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scumbag
 
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twin plug efi

hello, gents!

i've been reading a lot about the myriad options for ignition. as my car is slated to run full sequential ignition (MS3X) and COPs, my concern is misfiring.

my background with COPs is largely based on VW/AUDI and their fabulously clean, but famously unreliable ignition coils. so if i run 12 COPs (6 pairs), how would i know if half of each cylinder were to misfire? anyone can feel/hear/smell a dead hole. but what about half-dead? i was hoping to find a wasted spark pencil style smart COP...but apparently that is not a thing. so either i run 6 smart COPs (and don't run twin plug), run 12 smart COPs (and hope all the pairs fire/fail together), run 6 remote-mounted wasted spark coils (actually uglier than a dizzy), or brew up some other advanced level electronic sorcery.

i plan to drive this car a lot. like a lot a lot. so it needs to be reliable. (i do not want to hear about the reliability of CIS and a dizzy, thank you.) if i can't come up with a suitable solution to COP powered twin-plug, i can't run the compression i'd like. so i really need to get this figured out before i go any further buying parts.

please discuss and thank you in advance,
Chris
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Old 09-10-2018, 12:23 PM
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I just build EFI systems with a 12 plug distributor running twin MSD ignition boxes. The EFI runs a crank sensor and controls all timing. No issues with spark. If one box fails you will notice it. I find this to be highly reliable.

If you run COP then you want logic level coils. I am not a fan of having the ECU drive all the current. They require (minimum) 3 wires to each [+12V, GND and trigger signal]. There are some examples of Denso coils in the archives that work well.

The most simple implementation of COP is twin plug wasted spark. This means you have 4 COP units triggered off the same signal and this only requires 3 channels of ECU I/O pins. An example is Cylinder 1 and 4 with both top and bottom plugs.
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Old 09-10-2018, 12:32 PM
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Toyota Coils 9091902246 work well, I use them with my EFI conversion.
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Old 09-10-2018, 12:49 PM
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I have been thinking about Coil On Plug options using the wasted-spark type coils and wires like on my 98 Toyota Tacoma. It has three coils for 6 cylinders, with a wire going to the opposing cylinder on the other bank.

My thought would be to use 6 coils on the upper plugs, with the wire going to the lower plug on the same cylinder. People claim one spark will be weaker and that may be the case, but this doesn't seem to be an issue on the Toyota engine. As a bonus, since the coil only needs to fire on the compression stroke, rather than compression and exhaust on the Toyota Wasted Spark setup, the coils will work at a half the duty cycle than on the Toyota at any given RPM.

These:

https://www.amazon.com/Ignition-Toyota-90919-02212-88921337-UF-156/dp/B06XPS3RNS
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Old 09-10-2018, 02:16 PM
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scumbag
 
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Quote:
Originally Posted by jpnovak View Post
I just build EFI systems with a 12 plug distributor running twin MSD ignition boxes. The EFI runs a crank sensor and controls all timing. No issues with spark. If one box fails you will notice it. I find this to be highly reliable.

If you run COP then you want logic level coils. I am not a fan of having the ECU drive all the current. They require (minimum) 3 wires to each [+12V, GND and trigger signal]. There are some examples of Denso coils in the archives that work well.

The most simple implementation of COP is twin plug wasted spark. This means you have 4 COP units triggered off the same signal and this only requires 3 channels of ECU I/O pins. An example is Cylinder 1 and 4 with both top and bottom plugs.
My plan is run logic level COPs full sequential to maximize drivability and economy.

Quote:
Originally Posted by '76 911S 3.0 View Post
Toyota Coils 9091902246 work well, I use them with my EFI conversion.
Quote:
Originally Posted by emcon5 View Post
I have been thinking about Coil On Plug options using the wasted-spark type coils and wires like on my 98 Toyota Tacoma. It has three coils for 6 cylinders, with a wire going to the opposing cylinder on the other bank.

My thought would be to use 6 coils on the upper plugs, with the wire going to the lower plug on the same cylinder. People claim one spark will be weaker and that may be the case, but this doesn't seem to be an issue on the Toyota engine. As a bonus, since the coil only needs to fire on the compression stroke, rather than compression and exhaust on the Toyota Wasted Spark setup, the coils will work at a half the duty cycle than on the Toyota at any given RPM.

