Twin plugged.

[mycar]

This car appeared in Octane magazine back in September 2012. The spec given below the photograph is as standard for a B Super, 60bhp, 81 lb/ft... But... this engine is blatantly not standard, with twin coils and a busy looking dizzy cap.

Does anybody know more about this car or twin plugging a 356 engine ?



Regards, Mike.

[mycar]

Bigger picture... photobucket isn't what it used to be.



Mike.

[Nige]

Is that not a Carrera engine then?

[Lightweight_911]

No, it's not a Carrera (or a Factory twin-plug engine) - didn't see the article but I think it's an Andry Prill engine.

[mycar]

The article is about topless sports cars, namely this 356, an MGA and a Giulietta. Nowhere is there any mention of this Porsche being anything other than a standard B 1600S. bit misleading really.

Reading the article again, the car is credited to Taylor and Crawley but it's long since left their stock list.

(They do however show some wonderful vehicles, including the Silver TR, now sold. http://www.taylorandcrawley.com/current-stock/all/ )

[mycar]

This is the Carrera engine Nige, with the donut shaped fan cowl...

[/URL]

(Must get round to tidying my garage up.)

Mike.

[Nige]

Yes of course , my mind isn't functioning correctly today.

[mycar]

I knew you knew.

Sorry you're not feeling yourself.

Mike.

[neilbardsley]

Can I ask a stupid twin spark question?

Most/all twin spark systems I've seen in photos have double the number of spark plugs. Somewhat given away in the name you would probably quickly add. Seeing that the idea is that you have another plug in the head so that more of the fuel gets used. Has anybody just twin sparked the same plug. I was just think that you keep the distributor twin spark distributor but have the two leads going into a single lead and single plug? Therefore you get the same timing as a normal twin spark but from 1 plug so no need to remachine the heads. The idea being that the second spark uses an fuel not used in the first? Maybe this idea is complete rubbish because you need the plugs in different places?

[KS]

Maybe this idea is complete rubbish because you need the plugs in different places?

Answered!

[johnM]

Hi Neil

The reason you twin plug heads is this.

The two sparks are at the same time not staggered.

As you increase the compression ration the dome of the piston becomes more pronounced, ie higher the compression bigger the piston dome. In our 911 engines the spark plug is positioned to one side of the combustion chamber. When the piston is at top dead centre the dome effectively splits the combustion chamber in two and the flame struggles to propagate across the top of the dome with only one spark plug, the second plug is to ignite the other side of the dome and this provides a better, fuller burn.

Hope that helps.

[neilbardsley]

Hi Neil

The reason you twin plug heads is this.

The two sparks are at the same time not staggered.

As you increase the compression ration the dome of the piston becomes more pronounced, ie higher the compression bigger the piston dome. In our 911 engines the spark plug is positioned to one side of the combustion chamber. When the piston is at top dead centre the dome effectively splits the combustion chamber in two and the flame struggles to propagate across the top of the dome with only one spark plug, the second plug is to ignite the other side of the dome and this provides a better, fuller burn.

Hope that helps.

Thank you that helps a lot but why does the dome of the piston become more pronunced as the the compression ratio increase? I thought that this was about having less spaces in the cylinder at TDC so why does the shape of the of the piston change?

[johnM]

The cylinder head/combustion chamber is dished so the larger the dome on the piston the more space it takes up in the cylinder head and higher the compression ratio.

HTH

[johnM]

If you ignore the fact the exhaust valve has fallen off you can see the dish in the head and the offset spark plug.

[Nige]

Basically having two plugs aids even ignition of the fuel mixture, ensuring maximum energy (biggest bang) is extracted from it within the combustion chamber.

A bit like lighting a piece of paper at both ends, it will burn much quicker than just lighting one end.