MSD 6AL2 versus BTM ignition
 

I have basic question on what is the biggest advantage to the 6AL2 programmable ignition unit from MSD over the MSD BTM unit that has a boost retard function?
THe BTM from what I understand retards boost in adjustable increments and is set without a lap top. This would allow me to run the standard ignition distributor with the vacuum retard function intact and the mechanical advance intact. At the same time I could dial out adjustable boost retard via the BTM box.

Is there any more advantage to upgrading to the 6AL2 as the above seems to cover all my needs unless I am missing something.

Looking for some input from forum members before pulling the trigger on this.

thanks,
Fred

Mr. Fred:


The new 6al2 allows you to program a timing curve for both ignition timing and
boost retard. You can also set both programs to 0 and it acts like a stock 6al.
And you can set either at 0 and program the other. Good performance and response
to be gained by programming curves tailored to your engine specs. Programs with
your lap top. You can program and store multiple curves and switch between them
for street and track.


Cole

Someday I'll convert to the 6AL2, but for me I went with the BTM initially because my car came with the old MSD6AL and it was an easy thing to add the BTM and not have to mess with anything else other than indexing my distributor (which included grinding the adjustment slot a bit) to get 12 degrees advance at idle. Lots of excuses....like being a poor lazy man, and didn't have a laptop at the time.

Thanks Cole,
But I had a few questions on hooking the 6AL2 unit to receive the boost signal.

The BTM uses a hose connection but the 6AL2 requires an electrical MAP signal. I dont have a MAP sensor in my car but do have the Innovate AUX box which has in internal MAP sensor. I dont know what type of signal output I can get with this.
QUESTION: Do you know if the Innovate AUX box can send a signal to the 6AL2 control box to get the boost signal it needs or do I need to buy and install an additional MAP sensor?
QUESTION: Do I need a tach adaptor from MSD for the VDO tach or can I tap into the MSD wire directly? They dont address the Porsche specific ignition system on the MSD website......bastards, ha,ha.
I would like to leave the distributor untouched so that it uses the mechanical advance as is.
QUESTION: Are you saying that I can program the vacuum advance and boost retard functions into the 6AL2 independently of the mechanical advance on the distributor so that I can virtually eliminate the pot on the side of my dizzy? Basically superimposing the 6AL2 programming timing over the mechanical advance timing in the dizzy so that they both add together to alter final timing at the plug wires?
And finally, QUESTION: How do you wire the green coax signal wire from the dizzy to the MSD box which has a standard 2 wire type connector? Is there some special adaptor you found that splices into the coax and converts to 2 wire output?

Thanks for the excellent advice so far.....

Fred

Mr. Fred:

I'll try to take these in order:

MAP:
You will need a 3 Bar GM style MAP sensor ( Most common MAP there is)
I have 4 in my car easy to find on E Bay. You can not parallel MAP signals
you need seperate maps. MAPs use a 5VDC signal. With the MSD it will have
wiring to connect to the MAP you just provide the MAP sensor and feed a boost
line to it.

3 Bar Map Sensors:

GM Style 3 Bar Pressure Sensors

Manufacturer Part Numbers

GM (old)* 16040749
AC Delco (old)* 213-101

GM (new)** 12223861
AC Delco (new)** 213-1562

MSD** 2313
MSD (compact)** 23131

Borg Warner** EC1678

NAPA CRB219481

Electromotive Engine Controls 71130

Holley 538-23

Tach Adapter:

You won't know untill you hook the MSD up. Sometines you do
sometimes you don't so just hook it up directly and see if it works
If not get the adapter. Porsche CDI's over the years got mixed
between years a lot so you don't know till you try.

Programming

If you want to run the 6AL-2 as strictly a replacement for the stock CDI
you leave your distributor as is and simply program "0's" in as the timing
and boost retard maps. Then you are running exactly the way you are
now. If you want to run custom timing and / or boost retard maps you
strip out the weights and springs in the distributor, turn the advance
mechanism to full advance and pin it in place. Then you program maps for
ignition timing and boost retard, this completely replaces any original
mechanical mechanism You are not programming the vacumme advance
you are actually programming the ignition timing curve. You will be removing
the vacuum pot because it won't work with the distributor locked down so
just set your static timing around 12* - 15* You can go to the MSD web site
and hit the support button and download the installation manual as well as the
programming manual.

Wiring:

I contacted Permatune and bought a male CDI connector from spare parts
and wired the MSD into the connector so it plugs directly into the engine
harness just like the CDI did.

Go download the manuals from MSD and that will really help clear things
up for ya. When you put the distributer to full advance and lock it down
you'll have something like 30-40 degrees of advance dialed in permantly.
Instead of dialing in advance by turning the distributor ( setting timing at
4000 RPM for 29* AND THEN LETTING THE SPRINGS AND WEIGHTS
DETERMINE THE TIMING CURVE) you are now starting at full advance and
programming out (subtracting from lockrd down full advance) what timing
you don't need.

Cole

Good stuff, Cole! I'll be saving your "recipe for sucess" for future reference.
BTW, my '87 did not need a tach adapter. Fred, who knows about your '79?

I didn't mean to dodge the tach adapter question but when I bought my original
6AL I couldn't get a straight answer either. Seems like if you search the forum
some guy's have had to install them and some have not and it was that way on
early na cars, late cars, and turbos. Called MSD and they said a 5vdc sq wave input
should work fine ????? who knows.

Cole

Cole, that permatune connector tidbit you hid up there... IS AWESOME ADVICE!!! Allows you to not hack up the harness and go back to stock if ever desired. You are full of these little tidbits... LOL

dual plug
 

Hey guys; this thread comes at a good time. I'm doing my install over Christmas. I will be using the BTM boost retard. Can someone direct me to a thread on wiring the 2 -6AL boxes to the cars harness. Now I am running a single MSD 6AL. Is it as simple as doubling up the wires to the harness. I hope everyone is bored over the holidays, as I know I will have lots of questions. cheers Philip

Phil:

You can download install instructions off the MSD website. In fact, the BTM instructions
even had pictures for the dumb old guy. I like pictures, a picture is worth a thousand
words, now if I could just see and cure the chemo brain fade i'd get something done.


JB:

Even an old blind hog finds an acorn now and then.


Cole

Just to bump a good thread with info.

Fred