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Single Coil for MS

Truebeliever

Member
Joined
Aug 5, 2018
Location
Charleston sc
I'm not sure if this should go in the engine management section or not but

When I purchased my 86 244, I replaced the original coil with a $12 rock auto coil because it had worked its way loose and rubbed a hole in the canister, leaking all the oil out.

Fast forward to today, I've installed a MS3 with a direct ignition driver and +t with a 15g. I question the $12 coils ability to clear .28" gap under boost. I'm not having any real issues, I just don't wanna deal with any when I start increasing boost from 6psi.

Per this thread http://forums.turbobricks.com/showthread.php?t=9983&highlight=ignition+coil, it seems like the Accel super coil would be just fine or a Msd blaster 2, but I'm not sure if the MS3 would let run something better or what dwell/duration

I'd like a recommendation of what coil I should look for if possible.

End goal would eventually be COP or wasted spark, but that will a project for a stronger set of rods/transmission
 
not sure if I have the answer or not but If I remember correctly, the factory volvo coil is suppose be better than the aftermarket coils. I did run across an old Jacobs coild still in the box that I am running with MS with 20lbs boost of e85 with no problems.
 
When I did the MS swap in my old '80 GLE with the B21FT, I actually used an 80's Ford EFI coil. I had a spare in the garage from my Ford 2.3T stuff, so I used that.

I was running an LH2.2 dist and a T3 turbo and I think I was running 12-ish psi of boost on it when I sold the car. Never had any problems with that coil.
 
Go to a pick and pull and look for a late '80s early 90s 740 or 940 with single (round - not square) ignition coil. That coil worked just fine on turbo motors with OEM boost levels (and probably more) as long as you are respecting the original RPM limits.

Just about all ignition coils can generate way more voltage than is required to fire a spark plug in a single spark test. Typical firing voltages are in the 7 kV range and most coils (even lawnmower coils) can probably generate 15 kV relatively easily. The bigger issue is spark energy which becomes an issue of "do you have enough dwell" for the coil to provide the required spark energy to provide reliable ignition. The spark energy in the coil is determined by the equation 1/2xLxI^^2 where L is coil inductance and I is the current in the coil at the time spark occurs. If the coil is not dwell limited, peak current is set by V/R where V is the vehicle voltage and R is the resistance of the coil and the circuit supplying the coil.

If you go to B&Gs MS2 MegaManual website there is a section discussing ignition control. That site includes an on-line calculator that allows you to estimate spark energy and you can use it to evaluate the effect of dwell on spark energy in single coil systems. You can play around with the numbers on the calculator; but, you will likely find that if you have any typical ignition coil you are likely not dwell limited with the stock red line (adding extra dwell does not materially increase spark energy ).

On a specific coil, spark energy goes up as the square of the ignition coil current at the time the spark fires. Ignition coil current magnitude is directly related to the coil voltage. The simplest thing you can do is make sure that your charging system is running at 14.2 - 14.3 volts and that you have an excellent low resistance connection to the coil +. If you have crap wiring and the voltage at the coil + is only around 12 volts versus 14.3 volts you are potentially incurring a 30% reduction in spark energy. That is probably a bigger effect than changing to a performance coil of some kind.

I run MS2 Extra so I am not familiar with the details of MS3. When you say that you have MS3 with a direct ignition driver is that a driver external to the MS3 box or is it like the MS2 with a BIP 373 mounted on the board? The BIP373 mounted in the case is bad practise because of the noise that it can introduce into the ground plane. Mounting the driver outside of the case is the way to go.
 
Go to a pick and pull and look for a late '80s early 90s 740 or 940 with single (round - not square) ignition coil. That coil worked just fine on turbo motors with OEM boost levels (and probably more) as long as you are respecting the original RPM limits.

Just about all ignition coils can generate way more voltage than is required to fire a spark plug in a single spark test. Typical firing voltages are in the 7 kV range and most coils (even lawnmower coils) can probably generate 15 kV relatively easily. The bigger issue is spark energy which becomes an issue of "do you have enough dwell" for the coil to provide the required spark energy to provide reliable ignition. The spark energy in the coil is determined by the equation 1/2xLxI^^2 where L is coil inductance and I is the current in the coil at the time spark occurs. If the coil is not dwell limited, peak current is set by V/R where V is the vehicle voltage and R is the resistance of the coil and the circuit supplying the coil.