These:

https://www.amazon.com/Ignition-Toyota-90919-02212-88921337-UF-156/dp/B06XPS3RNS
I daily a gen3 4Runner. But my coils arenít logic level input and require more voltage than the ecu can safely put out. But yeah, my Runner is where the idea originated.
My thinking was exactly the same as what youíve outlined. One coil per cylinder driving both plugs.
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Old 09-10-2018, 05:19 PM
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Ignition full sequential should not improve drivability nor economy. Sequential fuel, yes.
Old 09-10-2018, 06:16 PM
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I run the very setup you mention. 12 Bosch coils for early 2000s Audi and VW. Works great but the need a lot of juice. Each set of 6 coils has its own dedicated 30 or 35 amp relay.
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Old 09-11-2018, 04:22 AM
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scumbag
 
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Quote:
Originally Posted by lvporschepilot View Post
I run the very setup you mention. 12 Bosch coils for early 2000s Audi and VW. Works great but the need a lot of juice. Each set of 6 coils has its own dedicated 30 or 35 amp relay.
do you have a method for verifying that all 12 are firing? this was my plan until i tried to devise a way to verify that i wasn't losing half of one cylinder. my thoughts are that if i lose one half of the cylinder, i'll get the detonation that twin-plugging is supposed to prevent. A NA motor should have an easier charge to ignite than a FI. maybe i'm worried about nothing. but i've replaced a lot of those coils on a lot of VWs/Audis that just dropped for little/no reason and with no warning.
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Old 09-11-2018, 04:30 AM
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Quote:
Originally Posted by Tippy View Post
Ignition full sequential should not improve drivability nor economy. Sequential fuel, yes.
I'll bite, what is "full sequential" ignition? Doesn't ignition have to be full sequential so the plugs fire at the right time?

Batch fire ignition isn't going to do anything for you.
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Old 09-11-2018, 06:48 AM
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scumbag
 
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Quote:
Originally Posted by emcon5 View Post
I'll bite, what is "full sequential" ignition? Doesn't ignition have to be full sequential so the plugs fire at the right time?

Batch fire ignition isn't going to do anything for you.
as opposed to wasted-spark
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Old 09-11-2018, 06:57 AM
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Aircraft with twin magnetos have a selector switch that allows you to switch off the magnetos individually as a pre-flight check. I've thought a system like this would be a good idea for a twin-plug setup, so if there was a dead coil it would be immediately apparent as a misfire when you are doing your pre-flight routine.

My understanding (but I could be wrong and would love to know if I am!!!) of the advantage of the twin plugs is that you still need to run less ignition timing compared to a lower compression engine, it just gets you some power back that you lose by running less advance. You aren't necessarily in danger of blowing it up if one coil fails.

EDIT - for example, a high compression 100mm bore engine might be "safe" with 30 degrees total advance and single plug, but will make more power with twin plugs and the same 30 degrees advance.
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Last edited by Jonny042; 09-11-2018 at 10:01 AM..
Old 09-11-2018, 09:57 AM
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Quote:
Originally Posted by lvporschepilot View Post
I run the very setup you mention. 12 Bosch coils for early 2000s Audi and VW. Works great but the need a lot of juice. Each set of 6 coils has its own dedicated 30 or 35 amp relay.
I am not a fan of the VW/Audi coils as they are extremely failure prone. The Denso coils are the same ones used by Papadakis Racing on their 1000hp 2AR Toyota engine. If they are good enough for them, they are good enough for me.
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Old 09-11-2018, 10:20 AM
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Quote:
Originally Posted by chrisbalich View Post
One coil per cylinder driving both plugs.
This isnít a good idea. The reason wasted spark systems work ok is that the plug not under compression does not sap as much energy (because of the lower dielectric strength of a non pressurised cylinder). If we use 30kV as an example, typically the wasted spark plug uses about 3kV to fire whereas the compressed plug will see the remainder - say 27kV.

If you have both plugs under pressure then the energy will be more equally divided resulting in perhaps 15kV per plug. That is two very weak sparks.
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Old 09-11-2018, 10:51 AM
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scumbag
 
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Quote:
Originally Posted by Jonny042 View Post
Aircraft with twin magnetos have a selector switch that allows you to switch off the magnetos individually as a pre-flight check. I've thought a system like this would be a good idea for a twin-plug setup, so if there was a dead coil it would be immediately apparent as a misfire when you are doing your pre-flight routine.

My understanding (but I could be wrong and would love to know if I am!!!) of the advantage of the twin plugs is that you still need to run less ignition timing compared to a lower compression engine, it just gets you some power back that you lose by running less advance. You aren't necessarily in danger of blowing it up if one coil fails.

EDIT - for example, a high compression 100mm bore engine might be "safe" with 30 degrees total advance and single plug, but will make more power with twin plugs and the same 30 degrees advance.
a method to verify ignition is exactly what i'm after. but idk that it's practical with the packaging constraints of our cars.

Quote:
Originally Posted by '76 911S 3.0 View Post
I am not a fan of the VW/Audi coils as they are extremely failure prone. The Denso coils are the same ones used by Papadakis Racing on their 1000hp 2AR Toyota engine. If they are good enough for them, they are good enough for me.
I think this may be the best solution.

