommend installing a twin-plug ignition system if the compression ratio is higher than 10:1.
911 engines need a high dome piston to get this high compression ratio.
The combustion chamber will then almost be split in 2.
It will take too long for the ignition flame front to spread across the combustion chamber.
For a high performance engine you need the second plug to inprove the power.
Most Historic race regulations will not allow you to use contact less, a modern ignition system or a 964 dual distributor.
If you must use contact points; raceservice4u has the reasonably priced solution.
This page explains what distributors are availble. And you find some instructions and manuals for the twin plug systems.
Here your
find pictures of twin plug cylinder heads.
Raceservice4u can do that for you @ 200euro per cylinder head.
Here your find some pictures of other Twinplug distributors reproduction as well very expensive original ones.
Raceservice4u twin plug distributor is a replica which is based on a Bosch 911 distributor and reproduced rotor and cap.
The other alternative with Bosch cap and Rotor is extreme expensive. More than 2500,- euros for the cap and rotor only.
Raceservice4u found a 150-degree rotor in the US, which is used, for the Magneti Marelli replica.
Which work well with the Jaguar V12 cap.
And we have also Bosch replica caps and rotors available.
Samples from customers UK and Germany.
The construction has evaluated now. The main body is now made of die-cast aluminium. Which is a very solid construction and looks like the original.
The Bosch die-cast house will follow soon.
Standard Specifications
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Reproduction of the Marelli twin plug distributor based on a Bosch 911 distributor.
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Extra bearing for the rotor. This is a must to have for a reliable distributor
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Jaguar V12 cap.
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US-made rotor
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Diecast aluminium body in Magneti Marelli style.
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Maximum advance angel and curve can be changed rather easy. See below.
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The design is tested on hard race conditions
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All units will be tested on an Allen syncrograph before delivery.
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Delivered with data sheet is availble on request.
Available Twin plug systems
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Twin plug distributor turning clockwise for 911 2.0L and 2.2L with points and 27mm shaft
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Twin plug distributor turning anticlockwise for 911 3.0L. with points and 30mm shaft
Also available with Bosch rotor and cap.
The prices are from 2250,- Euros. See the RSR Shop.
Or do you want the original? This one is available now for 2.4 and 2.7 911 engines.
Prices are from 4900,- euro.
.JPG)
This one has 4 sets of contact points.
No ploblem to do 9000 RPM with this distributor.
Caps and Rotors available
Here we show you 4 examples of Cap and rotor combinations. Which are available in the market.
A and B are the exact copies of the original Marelli twin plug distributor.
The original rotor and cap of Magneti Marelli is not produced any more and only available as very expensive NOS.
B is the best availble copy off the Marelli rotor and cap. The quality is even better than the originals.
C and D caps are the Jaguar V12 type.
C is of the Magneti Marelli brand and quality.
D is a plastic brandless cap.
The D cap is with our race experience even better in wet conditions then cap C.
Cap D is the standard for our Twin plug distributors. And cap C is availble as option for a better vintage look.
The rotor for C and D are the same and the just the best available.
Both rotors need the extra bearing to hold it in the centre.
Not all suppliers have this option. For Raceservice4u is this standard.
There is a risk damaging the expensive rotor and cap.
For orders, quotations, information or questions please mail to raceservice4u@base.be
You get a respons within 2 workdays.
An option for Twin Plug systems are special contactsets for high PRM tuned engines. (>8000 RPM)
They are also used in the original Magneti Marelli distributor.
The price is 140 euro to build them in and the spare price is 80 euro.
Turning clockwise for 911 2.4 or 2.7L with one set of points
Reproduction of the Marelli twin plug distributor based on a 911 SC or 2,7 L distributor.
Extra bearing for the rotor.
Reproduced distribution cap
US-made rotor
Body made of diecast aluminium.
Maximum advance angel 27 degrees plus static advance angle.
The unit is tested on an Allen syncrograph before delivery.
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Example Report Twin plug distributor for Porsche 911 2,4L
Twin plug distributor data sheet
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Special Instructions for dual plug cars (two ignitions firing simultaneously).
To reduce maintenance and to synchronize ignition on dual plug, dual points ignition systems, both ignition systems can be triggered by the same set of points. This is most commonly done on Porsche twin plug engines.
Diodes are required to eliminate feed back between the ignition boxes so that independent control of both upper and lower spark plugs can be retained by the two ignition switches on the dashboard. Refer to the drawing for installation of the diode. Any one-amp diode will work. Install the diode in series with each wire to connection C. And with the end of the diode marked with the band on the breaker points as shown in the after picture below.
This setup will work with Perma-tune boxes, with Bosch boxes with 3 connectors aswell other DC-boxes.
Plug wire connections;
How to change advance curve
When you use a twin-plug system for your flat-6 and more than 10:1 compression ratio, experts say the maximum ignition advance must be 25 degrees or less.
Raceservice4u experience is that the 911 engines can handle more ignition advance for more power.
The other example is the Porsche 911 RS 2,7 with MFI. This stock engine has an ignition advance of 36 degrees and maximum 38 degrees are allowed, which is written in the factory data.
The raceservice4u engine runs with 33 degrees at high RPMs. We did a test to increase it to 36 degrees and the result was an increase of 4 Kw. We need to do more tests to find the optimum.
Changing the advance curve of a centrifugal advance system is not difficult to explain but not easy to get the right settings.
You can change the springs or the weights(blue arrows) to change the advance curve.
To change the maximum ignition advance is easier. Bend the stops (red arrows) to the center for reducing the max degrees.
You can do that also from the outside.
On the button of the distributor is an opening. With a screw-driver you can bend the stops or even the change the spring settings. Test the result with a syncrograph or on the engine and a flashlight.
Copyright Jan van Elderen
Copyright(c) 2002 Jan van Elderen. All rights reserved.