MSD for Twin Plug
 

I seem to remember that the User Instructions for the MSD 6AL had a diagram showing how to connect 2 x Blaster Coils. I am fairly sure that the two coils were connected in parallel.

I have checked on line and the instructions for the 6420 unit don't seem to contain this schematic.

As the 6420 is no longer being supplied I wondered if the replacement 6425 could still fire 2 x coils and if so would they still be connected in the same manner.

The type of coil is also of interest as I have had problems with Blaster Coils failing mechanically and would be keen to know what primary impedance of coil will work.

Any ideas please.

You probably already know this but when you use two coils and one MSD box you're only getting half the spark voltage. It negates any benefit of using the MSD (high spark voltage) when you use two coils in parallel.

I am not sure the story is that simple.

I have been running one MSD and two coils wired in parallel for nearly 4 years on my RSR clone.

http://forums.pelicanparts.com/porsche-911-technical-forum/231256-msd-twin-plug-3.html

Hi Cris
We've been running race engines with one MSD at a time (two installed, one for back up) for 15 years.
I have never seen an issue with this set up.
There is a safety feature in having one CD drive two coils in that when the CD fails you know its gone and with two separate CDs you can engine up running your engine seriously retarded because only one plug is firing.
On low compression engines it's not so bad but with a high compression engine you can cause serious damage.
When your racing finishing is all that matters but with these high strung street engines and amateur racing perhaps saving the engine has value.

http://forums.pelicanparts.com/uploa...1333462396.jpg

MBruns shows in the link Tom provided that a 230 hp engine losses 15 hp changing from two MSD boxes to one. I also ran a single box but moved to two; noticeable difference on top.

I have been doing some research on this. Here is what I conclude thus far:

1. The "safety" benefit of running a single MSD 6AL and two coils for a twin plug application is obvious in that if there are certain types of MSD failures, there will be symptoms and you can respond accordingly. Many folks out there run this set up. It is obviously less expensive as well.

2. When running two MSD boxes driving two coils, the typical application is to drive both boxes from the same distributor trigger output.

3. It is possible in some of their race cars that Porsche decided to have an ability to switch between two CD box tach outputs with a dash mounted switch. In theory, if one signal was dead, then maybe the engine was only firing off of one CD box, and folks could respond accordingly. I can verify that with a visit to a local shop that does many historic car restorations.

4. In theory you could wire twin MSD box tach outputs to a switch, and emulate what the factory did in #3. If you suspected a problem, you could check to see if one of the tach signals was dead or compromised.

5. Another approach to explore with two 6AL units might be to wire the distributor trigger to the first box. Then use its tach output signal (a 0 and +12 volt square wave) to the "points" input of the second box.

If this worked, then any problems with the first box that manifested in its tach output signal would also theoretically be manifest in the second box's output. And theoretically this would give you a heads up. If you wired the second box's tach output to the tach, then you'd be able to "see" any of problems with its performance that manifested in its tach output.

So if this worked, you'd have some indication of problems with either box, as long as the problems were manifest in the bad box's tach out signals.

MSD claim that the "points" input circuitry cannot be driven by the tach output square wave from another MSD box. They tell me that the "points" input circuits expect to see a signal that switches between ground and some voltage (like from ignition points in a distributor), while the MSD tach output is square between 0 volts and +12 volts. I got that from two different MSD support techs, but I am curious anyway. And of course you could probably "condition/change" an MSD tach out square wave signal into something that the "points" input circuitry could see properly. Basic electronics problem likely solvable.

Finally...

6. You could run both boxes from a single trigger. Then run both tach outputs to rpm switches with normally-closed circuits, each connected to warning lights in your dash. Then set the RPM switches at some low value, like 2k rpm.

In normal operation above 2k rpm, these switches would be open, and the warning lights would be off.

If one of the tach outputs was dead above the 2k rpm set point, the NC contact would stay closed, and the dash warning light would light up. This would only work for an MSD box problem that manifested as a dead tach output. So maybe not all possible issues, but perhaps some could be caught with this approach. And of course this would work as long as the rpm switch was in good working order.

Oops, sorry:

2. a. Running two MSD boxes and two coils is superior to a single box/dual coil set up from a performance standpoint. Many Porsche engines are set up that way. I haven't read about any engines damaged as a result of an undetected MSD box failure in a dual box/dual coil set up, despite apparent theoretical possibilities. Perhaps other folks out there have experience with this.

