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Adrenaline Junkie
 
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Advantages of Twin Plug

I've done the search. And it's exhaustive, believe me. I can't find it so,,,

Please tell me from your own experiences or possibly statistically what horsepower/torque gains can be expected with just the addition of twin plug set up on the turbo. Do the numbers reflect the effort?

Of course numbers could be expected to be different depending on what the displacement, boost, compression figures are.

Another coupled question is; if considering the twin plug set up, are there other component's that ARE required to make this addition function properly? And if possible, could it be run on CIS or is another fuel type required?

Thanks for teaching!
Old 03-03-2008, 09:48 PM
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Old 03-04-2008, 08:07 AM
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I think twin plug is almost a must on a high compression, high piston dome engine, but I don't think there's a lot of benefit from twin plug on a 930 engine since the piston is virtually flat. I went ahead and did it anyway because of the large bore (98mm) and plug being off to the side of the combustion area. It was one of those, "well I've done everything else, I might as well twin plug"
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Old 03-04-2008, 08:34 AM
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Hi,
I'll bite! I have an older BMW R100RT bike that I twin plugged long before I did my Porsche. I twin plugged the Porsche for the same reason. Back in the Late 70's and 80's when Leaded gas was going away and getting 100 octane fuel started disappearing, air cooled BMW bikes started having real problems with Fuel issues. A very common mod to alleviate this was to twin plug the heads.

I'm listing these anecdotally and without reference or Engineering facts.

1) Twin Plugging makes you engine less prone to detonation
2) Makes your car less prone to Bad Gasoline related pinging
3) Given Identical Engines, you can retard the timing on the twin plugged engine relative to the non twin plugged engine to make the same power

I am moving and have packed up my Bruce Anderson book. But I know he addresses Twin plugging in the book.

People on the Forum have done it with CIS to good effect. I've seen MSD and Electromotive systems used.
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---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 03-04-2008, 08:42 AM
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I haven't done this to my own car but many of my colleagues have. It's not something I would do as a stand-alone but would consider it if the heads were already off.

The benefit for a mild 930 would be driveability, or a more smooth running engine. I would expect zero HP gains and minuscule torque gains. Added protection against detonation is a plus.
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Old 03-04-2008, 08:51 AM
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Quote:
Originally Posted by RarlyL8 View Post
I haven't done this to my own car but many of my colleagues have. It's not something I would do as a stand-alone but would consider it if the heads were already off.

The benefit for a mild 930 would be driveability, or a more smooth running engine. I would expect zero HP gains and minuscule torque gains. Added protection against detonation is a plus.
What he said ^^^^^^

I never expected 1 HP from it. I just wanted detonation mitigation. If it saved me from one bad tank of Gas it was worth it.

There were claims of increased HP because you could fire off your mixture later thru ignition retarding, but I've never seen a graph to show this.
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Last edited by les_garten; 03-04-2008 at 09:09 AM..
Old 03-04-2008, 09:07 AM
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Seems several articles I've read you can expect 10hp.
Old 03-04-2008, 10:37 AM
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Thanks, guys.

So, for the most part, increasing the spark insures that the combustion will be optimized, right?! Thus insuring the best chance or decreasing the chances of improper firing.

And, if any,, minimal horsepower gains could be expected.

Was that 10 hp in a N/A situation, Jess? Or could that be also measured in forced induction situations, too?
Old 03-04-2008, 10:56 AM
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Quote:
Originally Posted by les_garten View Post

I never expected 1 HP from it. I just wanted detonation mitigation. If it saved me from one bad tank of Gas it was worth it.
Lesson learned here, Les!
Old 03-04-2008, 10:57 AM
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Hi,
The Porsche head is a large deep bowl with the plug off to one side. You time a certain amount of degrees BTDC to give the flame time to travel across the head to light the mixture. This wouldn't be as big a problem if the spark plug was centrally located and there was a "squish" area to light.

The two flames of the dual spark help out with these issues. That is why you can actually retard from the normal timing.

Soon, some of the Engineers on the Forum will come in and correct or shore up my statements.

I'm just a shadetree after all.
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Old 03-04-2008, 11:20 AM
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Myself, and others like me, learn from people like yourself.

