Where to fit an MSD6A - Alfa Romeo Bulletin Board & Forums

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post #1 of 17 (permalink) Old 04-18-2017, 05:07 PM Thread Starter
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Where to fit an MSD6A

I'm looking for suggestions about where to locate an MSD6A ignition on my '72 Super. The engine compartment is pretty tight and so the usual locations are taken up by underhood hardware. It's looking like the most expedient, although not all that desirable, solution is to remove the stock plenum and air-box, although I hate to do that just ot make room for the ignition box.

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
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post #2 of 17 (permalink) Old 04-18-2017, 05:47 PM
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I put the Plex unit in my race car at the right rear firewall, horizontally. I didn't have an airbox though, just a foam filter. Will it fit?
Or run it through the firewall, put on the package shelf or behind the glove box.
Or, if you need a good reason to move the battery to the trunk...
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post #3 of 17 (permalink) Old 04-18-2017, 06:38 PM
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The passenger compartment is a friendlier environment than under the hood. Is there room under the dash/glove box?

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post #4 of 17 (permalink) Old 04-18-2017, 07:39 PM
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I put my MSD 6AL on the the passenger side firewall.

I did not do the interior because of easy access and to avoid extra noise inside the car.

It might be tighter with a Euro airbox than with a GTA airbox.

On the other hand the new digital MSD's tend to be smaller than the old ones.

Avoid heat as much as you can.

Worst for the old MSD - don't know about the new ones - is low battery voltage. That will kill it for sure.

Big downside of the MSD, at least the old ones, is that you cannot bump-start the car because of its massive voltage needs. Booster cable required.

On the plus side, the multi-spark feature below 3000 rpm will give much nicer torque down below and increase drivability as compared to standard ignition or programmable 123. I have run both.
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post #5 of 17 (permalink) Old 04-18-2017, 08:59 PM Thread Starter
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Alas, the Marelli Plex coil and heat-sink is mounted where you put your MSD. I could move the 'Plex and put the MSD there, however. In passing, I've thought about removing the splash cover and mounting the MSD on the back side of the inner fender (assuming it's not double walled) and then routing the wires the fender. In case of failure it's a no brainer to disconnect the MSD and hook up the GM trigger on the 'Plex. Mounting it in the passenger compartment on the firewall was my first thought although I'm told MSD's are noisy. Moving the battery to the trunk in order to get some room is also a possibility although I'm leaning toward keeping the MSD on the "cool" side of the engine.

How far away from a heat source is it safe to mount an MSD unit?

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series

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post #6 of 17 (permalink) Old 04-19-2017, 05:52 AM
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Yes, that's exactly where I put my Plex.
I'm not sure you can quantify "how far away" questions. Lots of mega-HP hotrods have these units; I had one on a Buick Skylark. Those monsters make heat in units Alfa never dreamed of.
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post #7 of 17 (permalink) Old 04-19-2017, 07:49 AM Thread Starter
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Quote:
I'm not sure you can quantify "how far away" questions. Lots of mega-HP hotrods have these units; I had one on a Buick Skylark. Those monsters make heat in units Alfa never dreamed of.

Humm. The reason I asked is that, off and on now, I've been thinking of mounting the MSD on the bottom of the battery tray. If I countersink the bolt holes the fitting won't interfere with the battery. This would put the MSD roughly in alignment with the alternator which should be an ok location. Just thinkin' . . .

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
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post #8 of 17 (permalink) Old 04-19-2017, 07:55 AM
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Put a little duct in, cold air blast. I think that's a great place.
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post #9 of 17 (permalink) Old 04-19-2017, 08:22 AM
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I have mine in my Giulia Spider on the inside firewall, behind the radio.

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post #10 of 17 (permalink) Old 04-19-2017, 09:04 AM Thread Starter
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I hadn't thought about putting it behind the radio, Neil. There's room there and the box would definitely be out of the way! I removed the package tray underneath the glove box and found ample space there to mount the box. I think I can place it high enough on the inside firewall that it would be out of the way. My car still has its rather thick insulation pad on the firewall which I can trim away but doing that will provide ample room to fit the box.

