MSD6AL-2 Locked distributor

OZ911SC · 09-22-2009, 09:49 PM

Has anyone played with one of these units yet? I am thinking it may be suitable to run with a locked distributor. I am installing some 46 PMO's on my 3.0L and need to do something with the advance.

Sigurd · 09-22-2009, 11:11 PM

I did it on my 2.7.

The problem I had was that the distributor I had available advanced to early. I did not lock it up but advanced the timing somewhat more than needed and retarded the timing with the MSD and an old PC with a RS 232 port. Using a timing light I programmed the curve within spec.

The tach did not work with the MSD tach adapter but perfectly without. The car is a ’73 with an Ignitor.

Could not be easier.

OZ911SC · 09-22-2009, 11:19 PM

Thanks Sigurd, sounds logical, does the 73 have a vacuum advance distributor?

EarlySport · 09-22-2009, 11:20 PM

Hey,

My RS replica runs a 3.0 SC motor with the distributor locked in the full advance position. I run an MSD timing computer with a 6AL box. The only negative I have with my setup is the maximum programmable advance is 20 degrees, so I have to run a little more static advance ( at idle ) than ideal. This is a minor problem however.

I intend to switch over to the new 6AL-2 programmable all in one box. My current system uses simple pots to set the curve and start and end points. The laptop port and software on the 6AL-2 looks super nice - it also looks to me like it will accept advance of more than 20 degrees. 30 will cover any 911 application.

I've been running my RS replica for 2+ years and it's been bulletproof - I'm a pretty big fan of this system, and it's very affordable.

OZ911SC · 09-22-2009, 11:28 PM

Thanks early sport, I agree it does appear to be a tidy little unit. What spec cam are you running? My 3.0L is 10.5:1 JE's, GE60 cam, 40mm ports, ssi's and 46mm PMO,s

Sigurd · 09-22-2009, 11:51 PM

The distributor I am using have vacuum.

Does it not make sense to not lock the distributor but to advance it more than needed and the retard it back to the required curve with the MSD? This way it the timing form the distributor is not more off than the retard possibilities of the MSD; it should be possible to have both control of timing at max rpm and idle.

OZ911SC · 09-23-2009, 12:00 AM

Your right, it allows you to split the difference where ever you want.

moneymanager · 09-23-2009, 06:32 AM

A side issue maybe, but don't I remember correctly that the 73 distributor has vacuum retard, not advance?

304065 · 09-23-2009, 06:45 AM

Don't lock the distributor.

The advance mechanism is necessary to put the rotor in the correct position for firing. If you lock it in position, you will experience misfires at the ends of the timing range.

Carrera 3,2 Motronic had an advance mechanism
964 Motronic had an advance mechanism

Both are systems with mapped ignition but rotor phasing still important.

jpnovak · 07:28 AM

rotor phasing is very important and you can not run a fully locked distributor with a large range advance curve. As John mentioned this can cause rotor to cap mis-match and create misfires. I would not want misfires at high rpm.

You can do the calculation yourself to determine the arc length of the rotor (use degrees of rotation and width of contact) for both the rotor and the cap tabs. Then determine the degrees of overlap from leading to trailing edge maintaining an 85% overlap. Depending on the magnitude of your advance curve you will see that the rotor may quickly be out of whack and not overlap on firing stroke. this would be the misfire.

The correct method is to pull your trigger signal from a static source (flywheel or crank pully pickup) and leave the advance mechanism to properly phase the rotor.

Yes, the aforementioned locked distributor can work in some cases but not all.

Tom C. · 09-23-2009, 09:46 AM

Quote:

Originally Posted by OZ911SC

Thanks early sport, I agree it does appear to be a tidy little unit. What spec cam are you running? My 3.0L is 10.5:1 JE's, GE60 cam, 40mm ports, ssi's and 46mm PMO,s

Hey Adam . . . Did you say the MSD6AL-2 has a programmable timing (advance) feature? I run them in my car and mine are not programmable. I was also wondering if your motor is twin-plugged and what type of fuel you are running. My interest is because I tried a 'locked-out' internal advance in my distributor and was not able to get it to work well. My motor is twin-plugged running pump gas.

Tom C. · 09-23-2009, 09:49 AM

Sorry about that last post . . . I see MSD makes a 6AL-2 Programmable unit now . . .

sc_rufctr · 09-23-2009, 01:39 PM

Quote:

Originally Posted by john_cramer

Don't lock the distributor...

Carrera 3,2 Motronic had an advance mechanism
964 Motronic had an advance mechanism

John

I thought the 964 (twin) distributor didn't have any sort of advance mechanism.

Am I wrong?

304065 · 09-23-2009, 02:02 PM

sc_rufctr · 09-23-2009, 02:16 PM

John

Thanks for the photo.

OZ911SC · 09-23-2009, 02:46 PM

So what I am reading here is keep the mechanical advance mechanisim (ditch vac as not that suitable for PMO's) and use a fixed trigger point aka a crank pulley mag pick up.

splinterAMG · 09-23-2009, 09:05 PM

Proper rotor alignment is imperative to help ensure proper ignition and more importantly, preclude cross-firing.
Note that most OE distributors allow a relatively large range of rotor ‘pointing’ owing to their engine speed -or vacuum canister- based timing variations.

I’ve drilled through otherwise expired distributor caps to view the respective terminals’ relationships at various engine speeds and loads. Without an electronic advance, they're invariably a crapshoot of minimizing the attendant speed and load compromises. Such is not the case in when utilizing an electronically programmable timing advance.

It’ll likely be necessary to selectively bush the centrifugal advance mechanism's pin and/or judiciously stake the vacuum advance/retard plate to obtain the ideal rotor-to-cap terminal alignment on some applications when fitting the upgrade.

www.msdignition.gr/download/tb_rotor_phasing.pdf

EarlySport · 09-23-2009, 10:19 PM

My distributor is locked in the full advance position, and I don't have any misfire issues due to rotor mis-alignment. The only way I could see this happenning is at low rpm, as at high rpm my rotor is in the same position it would be anyway ( with the mechanical advance all in ).

I need to run the distributor full advanced, as any electronic box can only retard the spark, so I guess the advance curve is in fact a retard curve.

I figured that we have a rotor with a wide arc contact for a reason - to ensure that regardless of mechanical advance position the arc is made with the correct cap contact.

Take my experience for what it's worth. I only have the one system set up this way.