If I go a day without learning, I certainly go a day without living.
Old 03-04-2008, 11:36 AM
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Actually you guys have hit it on the head with the explanations given:
1) Twin Plugging makes you engine less prone to detonation
2) Makes your car less prone to Bad Gasoline related pinging
3) Given Identical Engines, you can retard the timing on the twin plugged engine relative to the non twin plugged engine to make the same power
Expanding on item 3 allows you to advance the timing further than single plugs allow thus to gain more power. You can also run higher boost levels with the single plug timing values to make more power without detonation.
I have read that the theoretical limit to diameter size in the aircooled Porsche cylinder is around 95or 96mm before you start having trouble with combustion ie detonation. Basically the flame front takes too long to travel across the entire cylinder diameter at this range. This explains why Porsche went dual plug on the 3.6 liter engines.
Twin plugging allows you to run more technology improved ignition systems and smaller plug gaps as well since you will need to replace the single plug distributor anyway. It is alot of expense, you need to weight that against the overall advantages mentioned here.
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Old 03-04-2008, 12:01 PM
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I've scanned the postings and don't see it that twin plugging is generally accepted to allow one additional point of C.R.
This applies N.A. or TURBO, once boost is adjusted, so there is potential HP improvement IF you take it. I've read that all Porsches will run smoother and was considered to be good for 10% on the smaller motors. Those of us who fly can witness the impact of twin plugs on vs single and it's the same issue as offset plug(s) and flame front movement.
I think with todays fuels, and 930s not having knock sensors, it's best taken as an insurance policy than HP.
Old 03-04-2008, 12:31 PM
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I think it needs to be said that twin plugs alone do nothing for HP. The result of adding the second set of plugs is improved combustion efficiency that can be utlized to tune more power into the engine in the form of more boost, advanced ignition timing, etc. In other words the safety threshold is raised.
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Old 03-04-2008, 01:54 PM
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Quote:
Originally Posted by RarlyL8 View Post
I think it needs to be said that twin plugs alone do nothing for HP. The result of adding the second set of plugs is improved combustion efficiency that can be utlized to tune more power into the engine in the form of more boost, advanced ignition timing, etc. In other words the safety threshold is raised.
But that is the same as saying that your selection of fixed compression ratio alone has no bearing on HP which is not true. Certainly when you make any component change you will tune accordingly based on fuel octane. Twin plugs allow more power production while retaining the SAME safety margin on a given octane.
Old 03-04-2008, 03:00 PM
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Quote:
Originally Posted by RarlyL8 View Post
I think it needs to be said that twin plugs alone do nothing for HP. The result of adding the second set of plugs is improved combustion efficiency that can be utlized to tune more power into the engine in the form of more boost, advanced ignition timing, etc. In other words the safety threshold is raised.
Here we go again with this. Of course any change you make may require adjustments to make the change work correctly/efficiently. So what. You put on a low restriction exhaust or intake and you may need to adjust AFR. You drop in a CAM, you may need to adjust Fuel delivery, intake ports, manifolds, ignition timing, etc. So what.

It's a sliding scale as to what is the REAL performance enhancer, there are very few SAFE enhancements that are pure. Most of them rely on Facilitators Like Intercoolers, Headers, Blah Blah Blah.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Take a motor that is optimized, change nothing but dual plug it. Will it make more HP? Maybe an amount that is inconsequential, I don't know, and opinions vary.

Take that same setup and advance the timing some more and see higher HP. What made the HP? The timing advance? You couldn't have done it without the dual plugs.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Take a motor that is optimized, change nothing but dual plug it. Will it make more HP? Maybe an amount that is inconsequential, I don't know, and opinions vary.

Now up the CR 1/2 to 1 point and see higher HP. What made the HP? The Compression Ratio? You couldn't have done it without the dual plugs.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>

It's sorta like Huntin' Foxes. The Horse, The Gun, The Dog, and the Hunter have to work together as a team. It's called synergism. Who killed the Fox?? The Gun, it can't shoot itself. The Hunter?? He can't do it without the gun. The Horse?? The Dog?? They had to be let out, trained, and directed by the Hunter??