One more "oops..."

5. There might be a small time delay if the first box tach signal was fed to the input of the second box. This could be significant for dual plug firing.

you don't need redundant systems like in piston aircraft, one will drive both coils as stated. you could run a second as a backup with a switch but not really required, keep a spare in the glove box. That schematic Henry posted is from MSD.

I am fully aware of what can be done for some applications.

My application is racing, so all of the fuss is not about redundancy. It is about max performance. So two boxes and two coils. I think the benefits have been proven, depending on racing engine configuration.

Secondarily, I must consider ways that I can know whilst driving my race car that one of the boxes is not functioning properly. Hence all of the stuff I wrote.

I have found a technical report with a full set of schematics for the inside of a MSD 6A and I will study the topology carefully.

If I am not mistaken, MSD has phased out the analog box and has moved on to the digital 6AL. The new box may not be able to run in that configuration.

Has anyone tried running one digital box with two coils?

I have a friend running dual digital 6ALs in a twin plug application. But I don't know of anyone running a single digital box and two coils. I am sure MSD can tell you whether it would work. Likely it would.

I could see running one box and two coils for a street car to save money. But I am not sure about the magnitude of the safety benefit. A single box/dual coil set up may not help you if there is a problem with one of the coils. Or the distributor. Right?

I started with my current car/engine with twin plug heads but running a single coil and box back 10 years ago. I have always carried a spare box. And I have used it for troubleshooting at the track. The first time, it turned out that my Blaster 2 coil failed. Upside down mounting is not ideal for these oil-filled coils.

Another time, it turned out that I had a problem in my 3 liter distributor. Jerry Woods rebuilt it and it is now for sale.

Ideally one could have a "warning system" that would identify a problem with either box, either coil or the distributor, before any potential for damage could occur.

Very true and that's why MSD offered the "High-vibration" version which can be safely mounted in any direction. Another good option are the "E-core" coils which are much more reliable and can be mounted anyway you wish. The HVHC version works nicely with the 6AL's.

Well I have not had a Blaster 2 failure since I started mounting them right. But I carry spares anyway as do my friends.

Again, what would really be cool is a way to have a warning light if the top or bottom plugs have a firing problem. Need to think about this more.

dumb question- How are you directing spark with 2 coils?... 2 dizzys ?

Twin plug w/one MSD 6AL
2.45 with mod "S" cams and 9.5:1 compression 40 mm Webers stock exhaust.
180 RWHP @ 6400. Plenty more on tap just going easy on the new engine.
http://forums.pelicanparts.com/uploa...1341765054.jpg

Same engine design different car, same results 180 @ 6400. single 6AL

http://forums.pelicanparts.com/uploa...1341765244.jpg

Did you ever try the engine with two MSD units?

Scott

Very nice and very tidy looking engine. I am sure it performs well.

I don't think that there is any further question about whether one box/dual coils will work, nor whether you can get more performance from a dual box/dual coil set up. Both are true I am certain.

Sure, the former gives you some safety margin for certain types of failures in certain circumstances. But I have designed a simple scheme for the latter to be wired to give you a similar safety margin... and you get the increased performance.

In my application, a 3.8 liter twin-plugged racing engine, the dual box/dual coil deal is clearly the way to go. I may implement the safety scheme which is pretty easy in my case. But I am not sure it is necessary. In any case, neither approach helps you if one coil goes bad, or if you are running a belt-driven dual distributor and have a belt failure.

Spark voltage is not the principle benefit of the MSD ignitions. The primary benefit is multiple spark discharge (spark duration).

In our tests, using solid core wires (not suggested by MSD) we saw no performance benefit (up to 7400 RPM) using a second MSD unit. This is the functional red line on a 2.4/2.7 (70.4) crank so testing beyond that point was meaningless.

Quick side note from MSD tech assistance: "There is no voltage drop across the second coil. Even with two coils each coil receives 450 volts at all RPMs within the limit of the box."

Other reputable engine builders have made posts suggesting that in some configurations they have tested, there was a measurable difference in output between the one box/dual coil approach and two boxes/dual coil approach. These were apparently dyno tests. Of course, none of these tests are published with all of the pertinent details. But I believe that there can be a difference, depending on the variables. So sorry to suggest a contradiction to your experiences Henry.

My engine builder is at the top of the food chain, with decades of experience, and my application is racing. He has a lot of "area under the curve."