If you go to B&Gs MS2 MegaManual website there is a section discussing ignition control. That site includes an on-line calculator that allows you to estimate spark energy and you can use it to evaluate the effect of dwell on spark energy in single coil systems. You can play around with the numbers on the calculator; but, you will likely find that if you have any typical ignition coil you are likely not dwell limited with the stock red line (adding extra dwell does not materially increase spark energy ).

On a specific coil, spark energy goes up as the square of the ignition coil current at the time the spark fires. Ignition coil current magnitude is directly related to the coil voltage. The simplest thing you can do is make sure that your charging system is running at 14.2 - 14.3 volts and that you have an excellent low resistance connection to the coil +. If you have crap wiring and the voltage at the coil + is only around 12 volts versus 14.3 volts you are potentially incurring a 30% reduction in spark energy. That is probably a bigger effect than changing to a performance coil of some kind.

I run MS2 Extra so I am not familiar with the details of MS3. When you say that you have MS3 with a direct ignition driver is that a driver external to the MS3 box or is it like the MS2 with a BIP 373 mounted on the board? The BIP373 mounted in the case is bad practise because of the noise that it can introduce into the ground plane. Mounting the driver outside of the case is the way to go.

Older Volvos in pick-n-pulls around here are few and far between, Mostly late 90s an on...

Would going from battery directly to the coil be acceptable?

I do have the driver mounted internally, never knew I shouldn't
 
Older Volvos in pick-n-pulls around here are few and far between, Mostly late 90s an on...

Would going from battery directly to the coil be acceptable?

I do have the driver mounted internally, never knew I shouldn't

Rock Auto sells an NGK coil for the 740s and 940s. NGK are generally high quality. The Bosch coil sold by IPD and others is probably a good choice.

Direct connection to the battery is probably a bad idea. Best practise would be to switch off power to the coil somehow when the coil is not in use even though theoretically no current should flow when the engine is not running. You can dedicate a fuse position for the coil controlled by the main FI relay in your MS fuse panel (as typically shown in the MS wiring diagrams) which will work well if you have a good solid supply to the MS fuse panel. A dedicated fused relay supply for the coil controlled by the main FI relay will also work. Many ways to skin this cat. Just do a test with the car running measuring the voltage on the coil + terminal. If the coil + voltage is the same as the battery voltage (or within 0.3 volts) the wiring is probably good. If it is significantly less then time for improved wiring.

I briefly used a BIP mounted on the MS2 board. When the BIP switches the ignition coil on there are transient currents that get coupled directly into the ground plane of the circuit board. When the BIP switches the coil off you get a lot of transient voltages appearing across the BIP. In my case, it did not damage anything; but, it generated processor resets (a lot of them) which were quite detectable when driving. I completely eliminated that problem when I did COPS with integrated drivers. Mounting the BIP outside the MS3 case close to the coil (shorter wire is better) with its own dedicated ground in some kind of little protected enclosure should work until you figure out your final plan.

When OEMs first started doing COPS in production cars in the early 90s, they did not have integrated drivers in the coils. They mounted the drivers in a separate module called the ignitor which was far away from the ECU. They knew enough not to bring the nasty coil currents into the electrically protected environment of the ECU. B&G were pretty savvy dudes; but, why they ever thought mounting the coil driver inside the MS box would be a good idea is a bit of a mystery.
 
It is best to use and integrated coil/power stage for many reasons.
There are single coil versions similar to what I pictured available.

Switching a .7ohm spark coil makes a lot of noise.
 
I'm using a coil from a 94 2.0 Passat, I think. It's integrated just needs power, ground and input from my microsquirt. I think I've had it up to 7500 rpm or so, no problem. The caveat is I have to have Kingsborne make me a custom coil wire with the VW end on one side and the Volvo on the other.
 
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