This all being said, I go back to my original premise, I Dual plugged so that I could rest easier when I pushed the LOUD Pedal. The combustion chambers on Porsche's are Beautiful to look at. The make excellent paperweights!! Polish one up and put it on your desk and see what people say! The problem is that they are just waiting to detonate. Dual Plugging in this world or Gruel we call Gasoline just makes sense if you are a Hot Rodder. Don't change your CR, don't change your timing, just feel like you are a little safer out there.
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Old 03-04-2008, 05:37 PM
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I'm glad it's easy for you to understand, but it needs to be said in a way that everyone understands. It is important to know how and why not just yes or no. What works in one application may actually hurt you in another. If the spark plug on a 911 engine was mounted dead center we wouldn't even be having this discussion.
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Old 03-04-2008, 05:53 PM
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I've had experience with two examples of twin-plugging engines. The first was a slightly modified 1.9 liter 914. I discovered the ability to reduce the timing from 7 to 28 degrees down to 0 to 20 with much more reliable power delivery. Horsepower gains, probably not. However, there was a noticable difference through the middle of the usable power range - around 2500 to 4000 RPMs. ( I had the ability to swith from single to twin with timing adjustments from the driver's seat)It just plain felt stronger. It had a mild cam, 9.0 CR, Kerry Hunter header and Dellorto 44 carbs. I drove it almost every day and to and from Sebring to participate in several PCA DE events without a failure. The car had 25,000+ miles on that engine build when I sold it and I never had any service issues other that the usual maintenance. I was the least expensive and most enjoyable Porsche I ever owned prior to being spoiled by turbo power.
The second example was a '77 Triumph Bonneville 750 which is notiously prone to pinging. I used the experience gained to determine the advance curve which was similar to the 914, although I don't recall the exact numbers. It was nearly impossible to make it ping with the second plug and revised timing. It had to be insanely hot, such as idling in traffic for a while before it would make any unnerving noise.
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Old 03-04-2008, 06:14 PM
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Quote:
Originally Posted by RarlyL8 View Post
I'm glad it's easy for you to understand, but it needs to be said in a way that everyone understands. It is important to know how and why not just yes or no. What works in one application may actually hurt you in another. If the spark plug on a 911 engine was mounted dead center we wouldn't even be having this discussion.
Not sure what you mean here, we just talked about the location of the plug and why two plugs are better because of flame travel distance with one plug. I don't believe there is any detriment to twin plugging. Some people have mentioned cracks. Seems isolated and certainly not warned of by Bruce Anderson as FAIK.

Do you have experience where twin plugging had any detriment to safety or performance?? This isn't some VooDoo made up on this forum, Porsche Started it. They were Twin Plugging before Wayne ever saw a Pelican in Flight and said, Hmmm?? The point is it's not just yes or no. Have you read Bruce's book?? Why does every Porsche machine shop advertise these services?? I'm having some trouble figuring out where you are going with this other than the sake of argument.

Are you going to get 10% HP from this mod with "perfect" implementation?? I'm skeptical, but open to the possibility in a perfect environment. I think Using it as a safety factor in a Positive manifold pressure environment, with these head geometries, there really is no discussion. Maybe a little Pony advantage, maybe not, but I wouldn't bank on it.
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Old 03-04-2008, 07:05 PM
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Quote:
Originally Posted by 930turbo View Post
I've had experience with two examples of twin-plugging engines. The first was a slightly modified 1.9 liter 914. I discovered the ability to reduce the timing from 7 to 28 degrees down to 0 to 20 with much more reliable power delivery. Horsepower gains, probably not. However, there was a noticable difference through the middle of the usable power range - around 2500 to 4000 RPMs. ( I had the ability to swith from single to twin with timing adjustments from the driver's seat)It just plain felt stronger. It had a mild cam, 9.0 CR, Kerry Hunter header and Dellorto 44 carbs. I drove it almost every day and to and from Sebring to participate in several PCA DE events without a failure. The car had 25,000+ miles on that engine build when I sold it and I never had any service issues other that the usual maintenance. I was the least expensive and most enjoyable Porsche I ever owned prior to being spoiled by turbo power.
The second example was a '77 Triumph Bonneville 750 which is notiously prone to pinging. I used the experience gained to determine the advance curve which was similar to the 914, although I don't recall the exact numbers. It was nearly impossible to make it ping with the second plug and revised timing. It had to be insanely hot, such as idling in traffic for a while before it would make any unnerving noise.
When I twin plugged my Beemer, I was told to Retard the timing from the Factory setting to benefit from the twin plugging.

I never heard of twin plugging a Bonnie, thanx for that reference!
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Old 03-04-2008, 07:06 PM
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