Geoffrey

Adrian,

You are correct, the 964 has a number of significant improvements over the previous 911 and I won't mention them again. When comparing a 3.2l with twin plugs and without on a dyno, there is approximately 3-5hp to be gained...apples to apples comparison.

Jacks911

Adrian & Others,

Sorry for the triple post. My browser locked-up when I tried to post and when it reset ??? I should be more patient.

As to your comment Adrian, I just related what I read from Paul Frere's book. I am not an engineer, but do understand that a simple estimate of impact, i.e. horse power, of one design factor (twin plugs), cannot be extracted from the whole when so many changes come together as in the 3.6 engine.

I like reading the many books, reports, articles, and yes Rennlist Posts, that discuss the 964 and its design. I take all of this as I do most writings, to be some fact, and some opinion. Paul seems to be respected in his reporting of the 911 Story, so I felt comfortable passing the "Qoute" on to others. In his book, He picks the 217 hp Cat equiped 3.2 as a close comparison to the 3.6 to analyse the net performace improvement, because it comes close to the emmision standards the 3.6 exceeds.

I'll also note, that the same +4% hp / -3% fuel consumption statement is made in Tobias Aichele's book, Porsche 911 Engine History & Development.
Fact or Opinion ???

In any case the 964 3.6 was and is a significant development and what has come later evolves from this great engine (IMHO).

Adrian

Dear Jack,
I know you were only quoting from the books. I was not criticising yourself at all. I was sort of saying that it is hard to believe this stuff. A lot of it has become folk lore. I work in my day job in aviation. What sales and marketing deprtments tell us and the facts are often very wide apart indeed. I am also not criticising Paul Freres´authorship either. He is only writing what he was told. Having been down this track myself I have a fairly good insight into such things,
Ciao,
Adrian
911C4

Cupcar

Here's even more "folklore" (for what it's worth) I've "heard" over the years from guy's who have compared things on the dyno regarding twin plug ignition:
1)Twin plug increases knock resistance ie a higher compression ratio (and therefore more power) possible for a given octane fuel
2)There is a very modest power increase, 3-4 hp if twin ignition only change in engine. One person claimed he saw this increase if engine dyno runs were made with upper plug ignition off and with bottom plugs firing only-go figure on this one, maybe due to proximity of plug to exhaust valve if true?
3)The early 2 liter cars benefit most because combustion chamber is deeper and less efficient
4)Twin ignition engines seem to have better throttle response. <img src="graemlins/sleep.gif" border="0" alt="[sleep]" />

Bill Wagner

Cupcar:

I would have to question what you call "folklore". If I understand the reason the twin spark was used it was to allow a higher compression ratio with the car, hence more horsepower. The twin spark doesn't create the extra horse power...I suppose you could say it makes it possible though. Without the twin spark the car will suffer from pre-detonation.

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

Cupcar

Bill-Exactly, along with perhaps some emission related issues in modern times through improvements in combustion process. I say folklore because I have not done any hands on dyno runs myself nor have I seen dyno data. I have only talked with different people who have done dyno work through the years. Their stories=folklore to me until I see real results written up. Steve Weiner probably would be interesting to hear from on this topic. <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

roelricardo

I come to the conclusion that it would be easy to dyno a car with twinspark, run many times and then disconnect 6 of the plugs and compare!!, I think this will be a truly measure, same car, conditions this will conclude in interesting numbers!!

All of this is because I a planning to do my car twinspark, du to the cost effectiveness I am thinking this 2 times.

What do you think?

Any out there willing to do this experiment.

My car 911 SC 3.0 with PMO´s, Webcam and JB pistons in paper look like the twinspark upgrade could be a great option.

Ricardo

Steve Weiner-Rennsport Systems

Ricardo,

Done this MANY many times in the past 44 years,...

All things being equal, twin-ignition is worth 7-10 BHP over single-ignition, once timing values are optimized.

JohnK964

Back in the day we would twin plug Harley shovelheads
which have a very similar combustion chamber to a 964 we could run a bit more advanced timing run higher compression ratios all for the elusive MORE POWER and ain’t that what we all want😎👍

roelricardo

So, for more than 2,000 US on this project I will get no more than 10 HP, I think this mod is a waist of money IMHO!

I really appreciate you thoughts and comments, I have just decide not to do it!!

Sincerely

Ricardo

roelricardo

I made up my mind, for a project that is more than 2000 US, and a gain of 10 Hp I think is a very bad idea, I appreciate the info regarding twin Spark conversion. I prefer to spend that money on suspension or brakes upgrade that on any track day/Autocross will blow the 10 HP increase any day.

Turbohead

So why is it that Porsche Turbos of that era were designed for single plug.?? Compression pressures rise when engine goes on boost.
Elliot

Steve Weiner-Rennsport Systems

934's were single plug, per FIA Gp 4 rules. 935's were twin-plug, per FIA Gp 5 rules.

956's used a version of the watercooled Indy motor and naturally those were single-ignition engines.

Initially, IMSA required the 962's (aircooled) to use a single-ignition version of the single-turbo 935 engine, but later on, twin-ignition was permitted as other cars became more competitive. Finally, the 962C cars used a version of the 956 watercooled,twin-turbo motor.

Turbohead

Yes but production Turbos 930,965,993 TT all were single plug design. Why ?
Elliot

Porschenut_Lee