I'm leaning toward mounting the box on the underside of the battery tray. This would put it out of the way and, perhaps with a heat shield or ducted air remain cool enough. It gets seriously hot here in Texas but then MSD is in El Paso so one would think they understand protecting electronics from heat.

What has me energized about this is a re-reading of David Vizard's How To Build Power book. He points out that a multifiring ignition like the MSD will produce useful additional power when used with open-chamber heads----like Alfa's classic hemi design. Watch this space . . .

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
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post #11 of 17 (permalink) Old 04-19-2017, 09:21 PM Thread Starter
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Well, it looks like an upside down install on the bottom of the battery tray is out. From the MSD mouting instructions:

Quote:
The MSD can be mounted in most positions, except directly upside down (if upside down,
moisture or water cannot escape). It can be mounted in the engine compartment as long
as it is away from direct engine heat sources. It is not recommended to mount the unit in an
enclosed area such as the glovebox.
Dunno. Maybe I could drill holes in the top of the box . . . The search continues.

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
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post #12 of 17 (permalink) Old 04-20-2017, 06:46 AM
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Jim a pic of your engine bay will help others (like me) to think a place
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post #13 of 17 (permalink) Old 04-20-2017, 08:56 AM
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MSD & Marelli Plex

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In case of failure it's a no brainer to disconnect the MSD and hook up the GM trigger on the 'Plex.
If you are going to use a MSD and get it`s benefits the old components of the Plex are just baggage.

However there are issues that you need to know about to avoid what others have experienced.

The Plex distributor will trigger the MSD directly (the two wire input) but the coil should be one designed for a Capacitive Discharge / multi spark ignition unit, not a Marelli Plex coil.

The rotor on the distributor MUST be one with a full metal spark delivery bar, not a resistor type rotor. The ignition energy will burn out the resistor conductor hidden under the plastic between the center contact and the metal rotor tip.

Availability of the small diameter plex rotors with metal conductor has proven elusive, but those for Fiat`s with plex ignition are available, but require a little plastic removal to fit and clear the advance mechanisms in the Alfa plex distributor.

Richard Jemison
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post #14 of 17 (permalink) Old 04-20-2017, 09:19 AM Thread Starter
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Quote:
The Plex distributor will trigger the MSD directly (the two wire input) but the coil should be one designed for a Capacitive Discharge / multi spark ignition unit, not a Marelli Plex coil.

The rotor on the distributor MUST be one with a full metal spark delivery bar, not a resistor type rotor. The ignition energy will burn out the resistor conductor hidden under the plastic between the center contact and the metal rotor tip.

Availability of the small diameter plex rotors with metal conductor has proven elusive, but those for Fiat`s with plex ignition are available, but require a little plastic removal to fit and clear the advance mechanisms in the Alfa plex distributor.
[/QUOTE]

My 'Plex is the aftermarket version which I bought new a long, long time ago. I used it for a couple of years in my Alfetta sedan and, on reading an Alfa Owner article about the same, immediately bought an MSD6A. With the 8861 HEI bypass cable is plug compatable with the 'Plex distributor module. I thought it was a way cool setup. I want to keep the 'Plex heat sink/GM module to use as a back-up.


My rotor, original but in good shape, has the full metal spark delivery bar. I think I have a spare, but I'll look into the Fiat part. These are great systems but, alas, they're getting old.

This is good information, Richard. Thanks.

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series
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post #15 of 17 (permalink) Old 04-20-2017, 09:43 AM Thread Starter
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Quote:
Quote:
Originally Posted by quadrifolio View Post
Jim a pic of your engine bay will help others (like me) to think a place

For those interested in finding out more about MarelliPlex/MSD combinations, there's discussion with photos here:

Marelli Plex photo

[BTW: the resistor rotors Richard mentions are distinguished by a clear break in the center of bar. The non-resistor rotors have a full length, preferably brass, bar. Access to good rotors may finally put an end to a great MSD/MarelliPlex ignition.]

Jim . . . '72 Super 1300, '70, 1750GTV, 2nd series,
'62, Lancia Flaminia Zagato3c, 2nd series

Last edited by 180OUT; 04-20-2017 at 09:50 AM.
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