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Metal Guru
 
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Twin plugging is use on high compression N/A 911 engines because the piston dome cuts off half of the chamber, which retards the velocity of the flame front. The unburnt mixture on the other side of the dome then combusts in a uncontrolled manner which results in the pinging that can sometimes be heard.
As 125shifter stated, it stands to reason that the flat top pistons used in turbo motors have the same issues.
It's interesting that Porsche didn't use twin plugs on the 3.6 turbo engine. Could it be they didn't feel that the added complexity and expense were worth limited benefits?
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Old 03-04-2008, 07:16 PM
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In a related topic, what are the board's opinions on multi-electrode spark plugs. Bosch makes 1, 2, and 4 electrode plugs in platinum and some other rare earth metal with a crazy name.

Is there a similar benefit for multi-electrodes as for twin-plugging? Can compression be increased or timing changed? I realize that there will not be as much of a benefit as far as firing the 2 haves of the combustion chamber equally because the electrodes are all in 1 place. The flame front should be shaped differently than a single electrode, though. The single electrode covers the ignition point on top of the plug but the multi-electrode models allow flame travel directly above the plug.

Anyone have experience with these multi-electrode spark plugs?
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Old 03-04-2008, 08:56 PM
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Quote:
Originally Posted by Flieger View Post
In a related topic, what are the board's opinions on multi-electrode spark plugs. Bosch makes 1, 2, and 4 electrode plugs in platinum and some other rare earth metal with a crazy name.

Is there a similar benefit for multi-electrodes as for twin-plugging? Can compression be increased or timing changed? I realize that there will not be as much of a benefit as far as firing the 2 haves of the combustion chamber equally because the electrodes are all in 1 place. The flame front should be shaped differently than a single electrode, though. The single electrode covers the ignition point on top of the plug but the multi-electrode models allow flame travel directly above the plug.

Anyone have experience with these multi-electrode spark plugs?
There is a current spark plug thread that this would work better in??
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Old 03-04-2008, 09:19 PM
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Quote:
Originally Posted by 911nut View Post
Twin plugging is use on high compression N/A 911 engines because the piston dome cuts off half of the chamber, which retards the velocity of the flame front. The unburnt mixture on the other side of the dome then combusts in a uncontrolled manner which results in the pinging that can sometimes be heard.
As 125shifter stated, it stands to reason that the flat top pistons used in turbo motors have the same issues.
It's interesting that Porsche didn't use twin plugs on the 3.6 turbo engine. Could it be they didn't feel that the added complexity and expense were worth limited benefits?
Porsche is a small Auto company. It costs a lot to change a lot of things each year. The main thing is that Porsche has been using Twin Plugz for a long time in their racing cars, and are using it in their production cars.

Gentleman, this is no Humbug!!
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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, 09:22 PM
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For a 930, it's all about safety and reduced timing.
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Old 03-05-2008, 09:39 AM
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The advantages and theory of twin plugs and flame front travel vs igniton timing has all been said, but there's another VERY big advantage to it for a race car or aircraft.

Ignition systems all eventually fail and if you have twin ignition sytems and sparkplugs and one fails in service the plane won't crash and burn, and the race car will still finish the race.

Thats the biggest advantage for some folks.
Old 03-05-2008, 11:31 AM
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Quote:
Originally Posted by les_garten View Post
Is there a current spark plug thread that would work better in??
I to would like to find out more about spark plug applicability as I have a number of hot rodded 930s and some require lowering the motor for excess. Experimenting with heat ranges and different brands are not a good option. Getting in the best ( albeit not always is the newest or most expensive, best ), the first time would be good.
Old 03-05-2008, 11:49 AM
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Quote:
Originally Posted by voitureltd View Post
I to would like to find out more about spark plug applicability as I have a number of hot rodded 930s and some require lowering the motor for excess. Experimenting with heat ranges and different brands are not a good option. Getting in the best ( albeit not always is the newest or most expensive, best ), the first time would be good.
Hello,
There is a Spark Plug thread on the first page. I posted there on what NGK's I use.
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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 03-05-2008, 11:57 AM
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One argument I find extremely unconvincing in the Porsche world is that Porsche didn't originally do it, and that decision must somehow necessarily have been a technological judgment.

Wrongo.

Porsche, for reasons entirely unrelated to performance, was still using CIS on its flagship turbos through the 3.6 turbo, for just one example There is simply no question that a well-tuned EFI system would have been "better" for that car, even more so than it was "better" for its NA 911 cars at the time, which did have EFI. But Porsche was in economic trouble, and didn't want to spend the dough.

Twin-plugging is better, as well, for the reasons stated here. For high horsepower, modification apps, it is much better.
Old 03-05-2008, 12:21 PM
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Hello.

Twin plugging speeds up the combustion. Things go "booom" much faster so you don't need to advance as much as you do on single one in order to wait for slow "boom" to be finished.

Nice thing with fast "boom" (if you adjust the advance) is that it happeds nearer TDC so you can use more energy in "boom" to push piston downwards, instead if starting to lighten up when piston is movin upwards.

So yes, twin plugging makes power. But you *must* adjust ignition accordingly or you will have "boom" trying to push piston downwards as it happends sooner than with single plug.