He uses the dual box/dual coil set up for projects like mine. I don't think the small financial benefit of a single box/dual coil set up for my project is in any way justified, based on what I have learned thus far.

And as far as "safety," I think I have a really simple wiring approach that can provide at least some warning if one of the two boxes has a failure. How this compares to the "built-in" safety one gets with a single box/dual coil set up is really something only MSD could answer based on statistical analysis of field failures.

In my experience, the boxes have been reliable.

And to me, a description of the benefits of MSD should include words like reliable, cheap and ubiquitous.

Sorry to hijack this tread.

But i am looking for the left side heater ducting, that Will fit with the twin ignition distributor. Engine 2.3 1971.

Where can i buy it.?.

Thx. Olsen

What your looking for comes on the turbo cars.

930 106 321 01

Da.. You guys are fast....:)

Thanks, Will this also clear the convert 2.4 distributor with Jag. cover.?

Thx. Olsen

I have a custom piece that will work.

PM me with your email for pics and price.

Hello Tom.

Thanks, I have Sent PM.

Thx. Olsen

Has anyone tried the new 6AL-2 Digital System?

Will this unit still operate 2 x coils as the instructions aren't very clear.

4 years after the question was asked by Chris, I have the same concern: can 1 msd 6AL-2 trigger 2 coils for a dual plug application?
Thanks!

This is so debated. I bought one 6 Al digital, but I recently saw some data of actual testing and it showed that 2 was the way to go.

2 or 1 box
 

I have been following this for a bit.I have an experience is 1975 with a Factory 3.0 RSR ENGINE that one CD box failed & the motor ran but was not as sharp for power.I have used 2 MSD Boxes for 40 years & never had a failure.MSD 6A.I have put SC magnetic pickups in at least 50 964 twin plug setup set ups with no problems because in 30 plus years my shop never had to replace a SC magnetic pick up for a non run situation.I had a few Electramotive failures with one bank failing & the performance was less than two working.I drive a G-320 TWIN PLUG Mercedes here in Costa Rica and I have a relay every now & then that only fires 6 instead of 12 & it is noticed because the truck weighs 6400 lbs.& makes only 168 H.P & IT FEELS FLAT.CIAO Fred Bottom line is 2 is better than one.

Oh yes. :)

Yes, so it has always puzzled me why MSD units don't multispark beyond 3400 RPM despite their name. For me the fun is just getting started at 3400 RPM in a 911!

That's why we designed our units to dual spark (with adjustable gap) up to 10000 RPM.

This is the sort of results we are getting. Motor is bone stock 69S, setup by Loren Beggs using one of our CDI+ units.

Thin green and blue is Bosch CDI
Thick green and blue is our CDI+ on standard dizzy.
Red and purple are CDI+ on standard dizzy with an 'overlay' map.

http://www.classicretrofit.com/media...s_combined.jpg

We think this is the sort of gain approaching twin plug and are dyno testing at the end of the month to make the comparison.

Jonny,

I see nothing here that shows your product to be superior to an MSD setup, much less a dual MSD setup in a twin plug application. Since this is a thread about using one or two MSD units in a dual setup, don't you think that would be useful information?

Or are you just doing more advertising for your product even though there is no direct application?

Really? As stated, our product is multi spark right through the rev range. MSD can't do multi spark above 3400 rpm. Also, at 1ms spark intervals it is my belief that MSD subsequent sparks are too late to be of benefit at higher revs.

Also as stated, we are about to embark on dyno testing to compare the results of running our true adjustabke dual spark (with adjustable intervals down to 200us) against a proper twin plug setup.

if the test shows comparable results, isn't being able to get twin spark type performance from a single box that looks and fits like a stock unit of huge benefit to the Porsche community?

I'm sorry if you see this as pure advertising. I wish we had the marketing budget of MSD and sold thousands of units per year!

Our product has been created from pure passion for the flat six, not to mention in conjunction with probably the #1 engine builder in the UK. As we have actually taken the time and effort to do these dyno tests, I thought folks might like to see them?

Beliefs, wishes, and passion are not hard cold facts. If you are not going to do a direct comparison against the two possible MSD setups, why post in the thread about MSD setups?

We are back at advertising again.....

Dyno plot is pretty factual isn't it?

I don't see a dyno chart with MSD units involved.

Hold off criticism of the twin plug MSD setup and stop pushing your setup over it UNTIL you have data showing you have something better.

Also, twin plug is about more than just power.