Quote:
Originally Posted by Jonny H View Post
This isnít a good idea. The reason wasted spark systems work ok is that the plug not under compression does not sap as much energy (because of the lower dielectric strength of a non pressurised cylinder). If we use 30kV as an example, typically the wasted spark plug uses about 3kV to fire whereas the compressed plug will see the remainder - say 27kV.

If you have both plugs under pressure then the energy will be more equally divided resulting in perhaps 15kV per plug. That is two very weak sparks.
I hadn't considered that. what i was thinking was double the time between spark events combined with adjustable dwell time with MS3X would allow me to overcome any shortcomings. but i am/was 100% speculating.

i think maybe the very solution is to just run the Denso coils that last forever and devise a method for periodic (annual?) bench testing. i'm more than pretty sure the coils in my truck are original. (211k miles and 19 years)
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Old 09-11-2018, 11:03 AM
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Quote:
Originally Posted by chrisbalich View Post
do you have a method for verifying that all 12 are firing? this was my plan until i tried to devise a way to verify that i wasn't losing half of one cylinder. my thoughts are that if i lose one half of the cylinder, i'll get the detonation that twin-plugging is supposed to prevent. A NA motor should have an easier charge to ignite than a FI. maybe i'm worried about nothing. but i've replaced a lot of those coils on a lot of VWs/Audis that just dropped for little/no reason and with no warning.
Chris,
I think you are worrying over nothing.

With twin spark you'll be running about 7 or 8 degrees less advance than if you were running single plug. Consequently if one plug fails to fire you'll just have less power and no chance of detonation.

I agree the Audi/VW style coils get a bad rap but if you are worried about their reliability just spend the extra dollars and use the Denso ones that are universally endorsed. Another thing you could consider is to install a heat shield to protect them from the radiant heat of the headers if you think that could be an issue.

As for checking for function, if you don't notice the reduction in power or responsiveness, you could just pull the plugs every so often to inspect and you should see if they are firing or not by the cleanliness of the centre electrode.

Again I think you are worrying over nothing.
Old 09-11-2018, 01:39 PM
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Quote:
Originally Posted by '76 911S 3.0 View Post
I am not a fan of the VW/Audi coils as they are extremely failure prone. The Denso coils are the same ones used by Papadakis Racing on their 1000hp 2AR Toyota engine. If they are good enough for them, they are good enough for me.
Iím using the Audi cop on my 3.5 with Motec - do you know if the Denso items are interchangeable?

Iím currently running as single plug, but planning on running twin plug at a higher CR (~11.0:1 )
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Old 09-11-2018, 02:34 PM
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Quote:
Originally Posted by sp_cs View Post
Iím using the Audi cop on my 3.5 with Motec - do you know if the Denso items are interchangeable?

Iím currently running as single plug, but planning on running twin plug at a higher CR (~11.0:1 )
The Audi COP is a 4 wire coil: Logic 5v signal, +12v, Ground, and Sensor Ground. The Denso, although having 4 terminals, are a 3 wire coil: 12v, Ground, and 5v Logic signal. The fourth terminal is for the coil confirmation signal back to the factory Toyota ECU and is not used for our purposes.

The connectors are different, but you could simply cap the Sensor Ground wires at each of your Audi coil connectors and cut off the Audi coil connector and install the Denso coil connector. The Denso connector can be found here:

https://www.bmotorsports.com/shop/product_info.php/products_id/1667

Pinout:

Pin 1: Switched +12v
Pin 2: Not Used
Pin 3: 5v Logic Trigger from ECU
Pin 4: Chassis Ground (make sure this ground is not shared with the ECU ground, the valve cover is a great spot for these grounds, I have one for each bank on each valve cover).
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Old 09-11-2018, 03:28 PM
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Good info Jayson, many thanks indeed.

Apologies OP for the slight derail.
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Old 09-12-2018, 12:20 AM
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Quote:
Originally Posted by emcon5 View Post
I'll bite, what is "full sequential" ignition? Doesn't ignition have to be full sequential so the plugs fire at the right time?

Batch fire ignition isn't going to do anything for you.
Was referring to wasted spark
Old 09-12-2018, 05:40 AM
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VAG coils are actually very reliable. Problems arise when people use excessive dwell time on those (3+ ms, even seen 5+, sheesh) while they do not like anything over 2 ms and they give very strong spark. Their only problem is that they do not forgive stupidity.

P.S. Factory ECU's also used longish dwell times in the beginning paired with early revision coils that had them fail soon, issues have been resolved 10+ years ago.
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Old 09-12-2018, 06:21 AM
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