I recon that you can gain 7-10% in HP department on typical 930 engine based on speedy combustion and optimized ignition.

You can use it to gain power or gain detonation margin...but it's a nice thing.

Also, I don't believe in multi-pronged spark plugs. Ordinary NGK copper-plugs of suitable heat range is IMHO best solution. For extra 1%-2% procent, plug-indexing is possible.
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Old 03-05-2008, 12:53 PM
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Say your 930 is 300HP.
You don't get anywhere near a 7-10% increase in HP with just dual plugging and adjusting the ignition advance timing.

That would be a 21-30 HP increase... it's no where near that much.
Old 03-05-2008, 01:06 PM
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Quote:
Originally Posted by JFairman View Post
Say your 930 is 300HP.
You don't get anywhere near a 7-10% increase in HP with just dual plugging and adjusting the ignition advance timing.

That would be a 21-30 HP increase... it's no where near that much.
You can use twin plugging to increase your safety margin against knock or you can take a power increase up to the same margin with increased boost. That is how you get increased power. At the the risk of repetition, twin plugging allows the equivalent HP increase as 1 point C.R. increase before onset of knock. This is not about timing.

In the N.A. 911 forums this benefit is readily understood and accepted.
If we were talking about non turbo 911s would you dispute a 3.0L 11:1 C.R. (made possible by twin plugging) makes more power than one at 10:1 C.R.? Turbocharging does not change the impact of fixed and equivalent C.R. (fixed plus boost) on power output.

Last edited by copbait73; 03-07-2008 at 10:07 AM..
Old 03-05-2008, 06:21 PM
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To put it in turbo terms, each pound of boost is worth ~0.3:1 C/R. So a full CR point gained through twin plug = 3.3 pounds or ~0.2bar extra you can safely use. That's about 30HP (depending on the application). Sound about right?
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Old 03-05-2008, 08:38 PM
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I've been familair with it for a while...
I dual plugged my 1975 BMW R90S motorcycle back in the late eighties and raised compression along with lots of other stuff and the theory is exactly the same as a 911 motor.

I was just saying alone, it does very little.
Old 03-05-2008, 08:49 PM
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Quote:
Originally Posted by JFairman View Post
I've been familair with it for a while...
I dual plugged my 1975 BMW R90S motorcycle back in the late eighties and raised compression along with lots of other stuff and the theory is exactly the same as a 911 motor.

I was just saying alone, it does very little.
Bet ya wish you still had your R90S, ehhh? I certainly think you get efficiency and a good margin of safety with the two flame fronts. I think if you could get 30HP from it, it would be talked up here more as a must do. To me it was a must do as a safety stand point. Even the Beemer folks backed off of how much you benefit from it though. Back in the day, it was a must do on BMW bikes.
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Old 03-05-2008, 10:34 PM
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I still have it
along with a fixed up '84 Honda 500 Interceptor.

sorry if it's going off topic.
Old 03-05-2008, 10:57 PM
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Les, I would think that the reason twin plugging a 930 isn't all the rage is due to a very low return on the dollar. It's not a cheap undertaking and 30HP is nothing on a turbo motor.

Personally I would not use the advantages of twin plugs to bump the boost but rather as a safety margin for hot temps, hill climbs, and bad gas.
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Old 03-06-2008, 06:55 AM
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Quote:
Originally Posted by RarlyL8 View Post
Les, I would think that the reason twin plugging a 930 isn't all the rage is due to a very low return on the dollar. It's not a cheap undertaking and 30HP is nothing on a turbo motor.

Personally I would not use the advantages of twin plugs to bump the boost but rather as a safety margin for hot temps, hill climbs, and bad gas.
Hi,
You are prolly right. I did the Twin plug during a Head Job and EFI conversion. So it was virtually a free deal. Had to buy one coil pack and cut the holes.
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Old 03-06-2008, 08:05 AM
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Rarlyl8,
You have alot of good insight on this forum. I agree with your opinions on this and alot of other postings.
The reason for twin pluggung is clear, it is a benefit, but should be looked at from a safety standpoint first. It gives the ability ot run higher boost and timing by increasing the safety margin to detonation, but here the tuner is creeping up again to the danger zone when attempting this.
Porsche like any other OEM during the 80's had lots of trouble and this explains the ridiculously long time running CIS on the turbo models long after the switch was made on the 3.2 liter cars to Motronic.
The expense is prohibitive to dual plug when you look at the machining involved in not just the heads, but the valve covers, engine tin, changing over the ignition system. You could find easier uses for this dough to gain power from the 930 by first improving the exhaust breathing and other things on the car that were compromised in the sake of emissions.
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Old 03-06-2008, 08:40 AM
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It definitely is not a Beginning Mod. I think it's a must do for EFI conversions. It's the Intermediate Level of Mods where you would think a little bit about it. Here's what it cost me to do during EFI

Machine work I think about $300
CoilPack $150
PlugWires $140

Did valve covers myslef
Engine tin Had existing holes perfectly located

All other pieces were going in anyway.

If you were taking the motor apart, doing head refresh, and considering dropping your distributer for a crankfire system like Electromotive, then it would make sense to punch the holes
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Old 03-06-2008, 09:06 AM
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