Stephen Smith

I love telling people that my 964 is "twin spark" when they ask me about the engine, to have 12 spark plugs is great (except they cost twice as much to replace).
But does anyone know precisely what measurable value having "twin spark" does for the 964 engine in terms of any additional x hps or x torque or any other form of measurment or economy scale.
Oh, I'm going to the first F1 practice session tomorrow for 2002, pity there isn't any porsche in F1 at the moment, but I can always go home and enjoy my own F1 (964). I live 1.25 kms from the race track and its hysterical to drive along it during the year where the max speed limit is 50kph! I went along it the other day and in a 40kph zone (pit straight) was amazed to see police with a laser speed gun looking for speedsters.
<img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

Bill Wagner

The dual distributor allowed the fuel to be ignited more completely and faster than it did on engines preceding the 964. This allowed the compression ratio to be increased slightly, the car burned fuel more efficiently reducing emissions, and lower grade fuels can be used (91 using (R+M)/2 method instead of the typical 93).

All of this, of course, assumes the distributor belt hasn't broken or skipped a tooth

CHEERS <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Bill Wagner

Christer

The 3.6 engine is relatively short-stroked and therefore has a rather large bore. I think I read somewhere a while back that the twin ignition system was needed to actually ignite the fuel efficiently due to the size and shape of the combustion chambers....Can anyone else confirm this - i.e. that I didn't just make that up?

Christer

George Stevens

Christer

If you did make it up, it sounds quite impressive!!!

I think you deserve two more stars!!!!

<img src="graemlins/r.gif" border="0" alt="[king]" />

Adrian

As Bill quite rightly points out. The twin spark plugs were installed to improve burn efficiency purely for emissions purposes and for lower octane fuels used in various countries in the world. Hence the critical important of variant and country codes jumper plugs for the DME. Nothing else. You do not get more power or any other advantages except to help you pass the emissions test. End result is an increased maintenance cost, not just in parts but labour as well. Remember the dual ignition system has more than just six more spark plugs,
Ciao,
Adrian
911C4

Christer

George

If I did deserve 2 more stars it certainly wouldn't be for my technical expertise! I was going to say possibly for wit but that's even more debatable.....

BTW, I borrowed a digital camera to take pics of my Boxter S wheels. Unfortunately in the 2 weeks I had the camera, it and the car were never in the same location even for a few minutes. I have now had to return the camera to its rightful owner as he went skiing today - I WILL get them done when he gets back...

<img src="graemlins/oops.gif" border="0" alt="[oops]" />

slant911

How is it that the 993 series with the same basic size engine/layout produce more power with lower compression ratios? Just curious??

George Stevens

Slant

The 993 is essentially the same as a 964 motor.

For the 993 Porsche "optimised" the performance of the 3.6 engine.

The increase in power (on pre varioram cars) is mainly down to improved breathing, the 993 has an improved induction and exhaust system and better air metering with a film sensor rather than a flap.

That's why it is difficult to acheive good measurable gains in BHP and torque on a 964 without improving the breathing.

Geoffrey

To further add some technical tidbits. Since the Porsche cylinder head is a 2 valve design, one can't place the spark plug in a place where it will ignite the fuel mixture evenly. Some manufactures design the cylinder head with a "squish" area to keep the fuel located next to the spark plug. I believe Porsche expermented with this design on the 962 engine. Almost all of the Porsche race engines 906E, 2.7 RSR, 2.8 RSR, etc. have dual spark plugs to evenly burn the fuel. You get approximately 3-5hp out of having the dual plug setup depending on displacement and compression. The 964s have dual plugs primarily to reduce emissions especially on during the cold start situations and allows also it to run a higher compression ratio.

BlueMax

There is a distinct advantage to twin-sparking a gasoline engine. Effectively, when you ignite a gasoline/air mixture you create a flame front that travels across the combustion chamber at a fixed speed. So as a posted earlier, if you increase the bore, the time required increases for that front to travel across the whole cmbustion chamber and ignite all of the mixture.
If you use two plugs and ignite the mixture from two opposite ends, the time for complete ignition is decreased. As a result of more complete and faster ignition, you can typically run higher compression rations, which Porsche did with the 964. Without higher compression, you just get a motor that revs more willingly and faster but no power increase.

Paul

Stephen Smith

So from what Geoff and Max say eh, I was right, I think in thinking that the "twin spark" did offer an efficiency/power advantage than the "single spark" system. If the combustion occurs quicker then the acceleration of the engine must be faster.
Although it makes sense that the fuel combustion is more efficient, it seems to me that this must translate to more hp and therefore improved engine acceleration.
Regards
Stephen Smith
93 Tip C2 (Midnight Blue)

Jacks911

"At an early development stage, a switch to four-valve cylinder heads had been envisaged, but this caused serious cooling problems and was abandoned in favour of the twin plug heads, which provided a 4 per cent increase in power together with a 3 per cent reduction in fuel consumtion."

Paul Frere - in his book, Porsche Story

Paul has a lot of great things to say about this engine (he says great things about all Porsches).
Included are comments that confirm all of what has been said in this thread, but this summation nets it out.

The 4% if compaired to the previous 3.2 - 217 hp cat engine = about a 9 hp improvement from twin plugs.

I liked the book and recommend it as a resource to put into accurate perspective the significance of the 964 in the history of Porsche. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Jacks911

"At an early development stage, a switch to four-valve cylinder heads had been envisaged, but this caused serious cooling problems and was abandoned in favour of the twin plug heads, which provided a 4 per cent increase in power together with a 3 per cent reduction in fuel consumtion."

Paul Frere - in his book, Porsche Story

Paul has a lot of great things to say about this engine (he says great things about all Porsches).
Included are comments that confirm all of what has been said in this thread, but this summation nets it out.

The 4% if compaired to the previous 3.2 - 217 hp cat engine = about a 9 hp improvement from twin plugs.

I liked the book and recommend it as a resource to put into accurate perspective the significance of the 964 in the history of Porsche. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Jacks911

"At an early development stage, a switch to four-valve cylinder heads had been envisaged, but this caused serious cooling problems and was abandoned in favour of the twin plug heads, which provided a 4 per cent increase in power together with a 3 per cent reduction in fuel consumtion."

Paul Frere - in his book, Porsche Story

Paul has a lot of great things to say about this engine (he says great things about all Porsches).
Included are comments that confirm all of what has been said in this thread, but this summation nets it out.

The 4% if compaired to the previous 3.2 - 217 hp cat engine = about a 9 hp improvement from twin plugs.

I liked the book and recommend it as a resource to put into accurate perspective the significance of the 964 in the history of Porsche. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Adrian

Dear Jack,
I am afraid I do not see how a 3.2L single spark plug engine is compared to a 3.6L twin spark engine and out of all the changes made to create this new engine including a completely reprogrammed and remapped DME, 0.4L increase in capacity etc etc and somehow somebody can extrapolate from all these changes and allocate a HP increase percentage to just one change. I also have to disagree with the fuel consumption as well but this is somewhat subjective. My Carrera 3.2 colleagues get far better fuel consumption than I do. AWD doesn´t help either.
I always have problems with allocation of figures to just one change. Please forgive me if I am wrong but wasn´t one of the European versions of the 3.2 Carrera putting out 231HP at the flywheel. The 964 3.6L puts out 247HP(250HP) at the flywheel an overall increase of 16-19HP or let us say 10% all things considered.
Great for theoretical discussions,
Ciao,
Adrian
911C4